Rahmanc, Kyung Sook Kimc, Guinyun Kimc,*, Youngdo Ohd, Hee-Seok Leed, Moo-Hyun Chod, In Soo Kod, Won Namkungd a Institute of Physics, Vietnam Academy of Science and Technology, 10 Dao Ta
Trang 1Thermal neutron cross-section and resonance integral
of the 98 Mo(n, c ) 99 Mo reaction
Nguyen Van Doa, Pham Duc Khuea, Kim Tien Thanha, Bui Van Loatb, Md.S Rahmanc, Kyung Sook Kimc, Guinyun Kimc,*, Youngdo Ohd, Hee-Seok Leed, Moo-Hyun Chod, In Soo Kod, Won Namkungd
a
Institute of Physics, Vietnam Academy of Science and Technology, 10 Dao Tan, Hanoi, Viet Nam
b
College of Natural Sciences, Hanoi National University, 334 Nguyen Trai, Hanoi, Viet Nam
c
Department of Physics, Kyungpook National University, Daegu 702-701, Republic of Korea
d
Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea
a r t i c l e i n f o
Article history:
Received 28 May 2008
Received in revised form 26 November 2008
Available online 11 December 2008
PACS:
25.40.Lw
25.40.Ny
25.70.Ef
Keywords:
Thermal neutron cross-section
Resonance integral
98
Mo(n,c) 99
Mo
197
Au(n,c) 198
Au
65 MeV electron linac
Pulsed neutron facility
Activation method
a b s t r a c t
We measured the thermal neutron cross-section and the resonance integral of the98Mo(n,c)99Mo reac-tion by the activareac-tion method using a197Au(n,c)198Au monitor reaction as a single comparator The high-purity natural Mo and Au metallic foils with and without a cadmium shield case of 0.5 mm thickness were irradiated in a neutron field of the Pohang neutron facility The induced activities in the activated foils were measured with a calibrated p-type high-purity Ge detector The necessary correction factors for thec-ray attenuation (Fg), the thermal neutron self-shielding (Gth) and the resonance neutron self-shield-ing (Gepi) effects, and the epithermal neutron spectrum shape factor (a) were taken into account In addi-tion, for the99Mo activity measurements, the correction for true coincidence summing effects was also taken into account The thermal neutron cross-section for the98Mo(n,c)99Mo reaction has been deter-mined to be 0.136 ± 0.007 barn, relative to the reference value of 98.65 ± 0.09 barn for the197Au(n,c)198
Au reaction The present result is, in general, in good agreement with most of the experimental data and the recently evaluated values of ENDF/B-VII.0, JENDL-3.3, and JEF-2.2 by 5.1% (1r) By assuming the cad-mium cut-off energy of 0.55 eV, the resonance integral for the98Mo(n,c)99Mo reaction is 7.02 ± 0.62 barn, which is determined relative to the reference values of 1550 ± 28 barn for the197Au(n,c)198Au reaction The present resonance integral value is in general good agreement with the previously reported data by 8.8% (1r)
Ó 2008 Elsevier B.V All rights reserved
1 Introduction
Molybdenum (Mo) is a silvery-white, hard but softer transition
metal Molybdenum and molybdenum containing alloys are
important structural materials for accelerator-driven systems,
fu-sion reactors and many other fields It is also very useful as a
refractory and corrosion resistant material in accelerator
applica-tions [1] In addition, the radioactive 99Mo with half-life, t1/2=
2.7489 days is widely used in medicine The daughter technetium
radionuclide99mTc (called metastable technetium) formed by b
decay from 99Mo, (99Mo(b)99mTc with t1/2= 6.01 h) is used in
about 90% of the nuclear medicine examinations worldwide [2]
The parent radionuclide99Mo can be produced in principle in
var-ious ways Currently, the dominant route is the neutron fission of
natural or isotopically enriched 235U through the reaction
235U(n,f)99Mo, while the activation of a natural or isotopically
en-riched Mo by the proton induced reaction100Mo(p,pn)99Mo and
by the neutron capture reaction98Mo(n,c)99Mo From235U fission many long-lived radioactive wastes with total activity much more exceeding the activity of99Mo are formed[3] The proton in-duced nuclear reactions on natural molybdenum containing
92,94,95,96,97,98,100Mo isotopic composition can also form many radioactive products with high-activities [4] For the 98Mo(n,
c)99Mo reaction, practically waste is not created and the saturated activity of the98Mo(n,c)99Mo reaction can be increased by increas-ing the neutron flux[5]
The knowledge of the thermal neutron cross-section and the resonance integral for the98Mo(n,c)99Mo reaction would become important because the neutron activation cross-section data are used in the production of99Mo and may also used in other studies related to the interaction of neutrons with matter We found in lit-erature a number of experimental and evaluated data on the thermal neutron capture cross-sections and the resonance integrals for the98Mo(n,c)99Mo reaction However, most of the re-ported experimental data have been measured before 1990 The
0168-583X/$ - see front matter Ó 2008 Elsevier B.V All rights reserved.
