sơ lược về công nghệ bom nguyên tử và bom hydrogen

General Structure of Atomic bomb: The immense destructive power of atomic weapons derives from a sudden release of energy produced by splitting the nuclei of the fissile elements making

HO CHI MINH UNIVERSITY OF

TECHNOLOGY

HYDROGEN BOMB AND

NUCLEAR BOMB Team member:

Nguyễn Xuân Minh

Phạm Trọng Tân

Phạm Phú Duy Khương

Huỳnh Đức Nguyên

Nguyễn Ngọc Đăng Khoa

Nguyễn Quang Trường

Hồ Thiên Trường

Lecturer: Ms Nguyễn Thị Thuý Hằng

Table of contents

1

1.Brief history of all Nuclear bombs

Atomic science began many centuries ago with experimenting and probing into the nature and structure of matter This began with Thales had described the power of attraction in electricity long before electricity was known Democritus (460-370 BC), a Greek philosopher was called the "father of the atom.", argued that all matter must consist of a number of fundamental pieces James Clerk Maxwell (1831-1879) stated that atoms were the foundation stones of the universe Dimitri Mendeleef (1834-1907)-discoverer of the periodic system of the elements, opened new areas of atomic knowledge Pierre and Marie Curie discovered that the atom has a core, or nucleus, quite different from the shell of the atom

In 1905, Albert Einstein (1879-1955) wrote the mass-energy conversion equation in 1932, James Chadwick discovered the third fundamental particle of the atom, the neutron This would provide an ideal projectile for splitting the nucleus of the atom

In 1938, the discovery of fission of the uranium nucleus by neutron bombardment Leading names in this research carried out in Germany, were Dr Otto Hahn and Dr Fritz Strassmann And also in 1938, to the fear of Nazi Germany were trying to make an atomic bomb, project Manhattan was created under the command of President Franklin Roosevelt In June 1940, President Roosevelt organized the National Defense Research Committee The Uranium Committee became a part of this group, reporting to Dr Vannevar Bush Dr Bush and the National Defense Research Committee determined on an all out effort to develop an atomic bomb

Under the direction of Major General Leslie R Groves, the Manhattan Engineer District (the

Manhattan Project), a new branch of the Army Corp of Engineers, was established to administer work on military uses of uranium On December

2, 1942, the first self-sustaining chain reacting pile was successfully operated at the university of Chicago by Enrico Fermi

This success brought authorization for construction of the Clinton diffusion plant at Oak Ridge, Tennessee, and the giant plutonium producing plant on the columbia river at Hanford, Washington The Oakridge plant was designed to concentrate U-235, one of five known isotopes of uranium while the Hanford plant was the source

of a new, man-made element, Plutonium Dr J Robert Oppenheimer arrived at Los Alamos in

practical atomic bomb was completed On July 16, 1945, the first test, code named "Trinity" was exploded at Alamogordo, New Mexico

General Structure of Atomic bomb:

The immense destructive power of atomic weapons derives from a sudden release of energy produced by splitting the nuclei of the fissile elements making up the bombs' core The US 2 type of atomic bomb‘s cores: the gun-type weapon with a uranium core in the Little Boy and the implosion-type device with a plutonium core in the Fat Man

Little Boy and Fat Man utilized different elements and completely separate methods of construction in order to function as nuclear weapons Little Boy detonated due to a fission chain reaction involving the isotope U-235 of uranium, while Fat Man used plutonium (Pu-239 form)

3

2 Nuclear bomb

a Definition

+ Nuclear fission

In nuclear physics and nuclear chemistry, every nucleus has different stability, heavy nucleus is less stabilize than others since it has lots of proton Thus it easily splits into smaller parts (lighter nuclei) in either a nuclear reaction or a radioactive decay The fission process often produces free neutrons and gamma photons

Nuclear fission can occur without neutron bombardment as a type of radioactive decay This type

of fission is rare except in a few heavy isotopes In engineered nuclear devices, essentially all nuclear fission occurs as a "nuclear reaction" — a bombardment-driven process that results from the collision of two subatomic particles In nuclear reactions, a subatomic particle collides with

an atomic nucleus and causes changes to it Nuclear reactions are thus driven by the mechanics

of bombardment, not by the relatively constant exponential decay and half-life characteristic of spontaneous radioactive processes

