IEC 61005 Edition 3 0 2014 07 INTERNATIONAL STANDARD NORME INTERNATIONALE Radiation protection instrumentation – Neutron ambient dose equivalent (rate) meters Instrumentation pour la radioprotection –[.]
Terms and definitions
For the purposes of this document, the following terms and definitions, as well as those given in IEC 60050-395 apply
NOTE For sentence clarity and text conciseness in this standard the term “neutron ambient dose equivalent
The term "neutron dose (rate) meter" refers to a device that measures neutron ambient dose equivalent (rate) In this standard, whenever "neutron dose (rate) meter" is mentioned, it is implicitly understood to mean "neutron ambient dose equivalent (rate) meter."
An alarm is an audible, visual, or other type of signal that activates when an instrument's reading surpasses a predetermined value, falls outside a specified range, experiences a component failure, or detects radiation according to set conditions.
The H*(10) dose equivalent at a specific point in a radiation field is defined as the value that would be generated by the corresponding aligned and expanded field within the ICRU sphere, measured at a depth of 10 mm on the radius opposite to the direction of the aligned field.
Note 1 to entry: An instrument that has an isotropic response and is calibrated in terms of H*(10) will measure
H*(10) in a radiation field that is uniform over the dimensions of the instrument
1 Numbers in square brackets refer to the Bibliography
H*(10) ratio of dH*(10) by dt, where 𝑑𝐻*(10) is the increment of ambient dose equivalent in the time interval dt
3.1.4 background level radiation field in which the instrument is intended to operate, including that produced by naturally occurring radioactive material and cosmic radiation
3.1.5 calibration distance distance between the reference point of the assembly and the centre of the calibration source
3.1.6 coefficient of variation v ratio of the experimental standard deviation s to the arithmetic mean 𝐻� of a set of n indications H j It is given by the following formula: v= 𝐻� 𝑠 = 𝐻� 1 � 𝑛−1 1 ∑ 𝑛 𝑗=1 (𝐻𝑗− 𝐻�) 2
H t quantity value attributed by agreement to a quantity for a given purpose
Note 1 to entry: In this standard the quantity is the dose equivalent (rate)
Note 2 to entry: The term “conventional true quantity value” is sometimes used for this concept
Note 3 to entry: Sometimes a conventional quantity value is an estimate of a true quantity value
Note 4 to entry: A conventional quantity value is generally accepted as being associated with a suitably small measurement uncertainty, which might be zero
The difference in indicated values for a dose equivalent rate meter occurs when measurements are taken under reference conditions compared to when they are influenced by an external quantity.
H i is the indicated value under the effect of an influence quantity, and
H r is the indicated value under reference conditions
Note 1 to entry: The deviation can be positive or negative resulting in an increase or a decrease of the indicated value, respectively
Note 2 to entry: The deviation is of special importance for influence quantities of Type S
3.1.9 effective range of measurement range of values of ambient dose equivalent (rate) over which the performance of the ambient dose equivalent (rate) meter meets the requirements of this standard
H i value given by the (digital) indication of the dose (rate) meter in units of dose equivalent or dose equivalent rate
3.1.11 influence quantity quantity that is not the measurand but that affects the result of the measurement
Note 1 to entry: For example, temperature of a micrometer used to measure length
Note 2 to entry: If the effect on the result of a measurement of an influence quantity depends on another influence quantity, these influence quantities are treated as a single one
3.1.12 influence quantity of type F influence quantity whose effect on the indicated value is a change in response
Note 1 to entry: An example is radiation energy and angle of radiation incidence
Note 2 to entry: “F” stands for factor: The indication due to radiation is multiplied by a factor due to the influence quantity
3.1.13 influence quantity of type S influence quantity whose effect on the indicated value is a deviation independent of the indicated value
Note 1 to entry: An example is the electromagnetic disturbance
Note 2 to entry: All requirements for influence quantities of type S are given with respect to the value of the deviation D
Note 3 to entry: “S” stands for sum The indication is the sum of the indication due to radiation and due to the influence quantity, e.g., electromagnetic disturbance
3.1.14 lower limit of effective range of measurement
H 0 or (𝐻̇ 0 ) the lowest dose (rate) value included in the effective range of measurement
3.1.15 maximum dose equivalent rate for dose (rate) meters
H max dose rate, specified by the manufacturer, below which the effect of the dose rate on the dose rate reading is within specified limits
M value that can be obtained from the indicated value H i by applying the model function for the measurement
Note 1 to entry: The model function is necessary to evaluate the uncertainty of the measured value according to the GUM (see [3]:2008,3.1.6, 3.4.1 and 4.1)
An example of a model function is presented, which integrates the indicated value \( H_i \) with the reference calibration factor \( N_0 \), the correction for non-linear response \( r_n \), the deviations \( D_p \) (where \( p = 1 l \)) for influence quantities of type \( S \), and the relative response values \( r_q \) (where \( q = 1 m \)) for influence quantities of type \( F \).
Calculations based on this model function are typically not conducted unless specific influencing factors are well understood and suitable corrections are implemented.
Note 4 to entry: If necessary another model function closer to the design of a certain dose (rate) meter may be used
When calibration controls are adjusted per the manufacturer's guidelines, the reference calibration factor and corrections for non-linear response are standardized, resulting in an uncertainty of measurement This uncertainty can be quantified by analyzing the variations in response values and the measured deviations For a dose (rate) meter evaluated under this standard, all relevant data is accessible.
The minimal rated range of use refers to the smallest specified range for an influence quantity or instrument parameter, within which the dose equivalent (rate) meter must function to meet the established limits of variation in accordance with this standard.