* Corresponding author Tel.: +82 53 950 5326; fax: +82 53 939 3972.
E-mail address: gnkim@knu.ac.kr (G Kim).
Contents lists available atScienceDirect
Nuclear Instruments and Methods in Physics Research B
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / n i m b
Trang 2measured thermal neutron cross-sections for the98Mo(n,c)99Mo
reaction are varied from 0.12 barn[6]to 0.18 barn[7] This fact
shows that, there are still large discrepancies among the
experi-mental results The measured resonance integrals for the98
Mo(n,-c)99Mo reaction are varied from 4.72 barn[8]to 8.2 barn[9] The
difference between the lowest and the highest values of the
reso-nance integral found in literature is 73.73% Obviously, there are
still large discrepancies among the experimental results for the
98Mo(n,c)99Mo reaction, especially among the resonance integral
values Therefore, it is necessary to measure more new data for
better comparison and evaluation
We measured the thermal neutron capture cross-section and
the resonance integral of the 98Mo(n,c)99Mo reaction by using
the activation method at the Pohang Neutron Facility (PNF) based
on the 65-MeV electron linac The thermal neutron cross-section
and the resonance integral for the98Mo(n,c)99Mo reaction were
determined relative to the reference values ofr0,Au= 98.65 ± 0.09
barn and I0,Au= 1550 ± 28 barn for the 197Au(n,c)198Au reaction
In order to improve the accuracy of the experimental results, the
correction factors for gamma-ray attenuation (Fg), thermal neutron
self-shielding (Gth), and resonance neutron self-shielding (Gepi)
ef-fects, and the epithermal neutron spectrum alpha shape factor (a)
were taken into account In addition, the true coincidence
sum-ming corrections were also taken into account in the99Mo activity
measurements The present results are compared with the
experi-mental data and the evaluated values
2 Experimental procedure
2.1 Neutron source
The PNF based on an electron linac was proposed in 1997[10]
for nuclear data production in Korea and was constructed at the
Pohang Accelerator Laboratory (PAL) on December 1998[11] The
characteristics of the PNF are described elsewhere[12–16], so only
a general description is given here It consists of an electron linac, a
photo-neutron target, and a 12-m long time-of-flight (TOF) path
The photo-neutron target was composed of ten Ta plates with a
diameter of 4.9 cm and an effective thickness of 7.4 cm There
was a 0.15 cm water gap between Ta plates in order to cool the
tar-get effectively The housing of the tartar-get was made of titanium The
photo-neutron target was located in the center of a cylindrical
water moderator The water moderator made by an aluminum
cyl-inder with a thickness of 0.5 cm, a diameter of 30 cm and a height
of 30 cm
The distributions of neutrons with and without water
moder-ator were described elsewhere[17,18] The photo-neutrons
pro-duced in the giant dipole resonance region consist of a large
portion of evaporated neutrons and a small fraction of directly
emitted neutrons which dominated at high energies The
neu-trons produced in the Ta target without water moderator have
a Maxwellian energy distribution with a nuclear temperature of
0.45 MeV The estimated neutron yield per kW of beam power
for electron energies above 50 MeV at the Ta target is about
1.9 1012n/s[17], which is consistent with the calculated value
based on Swanson’s formula, 1.2 1011 Z0.66, where Z is the