Nuclear fission of heavy elements produces exploitable energy because the specific binding energy (binding energy per mass) of intermediate-mass nuclei with atomic numbers and atomic masses close to 62Ni and 56Fe is greater than the nucleon-specific binding energy of very heavy nuclei, so that energy is released when heavy nuclei are broken apart The total rest masses of the fission products (Mp) from a single reaction is less than the mass of the original fuel nucleus (M) The excess mass Δm = M – Mp is the invariant mass of the energy that is released as photons (gamma rays) and kinetic energy of the fission fragments, according to the mass-energy equivalence formula For example, an uranium nucleus fissions into two nuclei fragments, about 0.1 percent of the mass of the uranium nucleus appears as the fission energy of ~200 MeV

+ Chain reactions

A nuclear chain reaction occurs when one single nuclear

reaction causes an average of one or more subsequent nuclear

reactions, thus leading to the possibility of a self-propagating

series of these reactions The specific nuclear reaction may be

the fission of heavy isotopes (e.g., Uranium-235, ) The nuclear

chain reaction releases several million In nuclear physics and

nuclear chemistry, every nucleus has different stability, heavy

nucleus is less stabilize than others since it has lots of proton

Thus it easily splits into smaller parts (lighter nuclei) in either a

nuclear reaction or a radioactive decay The fission process

often produces free neutrons and gamma photons

Nuclear fission can occur without neutron bombardment as a

type of radioactive decay This type of fission is rare except in a

few heavy isotopes In engineered nuclear devices, essentially

all nuclear fission occurs as a "nuclear reaction" — a

bombardment-driven process that results from the collision of

two subatomic particles In nuclear reactions, a subatomic particle collides with an atomic nucleus and causes changes to it Nuclear reactions are thus driven by the mechanics of bombardment, not by the relatively constant exponential decay and half-life characteristic of spontaneous radioactive processes

Nuclear fission of heavy elements produces exploitable energy because the specific binding energy (binding energy per mass) of intermediate-mass nuclei with atomic numbers and atomic masses close to 62Ni and 56Fe is greater than the nucleon-specific binding energy of very heavy nuclei, so that energy is released when heavy nuclei are broken apart The total rest masses of the fission products (Mp) from a single reaction is less than the mass of the original fuel nucleus (M) The excess mass Δm = M – Mp is the invariant mass of the energy that is released as photons (gamma rays) and kinetic energy of the fission fragments, according to the mass-energy equivalence formula For example, an uranium nucleus fissions into two nuclei fragments, about 0.1 percent of the mass of the uranium nucleus appears as the fission energy of ~200 MeV

Times more energy per reaction than any chemical reaction

The effective neutron multiplication factor, k, is the average number of neutrons from one fission that cause another fission The remaining neutrons either are absorbed in non-fission reactions or leave the system without being absorbed The value of k determines how a nuclear chain reaction proceeds:

k < 1 (subcriticality): The system cannot sustain a chain reaction, and any beginning of a chain reaction dies out over time

k = 1 (criticality): Every fission causes an average of one more fission, leading to a fission (and power) level that is constant Nuclear power plants operate with k = 1 unless the power level is being increased or decreased

5

k > 1 (supercriticality): For every fission in the material, it is likely that there will be "k" fissions after the next mean generation time Nuclear weapons are designed to operate under this state There are two subdivisions of supercriticality: prompt and delayed

In nature, uranium is found as (99,3 %), : (0.7%) becomes fissionable by absorbing fast neutrons with energy greater than 1 MeV However, when absorbing slow neutrons, will transmute to by following diagram:

Half-life of the reaction above is 23 minutes.Then isotope becomes Plutonium: Plutonium-239 has a half-life of 24,110 years and becomes isotope Uranium : will fission when either absorbing slow neutrons or fast neutron In conclusion, if the concentration of in a medium is high then the reaction cannot happen Nonetheless, with sufficient mass can cause a chain reaction which leads to a nuclear explosion releasing a tremendous amount of energy

b.Nuclear bomb’s operation

The isotopes uranium-235 and plutonium-239 were selected by the atomic scientists because they readily undergo fission Fission occurs when a neutron strikes the nucleus of either isotope, splitting the nucleus into fragments and releasing a tremendous amount of energy The fission process becomes self-sustaining as neutrons produced by the splitting of atom strike nearby nuclei and produce more fission This is known as a chain reaction and is what causes an atomic explosion

When a uranium-235 atom absorbs a neutron and fissions into two new atoms, it releases three new neutrons and some binding energy Two neutrons do not continue the reaction because they are lost or absorbed by a uranium-238 atom However, one neutron does collide with an atom of uranium-235, which then fissions and releases two neutrons and some binding energy Both of those neutrons collide with uranium-235 atoms, each of which fission and release between one and three neutrons, and so on