Note 1 to entry: The minimal rated ranges of the influence quantities dealt with in this standard are given in the second column of Tables 2, 4, 5 and 6
3.1.18 neutron ambient dose equivalent (rate) meter assembly intended to measure the ambient dose equivalent dose and/or rate from neutron radiation
𝑹 𝐇 ratio, under specified conditions, given by the relation Φ
R Φ is the neutron fluence response (see definition 3.1.22) and h Φ is the neutron fluence-to-dose conversion coefficient (see definition 3.1.23)
3.1.20 neutron fluence Φ quotient of dN by da, where dN is the number of neutrons incident on a sphere of cross- sectional area da: Φ = 𝑑𝑁 𝑑𝑎
Note 1 to entry: The unit of neutron fluence is m –2
3.1.21 neutron fluence rate (flux density)
𝛷̇ quotient of dΦ by dt, where dΦ is the increment of neutron fluence in the time interval dt:
Note 1 to entry: The unit of neutron fluence rate is m –2 ∙s –1
𝑹𝜱 ratio, under specified conditions, given by the relation
The reading \( M \) represents the measurement obtained from the dosemeter for neutron fluence, while \( \Phi \) denotes the conventional quantity value of the neutron fluence that the instrument has encountered.
Note 1 to entry: The unit of neutron fluence response is m 2
3.1.23 neutron fluence-to-ambient dose equivalent conversion coefficient
ℎ 𝛷 quotient of the neutron ambient dose equivalent, H*(10), and the neutron fluence, Φ, at a point in the radiation field, undisturbed by the irradiated object
Note 1 to entry: The conversion coefficients are given in Annex A
3.1.24 non-linearity variation of the value of the (relative) response with the dose (rate) being measured
The 3.1.25 point of test for a dose (rate) equivalent meter is the specific location where the conventional quantity value is established This point serves as the reference for calibrating and testing the dose equivalent (rate) meter.
For all radiation tests, the assembly's reference point is positioned at the test point according to the manufacturer's specified orientation, except for tests assessing the variation in response based on the angle of incidence.
The quantity value of the ambient dose equivalent (rate), denoted as 𝐻 𝑡 ∗ (10), serves as the best estimate for the true ambient dose equivalent (rate) used in the calibration of the assembly This value, along with its associated uncertainty, is derived from either a primary or secondary standard, or through a reference instrument that has been calibrated against these standards.
Note 1 to entry: Primary or secondary standards for neutron radiation are usually standardized in terms of fluence
To convert the fluence rate to the conventional true value of the ambient dose equivalent rate, it is essential to utilize the appropriate conversion coefficients provided in Annex A.
The rated range of a dose equivalent (rate) meter refers to the specific values of an influence quantity or instrument parameter within which the meter functions effectively This range is defined by its maximum and minimum rated values, ensuring that the meter operates within specified limits of variation.
3.1.28 reference direction direction in the coordinate system of the dose (rate) meter with respect to which the angle of the direction of radiation incidence is measured in unidirectional fields
A reference point in an assembly is a physical or virtual mark used to accurately position the assembly at the test point Typically, this mark corresponds to either the geometric center of the detector or its effective center.
𝐑 𝒓 response for a reference value of the quantity to be measured under reference conditions t r H r
H r is the corresponding indicated value of the quantity to be measured under reference conditions and
H t is the conventional quantity value (3.1.7) under reference conditions
Note 1 to entry: The reference response is the reciprocal of the reference calibration factor
Note 2 to entry: The reference values for the dose (rate) are given in Table 1
3.1.31 reference standard standard generally having the highest metrological quality available at a given location or in a given organization from which measurements made are derived
3.1.32 relative response rquotient of the response R (3.1.22) and the reference response R r (3.1.30)
3.1.33 response of a radiation measuring assembly
R ratio, under specified conditions, given by the relation t i
H i is the indicated value of the quantity (3.1.10) measured by the instrument under test and
H t is the conventional quantity value of this quantity (3.1.7)
3.1.34 standard test conditions conditions representing the range of values of a set of influence quantities under which a calibration or a determination of response is carried out
Test nomenclature
3.2.1 qualification tests tests, which are performed in order to verify that the requirements of a device specification are fulfilled Qualification tests are subdivided into type tests and routine tests
3.2.2 type tests conformity testing on the basis of one or more devices representative of the production
3.2.3 routine tests tests to which each individual device is subjected during or after manufacture to ascertain whether it complies with certain criteria
3.2.4 acceptance tests contractual tests to prove to the customer that the device meets certain conditions of its specification
3.2.5 supplementary tests tests intended to provide supplementary information on certain characteristics of the device
Abbreviations and symbols
Abbreviations and symbols are provided in Table 8.
Quantities and units
This standard utilizes units from the International System (SI), with definitions of radiation quantities provided in IEC 60050-395 The previous non-SI units are also noted in brackets for reference.
Nevertheless, the following units may also be used:
– for energy: electron-volt (symbol: eV), 1 eV = 1,602 × 10 –19 J;
– for time: days (symbol: d), hours (symbol: h), minutes (symbol: min)
Multiples and submultiples of SI units will be used, when practicable, according to the SI system
Test requirements
All the tests enumerated in the following clauses are to be considered type tests (see 3.2.2)
During type tests, all values of influence quantities which are not the subject of the test are fixed within the interval of the standard test conditions
Nevertheless, some of these tests may, by agreement between manufacturer and purchaser, be considered as acceptance tests
Reference conditions and standard test conditions are defined in Table 1
The tests outlined in this standard can be categorized based on whether they are conducted under standard test conditions or alternative conditions For tests performed under standard conditions, it is essential to specify the temperature, pressure, and relative humidity during the test, and to apply the necessary corrections to reflect the response under reference conditions.
Tests performed with variation of influence quantities
The tests aim to assess the impact of varying influence quantities, with the acceptable limits of these variations outlined in Table 2 This table defines a nominal operating range, ensuring that the manufacturer's specified limits for indication variations are maintained Importantly, these limits must not exceed those established in Table 2.
To evaluate the impact of changes in a specific influence quantity from Table 2, all other influence quantities are typically kept within the standard test conditions outlined in Table 1, unless the test procedure indicates otherwise.
Tests for influence quantities of type F
These tests may be performed at any value of the quantity to be measured above or equal to
10 H 0 or 10 H 0 From the result of each test, the respective variation of the relative response r can be determined
2 International Bureau of Weights and Measures: The International System of Units, 8 th edition, 2006
Some effects from type F influence quantities may be considered similar to those from type S influence quantities If these effects are minor, they can be disregarded in the context of this standard However, if significant effects from type S are detected during testing, the test should be conducted at a dose value of 10Ḣ₀ or 10H₀, and the results must be documented in the type test report.