atomic number of the target material [19] The total neutron
yield per kW of beam power was also measured by using the
multiple-foil technique and found (2.30 ± 0.28) 1012n/s [18]
The neutron energy spectrum with the water moderator is
shifted to lower energy region because of the effect of
modera-tion by water To maximize the thermal neutrons in this facility,
we have to use water to a level of 3–5 cm above the Ta target
surface[17] In this experiment the water level was 3 cm above
the target surface
2.2 Sample irradiation Natural Mo metallic foils, 12.7 mm in diameter and 0.1 mm in thickness, were used as the activation samples The Au and In metallic foils were used as the comparator reactions and the neu-tron flux monitors, respectively The characteristics of Mo, Au and
In foils are given inTable 1
In order to measure the thermal neutron cross-section and the resonance integral for the 98Mo(n,c)99Mo reaction by activation method relative to the 197Au(n,c)198Au reaction, the natural Mo and Au foils were irradiated with and without a Cd cover with a thickness of 0.5 mm The neutron fluxes exposed to each sample during the irradiation were determined from activities of the In monitors stacked alternatively between Mo and Au foils The Mo,
Au and In foils were stacked on the sample holder as shown in Fig 1, where Mo(Cd) and Au(Cd) denote the activation foil covered with a 0.5-mm thick Cd The irradiation time was 150 min yielding enough the activities to be measured in ac-ray counting system The thermal neutron flux at the center of the moderator surface was determined based on the activity of the197Au(n,c)198Au reac-tion (t1/2= 2.69517 d, Ec= 411.80 keV, Ic= 95.58% andr0= 98.65 barn), and the obtained value was (5.85 ± 0.31) 108n cm2
s1kW1 The neutron flux exposed to each sample was extrapo-lated from the measured activities of In foils irradiated simulta-neously with the foil samples The cadmium ratio is defined by
CR = (R/RCd), where R and RCdare reaction rates per atom for bare and Cd-covered isotope irradiation, respectively The obtained cad-mium ratio for197Au is 2.77 ± 0.04 and that for98Mo is 1.21 ± 0.02, respectively The main nuclear data together with their uncertain-ties indicated in the bracket for the nuclear reactions considered such as 98Mo(n,c)99Mo, 197Au(n,c)198Au and 115In(n,c)116mIn are listed inTable 2based on the table of isotopes[20]
2.3 Measurement of activity The induced gamma activities emitted from the activation foils were measured by using a high-resolutionc-ray spectrometer The
c-ray spectrometer was a p-type coaxial CANBERRA high-purity germanium (HPGe)-detector with a diameter of 59.2 mm and a thickness of 30 mm The HPGe-detector was coupled to a com-puter-based multichannel analyzer with the associated electronics
to determine the photopeak area ofc-ray spectrum The spectrum analysis was done using the GENIE-2000 computer program The energy resolution of the detector was 1.80 keV full width at half maximum (FWHM) at the 1332.5-keV peak of60Co The detection efficiency is 20% at 1332.5-keV relative to a 76.2-mm diame-ter 76.2-mm length NaI(Tl) detector The detection efficiency for thec-ray spectrometer was calibrated with a set of standard sources:241Am (59.541 keV),137Cs (661.657 keV),54Mn (834.848 keV), 60Co (1173.237 keV and 1332.501 keV), and 133Ba (80.997 keV; 276.398 keV; 302.853 keV 356.017 and 383.815 keV) The
Table 1 Characteristics of Mo, Au and In foils.
