Hello Folks!

This is an explanation of how nuclear decay happens, and where the
alpha, beta and gammas we all love to measure come from.

For all intents and purposes, nuclear decay is always by a particle
exchange mechanism. The nucleus either emits or captures a partial.
Generally, this is either by:

1) Alpha decay - the nucleus undergoes what amounts to a very uneven
spontaneous nuclear fission, and emits a He nucleus (2 neutrons, and
2 protons). It steps 2 elements down the periodic table, and loses 4
mass units. This is the alpha decay we all talk about, though I've
read that many other forms of alpha decay do exist in some more
exotic isotopes, where the emitted "alpha" is other than a helium
nucleus, but is some other light nucleus. We're pretty unlikely to
encounter this in the home lab, methinks.... In my mind, any
spontanious fission is actually an exotic alpha decay.

2) Beta- decay - the nucleus emits an electron, and thus the nucleus
charge goes +1, and the nucleus "climbs" one step up the periodic
table. The beta (electron) is emitted by a neutron in the nucleus,
and in doing so, the neutron becomes a proton. The mass is
essentially the same, but the charge is now different

3) Beta+ decay - The nucleus emits a positron (Anti-matter in the
Home Lab!), or a positively charged "electron". Na22 is one such
isotope. In this case, the nucleus charge goes -1, but again the
mass is essentially the same.

4) Electron Capture (EC) - another rather exotic process, basically
the reverse of beta decay. A proton in the nucleus absorbs an
electron and becomes a neutron. Mass is the same, charge is -1, as
in beta+ decay.

All these decay modes may leave the nucleus in an upset state. Like
a Jenga tower with bricks removed from below, it's unstable. As
it "collapses" to a more stable state (the jenga tower sees this as
a pile of rubble), it has to release energy. That energy is
typically a Gamma Ray, a high energy photon. Gammas are simply a
result of the new nucleus relaxing and coming to terms with its new
form.

In the case of the natural decay chains, each step is by one of the
processes above (generally B- or Alpha). After each step, a gamma
may be emitted as the new nucleus relaxes. Decay chain charts don't
always list these gammas because they're not relevant to the actual
changes. But, if you look at each isotope in the decay chain, look
it up in Wiki or whatever you like, you'll see what gammas it
typically emits in its decay.

As an aside, the difference between Gammas and X rays: To your
geiger counter, there is NO DIFFERENCE! The only difference is that
the gamma is made by a nucleus performing an energy balancing act
(as I described above), while an X-ray is the result of the atom's
electrons moving to a lower energy state. So Gammas come from the
nucleus, and are a nuclear event, while Xrays are from the electron
cloud, and are an electronic event.

Hope it helps...

J