Tests for influence quantities of type S
Tests must be conducted at a measurement value that is less than or equal to 10 times the lower limit \( H_0 \) of the effective measurement range, including scenarios with a zero dose.
(rate) is possible if no other specification is given in the respective subclause and a negative deviation can be excluded The result of each test is a deviation D
Some minor effects of type S influence may be considered as arising from type F influence quantities; however, if these effects are negligible, they can be disregarded in the context of this standard In cases where larger or significant negative effects of type F are detected during testing, it is essential to conduct the respective test at a dose value of 10 H 0 or 10 H 0, and to document these results in the type test report This is particularly important due to the generally lower indicated values when compared to tests for influence quantities of type.
F the necessary number of measurements may be increased.
Consideration of non-linearity
The effect of a non-linear response shall be regarded
Testing should be conducted in a dose (rate) region where non-linearity is minimal A practical approach involves initially performing a linearity test to determine the non-linearity region, followed by additional tests in a dose (rate) area where non-linearity is negligible, ideally between 1% to 2%.
Consideration of several detectors or signals in a dose (rate) meter
When multiple signals or detectors are employed to assess the indicated value, each must undergo individual testing This separate testing is essential only when the various signals are utilized to evaluate the indicated value across different dose (rate) regions within the measuring range or in distinct regions of an influencing quantity, such as energy.
Statistical fluctuations
In tests involving radiation, if the statistical fluctuations from radiation are a significant portion of the allowed variation, it is essential to take enough readings to accurately estimate the mean indicated value for compliance Adhering to the guidelines of ISO 11929 is recommended to ensure precision in these measurements.
The time interval between such readings shall be sufficient to ensure that the indicated values are statistically independent.
Radiation sources
The reference neutron radiation source must comply with ISO 8529-1 and can include options such as a 241 Am-Be radionuclide source, a 252 Cf spontaneous fission source, or a 252 Cf source moderated by a 30 cm diameter D 2 O sphere or a well-defined moderator/filter For thermal and epithermal neutron reference fields, suitable sources include accelerator targets, reactor beams, and 241 Am-Be or 252 Cf sources with specific moderator/filter configurations.
The nature, construction and conditions of use of the source shall be in accordance with recommendations of ISO 8529-1, ISO 8529-2, and ISO 8529-3
The ambient dose equivalent rate can be determined from the spectral fluence rate distribution provided by the source, along with the fluence-to-ambient dose equivalent conversion coefficients (refer to Annex A, Table A.1) Average conversion coefficients for five reference sources are also presented.
Annex A, Table A.2 The neutron fluence-to-ambient dose equivalent conversion coefficients employed shall be specified by the manufacturer (see 13.2 e).)
The ambient dose equivalent rate from photon emissions must be considerably lower than that from neutrons, or appropriate shielding must be implemented to guarantee this at the detector Additionally, the device's response to gamma rays needs to be accurately assessed.
137Cs or 60 Co source and/or with other photon sources if necessary.
Work place neutron fields
Workplace neutron fields can be categorized into two types: a) simulated fields as outlined in ISO 12789, and b) other workplace environments where the neutron fields are clearly defined through spectral calculations or measurements that are traceable to or recognized by a primary standards laboratory.
The nature, production and conditions of use of the fields shall be in accordance with the recommendations of ISO 12789
The standard true ambient dose equivalent rate at the measurement location can be derived from the spectral fluence rate distribution along with the fluence-to-ambient dose equivalent conversion coefficients (refer to Annex A, Table A.1).
Survey fields can vary significantly from reference radiation fields To enhance measurement accuracy in these fields, correction factors are applied to instrument readings These factors are derived from the device's fluence response, fluence-to-ambient dose equivalent conversion coefficients, and the spectral fluence of both the calibration and survey fields.
Summary of requirements
In Tables 2, 4, 5, and 6 instrument requirements are summarized.
General characteristics
The effective measurement range, starting at H 0 or H 0, must meet specific criteria: a) for analogue dose equivalent (rate) meters, there should be one range per order of magnitude from 10% to 100% of the maximum scale deflection, and for those with two ranges per order of magnitude, from 30% to 100%; b) for digital dose equivalent (rate) meters, the range should extend from the second least significant digit to the maximum indication on each range For instance, with a maximum display of 9,999.9, the effective range can start from 1.0.
Dose equivalent meters with digital and scientific displays must feature a mantissa with at least three digits, ranging from 1.00 to 9.99 The effective measurement range should be defined by the manufacturer, typically spanning from 1.00 × 10⁻⁷ to 9.99 × 10⁻², with the unit expressed in Sv⋅h⁻¹ This ensures precision across various orders of magnitude, specifically four orders from 9,999.9 or three and a half orders from 3.0 to 9,999.9.
Dose equivalent (rate) meters featuring multiple scales should have an effective measurement range that spans from 10% of the lowest scale to 100% of the highest scale Additionally, all scales must be organized to ensure comprehensive coverage of the total effective measurement range.
If the test methods do not cover the full effective measurement range and observed variations are close to the allowed limits, additional tests may be required to ensure compliance across the entire range It is essential for the purchaser and manufacturer to agree on these supplementary tests.
The minimum effective range of measurement of dose equivalent rate shall cover at least four orders of magnitude and shall include 10 àSv⋅h –1 for the measuring quantity H*(10)
The minimum effective range of dose equivalent shall cover at least four orders of magnitude and shall include 0,1 mSv
Rated range of an influence quantity
The rated range of any influence quantity has to be stated in the documentation In addition, some rated ranges have to be stated on the instrument, see 5.3.2
Minimum rated range of influence quantity
The minimum rated range of the specified influence quantity is given in the second column of
The assembly should indicate the ambient dose equivalent rate in millisieverts per hour, utilizing either an analogue or digital display It is advisable for the indication to be readable from a remote location.