Foil Diameter (mm) Thickness (mm) Weight (g) Purity (%)
Trang 3measured detection efficiencies were fitted by the following
function:
lne¼X5
n¼0
anðlnðE=E0ÞÞn; ð1Þ
whereeis the detection efficiency, anrepresents the fitted
parame-ters, E is the energy of the photopeak, and E0= 1 keV
The waiting and the measuring times were chosen based on the
activity and the half-life of each radioactive isotope In order to
minimize the uncertainties caused by random coincidence and
pile-up effects, we have chosen the appropriate distance between
the sample and the detector for each measurement Generally,
the dead times were kept below 0.4% during the measurement
The activated foil was attached on a plastic sample holder and
can be set at a distance from 5 to 105 mm from the radioactive
source to the surface of the detector
To measure the activities of the98Mo(n,c)99Mo,197Au(n,c)198Au
and 115In(n,c)116mIn reactions, we have chosen the c-ray peaks
with high intensity, well separated, and relatively low background
The activity of the 99Mo was determined by using the c-ray of
739.50 keV (12.13%) The activity of the 198Au was determined
using the 411.80 keV (95.58%) c-ray peak In case of the 116mIn,
the activity was measured using the 1293.54 keV (84.4%) c-ray
peak The measuring times were varied from several ten minutes
to several hours depending on the statistics of thec-ray peaks
3 Data analysis
A high-purity (>99.99%) Mo foil with a natural isotopic compo-sition (92Mo 14.84%,94Mo 9.25%,95Mo 15.92%,96Mo 16.68%,97Mo 9.55%,98Mo 24.13%, and100Mo 9.63%) was used for measuring the thermal neutron cross-section and the resonance integral of the
98Mo(n,c)99Mo reaction We thus considered the following possible competing reactions: (1)100Mo(n,2n)99Mo caused by fast neutrons with threshold energy of about 8.37 MeV and (2)100Mo(c,n)99Mo reaction caused by high-energy photons with threshold energy of about 8.29 MeV The fast neutron flux was also checked based on the well known 27Al(n,a)24Na reaction (t1/2= 14.9590 h,
Ec= 1368.633 keV (100%) and 2754.028 keV (99.94%) and cross-section r(n,a)= 725lb) [21] According to the characteristics of neutron flux distribution on the present experimental configura-tion[17], the neutrons were well thermalized, and the activity con-tribution from the100Mo(n,2n)99Mo reaction to the98Mo(n,c)99Mo reaction can be neglected For the100Mo(c,n)99Mo competing reac-tion, the activity can be calculated based on the integral sec-tion and the photon flux exposed to the sample The integral cross-section of the100Mo(c,n)99Mo reaction was taken from reference [22] The photon flux was determined by the activation method using the well known197Au(c,n)196Au reaction The activity contri-bution from the photonuclear reaction of100Mo(c,n)99Mo to the
98Mo(n,c)99Mo reaction was estimated to be 0.11%
Fig 1 Configuration of the neutron source based on the Ta target and water moderator system and the experimental arrangement of the activation samples The samples are arranged slightly off-center to minimize the photon background from the Ta target The numbers in this figure refer to dimension in cm.
Table 2
Nuclear decay data and their uncertainties given in parenthesis used for the determination of the radioactivities [20]
Reaction Main resonance energy (eV) Half-life Mainc-rays Isotopic abundance (%)
Energy (keV) Intensity (%)
98
Mo(n,c) 99
158.782 (15) 0.0189 (8) 181.068 (8) 5.99 (11) 580.51 (7) 0.0032 (5) 739.500 (17) a 12.13 (22) 777.921 (20) 4.26 (8)
197
Au(n,c) 198
675.8836 (7) 0.084 (3)
115
In(n,c) 116m
1097.3 (2) 56.2 (11) 1293.54 (15) a
84.4 (17)
ac-Rays used in calculations.
