(b) These factors normally make beta emitters a less serious internal
hazard than alpha emitters. However, since the beta particle can penetrate skin and
damage living cells, the beta emitter can also be an external hazard.
(3) Gamma radiation. Gamma radiation is identical to x-radiation except for
its origin and method of production. It can be considered as bundles of pure energy
(photons) generally expressed in keV or MeV.
(a) Gamma radiation results when protons and neutrons are
rearranged in the nucleus of the unstable atom without emission of a particle. Because
the components are found with different energies in different nuclear configurations,
energy is released in the form of electromagnetic waves called gamma rays when the
components are rearranged. Gamma radiation sometimes accompanies beta and
alpha emission.
{b} Gamma radiation wavelengths are extremely short, and the
radiation is the most highly penetrating. The A and Z numbers undergo no change in
gamma emission.
(4) Half-life. Half-life is the time required for a given quantity of radioactive
substance to disintegrate until one-half of its initial activity remains. For example,
radium decays at such a rate that an initial amount of radium will decay to one-half its
value in about 1600 years. Therefore, starting with 1 gram of radium-226, we will find
its value to be only 0.5 gram after 1600 years. After another 1600 years, it will be only
0.25 gram in value. The other 0.75 gram will have been converted into daughter
products of the decay family.
(a) Applied to dose rate, the concept of half-life takes on a new
meaning. That is, the half-life of any radioactive nuclide is the time required for the
dose rate from a sample of that nuclide to drop to one-half its initial value.
(b) Half-life values among nuclides will vary from a fraction of a second
for one to several billion years for another. Each radioactive nuclide has its own half-
life.
1-16. X-RADIATION
X-radiation (x-rays) and gamma radiation are identical to each other except for
their origin and method of production. X-radiation is the result of the conversion of
either the kinetic or potential energy of electrons into another form of energy while
gamma radiation is emitted from radioactive nuclei. X-radiation is produced by radiative
interactions of electrons with matter and collisional interactions of electrons with matter.
a. Radiative Interactions. When an electron (which is negatively charged)
approaches the nucleus (which is positively charged), it may be deflected from its
original direction by the attractive force of the nucleus. The change of direction causes
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