Mechanical characteristics
The IP classification shall be stated by the manufacturer according to IEC 60529 The minimum IP requirement for hand-held instruments is given in IEC 62706
An assembly for the measurement of neutron ambient dose equivalent (rate) shall be labelled with a specific indication of its intended use
The dose (rate) meter must prominently display essential information, including the measured quantity, effective measurement range, suitable radiation type (e.g., neutron), rated particle energy range, reference point and direction (or in the manual), and the instrument's serial number.
The assembly must be designed for easy decontamination, featuring a smooth, non-porous external surface without crevices Additionally, it should be compatible with a thin, flexible envelope that includes transparent sections for clear visibility of the instrument scale.
Interface requirements
The provision of an output connection for a remote readout, which shall be appropriately marked, is recommended (for example for an external counter or integrator, a recorder or a secondary digital display)
If the assembly is equipped with a data processor and memory, an output to an external data device is recommended, for example by a serial data interface.
Algorithm to evaluate the indicated value
For the type test of multiple detector assemblies, manufacturers must provide the evaluation algorithm that processes signals from the detectors to produce the indicated value, including all necessary calculations and decision trees.
NOTE This algorithm may be confidential (proprietary) and only be used by the testing laboratory for the purpose of type testing
General
All influence quantities dealt with in this clause are regarded as of type F
The influence quantity for radiation energy and angle of incidence is defined in relation to the reference response \( R_r \) under specified conditions, including reference radiation at 0° incidence, reference dose, and dose rate, as outlined in Table 1 For neutron radiation, the applicable reference radiations are detailed in Table 1 of ISO 8529-1:2001 While the most commonly used reference radiations are listed, it may be necessary to select alternative radiations to meet the requirements for this influence quantity In some cases, a reference energy value may be chosen even if no physical radiation exists; in such instances, this (virtual) reference radiation is represented by an available reference radiation, along with the response deviation to the (virtual) reference radiation.
NOTE 2 For details regarding the reasons for the non-symmetric limits for the relative response due to radiation energy and angle of radiation incidence see IEC TR 62461.
Consideration of the uncertainty of the conventional quantity value
The expanded (k = 2) relative uncertainty, U rel , of the conventional quantity value of the dose equivalent or dose equivalent rate shall be taken into account and should be less than ±20 %
To account for the allowed variation in relative response, U rel is added When conducting multiple tests with the same radiation quality, such as testing for response constancy, only the uncertainty in the ratio of the actual dose equivalent value to the reference value is considered Any additional requirements are specified in the corresponding testing method.
Constancy of the dose rate response, dose dependence and statistical
The tests for constancy of dose rate response, dose dependence and statistical fluctuations are performed using the same measurement data
If a manufacturer demonstrates that the technical design of the dose rate meter meets the requirements for consistent dose rate response across a wide range of values, the number of required tests can be minimized.
Under standard test conditions, the calibration controls must be adjusted according to the manufacturer's instructions The relative response variation due to non-constancy of the dose rate response should not exceed -17% to +25% across the entire effective measurement range for selected neutron reference radiations Additionally, the dose must be varied throughout the complete range specified by the manufacturer for dose rate measurements The statistical fluctuations of the measured indication, represented as the coefficient of variation, must meet the requirements outlined in Table 3.
For this test, it is essential to establish the conventional quantity value of the ambient dose equivalent (rate) at the testing location The tests will utilize reference sources with suitable activity to irradiate the dose (rate) meter in free air, as outlined in Table 1, such as 241 Am-Be for neutron radiation.
The response should be evaluated at three distinct dose rate values within each order of magnitude of the effective measurement range, specifically at approximately 20%, 40%, and 80% of each full order Additionally, varying dose values within the rated range will be applied at these different dose rate levels A total of \( n \) repeated measurements will be conducted for each of the \( w \) dose rate values, based on the effective measurement range These measurements will allow for the determination of the variation in relative response due to the non-constancy of the response.
Interpretation of the results of the test using sources
Determine the mean value and the coefficient of variation of the n values of the indication for each of the w dose rate values
The relative response variation, based on the w mean values, is constrained within the limits of -17% to +25% Additionally, by utilizing the w values of the coefficients of variation along with the c1 and c2 values provided in Table 3, the analysis can be further substantiated.
• for (w – 2) dose rate values the coefficients of variation are less than c 1 times the limits given in Table 3 and
• for the remaining two dose rate values – which shall not be adjacent – the coefficients of variation are less than c 2 times the limits given in Table 3
In that case, the requirements a) and b) of 6.3.2 can be considered met
NOTE 1 The value of c 1 is always smaller than that of c 2
This method guarantees that the likelihood of successfully passing the test remains unaffected by the number of dose values, denoted as \( w \), at which the test is conducted In the absence of factors \( c_1 \) and \( c_2 \), the probability of passing the test diminishes as the number of dose values increases.
NOTE 3 More information on the test procedure is given in [8]
Test procedure with variation of the calibration distance
ISO 8529-2 outlines practical procedures for assessing instrument response using reference neutron radiation sources, while considering the effects of scattered radiation and the device's reference point position These procedures involve determining indicated values at various calibration distances, which can vary significantly across one or more orders of magnitude.
Data analytical fitting methods are used to determine response, scatter contribution, and geometry parameters Any indicated value can be considered a point within the specified scale ranges outlined in section 6.4.2 To assess the relative error in these scale ranges, fitted indicated values can be utilized, provided that the fitted scatter and geometry parameters align with calculated or experimentally determined values.
If the available neutron radiation sources cannot supply the complete range of ambient dose equivalent rates needed for testing, it is acceptable to use an equivalent electrical test to assess the relative error at the ambient dose equivalent rates that are unavailable.
Radiation sources must provide at least one ambient dose equivalent rate in both the upper and lower parts of the effective measurement range for type testing The electrical signal should closely mimic the signal produced by the detector and be injected at a point that tests the entire assembly, excluding the detector or photomultiplier in scintillator detectors.