Trang 4In this work, the 99Mo activity was determined by using the
c-ray peak of 739.50 keV The 99Mo emits multiple c-rays, and
some of them are in cascade (seeFig 2)[20] FromFig 2we can
rec-ognize that the net peak area of the 739.50 keV is increased due to
the contribution of the sum peak formed by the true summing (also
called cascade summing) of the 158.78 and 580.51 keV c-rays
(summing-in) However, thec-ray of 739.50 keV is also in
coinci-dence with thec-ray of 181.06 keV, and the true coincidence
sum-ming from these twoc-ray peaks leads to decrease the net peak
area of the 739.50 keV (summing-out) The true coincidence
correc-tions for the 739.50 keV were calculated based on the measured
to-tal and absolute photopeak efficiency curves of the detector and the
formulae for complex decay schemes given in references[23,24]
When the measurement carried out at a distance of 3 cm from
the detector, the summing-in and the summing-out correction
fac-tors for the 739.50 keVc-ray peak were estimated to be 0.99 and
1.15, respectively
3.1 Thermal neutron cross-section
The thermal neutron cross-section for the98Mo(n,c)99Mo
reac-tion, r0,Mo, has been determined relative to that for the 197Au
(n,c)198Au standard reaction as follows[25]:
r0;Mo¼r0;AuRMo FMo;CdRMo;Cd
RAu FAu;CdRAu;Cd
Gth;Au
Gth;Mo
gAu
gMo; ð2Þ
where r0,Au is the thermal neutron cross-section of the 197Au
(n,c)198Au reaction, Rxand Rx,Cdare reaction rates per atom for bare
and Cd-covered x (Mo or Au) isotope irradiation, respectively The
cadmium correction factor, Fx,cdaccounts for the difference in count
rate for Cd covered and bare samples, and Gth,xis the thermal neutron
self-shielding factor for x samples The Westcott factor gx, correction
for departure from 1/v cross-section behavior, for the98Mo(n,c)99Mo
reaction is 1.001[26], and that for the197Au(n,c)198Au reaction is
1.006[27,28] The details of some other correction factors for the
rel-evant nuclear reactions will be given in Section3.3
After a bare and Cd-covered sample irradiations, the reaction
rates RMo(Au)and RMo(Au),Cdfor Mo and Au samples are determined
by[18]
kt cpÞ
noeIcð1 eksÞð1 ekt iÞekt wð1 ekt cÞ;
ð3Þ
where Nobsis the net number of counts under the full-energy peak collected during the measuring time tc, nois the number of target nuclei,eis the detector efficiency, Icis the intensity of thec-ray,
kis the decay constant, tiis the irradiation time, twis the waiting time,sis the pulse width, and tcpis the cycle period
3.2 Resonance integral The resonance integral for the (n,c) reaction in an ideal 1/E epi-thermal neutron spectrum is defined by the following relation:
I0¼
Z 1
Ecd
rðEÞ
wherer(E) is the cross-section as a function of neutron energy E, and Ecdis the cadmium cut-off energy, which is usually defined as 0.55 eV However, the resonance integral defined in Eq.(4)is not va-lid in a non-ideal, real epithermal neutron spectrum[29] The reso-nance integral, I0(a) for a 1/E1+areal epithermal neutron spectrum is defined as follows[29,30]:
I0ðaÞ ¼
Z 1
ECd
rðEÞ ð1eVÞa
whereais an epithermal neutron spectrum shaping factor, which is energy independent The relationship between I0and I0(a) is given
by[29]:
I0ðaÞ ¼ ð1eVÞa I0 0:426gr0
ðErÞa þ
0:426gr0
ð2aþ 1ÞðECdÞa
where Er effective resonance energy (eV), as defined by Ryves [31,32], the term (I0 0.426gr0) represents the reduced resonance integral, i.e with the 1/v tail subtracted The literature values of Er
are 5.65 eV for197Au[33]and 241 eV for98Mo[33], respectively The epithermal neutron spectrum shape factor, a at the sample irradiation position was experimentally determined by using the dual monitor method using the measured Cd ratios for the
197Au(n,c)198Au and the186W(n,c)187W reactions The half-life of the187W is 23.72 h, and the mainc-ray energies and intensities (%)
of 187W used in the calculation are 479.53 keV (21.8%) and 685.77 keV (27.30%) After having the Cd ratios for the
197Au(n,c)198Au and the186W(n,c)187W reactions with the Cd cover thickness of 0.5 mm, the a-shape factor was derived from the following equation[27,30,34]:
ðCR 1ÞAu
ðCR 1ÞW¼
fðQ0 0:4264ÞGgWðEr;WÞaþ Ca
fðQ0 0:4264ÞGgAuðEr;AuÞaþ Ca
where CR* = CR/Fcd,Ca¼ 0:4264
ð2 a þ1ÞEaCd; Q0¼ I0
g r 0, G is the ratio of the epi-thermal neutron self-shielding factor Gepito the thermal neutron self-shielding factor Gthgiven inTable 3for Au and W foils By using the nuclear data given inTable 3, thea-shape factor has been found
to be 0.068 ± 0.005
The measured resonance integral I0(a) for the 98Mo(n,c)99Mo reaction has been determined relative to that for the
197Au(n,c)198Au reaction as a standard by the following relation[25]:
I0;MoðaÞ ¼ I0;AuðaÞ gMor0;Mo
gAur0;Au CRAu FAu;Cd
CRMo FMo;Cd
Gepi;Au
Gth;Au
Gth;Mo
Gepi;Mo
; ð8Þ
where Gth,Mo(Au)and Gepi,Mo(Au)are the thermal and the epithermal neutron self-shielding factor for Mo (or Au) sample, respectively
In the determination of the resonance integral from Eq.(8), the thermal and the epithermal self-shielding factors, Gthand Gepiwere calculated according to the Section3.3 Then, the obtained I0,Mo(a) value was converted to I by using Eq.(6)
Fig 2 Simplified decay scheme of 99 Mo.
