How are alpha beta and gamma radiation created?
Forms of all three can be created by nuclear reactions. Alpha
radiation is actually particles (a helium nucleus), beta
radiation consists of either electrons or positrons, and
gamma rays are the only one of the three that is actually a
form of radiation energy (photon).
Alpha decay involves the release of a helium nuclei (alpha
particle) from the nucleus of the parent nuclide. This reduces the
atomic number by two and reduces the atomic mass number by
Some physicists actually consider it an extremely tilted form
of spontaneous fission, with 24He2+ (alpha) being one daughter, and
AN-2AMU-4Something being the other daughter.
Beta- decay starts with the weak interaction that causes a down
quark in a neutron to change into an up quark, releasing a W-
boson. The neutron becomes a proton, increasing the atomic number
by one, and keeping the atomic mass number the same. The W- boson
then decays into an electron and an electron antineutrino.
Beta+ decay involves energy, which is used to change an up quark
in a proton into a down quark, changing the proton into a neutron,
decreasing the atomic number by one, and keeping the atomic mass
number the same. It also emits a positron, and an electron
neutrino. Sometimes, K capture is involved in order to achieve the
extra energy. K capture is when an inner (K) shell electron is
absorbed into the nucleus, transferring its energy into the
nucleus, followed by reshuffling of the electron cloud. K
capture can also occur without beta+ decay.
All of the above events, as well as things like fission, fusion,
neutron absorbtion, and a few others, can leave the nucleus in an
excited state. When it comes back down to ground state, a photon is
emitted with an energy that corresponds to the energy level
transition of the step that just occurred. This is a gamma ray.
Usually, if there is going to be a gamma event following, say, a
beta- event, it occurs quickly, typically within 1 x 10-12 seconds.
Some nuclides, however, have a meta stable form where the gamma
event is delayed, sometimes for a very long time. In the case of
Technetium-99m, for instance, the gamma event has a half-life of 6
hours. This is very useful in the medical field, where
Technetium-99m can be tagged to certain biologically sensitive
materials, injected, and then scanned, such as for a heart scan,
impacting the body with only the gamma and not the beta.
Not asked, but answered for completness and due to its
similarity to gamma...
The electron cloud can also become excited, for various reasons,
such as K capture, or when an alpha particle flys by and steals an
electron. When it does so, it also "wants" to come back to ground
state. As each electron comes down in energy, it emits a photon,
just like the nucleus does. When this happens, it is called an
x-ray. Usually, gamma and x-rays have different energies, but there
is some overlap, and it is possible that they can be
indistinguishable from each other. For more information on the
difference between gamma radiation and x-rays, please see the
related question below.