When the indicated ambient dose equivalent rate, \$\dot{H}_{i1}^*(10)\$, is measured against a conventionally true ambient dose equivalent rate, \$\dot{H}_{t}^*(10)\$, from a neutron reference source, an electrical signal, \$S_1\$, is applied to match the indicated value, \$\dot{H}_{i1}^*(10)\$ If a different indicated value, \$\dot{H}_{i2}^*(10)\$, is generated by another input signal, \$S_2\$, the relative error can be calculated accordingly.
and the observation shall be within the limits given in 6.3.7 If the electrical test method is used, this should be stated in the accompanying documents
Interpretation of the equivalent electrical test results
When conducting tests, it is essential to account for the relative uncertainty U(k = 2) in the conventional true ambient dose equivalent rates If the observed mean value of the relative error, U, remains within the range of ±(20 % + U), the consistency of the dose rate response is deemed satisfactory.
Variation of the response due to neutron energy
The response of all neutron dose (rate) meters is very dependent on the neutron energy [1]
For effective radiological protection, it is ideal that the response variation with neutron energy remains within a factor of 1.5 across the entire range from thermal to the maximum energy specified by the manufacturer However, this requirement is currently not feasible.
All current and developing devices rely on accurate detector response calculations, necessitating the availability of results across the entire neutron energy spectrum, with data provided at a minimum of two energy points per decade of neutron energy.
The manufacturer must specify the variation of the relative ambient dose equivalent response, r H*(10), due to changes in neutron energy within the thermal to 50 keV range This relative response should fall within a range of 0.2 to 8.0.
50 keV – 10 MeV energy range within the range from 0,5 to 2,0
For neutron energies between 10 MeV and 20 MeV, manufacturers must define how the ambient dose equivalent response varies with neutron energy This variation in relative response should fall within a range of 0.2 to 2.0.
The relative response is based on the reference neutron energy and the angle of 0° between the incident neutron radiation and the reference direction The manufacturer will define the instrument axis, reference plane, and direction of incidence.
Every instrument must meet the mandatory neutron energy range of 50 keV to 10 MeV Additionally, manufacturers are required to specify the energy range in which their instruments fulfill the stated requirements for any remaining energy ranges.
All indicated dose values shall be corrected for non-constant response and, if necessary, for the effect of the influence quantity dose rate on dose measurements
For this test, the dose (rate) meter shall be placed free in air The neutron radiation qualities specified in ISO 8529-1, ISO 8529-2, ISO 8529-3 and ISO 12789-1, ISO 12789-2 shall be used
Due to the impracticality of assessing assembly performance and validating calculated data across nine decades of neutron energy, specific energy ranges are recommended for testing These include: a) at least two neutron energies below 50 keV, with one being thermal neutron energy; b) at least three neutron energies between 50 keV and 10 MeV; c) at least one broad source, such as 252 Cf or 241 Am-Be; and d) at least one neutron energy above 10 MeV.
Only tests at energies that are within the manufacturer’s specified energy range are required
In addition, it is recommended to state the response to standardized simulated work place neutron field sources
The test distance must be a minimum of three times the combined largest linear dimensions of both the source and the detector Additionally, the contribution of scatter to the device's indicated value should not surpass 20% of the value attributed to unscattered neutrons The assessment of scatter contribution must adhere to the guidelines set forth in ISO 8529-2.
For optimal results, the test should ideally be conducted at a consistent ambient dose equivalent rate for each neutron energy However, if this is not feasible, adjustments must be made to the indicated ambient dose equivalent rate for each neutron energy to account for the relative response.
(interpolated if necessary) at the same indication as for the reference neutron radiation
Using the provided computational response function calculate the ambient neutron dose equivalent (rate) at the selected neutron energies in 6.4.3 a) through d) and compare them with the experimentally determined values
NOTE Details of the reference radiations and the calibration procedure are given in ISO 8529-1, ISO 8529-2 and
ISO 8529-3 For simulated realistic work place neutron field sources, see ISO 12789-1 and ISO 12789-2
If the experimentally measured relative response values for neutron energy variation fall within the specified ranges in section 6.4.2, and the calculated ambient dose equivalent rates are within ± 20% of the measured values, then the criteria outlined in section 6.4 are deemed satisfied.
Monte Carlo calculation of the instrument response
The response of current and developing neutron dose meters in energy regions lacking feasible measurements relies primarily on Monte Carlo simulations Typically, the calculated relative response curve is referenced against established standards.
The manufacturer must provide a Monte Carlo response curve that encompasses the specified energy range This includes calculated numerical values for each measured energy as outlined in section 6.4.3 a) through d) Furthermore, additional calculated values should be supplied at various energies to bridge gaps between available monoenergetic fields and to ensure comprehensive coverage of the entire energy range It is essential to include calculated numerical values for each order of magnitude of neutron energy, such as 10^{-2} eV, 10^{-1} eV, 10^{0} eV, 10^{1} eV, up to 10^{7} eV.
>10 7 eV) The accuracy of the Monte Carlo results for the detector response shall be such that the calculated ambient neutron dose equivalent (rate) at the selected neutron energies in
6.4.3 a) through d) is within ±20 % of the measured ambient neutron dose equivalent (rate)
Monte Carlo calculations shall be fully documented so that they can be repeated (or verified) by independent entity or laboratory
NOTE This information may be confidential and only be used by the testing laboratory for the purpose of type testing
Ensure that the Monte Carlo calculated response curve encompasses the entire energy range specified by the manufacturer Confirm that the Monte Carlo calculations are thoroughly documented and can be independently replicated, either by repeating parts of the calculations or by reviewing the provided documentation Additionally, verify that the calculated numerical response values at the selected energies outlined in section 6.4.3 a) through d) are included, as well as the response values at energies between those selected, ensuring coverage in each order of magnitude of neutron energy.
The instrument complies with the requirements outlined in section 6.5.2 if it provides a Monte Carlo calculated response curve that encompasses the entire energy range specified by the manufacturer Additionally, the Monte Carlo calculations must be thoroughly documented and reproducible Furthermore, the calculated and experimental data at the designated energy points must fall within ±20% Lastly, the instrument should present calculated numerical response values for each order of magnitude of neutron energy between the specified energy points.
Variation of the response due to angle of incidence
This standard pertains to detector assemblies characterized by a broad acceptance angle and circular symmetry in one plane It acknowledges the practical challenges in attaining a uniform response across a 4π solid angle.