Trang 53.3 Correction factors
In order to improve the accuracy of the experimental results,
the following correction factors such as the neutron self-shielding,
the c-ray attenuation, the cadmium correction, and the g-factor
were considered
The thermal neutron self-shielding correction factor for thin
slabs was calculated as follows[36]:
Gth¼ð1 e
nÞ
where n ¼ 2=pffiffiffiffi
R0t,R0is the macroscopic capture cross-section for
thermal neutrons (En= 0.0253 eV), and t is the foil thickness
The epithermal neutron self-shielding factor was calculated as
follows[37]:
Gepi¼ 0:94
1 þ ðz=2:70Þ0:82þ 0:06; ð10Þ
where a dimensionless variable z =P
tot(Eres) 1.5t (Cc/C)1/2, which converts the dependence of Gepion the dimension and
phys-ical and nuclear parameters into an unique curve [38] and
P
totðEresÞ ¼qN A
M rEresis the macroscopic cross-section at the
reso-nance peak (Eres) (whereqis the density; NAis the Avogadro’s
num-ber; M is the atomic weight;rEresis the microscopic cross-section at
Eres), t is the foil thickness, and C is the total resonance width
(C=Cc+Cn, whereCcandCnare resonance widths for (n,c) and
(n,n0) reactions)
The correction factor forc-ray attenuation, Fg, in the activation
foil at a givenc-ray energy was approximated as follows[34]:
Fg¼ lt
wherel is the linear attenuation coefficient (cm1), and t is the
sample thickness in cm
The cadmium correction factor for the 98Mo(n,c)99Mo and
197Au(n,c)198Au reactions are 1.000 and 1.009 [35], respectively
The main correction factors used for the determination of thermal
neutron capture cross-sections and resonance integrals for the
98Mo(n,c)99Mo and197Au(n,c)198Au are listed inTable 4
4 Results and discussion
The thermal neutron cross-section and the resonance integral
for the 98Mo(n,c)99Mo reaction have been measured relative to
r0= 98.65 ± 0.09 barn and the resonance integral value of
I0= 1550 ± 28 barn of the197Au(n,c)198Au reaction The obtained
results are the mean value from three replicate measurements
The main sources of the uncertainties for the present results were
estimated as given inTable 5
We can see fromTable 5that the main sources of the uncertain-ties for the thermal neutron cross-section measurement are due to the statistical error (2.5%), the detection efficiency (2.75%) and the
c-ray intensity (1.8%) The main sources of the uncertainties for the resonance integral measurement are due to the reference thermal neutron cross-section (4.61%), thea-shape factor (4.5%), the cad-mium ratio (2.18%), and the epithermal neutron self-shielding fac-tor (1.35%) The total uncertainties for the thermal neutron cross-section and the resonance integral for the98Mo(n,c)99Mo reaction
of 5.1% and 8.8%, respectively, have been obtained by combining the uncertainties for Mo and Au listed inTable 5
4.1 Thermal neutron cross-section for98Mo(n,c)99Mo reaction The present result for the thermal neutron capture cross-section
of the98Mo(n,c)99Mo reaction is 0.136 ± 0.007 barn and is com-pared with the existing experimental and evaluated data inTable
6and inFig 3
As seen inTable 6andFig 3, the previous experimental thermal neutron cross-sections of the98Mo(n,c)99Mo reaction are varied from 0.12 barn[6]to 0.18 barn[7] Maximum deviation between two values is about 50% The present result, 0.136 ± 0.007 barn is
Table 3
Nuclear data used foradetermination.
