Radioactivity, Temperature, Pressure
Name: Bob B.
Date: Thursday, August 22, 2002
Does the decay rate of U238 vary with temperature and pressure?
Not significantly. U238 decays by emitting an alpha particle (a helium
nucleus). The decay rate is determined almost entirely by the environment
in the nucleus. Temperature and pressure changes that we are capable of
making affect the electron cloud and do not affect the nucleus.
Maybe the sorts of temperatures and pressures you could get in a fusion
reactor would measurably affect the decay rate, but I doubt it.
Richard E. Barrans Jr., Ph.D.
Director of Academic Programs
PG Research Foundation, Darien, Illinois
Radioactive decay is a nuclear process. The rate of fission (in the case
of U238 as well as other decays is proportional to the concentration of
nuclei. So the rate will change slightly with large changes in the
temperature and pressure because the volume of the fissionable material
increases with increasing pressure and decreasing temperature. However, this
is a minor effect if the concentration of nuclei is significantly less than
the so-called critical mass.
When the concentration of nuclei reaches the critical mass, the decay
events produce sufficient neutrons to cause a chain reaction, i.e. the
neutrons strike other nuclei causing them to decay, which produces more
neutrons which cause other nuclei to decay,......
This is what happens in an atomic bomb, and under more controlled
conditions in a nuclear reactor. You can find this discussed in lay terms in
the book: "The Making of the Atomic Bomb" by Richard Rhodes.
However, the temperatures and pressures that can be obtained with
standard equipment do not affect the rate of radioactive decay. What happens
in stars etc. where enormous pressures are generated is also excluded.
So far as is known, decay rates of radioactive elements are constant and
independent of the conditions about which you ask. If decay rates were found
to be temp/pressure dependent, a good deal of geologic dating work would be
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