The assembly's indication of radiation incident at angles ranging from 0° to 90° relative to the calibration direction must not vary by more than ±25% within the rated energy range.
The variation of the indication of the assembly to radiation incident at any angle from +90° to
Manufacturers must specify the angles of +180° and –90° to –180° relative to the reference direction in the reference plane Additionally, they should indicate how the assembly's readings vary with radiation incident at any angle to the reference direction in a plane orthogonal to it The definitions of the reference plane and the reference direction of incidence are also the responsibility of the manufacturer.
The detection assembly must be positioned in its reference plane and exposed to a specified reference neutron radiation source The calibration distance should be at least three times the sum of the largest linear dimensions of both the source and the detector, ensuring that the scatter contribution from unscattered neutrons does not exceed 20% of the indicated value, in accordance with ISO 8529-2 The assembly should then be rotated in the reference plane at 30° intervals from 0° to ±180°, with the indicated values recorded at each angle.
Similar observations shall then be taken as the assembly is rotated in a plane orthogonal
(perpendicular) to the reference direction
The instrument meets the requirements of 6.6.2 if a) the variation of the indication of the assembly to radiation incident at any angle from 0° to
The variation of the assembly's indication to radiation incident at angles from +90° to +180° and -90° to -180° relative to the reference direction in the reference plane must not exceed the manufacturer's specified limits Additionally, the deviation at any angle in a plane orthogonal to the reference direction should also remain within the values set by the manufacturer, ensuring that the variation does not surpass ±25% when measured at 90° to the reference direction.
Overload characteristics
The dose equivalent meter must indicate overload or read off-scale when exposed to doses exceeding its maximum measuring range, applicable across all ranges Additionally, if the meter encounters dose rates that could lead to inaccurate readings, it must provide a clear indication that it cannot deliver correct dose measurements.
The test can be conducted using an appropriate neutron source or by injecting a suitable signal into the measuring assembly's input if high neutron dose rates are unavailable It is essential to expose the dose equivalent meter to a dose ranging from 1 Sv to 50 Sv or higher.
The maximum allowable dose should not exceed ten times the specified limit, and the dose rate during exposure must remain below the manufacturer's maximum capability After testing, the equipment must remain powered on for at least 30 minutes without resetting Additionally, the dose equivalent meter should be tested at a dose rate 10% above the manufacturer's limit for 100 seconds If no overload error is indicated, the meter should then be subjected to progressively higher dose rates in 10% increments for 100 seconds until an error in the dose value is detected.
(due to dose rate overload) is displayed
The results interpretation requires that any high-side indication or overload must be displayed and persist until the dose indication is reset or the equipment is powered off It is essential to verify that the dose indication has increased correctly, adhering to the manufacturer's specified tolerance, or to receive an error indication if the dose reading is inaccurate due to dose rate overload Before any error indication occurs, the dose indication should appropriately increase within its tolerance limits.
The dose rate equivalent meter must display off-scale readings on the high side or indicate overload when subjected to dose rates exceeding its maximum measuring range, a requirement that applies across all ranges.
The test can be conducted using an appropriate neutron source or by injecting a suitable signal into the measuring assembly's input when high neutron dose rates are unavailable.
The dose rate equivalent meter shall be submitted for a period of 5 min to a dose equivalent rate 10 times the range (scale) maximum
The dose equivalent rate must read off-scale on the high side or indicate overload during the test period The dose rate equivalent meter should operate within specifications five minutes after the test concludes If the device fails to meet these specifications, a warning will be displayed, which will only turn off once the device complies with the specifications without restrictions This test applies to all ranges.
Response time
The response time shall be such that, if there is a sudden change in the ambient dose equivalent rate, the indication shall reach the following value:
The initial indicated value, H i * ( )10, and the final indicated value, H f * ( )10, must be measured within a time frame of less than 30 seconds for changes in the ambient dose equivalent rate that are less than specified.
0,1 mSv⋅h –1 ; b) 10 s for the increases or decreases of the ambient dose equivalent rate between
0,1 mSv⋅h –1 and 1 mSv⋅h –1 ; c) 4 s for the increases or decreases of the ambient dose equivalent rate greater than
The manufacturer shall state the response time
The test may be carried out either with a suitable neutron source or by the injection of a suitable electrical signal into the input of the measuring assembly
The ambient dose equivalent rates at the beginning and end of measurements must vary by a factor of at least 10, necessitating assessments for both increases and decreases in these rates.
If the electrical test method is employed, the injected signals shall correspond to the above requirements
For the increasing ambient dose equivalent rate test, the detection assembly shall be subjected first to the higher ambient dose equivalent rate and the indicated value H f * ( )10 shall be noted
The assembly will be exposed to a lower ambient dose equivalent rate for a duration adequate for the indication H i * ( )10 to stabilize, and the resulting steady value will be recorded.
The ambient dose equivalent rate must be adjusted promptly to match the specified value of H f * ( )10 Additionally, the duration required to achieve the value outlined in formula 6.8.1 should be recorded.
The test for decreasing ambient dose equivalent rate shall be performed in the same way with the values of ambient dose equivalent rates corresponding to H f * ( )10 and H i * ( )10 interchanged
The instrument is considered compliant if the indication after a sudden change in the ambient equivalent dose rate meets the value specified by the formula in section 6.8.1 within the time limits outlined in the same section.
Relationship between response time and statistical fluctuations
The response time and the coefficient of variation of the statistical fluctuations are interdependent characteristics, for which acceptable limits are given above in 6.8.1 and 6.3.2
For high ambient dose equivalent rates, it is recommended that, whenever possible, while conforming to the limits laid down for the statistical fluctuations, the response time should be reduced
There is little advantage in reducing response time much below 1 s; in such cases, it would be more advisable to reduce the statistical fluctuations.
Dose equivalent rate alarm
Under standard test conditions, a dose equivalent (rate) meter should not activate its alarm for more than 10% of a 10-minute test period when exposed to a dose equivalent rate of 0.8 times the alarm set point Conversely, at a dose equivalent rate of 1.2 times the alarm level, the alarm must activate for at least 90% of the test duration Additionally, when subjected to dose equivalent rates of 1.2 times the alarm set point, the alarm should trigger within 5 seconds or within a time frame that ensures the product of this time and the dose equivalent rate remains below 10 µSv.
