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Alpha, beta, gamma radiation!

alpha rays
... consist of α-particles which are Helium nucleii. They are charged positive and can be deflected by electric and magnetic fields. Their exit speed is about 107m/s.

beta rays
... consist of electrons of different speed between 108m/s and 0.999c0. Because of their negative charge, they are deflected contrarily to alpha particles in electric and magnetic fields.

gamma rays
... are electromagnetic waves with a wave-length of about 10-12m (frequency of ~1020Hz). There is no deflection in electric or magnetic fields.

Radioactive decay

The proportion of neutron number N to proton number Z increases with mass number A (A = N + Z). Only nucleii with a certain Neutron-Proton proportion are stable.
We know about 1700 different nucleii - 270 of these are stable and 1430 are unstable. Abundant nucleii in nature with even Proton and Neutron numbers are especially stable.

alpha decay
...happens with nucleii with high mass numbers (A > 200). An alpha particle is thrown out and therefore the mass number decreases by 4 and the atomic number decreases by 2.

A K1 -> A-4 K2 + 4 α
Z Z-2 2


beta- decay
...happens with nucleii with relative excess of Neutrons. The thrown out electron is produced by the transformation of a Neutron in a Proton:
Neutron -> Proton + Electron + Anti-Neutrino
1 n -> 1 p + 0 e + ν
0 1 -1
A K1 -> A K2 + 0 e
Z Z+1 -1
The neutron (quark makeup: ddu) decays into a proton (uud) by transforming one "d" quark into a "u" quark. During this transformation, a W- boson is emitted, which itself decays into an electron and anti-neutrino.
d -> u + W- ; W- -> e- + ν

beta+ decay
...happens with nucleii with relative excess of Protons. The thrown out positron is produced by the transformation of a Proton in a Neutron:
Proton -> Neutron + Positron + Neutrino
1 p -> 1 n + 0 e + ν
1 0 1
A K1 -> A K2 + 0 e
Z Z-1 1
The proton (quark makeup: uud) decays into a neutron (udd) by transforming one "u" quark into a "d" quark. During this transformation, a W+ boson is emitted, which itself decays into an positron and neutrino.
u -> d + W+ ; W+ -> e+ + ν



gamma rays
...are a concomitant phenomenon of alpha and beta decay. After these decays the nucleus transforms from an excited state into a lower energy state. Atomic number and mass number stay the same.
effects of gamma rays on matter:
photo-effect:
A photon (gamma quantum) penetrates an atom and releases one electron (mostly in the K-shell). This effect mostly occurs at gamma quantum energies under 0.5MeV.
compton-effect:
A photon hits an outer electron of an atom and transfers some of it's energy. Therefore the direction of the photon is altered (Compton diffusion) and the energy and frequency is decreased.
pair creation:
A photon almost reaches the nucleus of an atom. If the energy is at least 1.02MeV, it may transform into an electron-positron-pair.

Last-Modified: Fri, 26 Aug 2005 19:19:27 GMT

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