197
Au(n,c) 198
186
W(n,c) 187
Table 4
Correction factors used for the calculation of thermal neutron capture cross-section and resonance integral.
197
Au(n,c) 198
Table 5 Uncertainties for the thermal neutron cross-section and the resonance integral measurements.
Uncertainties due to Uncertainties (%)
197
Mo Thermal neutron cross-section measurements
Thermal neutron self-shielding factor 0.75 0.60 Reference thermal neutron cross-section 0.09 –
Total experimental uncertainty 2.76 4.27 Resonance integral measurements
Epithermal neutron self-shielding factor 1.70 1.35 Thermal neutron self-shielding factor 0.70 0.50 Reference thermal neutron cross-section 0.01 4.61
Total experimental uncertainty 5.35 6.95
Trang 6in good agreement with the experimental results reported by
Bab-ich and Anufriev[41], De Corte and Simonits[42], Gryntakis et al
[43], Wyrich and Poenitz[45], Sims and Juhnke[49], and Cabell
[50] On the other hand, the measurements reported by Kurosawa
and Shimizu[46], Heft[47], Gleason[48], Fabry and Jacquemin[6],
and Dahlberg et al.[7]differ by more than 5.1% from the present
result The evaluated values from ENDF/B-VII.0 [39], JENDL-3.3 [26], and JFF-2.2[40]are agreed with the present result
4.2 Resonance integral for98Mo(n,c)99Mo reaction The present resonance integral value for the 98Mo(n,c)99Mo reaction given in Table 7has been found to be 7.02 ± 0.62 barn,
Table 6
Thermal neutron capture cross-section for the 98
Mo(n,c) 99
Mo reaction.
Co
% Difference means that the percentage difference = 100 (1 – this work/literature value).
Fig 3 Thermal neutron cross-sections of the 98
Mo(n,c) 99
Mo reaction.
Table 7
Resonance integrals for the 98
Mo(n,c) 99
Mo reaction.
Fig 4 Resonance integrals of the 98 Mo(n,c) 99 Mo reaction.
Trang 7by assuming the cadmium cut-off energy as 0.55 eV and relative to
the reference value of 1550 ± 28 barn of the197Au(n,c)198Au
reac-tion The Fig 4 compares the present result with the existing
experimental data and evaluated data
As seen inTable 7andFig 4, the existing resonance integrals for
the98Mo(n,c)99Mo reaction are in the range of 4.72 barn[8]to 8.2
barn[9] The present result, 7.02 ± 0.62 barn is in good agreement
with the values obtained by Gryntakis [43], Heft [47], Stainnes
[51], Sims and Juhnke[49], and Cabell[50] However, the present
result differs from the data obtained by Koehler and Schneider
[52], De Lange and Bigham[53], De Soete et al.[9], Gleason[48],
and De Corte et al [8] The evaluated resonance integral values
of JEF-2.2[40], ENDF/B-VI[40], and JENDL-3.3[26]are lower than
the present result by about 1–7%
5 Conclusion
The thermal neutron cross-section and the resonance integral
for the 98Mo(n,c)99Mo reaction have been measured relative to
the reference reaction 197Au(n,c)198Au by the activation method
at the Pohang Neutron Facility The results obtained for the
ther-mal neutron cross-section and the resonance integral of the
98Mo(n,c)99Mo reaction are 0.136 ± 0.007 barn and 7.02 ± 0.62
barn, respectively The present results for the thermal neutron
cross-section value and the resonance integral value are in good
agreement with most of the existing experimental and the
evalu-ated data within the limits of error as shown inFigs 3 and 4
Acknowledgments
The authors would like to express their sincere thanks to the
staff of the Pohang Accelerator Laboratory for excellent operation
of the electron linac and their strong support This work was
sup-ported by the Korea Science and Engineering Foundation (KOSEF)
through a Grant provided by the Korean Ministry of Education,
Sci-ence and Technology (MEST) in 2007 and 2008 (Project No M2
07B090010810 and M2 08B090010810), by the Science Research
Center project of the Center for High Energy Physics, Kyungpook
National University, and by the Vietnam National Basic Research
Program in Natural Science One of authors (Y.D.O) is supported
by the Korea Research Foundation Grant (KRF-2006-353-C00014)
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