A dose equivalent rate meter that employs multiple radiation detectors to measure a comprehensive range of dose equivalent rates must adhere to specific requirements for each detector's respective range.
Two tests must be conducted: one with the alarm set close to the maximum effective indicated value and another near the maximum of the second least significant decade.
The instrument complies with the dose equivalent rate alarm requirement by meeting the specifications of 6.11.1, which includes two alarm set points: one close to the maximum effective indicated values and another near the maximum of the second least significant decade It is essential to account for the relative uncertainty (k = 2) in the conventional true dose equivalent rate affecting the neutron dose meter The dose rates utilized are 0.8(1 - U).
1,2(1 + U) of the dose equivalent alarm rate set point.
Dose equivalent alarm
Under standard testing conditions, a dose equivalent meter will not trigger an alarm when exposed to a dose equivalent of 0.8 times the set alarm level However, if the meter experiences a dose equivalent rate of 1.2 times the alarm set point, the alarm will be activated.
Two tests must be conducted: one with the alarm set close to the maximum effective indicated value and another near the maximum of the second least significant decade After resetting the alarm, the dose equivalent meter should be exposed to a conventionally true dose equivalent rate that prevents the alarm from triggering for a minimum of 100 seconds.
The time of exposure of the dose equivalent meter shall be measured
The instrument complies with the dose equivalent alarm requirement by fulfilling the criteria outlined in section 6.12.1, which mandates two alarm set points: one close to the maximum effective indicated value and another near the maximum of the second least significant decade Additionally, the ratio of the alarm set point to the product of the dose equivalent rate and the measured time must fall within a specified range.
0,8(1 – U) to 1,2(1 + U), where U is the relative uncertainty (k = 2) in the conventionally true dose equivalent rate.
Response to photon radiation
Practically all neutron radiation fields are contaminated by photon radiation, which leads to the necessity to determine the response to photon radiation
The response to photon radiation shall be quoted in terms of the indication of the assembly per unit of photon ambient dose equivalent rate at the point of test
Photon radiation incident on a neutron assembly may not only cause the assembly to give an indication, but it may also modify the response of the assembly to neutron radiation
Therefore, there are two separate requirements a) The indication produced by a 137 Cs or 60 Co photon ambient dose equivalent rate of
The neutron ambient dose equivalent rate must not exceed 0.1 mSv⋅h –1 when the indicated value is 10 mSv⋅h –1 Additionally, in a neutron reference field with an indication of 1 mSv⋅h –1, exposure to 10 mSv⋅h –1 from 137 Cs or 60 Co photon radiation should not alter this neutron indication by more than a specified limit.
The sources of 137 Cs or 60 Co used in tests must meet the ISO 4037 series requirements Additionally, when measuring neutron ambient dose equivalent rates, it is important to consider the presence of high-energy photon radiation, such as 6 MeV from 16 N The response to this photon radiation should be verified at higher energies, as agreed upon by the manufacturer and purchaser, with the manufacturer providing details on the response to high-energy photon radiation.
For requirement a) of section 6.13.1, the assembly must be subjected to a 137 Cs or 60 Co radiation source within a field that maintains an ambient dose equivalent rate of 10 mSv⋅h –1 at the assembly's reference point.
For requirement b) of 6.13.1, the assembly must be subjected to a neutron reference source to achieve an indicated value of 1 mSv⋅h⁻¹ Additionally, the assembly is exposed to a 137 Cs or 60 Co source to measure the photon dose equivalent rate at the test point.
For requirement c) of 6.13.1, the radiation sources used for this test shall conform to the
The requirements outlined in section 6.13.1 a) and c) are met when the indication from a 137 Cs source and higher energy photons (greater than 1.5 MeV) shows an ambient dose equivalent rate of 10 mSv⋅h –1 that is lower than the specified value due to a neutron ambient dose equivalent rate of 0.1 mSv⋅h –1 The response to photon radiation must be expressed in relation to the assembly's indication per unit of photon ambient dose equivalent rate at the testing location.
The requirement in 6.13.1 b) is met if the indication of the neutron ambient dose equivalent rate does not change by more than 10 % when exposed to photon dose equivalent rate of
Response to other external ionizing radiations
Due to the design of this type of assembly, it will not respond to alpha or beta radiations
Accordingly, no tests are specified
Requirements
The specified value is additive when exposed to various types of radiation, such as photons and neutrons, as well as differing neutron energies and angles of radiation incidence.
If the dose (rate) meter uses only one signal (measured with one detector) to evaluate the indicated value, then this requirement is fulfilled
A dose rate meter that utilizes multiple signals, whether from several detectors or a single detector employing methods like pulse height analysis, does not automatically meet the required standards It is essential to ensure that the relative change in indication, denoted as ∆g mix, resulting from the radiation mix does not exceed ±0.1.
If the algorithm for evaluating the indicated value is based on a linear combination of signals or their linear optimization, then the requirement is satisfied, eliminating the need for additional tests.
Test method
Perform subsequently two irradiations under the two different irradiation conditions K and L
In this study, we analyze various energies, angles of incidence, and types of radiation, focusing on the conventional quantity values \( H_{tK} \) and \( H_{tL} \) We aim to determine the indicated values \( H_{iK} \) and \( H_{iL} \) for two distinct irradiations Additionally, we will conduct a third simultaneous irradiation under conditions K and L, utilizing the conventional quantity value \( H_{t(K + L)} = H_{tK} + H_{tL} \), and subsequently determine the indicated value \( H_{i(K + L)} \) for this mixed irradiation.
The relative change in indication is then given by:
The value of ∆ can be determined for any combination of H tK and H tL along with radiation fields S K and S L Due to the challenges of conducting simultaneous irradiations, calculations are recommended as a substitute for this test However, to utilize calculations, it is essential to have measured response values for each signal under all irradiation conditions K and L, as well as a clear evaluation procedure for deriving the indicated value from these signals It is important to note that using radiation transport simulations to calculate the response of the entire dose (rate) meter is not allowed.
