Science/Physics of the Atomic Bomb

Science/Physics of the Atomic Bomb

 

Nagasaki, Hiroshima, Chernobyl, and Fukushima, the world has witnessed the dreadful consequences of nuclear reactions. Nowadays any term that associates ‘nuclear’ would frighten people because no one actually understands what ‘nuclear energy’ actually is. It only takes some bits of knowledge to have a macro vision of ‘nuclear’ energy is and the principles of the ‘Atomic bomb’.

 

 

*The below descriptions are very simplified explanations.

To start off, every element consists of a proton, neutron and electron.

 

What is a Proton

The proton is a (+) charged particle that consists the nucleus which is the core of an atom. The number of protons is equivalent with the atomic number.

In other words, the number of protons define ‘each element’ and differentiates ‘each element’ from another. In terms of chemistry, protons may be referred as a hydrogen ion H+.

 

 

Because a hydrogen atom has one proton and one electron but a hydrogen ion would lose the negative charged electron leaving only the positive charged proton by +1.

 

What is a Neutron

The neutron is a particle that doesn’t have a charge. The neutron also consists the nucleus of an atom.

However, neutrons don’t interfere with the original properties of an element but it contributes to the physical properties of an atom such as its nuclear weight.'

 

 

 

Isotopes are elements that have the same number of protons but different number of neutrons. In other words, isotopes are elements with same number of protons but with different nuclear weights.

Neutrons create isotopes and depending on the number of neutrons on an isotope it might make the isotope ‘unstable’ which may in simple ‘ready to emit energy’.

 

 

Neutrons also play an important role in nuclear reactions. A ‘nuclear reactor’ controls the speed and number of neutrons to overall cause and maintain control nuclear reactions.

 

 

What is an Electron

An electron is a particle that orbits around the nucleus of an atom with a (-) charge. Neutron and protons are ‘heavy weighted’ compared to an electron in which the mass of electrons is neglected.

Electrons don’t play much of a role in terms of ‘nuclear energy’. As ‘nuclear energy’ itself refers to the energy produced by the reaction of the nucleus of atoms (isotopes to be exact).

 

 

Wh is E=mc2 so important?

Albert Einstein and his famous equation E=mc2 is so famous but what does this equation imply? E stands for Energy and m stands for mass while c stands for the speed of light.

The essential message from this equation is that energy could be converted to mass while mass could be converted to energy.

 

 

Thus, a particle which itself is a form of mass it could be converted into energy whilst energy could be converted into mass or a particle. This equation alone explains how the universe could have started from a large explosion often known as the Big Bang.

 

 

Energy could be converted to mass or a particle that could make ‘an object’ out of only energy. Also, the equation implies that out of mass, energy could be produced.

 

What is Radioactivity

Radioactivity is release of energy by the decay of a nucleus of atoms or isotopes or electromagnetic reactions.[1] In common, radioactivity could be classified to two types of radioactivity.''

 

 

Nuclear radiation is radioactivity where energy is released by an interaction that originates from the nucleus of an atom or element.

This includes the nuclear reactions such as atomic bombs, nuclear electricity generation, Alpha Decay, Beta Decay, and Gamma Decay etc

 

 

Ionizing radiation is radioactivity where energy is released by an electromagnetic reaction. This includes X-rays which may be caused by an electron with a negative charge in high velocities or even protons in high velocities.

Ionizing radiation doesn’t originate from the nucleus which is the major difference between both

 

 

 

Alpha Decay / α-decay

Alpha decay is a radioactive decay where a nucleus emits an alpha particle. An alpha particle is a Helium nucleus with two protons and two neutrons.

Thus, after alpha decay, the element or atom changes into a totally different atom or element. Uranium-238(This means Uranium with an atom weight of 238) would become a Thorium-234 after alpha decay.

 

 

99% of the Helium that exists on Earth is a result of alpha decay. Alpha decay itself isn’t a high energy radiation emission which couldn’t even penetrate a paper thick barrier. However, it may be part of much bigger radioactive emissions.

 

Beta Decay

Beta decay is a decay where the balance between neutrons and protons is unstable that neutron would turn into a proton or vice versa. Beta decay emit subatomic particles that weren’t discussed in this session. The beta particle refers to an electron.

 

 

There are two types of Beta Decay where positive beta decay emits a positron and a neutrino (both aren’t discussed in this session but refer them as subatomic particles)

As a result of positive beta decay, a proton converts to a neutron. While negative beta decay emits an anti-neutrino and a beta particle(electron).

As a result of beta decay, a neutron converts to a proton.[2] Beta Decay has much energy than Alpha decay but it could be blocked by a layer of aluminum.

