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Gamma Rays and Kinetic Energy
Name: Nikky
Status: student
Grade: 9-12
Location: NY
Country: N/A
Date: 4/18/2005
Question:
Does gamma radiation have kinetic energy?
Replies:
Yes, it does. In fact, since photons have zero rest mass, all their energy
is kinetic. In fact, if you could slow them every so little from the speed
of light, they would cease to exist, since they would have zero energy.
Relativity is very strange, isn't it? A photon is a quantum (a little
piece) of light.
Best, Dick Plano, Professor of Physics emeritus, Rutgers University
I would call that a yes.
Gamma radiation is photons.
Photons are all energy, and they are moving.
They have mass, velocity, and momentum, just like anything with kinetic
energy.
When they strike some small particle, that particle does get bumped
in the direction of the gamma-ray's motion.
Suppose their energy is referred to as "E",
and their speed "v" is the speed of light "c":
v=c.
By E=mc2, photons have mass "m":
m = E/c2.
They have momentum "M":
M = m * v
=(E/c2)*c
= E*c.
The classical definition of kinetic energy "Ke":
Ke= (1/2) * m * v2
= 1/2 * (E/c2) * c2
= E/2
So I think it is fair to say that half the total energy of any gamma ray
is kinetic energy.
The other half might be considered the energy it takes to build the
electric and magnetic fields in the photon's wave,
but I have not thought through what it takes to evaluate that, to see
whether it comes to E or E/2.
This kind of intuitive. classical thinking may break down for something as
fundamental and non-classical as a photon.
Jim Swenson
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