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04 February 2012

Answer to Question #1259 Submitted to "Ask the Experts"

Category: Radiation Basics — Beta Particles (negative and positive) and Electrons

The following question was answered by an expert in the appropriate field:

When a positron is emitted in beta radiation, it seems that a proton is changed into a neutron. However, a neutron weighs slighty more than a proton. How is it possible then for a proton to change into a neutron and positron when a neutron and positron weigh more than the proton did? Where is the extra mass coming from?

The net effect of positron decay reduces the number of protons in a nucleus by one and increases the number of neutrons by one. Whereas the effect is "to change a proton into a neutron," the process does not occur by this mechanism. Rather, a positron and a neutrino are created in the nucleus at the moment of disintegration. This spontaneous nuclear process releases an amount of energy equal to the energy equivalent of the rest mass that disappears in the process. That positron decay is a nuclear process is consistent with the fact that the decay of free protons by positron emission is not observed in nature. On the other hand, the beta decay of free neutrons is a familiar fact.

Jim Turner, CHP

Answer posted on 9 October 2001. The information and material posted on this website is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Website. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.