Beta Spectrometer

an instrument for analyzing beta spectra.

The basic characteristics of a beta spectrometer are its aperture ratio and resolving power. The aperture ratio is taken to be the ratio of the number of electrons (or positrons) penetrating into the detector in time τ to the total number of particles emitted by the radioactive source in the same time. The aperture ratio of a beta spectrometer depends on its construction and is usually from several tenths of a percent to several dozen percent. The resolving power of a beta spectrometer is the smallest difference in the energy of electrons that can be measured by the instrument. The resolving power of precision beta spectrometers reaches 0.01 percent. As a rule, the instruments with the best resolving power have the lowest aperture ratio.

There are two kinds of beta spectrometers: those that measure the energy of electrons according to their action on a substance, and those whose action is based on the spatial distribution of electrons and positrons with various energy. Among instruments of the first type are scintillation spectrometers and ionization chambers. Instruments of this type have a high aperture ratio, but they do not have the capability of measuring electron energy with an accuracy greater than several percent (or even several dozen percent). Instruments of the second group include beta spectrometers that use magnetic fields or electrical fields (for slow electrons).