Nuclear Transformations
- During radioactive decay, the atomic (proton) number and mass (nucleon) number of the nuclei will change
Alpha Emission
- An alpha particle consists of 2 protons and 2 neutrons (same as a helium nucleus)
- It is emitted from large unstable nuclei
Nuclear notation for an alpha particle
- When an alpha particle is emitted from a nucleus:
- The nucleus loses 2 protons
- The atomic (proton) number decreases by 2
- The nucleus loses 4 particles (nucleons) in total
- The mass (nucleon) number decreases by 4
- The nucleus loses 2 protons
Beta emission
Nuclear notation for beta minus and beta plus particle
- Beta minus decay is when a neutron turns into a proton emitting an electron
- When a beta minus particle is emitted from a nucleus:
- The number of protons in the nucleus increases by 1
- The atomic (proton) number increases by 1
- The total number of particles in the nucleus remains the same
- The mass (nucleon) number does not change
- The number of protons in the nucleus increases by 1
- Beta plus decay is when a proton turns into a neutron emitting a positron
- When a beta plus particle is emitted from a nucleus:
- The number of protons in the nucleus decreases by 1
- The atomic (proton) number decreases by 1
- The total number of particles in the nucleus remains the same
- The mass (nucleon) number does not change
- The number of protons in the nucleus decreases by 1
Gamma Emission
Nuclear notation for a gamma particle
- Gamma waves are emitted from a nucleus when the nucleus needs to lose some energy
- This usually occurs because the nucleus has excess energy following a previous decay
- Therefore, no protons or neutrons are lost from the nucleus in this process
- The atomic (proton) and mass (nucleon) numbers do not change
Neutron Emission
- A small number of isotopes can decay by emitting neutrons
- When a nucleus emits a neutron:
- The number of protons does not change
- The atomic (proton) number does not change
- The total number of particles (nucleons) in the nucleus decreases by 1
- The mass (nucleon) number decreases by 1
- The number of protons does not change
Worked example
A nucleus with 11 protons and 13 neutrons undergoes beta minus decay. It forms magnesium, which has the element symbol Mg.Which is the correct isotope of magnesium formed during the decay?
ANSWER: D
Step 1: Calculate the mass number of the original nucleus
- The mass number is equal to the number of protons plus the number of neutrons
- The original nucleus has 11 protons and 13 neutrons
11 + 13 = 24
- The mass number of the original nucleus is 24
Step 2: Calculate the new atomic number
- During beta decay a neutron changes into a proton and an electron
- The electron is emitted as a beta particle
- The neutron has an atomic number of 0 and the proton has an atomic number of 1
- So the atomic number increases by 1
11 + 1 = 12
- The new nucleus has an atomic number of 12
Step 3: Calculate the new mass number
- Protons and neutrons both have a mass number of 1
- Changing a neutron to a proton will not affect the mass number
- The new nucleus has a mass number of 24 (the same as before)