From Big Medical Encyclopedia

PHOTO MULTIPLIERS (synonym: photoelectronic multipliers, FEM) — the electrovacuum devices transforming radiation in ultra-violet, visible and infrared spectral ranges to an electric signal with the subsequent its strengthening. First-ever multicascade F. it was designed in 1934 by the Soviet engineer of JI. A. Kubetsky.

T. find application in various optical, spektrofotometrichesky and isotope installations, tomographies (see), luminescent microscopy are widely used for the biological and medical purposes, in particular for registration of a biokhe-milyuminestsention (see), in a cytophoto-metrii (see), (see) etc.

Work F. it is based on two physical phenomena — an outer photoelectric effect (photoeffect) and secondary electronic issue. The external photoeffect arises when substance of the photocathode F. under the influence of light lets out electrons (primary electrons) therefore the radiant energy will be transformed to electric. Secondary electronic issue is caused by the fact that the accelerated primary electron which got on an intermediate electrode F., beats out from it already several secondary electrons, strengthening thereby photocurrent. As a rule, T. have several intermediate electrodes (dynodes). Everyone iosleduyu-

Fig. Schematic diagram of the device and operation of the photo multiplier: the photocathode

(FC) «under the influence of the light quantum (hv) which got on it lets out primary electrons which go consistently to the first and the subsequent electrodes (Dts, D2, Dz-. - Dp), beating out from them secondary electrons. Secondary electrons (are specified by shooters) under the influence of high tension get on the anode (A), creating the current proportional to number of the light quantums which got on FC in its chain, and registered by a galvanometer (). The high tension given on the photocathode and the anode by means of a divider (R1} H2, R3... Rn+i), is distributed between electrodes.

shchiya dinbd is under more high tension, than previous. In such multicascade F. the quantity of the secondary electrons which are beaten out from each subsequent intermediate dynode repeatedly increases (fig.). E.g., at potential difference between the photocathode and the anode of 1 — 1,5 kV strengthening of primary photocurrent can reach 105 — 106.

Bibliography: Anisimova I. I. and

Glukhovsky B. M. Photoelectronic multipliers, M., 1974; The Sable -

in and N. A. and Chalk and d A. E. Photoelectronic devices, M., 1974; H e-

h and to N. O., Fayn matte C. M. and JI and f in and T. M c. Secondary emission multiplier tubes, M., 1957. V. S. Marenkov.