 

 

Gamma Decay

Gamma Decay is the emission of a gamma ray photon that have an extremely high level of energy. This energy itself could lead to a series of ionizing radiation as well.

Usually Gamma Decay is the ‘terrible’ level of radiation that causes all kinds of thermal burning, genetic mutation etc. Gamma Decay occurs as a result of a highly unstable nucleus of an atom or element with so much energy to emit.

 

 

The unstable nucleus would emit gamma photons and become a stable nucleus. Thus, there aren’t ‘charged’ particles that are emitted during the Gamma Decay.

Gamma radiation cannot penetrate materials such as Lead. Thus lead is often mentioned as an essential indicator of protection of radiation.

 

 

Nuclear Fission

Nuclear fission is the splitting of a nucleus of an atom into fragments of nuclei, neutrons and energy. Nuclear fission could be induced by collision of high velocity neutrons that would collide with the atom of target and fragment the nucleus of the atom.

For atoms with heavy nucleus with many protons and neutrons, such collision would induce massive electromagnetic radiation, kinetic energy and heat energy.

 

 

Often times the energy releases gamma photons, so it accompanies much of gamma radiation release as well. (Gamma decay). Some nuclear reactors collide high velocity neutrons to the target material to cause such nuclear fission.

Uranium-235 and Plutonium-239 would cause a consecutive nuclear reaction once the initial collision causes nuclear fission that causes high velocity neutrons during the process causing more nuclear fission reactions.  

 

 

Nuclear Fissile Material

Nuclear fissile material is a material that could go through a nuclear chain reaction of nuclear fission in a certain concentration of the material.

 

 

 

That is Nuclear fissile material would have enough free neutron that would react to cause a nuclear fission reaction and lead to a chain of such volatile reactions.

Uranium-233(which is very rare as Uranium-235 is also rare), Uranium-235 and Plutonium-239 are the primary materials that are Nuclear fissile.[3]

 

 

Prompt Criticality

The Prompt Criticality is the point or concentration where Nuclear fissile material are massed enough that neutrons are emitted to cause a chain nuclear reaction.

The condition of a Prompt Criticality is when k = 1 + β, where β is the delayed neutron fraction.

 

 

The prompt criticality is the standard for safety management of nuclear reaction.

The Chernobyl nuclear disaster is a result of systematic failure and human management of a reactor that became prompt critical, thus unable to control the chain nuclear reactions.[4]

 

 

Uranium

Uranium has 92 protons; thus, it has the atomic number 92. Although there are 118 atoms recognized as of 2021, Uranium is the heaviest atom that naturally exists on the planet earth.

It is actually a metal which is why often times it is referred as ‘mined’. Uranium ore often exists as U3O8 and unlike common sense, Uranium is very cheap as it is only about 50~100 USD per kg.[5]

 

 

This would be surprising but most of such Uranium is 238-Uranium or ‘Depleted Uranium’ that result as a byproduct of Uranium enrichment and commonly used more than we think.

For example, ‘Depleted Uranium rounds’ are common armor-piercing ammunition to penetrate thick armors in the military. Also depleted uranium is used for construction of nuclear bunkers as well. It is even used in pottery.

 

 

These facts themselves would confuse the general public. Uranium is such a dangerous material but why is it so cheap and abundant?

 

Difference between Urainum-238 and Uranium-235

Uranium-238 isotope takes over 99% of the total Uranium of the world. Uranium-235 isotopes only take 0.7% of the total Uranium proportion.

Uranium-238 doesn’t cause a nuclear chain reaction even though it is concentrated in large quantities. In other words, Uranium-238 doesn’t cause nuclear fission.

 

 

In other words, it wouldn’t go through volatile consecutive reactions that produce gamma radiation, massive energy, and neutrons to consecutively cause such reactions.

Uranium-238 rather only goes through a series of alpha decay which makes it safer than its infamy.

 

 

However, Uranium-235 in specific conditions and clustered in quantities over 15~40kg(depends on the environment) becomes nuclear fissile that it could cause numerous nuclear chain reactions.

Thus, only through ‘Uranium Enrichment’ which isolates Uranium-235 and concentrate or ‘enrich’ Uranium 235, could such a volatile nuclear reaction could occur.

 

Why Uranium?

Among the natural radioactive elements, Uranium decays very easily and it is easy to control the reactions of Uranium. Uranium Enrichment where Uranium 235 concentration is raised to favor nuclear chain reaction.

 

 

 

Uranium Enrichment

Natural Uranium-235 proportion is only about 0.7% of the total Uranium resources. Uranium Enrichment is the process of increasing the Uranium-235 proportion to certain concentrations that could become a nuclear fissile condition.

3~5% of Uranium-235 is referred as ‘Low Enriched Uranium’ where it is usually ‘reactor-grade’.

