Nuclear Decay: Pure Beta vs. Mixed Beta/Gamma Emitters

[daveb]

This may be better suited for the nuclear engineering forum, so feel free to move it.
In decay processes that involve beta decay (or positron decay), there are pure beta emitters and mixed beta/gamma emitters. What determines whether a specific nuclide is just a pure emitter as opposed to a mixed?

 

[Astronuc]

This forum is fine for this question.

Actually, there are very few pure beta emitters, IIRC, for example tritium, C-14, Sr-90, and S-35. They generally produce low energy betas.

The phenomenon depends on the energy states of the nuclei (e.g. T -> He-3), C-14 -> N-14. (from http://www.hps.org/publicinformation/ate/faqs/radiationtypes.html) Check the binding energy of both of the pair nuclei (radionuclide and subsequent decay product, or stable daughter nuclide).

In beta decay, the daughter nucleus would emit the subsequent gamma to dump extra energy dropping into its final stable state.

 

[Grogs]

The phenomenon depends on the energy states of the nuclei (e.g. T -> He-3), C-14 -> N-14. (from http://www.hps.org/publicinformation/ate/faqs/radiationtypes.html) Check the binding energy of both of the pair nuclei (radionuclide and subsequent decay product, or stable daughter nuclide).

You can check out the excited states for nuclei here:

http://atom.kaeri.re.kr/ton/

In most cases, for the pure beta emitters, the Q value of the reaction is less than the energy of the lowest excited state in the daughter nuclei. For example, N-14's first excited state is at 5.1 Mev, but the Q-value of C-14 decay is only 0.156 Mev. Since the Q-value is less than the first excited state of N-14, C-14 decays directly to the ground state of N-14 and all of the decay energy goes to the beta/neutrino/recoil nucleus kinetic energy.