Beta-ray emission

beta-ray emission (also β-radiation written) is a kind of ionizing radiation.

The elementary particles of the beta rays are negative electrons - - radiation) or positrons + - radiation), those with high energy (speed) from the atomic nucleus one itself straightby radioactive decay (beta decay) of changing atom to be discharged.

To table of contents


with the beta decayone differentiates between two cases: With cores with Neutronenüberschuss a neutron is converted under sending an electron into a proton - - radiation), while with cores with lack of neutron a proton under sending a positron transforms into a neutron (β+ - radiation). At the same time with the electron an electronic antineutrino is in each case sent, with the positron an electronic neutrino. These nearly unobservable particles take up a part of the freed energy.

That negative beta rays are the same as electrons, thus the particles,of those the atomic shell consists, is proven by the fact that β - - particles are subject to the Pauli-Prinzip when meeting with orbital electrons obviously. If they would be another kind of particle, they could independently of the existing electrons on all quantum-mechanically possible “courses” (orbital)are caught; the absorption of beta-ray emission in subject would have to be stronger then around orders of magnitude than observed. Accordingly the Annihilation of β + - radiation in subject proves,that it itself around positrons, which antiparticle of the atom bound electrons acts.

From the characteristic thatthe electron in two different “places” in the structure of the subject occurs, can assume one that all atom bound electrons originally developed as beta-ray emission.

In the early period of nuclear physics the observation of beta electrons led temporarily to the false conclusion, electrons is components of theAtomic nucleus. However the two emitted particles are produced only at the time for the nuclear transformation.

reciprocal effect with subject

beta rays leave themselves with some millimeters thicken absorbers well to shield. However thereby a part of the energy of the beta particles becomes converted into X-raying, the bremsstrahlung in such a way specified. In order to reduce this process, the shielding material should exhibit as light an atomic nuclei as possible. Behind it then a heavy metal can serve as the second absorber, which shields the bremsstrahlung.

If beta particles penetrate into a material, findsthe highest energy transfer on the material and the highest ionization in a thin layer instead of, which corresponds to the penetration depth of the particles. If the human body is exposed to beta rays, only Hautschichten are damaged. There it can however to intensive burns and from itresulting late sequences such as skin cancer come. If the eyes are exposed, it can come to the lens turbidity. Therapeutically this effect is used, in order to illuminate closely under the skin surface lying cancer ulcers.

If beta emitters are taken up to the body (inkorporiert), are high radiation dosesin the environment of the emitter the consequence. Well thyroid cancer documented -131, which collects itself in the thyroid as consequence of radioactive iodine. In the literature one finds also fears that strontium -90 can lead to bone cancer and leukaemia, therestrontium such as calcium in the bones enriches itself.

maximum range (cm) in the research of common β-emitters in different subjects

for β-emitters can be defined a material-dependent maximum range, because its energy indicates to β-radiation in many single impactsAtom bound electrons off, one weakens thus not exponentially. From this realization the selection of shielding materials results. See also ionizing radiation, screen (radiation).

Nuclide energy in MeV range in cm
air plexiglass glass
of H-3 0.019 8 - -
C-14 0,156 65 - -
P-32 1.71 710 0.72 0.4
S-35 0.167 70 - -
J-131 0.6 ,250 0.26 -

from this list the relative danger of the radionuclide P-32, that spread in the research results in the radiation protection regulation of 2001 calculationone carried. For screen a plexiglass sign of 1 cm strength is optimal; into materials of higher ordinal number it can come to the emergence of bremsstrahlung.

see also

Web on the left of


  > German to English > (Machine translated into English)