Atomic Physics Module
- Define isotope.
Isotopes are elements with the same number of protons and different numbers of neutrons.
- What is the relationship between the atomic mass number, the atomic number, and the number of neutrons in a nucleus.
A = N + Z
where A is the atomic mass number, N is the number of neutrons and Z is the atomic number.
- What does E=mc2 mean?
When mass is converted into energy the amount of energy released is equal to the mass multiplied by the speed of light squared.
- How many protons and neutrons are in Plutonium 239?
Z = 94
N = A - Z
239 - 94 = 145
- How much energy is released in the total conversion of 10g of mass into energy? How many megatons of TNT equivalent are released?
E = mc2 (Make sure you use consistent units i.e. mks, cgs)
10 g = 0.1 kg
Energy = .01 kg (3.0 x108 m/s)2 = 9 x1014 joules = .22 Mt.
- What is an alpha particle? What is a beta particle?
An alpha particle is a helium nucleus. A beta particle is an electron.
- What is meant by the half-life of a radioactive substance?
The half life is the time it takes for one half of a given radioactive substance to decay.
- What is spontaneous fission? Why is it important?
Spontaneous fission is fission that occurs without any external trigger i.e. a neutron. It is important because neutrons are released in this process. Those neutrons can then trigger other fission reactions. If spontaneous fission were to occur just as two halves of a gun type weapon were being assembled there is a chance that the weapon will fizzle.
- Iodine 131 is a prominent fallout particle. After undergoing beta decay what element does it become?
I 131 → Xe 131 + b ; where Xe is xeonon.
- When uranium 238 decays by alpha particle emission, what nucleus is formed?
U 238 → Th 234 + a ; where Th is thorium.
- Plutonium is usually the radioactive material used in the primary of a hydrogen bomb. If we eliminated all of our existing nuclear weapons today, and then Stored the plutonium, how long would it take for this stockpile to decay to one-quarter of its original amount? To one-sixteenth? Is there anything we can do to speed up this process? (Pu 239 has a half-life of 24,400 years).
For plutonium to decay to one-quarter of the original amount it will take two half-lives (1/2 x 1/2 = 1/4) or 48,800 years. To decay to one-sixteenth, (1/2 x 1/2 x 1/2 x 1/2= 1/16), or 97,600 years. It is not possible to speed up nuclear reactions. However, you can artificially transmute the element into another radioactive that has a shorter half-life. This is being pursued as a clean-up option for nuclear reactors.
- Why is an antineutrino needed in beta decay?
The antineutrino is necessary in beta decay to conserve energy.