While over 20% of Uranium-235 is referred as ‘Highly Enriched Uranium’ and used as dangerous military level.

 

 

Thus, nuclear enrichment facilities are treated as very dangerous facilities and would cause very tense political tensions among countries that is often depicted in media.

 

 

Plutonium: What is Plutonium and How is it made?

Uranium is the heaviest naturally occurring element on planet Earth. Nuclear scientists discovered that when 238 Uranium was collided with neutrons, sometimes it would capture the neutron into its nucleus.

Shortly after 23 minutes, this Uranium-239 would go through negative beta decay which would change a neutron into a proton.

 

 

Thus, Neptunium with an atomic number of 93 is synthesized. However, Neptunium also shortly goes through another negative beta decay that only takes about 2 and a half days to make Plutonium that is atomic number 94.

 

 

Why 239-Plutonium? Why not 240-Plutonium or other isotopes

Plutonium could be synthesized from the abundant 238-Uranium with a nuclear reactor which by chance the Uranium would capture neutrons and decay into Plutonium.

Isolation of 238-Urainum from 235-Uranium is relatively difficult because the only difference between the two isotopes is the atomic weight.

Also 235-Uranium exists in such low quantities. However, Plutonium especially Plutionium-239 could be synthesized from the abundant 238-Uranium.

 

 

239-Plutonium is not able to be synthesized by the abundant 238-Uranium but it is also highly nuclear fissile. It causes nuclear chain reactions at even lower concentrations of 235-Urainum.

240-Plutonium is also produced as a byproduct during 239-Plutonium synthesis. However, 240-Plutonium is not as highly nuclear fissile as 239-Plutonium.  

 

 

Plutonium grade

It is even difficult and expensive to isolate 239-Plutonium from 240-Plutonium. Because there isn’t any chemical differentiation possible and the purification/isolation would depend on the only 1 atomic mass difference.

However, 239-Plutonium is highly nuclear fissile while 240 Plutonium isn’t.

 

 

Thus, the grade of Plutonium depends on how much 240-Plutonium is present. The higher the 239-Plutonium and lower the 240-Plutonium, it has a much higher grade.

Super grade Plutonium has 2~3 % of 240-Plutonium.

Weapon grade Plutonium has 3~7% of 240-Plutonium.

Fuel grade Plutonium is 7~18% of 240-Plutonium.

Reactor grade Plutonium is 18% equal or higher of 240-Plutonium

 

 

 

Fat man – First Plutonium Fission Bomb / Little Boy – First Uranium Fission Bomb

Under the command of Leslie R. Grover of the United States of America Army Crops of Engineers, Leslie R.Grover appointed J. Robert Oppenheimer the leader of the Manhattan Project.

Under several laboratories across the United States under Oppenheimer’s main laboratory in Los Alamos Laboratory in New Mexico, the atomic bomb was developed under the Manhattan Project.

 

 

J. Robert Oppenheimer and scientists developed two types of nuclear fission bombs. Little Boy used Uranium-235 which used a ‘gun’ like trigger that would shoot particles and cause a nuclear chain reaction. This was a gun-type nuclear bomb. 

 

 

Fat Man used Plutonium-239 and it was designed as an implosion type bomb which in simple consisted of layers of materials with different chemical-physical properties to cause a chain reaction and explode from the center.

 

 

Elements of the 509th Composite group were ordered the bombardment with the atomic bomb. The 393rd Bombardment squadron B-29 Enola Gay bombs Hiroshima with Little Boy on 6th August 1945.

The B-29 Bockscar carrying Fat Man originally aimed the port city of Kokura but detoured to Nagasaki due to the bad weather conditions on 9th August 1945.

 

 

Around 129,000 to 226,000 people including numerous civilians were sacrificed by the two bombs. It was such a tragic event but it also demoralized the Japanese Empire that was about to commence “The Glorious Death of One Hundred Million” campaign to fight until the very last.

The Japanese Empire made an unconditional surrender on 15th August 2023.

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[1] “Doe Explains...Radioactivity.” Energy.Gov, www.energy.gov/science/doe-explainsradioactivity. Accessed 10 July 2023.

[2] Beta Decay, www.atomicarchive.com/science/physics/beta-decay.html. Accessed 10 July 2023.

[3] “Fissile Material.” NRC Web, www.nrc.gov/reading-rm/basic-ref/glossary/fissile-material.html. Accessed 10 July 2023.

[4] Nuclear Criticality Safety Engineering Training Criticality Safety In ..., ncsp.llnl.gov/sites/ncsp/files/2021-05/Module11.pdf. Accessed 10 July 2023.

[5] “Uranium.” FocusEconomics, www.focus-economics.com/commodities/energy/uranium/. Accessed 10 July 2023.