# Is the ionising power of alpha particles greater than that of gamma

1. Nov 17, 2009

### kihr

I request for help in understanding the following:

Q1. Why is the ionising power of alpha particles greater than that of gamma rays?

Q2. Why does the ratio of neutrons to protons in a nucleus increase after the emission of
an alpha particle? I would like to have a quantitative idea, as I could not figure this
out myself.

Q3. How is the formula to be derived for the kinetic energy of electrons emitted during
beta decay?

Thanks

2. Nov 17, 2009

### Bob S

Q1) The ionizing power of an alpha particle is by a direct interaction of the alpha particle with the atomic electrons in the material or gas. The interaction rate is dependent on the alpha particle velocity, and the energy loss of the alpha particle is given by the Bethe Bloch equation.

http://en.wikipedia.org/wiki/Bethe_formula

Photons ionize only by the photoelectric effect or deep-core photoionization of bound electrons, or by Compton scattering off of free electrons. These electrons then ionize other electrons by scattering off atomic electrons.

http://en.wikipedia.org/wiki/Photoelectric_effect

http://hyperphysics.phy-astr.gsu.edu/HBASE/quantum/compeq.html

Q2) In alpha particle decay, both the number of protons and the number of neutrons in a nucleus are reduced by 2.

Q3) In beta decay, lepton number has to be conserved. Leptons include electrons, muons taus and 3 flavors of neutrinos, and their antiparticles. In negative beta decay, both an electron and an anti-neutrino are emitted. These two particles have to share the available energy. This leads to a continuous energy distribution for the electron, depending of the relative angle of the emitted electron and anti-neutrino..
For a discussion of the derivation, see
http://hyperphysics.phy-astr.gsu.edu/Hbase/nuclear/beta2.html

http://www.princeton.edu/~romalis/PHYS312/Beta_spectrum.pdf

Bob S

Last edited: Nov 17, 2009
3. Nov 17, 2009

### kihr

Thanks for the references which I will go through. In the meanwhile I would request for clarity with respect to Q 2, as I am still not able to figure out as to how the ratio of neutrons to protons goes up following the emission of an alpha particle. By working out the ratios of N/Z in either case (i.e. for the mother nucleus and the daughter nucleus) I am not able to come to this conclusion. Hence I would request your help on this. Thanks.

4. Nov 17, 2009

### Bob S

Hi kihr-

This URL discusses the decay of polonium 210 to lead 206 by alpha decay.
http://www.lbl.gov/abc/wallchart/chapters/03/1.html

The polonium nucleus has 126 neutrons and 84 protons: n/p = 126/84 = 1.5000

The lead nucleus has 124 neutrons and 82 protons: n/p = 124/82 = 1.5122

(126-2)/(84-2) = 124/82

Bob S

5. Nov 17, 2009