Nuclear reactions change an atom's nucleus. They start with unstable (radioactive) isotopes. These isotopes undergo changes to their nuclei to become more stable. These changes are not affected by variables like temperature, pressure, or catalysts.
Alpha particles are ejected helium atoms. They change the element.
Beta particles are electrons. This also changes the element
Gamma radiation is not a particle. It is pure energy. It is often a part of alpha or beta decay.
The nucleus is held together by nuclear forces. This force counter acts the repulsion of electrical charges.
The ratio between protons and neutrons affects how stable a nucleus is. The ideal ratio is about 1:1. If there are too many neutrons the nucleus will undergo beta decay. If there are too many protons the nucleus may undergo alpha decay or positron emission. A positron has the mass of an electron but positive.
Every radioactive isotope has a predictable rate of decay. This decay is measured in half-lives.
A half life is the amount of time it takes for half of the original atoms to decay into new elements.
Half lives follow an exponential decay model.
Mathematically can be expressed by:
A = A0 (1/2 )n
A = amount remaining
A0 = Initial amount
If there are 60 grams of Np-240 present, how much Np-240 will remain after 4 hours? (Np-240 has a half-life of 1 hour)
Solution:
how much mass remains = (60grams)
how much mass remains = A = (60g)(1/2 )4 = 3.75g
After 4 hours, only 3.75g of our original 60g sample would remain the radioactive isotope Np-240.
Because Radioisotopes decay at a constant rate we can use the ratio of the radioisotope to its products to determine age, i.e. by comparing the amount remaining to the initial amount. This is commonly done in radiocarbon dating.
How long will it take for 18.0 grams of Ra-226 to decay to leave a total of 2.25 grams? Ra-226 has a half-life of 1600 years.
Solution:
18.0g ⇒ 9.0g ⇒ 4.5g ⇒ 2.25g, this is three half-lives
how old (time)=3×1600years
how old (time)=3×1600years
This decay process takes 4800 years to occur.
Fusion reactions occur when two atoms combine together.
Fission reactions occur when a single atom splits apart.
Modern nuclear reactors use nuclear fission to generate power. Fission causes a chain reaction to occur, which heats up water. The steam turns a turbine which generates electricity.
When Uranium-235 splits it ejects 3 neutrons. These neutrons can collide with another uranium causing it to undergo fission, which also generates 3 more neutrons. This will continue until all the radioactive material decays.
Nuclear reactors use control rods to slow the chain reaction. Lead control rods block some of the neutrons and stop them from cascading.