2. Deflected by electric and magnetic fields. 3.
Relatively slow moving 4. Strongly ionizing. 5. Are a doubly ionized helium nucleus. Beta Particles:1. Can penetrate thin sheets of aluminium. Penetrating power varies with the energy of particles.
2. Strongly deflected in electric and magnetic fields. 3. Are high velocity electrons.
1. Can penetrate several cms of lead depending on energy of radiation 2L Undeflected in magnetic fields. 3. Are very high frequency photons.
This is a spontaneous process arising from a nuclear instability of some sort.
It is random, /. e., the probability that a given nucleus will decay, in unit time, is independent of when the time interval occurs and of any chemical or physical conditions.
It is the time taken for half of the nuclei present to decay.
Basic Terms Ionization:
Energy transferred by the atomic particle to the surrounding matter brings about ionization of atoms and excitation of molecules.
Molecules with atoms which have either lost or gained an electron are called ions. (They exist in addition to free radicals.) The biological effects of radiations depend largely on the reaction of free radicals which result as secondary products in the aqueous environment in living cells.
Every time an ion is produced (or molecule excited) the energy of the particle is reduced (around 34 eV per ton pair production). The rate of loss of energy (RLE) in a given material depends upon 1. Magnitude of charge 2.
Velocity of particle. As the ionizing particle travels through matter, it loses energy and its velocity reduces until it is too slow to produce further ionizations (i.e., it is moving at roughly the same speed as the surrounding molecules). At the same time as it slows down, its RLE increases and the ionizing density, therefore, increases progressively towards the end of the track, e.g.
, 1 MeV electron has an RLE 200 eVm initially and RLE 60000 MeV attend. Width indicates 12 meV particles Amount of energy lost on track 3 meV proton penetration into tissue 100 keV electron All three have the same range 140 (in tissue). The RLE is proportional to the density for a given material, thus, the range must be inversely proportional.