1. Jun 25, 2006

Hey
Recently I have been studied for a physics test on Nuclear Technology. A question I came across asked me to explain the difference between the penetrating ability of the three different types of radiation, alpha, beta and gamma and explain why. I know that gamma has the highest penetrating ability and alpha the smallest, but I do not know the reasons behind this. Also, how come when food becomes irradiated it does not become radioactive? Alpha particles are stopped by a piece of paper. Would this piece of paper become radioactive? Why or why not?
Many thanks,

2. Jun 25, 2006

### Staff: Mentor

The alpha particle has a 2+ charge, beta has 1- charge, and the gamma is neutral (no charge). All three particles primarily interact with atomic electrons in the matter through which they pass, and they ionize those atoms. Also the alpha is massive compared to the beta and gamma, and the beta is more massive than the gamma, so more momentum is transfered from the heavier particles to atoms encountered along the path.

The interaction is strongest for the alpha particle with the 2+ charge, and weakest for the gamma with no charge.

Electrons can interact by the brehmsstrahlung (braking radition) reaction when they interact with the nuclear electric field.

Gamma rays can be absorbed (photoelectric effect or pair production) or scattered (Compton effect). In the photoelectric effect, the gamma interacts with an atomic electron an is completely absorbed. In pair production, the gamma interacts with the nucleus and forms a positron-electron pair. The threshold for pair production is 1.022 MeV or twice the rest mass of the electron.

Food irradiation is usually accomplished with gamma radiation, so the food atoms/molecules are only ionized. The nuclei of the food molelcules are not affect, i.e. no radioactivity is induced.

Activation (making something radioactive) requires the use of neutrons which interact (are absorbed) by nuclei, which increases the nuclear mass by 1 amu, and the resulting nuclei then decay by beta decay. Some nuclei, like B-10 experience alpha decay upon absorption of a neutron, otherwise alpha decay occurs in heavier nuclear starting with isotopes of Bi-211, although Po has several lighter isotopes, which undergo alpha decay.

For future reference - http://www.nndc.bnl.gov/nudat2/

Last edited: Jun 25, 2006
3. Jun 25, 2006

thank for your help Astronuc, greatly appricated

4. Jun 25, 2006

in my book its speaks of a beta particle having a 1+ charge and a 1- charge. What is the difference between these beta particles? I know that the 1- charge particle is the deacy of a neutron into a proton and an electron, but as for the other one, it is not explanied in the book.
many thanks

5. Jun 25, 2006

### nrqed

Beta radiation is made of electron or its antiparticle, the positron. (you know that there is beta decay as well as inverse beta decay).
So when they give a charge of +e, they are referring to the positron.

6. Jun 25, 2006

### Hootenanny

Staff Emeritus
Just further to what nrqed said a couple of examples of beta decay;

Beta+ Decay:
$$p \rightarrow n + \upsilon_{e} + e^{+}$$

Beta- Decay;
$$n \rightarrow p + \overline{\upsilon_{e}} + e^{-}$$

I was going to draw Feynman diagrams but then I realised PF doesn't support them in latex

7. Jun 25, 2006

### nrqed

Hi Hoot.

How does one draw Feynman diagrams directly in Latex???
It must involve some extra package, Any link to the package/tutorial?

Thanks

Patrick

8. Jun 25, 2006

### Hootenanny

Staff Emeritus
Hey Patrick,

Yes, there is although I've only just started playing with it, it doesn't seem to be fully operational yet:grumpy: . I'm going to ask in the Latex tutorial if someone can help me out. Anyway the package is called feynmf and is located here http://tug.ctan.org/tex-archive/macros/latex/contrib/feynmf/

9. Mar 10, 2010

### SCIBERBABE

Any ideas on how to teach the penetrating powers of alpha, beta and gamma radiation in the absenc of radiation sources?