Decay modes

Question 1

For light isotopes:

Answer 1

Z from 0 to 20, the stable nuclei follow the straight line N = Z. Such nuclei have numbers of protons and neutrons.

Question 2

As Z increases beyond 20:

Answer 2

• Stable nuclei have more neutrons than protons. The neutron/proton ratio increases.
• The extra neutrons help to bind the nucleons together without introducing the repulsive force as more protons would do.

Question 3

α emitters occur when:

Answer 3

Beyond about Z=60, most emissions occur where Z > 80 and N> 120 and has more neutrons than protons, and are too large to be stable as strong nuclear force cannot overcome the electrostatic force between the protons.

Question 4

β+ emitters occur:

Answer 4

• To the right of the stability line where the isotopes are proton-rich compared to stable isotopes.
• A nucleus that emits a β+ loses a proton and gains an neutron.
• Moving -Z + N.

Question 5

β- emitters occur:

Answer 5

• To the left of the stability line where the isotopes are neutron-rich compared to stable isotopes.
• A nucleus that emits a β- loses a neutron and gains an electron.
• Moving Z + -N.

Question 6

What happens in gamma emission?

Answer 6

• If the nucleus is formed in an excited state after it emits an α or β particle or undergoes electron capture.
• The excited state is usually short-lived and the nucleus moves to its lowest energy state, the ground state.
• Via one or more lower energy excited states.

Question 7

What is a metastable state?

Answer 7

An excited state of the nuclei of an isotope that lasts long enough after α or β emission for the isotope to be separated from the parent isotope