In the Fat Man Bomb,we could not use the same gun-type design that allowed Little Boy to explode effectively due to the fact it was powered by plutonium Therefore, Physicist Seth Neddermeyer at Los Alamos constructed a design for the plutonium bomb that used conventional explosives around a central plutonium mass to quickly squeeze and consolidate the plutonium, increasing the pressure and density of the substance An increased density allowed the plutonium

to reach its critical mass, firing neutrons and allowing the fission chain reaction to proceed To detonate the bomb, the explosives were ignited, releasing a shockwave that compressed the inner plutonium and led to its explosion

Criticality

In order to detonate an atomic weapon, you need a critical mass of fissionable material This means you need enough U-235 or Pu-239 to ensure that neutrons released by fission will strike another nucleus, thus producing a chain reaction The more fissionable material you have, the greater the odds that such an event will occur Critical mass is defined as the amount of material

at which a neutron produced by a fission process will, on average, create another fission event

7

Enrich Uranium process:

Uranium found in nature consists largely of two isotopes, U-235 and U-238 Enriched

uranium is a type of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation Natural uranium is 99.284% 238 Uisotope, with 235U only constituting about 0.711% of its mass 235U is the only nuclide existing in nature (in any appreciable amount) that is fissile with thermal neutrons The production of energy

in nuclear reactors is from the 'fission' or splitting of the U-235 atoms, a process which releases energy in the form of heat U-235 is the main fissile isotope of uranium Natural uranium contains 0.7% of the U-235 isotope The remaining 99.3% is mostly the U-238 isotope which does not contribute directly to the fission process During the Manhattan Project enriched

uranium was given the codename oralloy, a shortened version of Oak Ridgealloy The term oralloy is still occasionally used to refer to enriched uranium The 238U remaining after enrichment is known as depleted uranium (DU), and is

considerably less radioactive than even natural uranium,

though still very dense and extremely hazardous in granulated

form and was used to make armor-penetrating

weapons and radiation shielding and in some cases: outside

armour for tanks which the US had did with the M1 Abrams

tanks

3 Hydrogen bomb

2 Definition

+ Synthesis reaction

In nuclear physics, nuclear fusion is a reaction in which two or more atomic nuclei come close enough to form one or more different atomic nuclei and subatomic particles (neutrons or protons) The difference in mass between the products and reactants is manifested as the release

of large amounts of energy This difference in mass arises due to the difference in atomic

"binding energy" between the atomic nuclei before and after the reaction Fusion is the process that powers active or "main sequence" stars, or other high magnitude stars

It takes considerable energy to force nuclei to fuse, even those of the lightest element, hydrogen This is because all nuclei have a positive charge due to their protons, and as like charges repel, nuclei strongly resist being pushed close together When accelerated to high enough speeds, nuclei can overcome this electrostatic repulsion and brought close enough such that the attractive nuclear force is greater than the repulsive Coulomb force As the strong force grows very rapidly once beyond that critical distance, the fusing nucleons "fall" into one another and result is fusion and net energy produced The fusion of lighter nuclei, which creates a heavier nucleus and often

a free neutron or proton, generally releases more energy than it takes to force the nuclei together; this is an exothermic process that can produce self-sustaining reactions

+ Fusion fuel

The 2nd reaction, at the lowest energy, is common in research, industrial and military applications, usually as a convenient source of neutrons Deuterium is a naturally occurring isotope of hydrogen and is commonly available Tritium is a natural isotope of hydrogen, but because it has a short half-life of 12.32 years, it is hard to find, store, produce, and is expensive

+ Nuclear fusion reaction on Earth:

The first successful man-made fusion device was the boosted fission weapon tested in 1951 in the Greenhouse Item test This was followed by true fusion weapons in 1952's Ivy Mike, and the first practical examples in 1954's Castle Bravo This was uncontrolled fusion In these devices, the energy released by the fission explosion is used to compress and heat fusion fuel, starting a fusion reaction Fusion releases neutrons These neutrons hit the surrounding fission fuel, causing the atoms to split apart much faster than normal fission processes—almost instantly by

comparison This increases the effectiveness of bombs: normal fission weapons blow themselves

apart before all their fuel is used; fusion/fission weapons do not have this practical upper limit Research into controlled fusion, with the aim of producing fusion power for the production of electricity, has been conducted for over 60 years It has been accompanied by extreme scientific and technological difficulties, but has resulted in progress At present, controlled fusion reactions