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Name: Buddy O.
Status: N/A
Age: 20s
Location: N/A
Country: N/A
Date: 2001-2002

If alpha particles are less penetrating then a beta....are they more damaging then a beta?..and does that mean the wavelength for an alpha is shorter then the beta particle?


The main reason that an alpha particle is less penetrating is that it is much larger than a beta particle. An alpha particle is a "helium nucleus", two protons and two neutrons joined together as a nucleus. A beta particle is an electron. Given the same energy, an alpha particle's relatively huge mass gives it much less momentum than a beta particle of the same energy.

In addition, alpha particles tend to be released with much less kinetic energy than beta particles. A nucleus that is too big to hold together sometimes releases an alpha particle to become more stable. There is nothing dramatic about it. Beta particles work differently. A nucleus with too many neutrons can change a neutron into a proton through beta decay. A neutron becomes a proton and a fairly high energy electron (as well as a tiny anti-neutrino).

Actual wavelength of an alpha or beta particle depends on the energy of the particle. The more kinetic energy a particle has, the smaller its wavelength (and larger its frequency). The average alpha particle has less kinetic energy than does the average beta particle, so alpha particles tend to have lower frequencies and longer wavelengths.

Dr. Ken Mellendorf
Illinois Central College

Generally speaking, alphas are more damaging than betas because their energy is dissipated over a smaller volume of the target. Alphas have much higher masses then betas, by a factor of around 8000.

A particle's wavelength depends on both its energy and its mass. It depends on the energy because the frequency is proportional to the energy by the relation E = hv, where E is the energy, h is a constant, and v is the frequency. It depends on the speed because

L = s/v,

where c is the speed of the particle and L is the wavelength. Now, for particles with mass traveling at speeds less than about 1/10 the speed of light, the speed and kinetic energy are related by

E = (ms^2)/2,

where m is the particle's mass.

We need one more piece of information to really get a handle on the relative wavelengths of alpha and beta particles: their energies. It turns out that generally beta particles have energies of less than 2 MeV (million electron volts: 1 MeV is the energy of an electron accelerated through an electric field of 1 million volts), and alpha particles have energies above 4 MeV.

So, to summarize: alpha particles are more massive than betas, and they have higher energies. This translates, as you suspect, to shorter wavelengths.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois

Alpha particles are He(4) nucleii, i.e. (He(4)++). Beta particles are electrons. They both have a wavelength in the quantum mechanical sense that they can undergo interference like waves. The wavelength of an alpha particle is much smaller than a beta particle.

The damage that they can cause depends not only on their relative ability to penetrate a target, but also the nature of the target (animal, vegetable, or mineral) and the energy of the particle (i.e. its speed).

Vince Calder

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