The non-linearity of the signals is addressed in sections 4.3 and 6.3 Consequently, in the absence of calculations, the signals must be adjusted for non-linearity during this test, particularly when varying doses are involved.
(rate) meters are used to determine H iK , H iL and H i(K + L), any difference in the reference calibration factor shall be corrected.
Interpretation of the results
The relative change in indication, ∆H imix shall not exceed ±0,1 In this case, the requirements of 7.1 can be considered met
General
The final software version will be ready at the start of the type test, as much of the software testing is indirectly addressed through the metrological test The manufacturer must understand that any modifications to the "data relevant part" of the software could jeopardize the validity of the type test.
In contemporary instruments, software plays a crucial role in generating measured values, making it essential for type testing to encompass the performance of the software within the device being tested, as stipulated by the specified requirements.
The requirements outlined are based on the WELMEC software guide 7.2 and pertain to instruments featuring embedded software designed for specific measurement purposes (Type P) within a low-risk class B category.
Requirements
To ensure data integrity, strict requirements are established to prevent unauthorized modifications of the software Any attempts to alter the software must be conducted under the supervision of authorized personnel and follow the designated procedures.
Design and structure of the software
The software will be developed to ensure that the components related to the specified value remain unaffected by other software, unless such interaction is necessary for the accurate operation of the dose equivalent (rate) meter.
A recommended technical solution involves dividing the software into two distinct components: the "data relevant part," which handles the evaluation, storage, and display of values, and the "non data relevant part," which may include elements like value, date, and time of indications This separation allows for well-defined functions in the data relevant part to communicate with the non data relevant part, enabling modifications to the latter without affecting the former This approach of software separation is considered a best practice in software engineering.
Protection of the software and data
The software must include a clearly identifiable "data relevant part" that can be displayed during operation This identification should be easily compared with the details provided in the test record or user instructions.
If the identification changes automatically with software modifications, a simple version number is inadequate, providing an additional advantage Any alteration in the stored software of the dose equivalent (rate) meter, such as that caused by radiation, can be detected A potential technical solution involves implementing a checksum algorithm, like CRC-16, over the software The checksum of all software bytes is calculated and stored as a reference value Upon instrument startup, the checksum is recalculated and compared to the stored reference; if a discrepancy is found, the software halts and displays an appropriate error message.
8.2.3.2 Alarm under abnormal operating conditions
Abnormal operating conditions in dose equivalent (rate) meters must be clearly indicated, as they can result in inaccurate readings or loss of dose information Such conditions may include issues like high voltage failures in photomultiplier tubes.
All data used for the determination of the indicated value, for example, calibration factors and high voltage, shall be secured against unauthorized modification
NOTE One possible technical solution is to require a password before any change of such data
8.2.3.4 User interfaces, hardware interfaces and software interfaces
All commands and values input through user interfaces, such as keyboards or software interfaces, must only affect the instrument's data and functions in an acceptable manner Each command or value must be clearly defined, ensuring that they either have a valid meaning that the instrument can process or are recognized as invalid Invalid commands must not impact the instrument's data or functions in any way.
It is generally feasible to bypass a software interface; however, this can often be prevented through software separation, as indicated in section 8.2.2, where the critical data components of the software are implemented in a distinct binary file.
8.2.4.1 Documentation in the instruction manual
All functions, menus and submenus of the software shall be described in the instruction manual, see 13.1
8.2.4.2 Documentation for the type test
In addition to the documentation listed in Clause 13, the following information shall be given by the manufacturer for the purpose of type testing:
– a description of the structure of the software according to 8.2.2;
– the method to evaluate and display the identification, and to prevent measurements conducted with changed software, see 8.2.3.1;
– the measures to recognize abnormal operation conditions, see 8.2.3.2;
This article provides a comprehensive overview of all relevant parameters, including their ranges and nominal values It outlines the methods for ensuring these parameters remain within allowed limits, details their storage locations, and explains how they can be viewed and modified For more information, refer to section 8.2.3.3.
– a complete list of all commands (e.g menu items) and values that can be received via the interfaces, including their effect, see 8.2.3.4.
Test method
Testing of software can be very complex; however, it shall not dominate the testing-time
Manufacturers bear significant responsibility as no specific tests are mandated; instead, type testing is conducted indirectly using the final software version and the manufacturer's documentation, as outlined in section 8.2.4.
The only test is on the documentation
During the type test, various menus will be utilized within the software, all of which will be documented in the instruction manual To ensure consistency, users should explore the software and compare it with the manual If the menus in the software align with those in the instruction manual, the requirement is satisfied This verification process should also extend to any additional software and interfaces Furthermore, the identification must be displayed and included in the certificate as specified in section 8.2.3.1.
Stability of zero indication with time
The dose equivalent (rate) meter's indication must remain stable, varying by no more than ± 0.2 H₀ or ± 0.2 Ḣ₀ within 300 minutes of being powered on, accounting for any changes in H₀ caused by ambient background conditions during this time.
To properly use a dose equivalent (rate) meter, first switch it on and allow it to stabilize for 30 minutes If the meter has a zero-set control, adjust it according to the manufacturer's specifications For meters with a non-linear scale, this control should be set to a designated reference point instead of zero.
The dose equivalent (rate) meter shall be left in this condition and the reading noted every
30 min for a further 270 min period
If the noted readings are proved to be within the limits of 9.1.1, then the requirements are met.
Warm-up time
The manufacturer shall state the warm-up time
Ensure the assembly is powered off before exposing it to a suitable reference radiation source, which should indicate at least half of the maximum scale on the most sensitive range or decade.
Switch on the assembly and wait for the manufacturer stated warm-up time Then take 10 to
20 measurements of the dose equivalent (rate) and take the average value
After powering on the assembly, wait thirty minutes before taking an additional 10 to 20 measurements of the dose equivalent rate The average of these measurements will serve as the final value for the indication.
If the final value and the average value taken immediately after the manufacturer stated warm-up time are within ±10 %, then the requirements of this test are met.