From Big Medical Encyclopedia

GAMMA AND CONSTANT — the power of an air dose created by not filtered gamma radiation of this radioisotope at distance of 1 cm from a point isotope source activity 1 mkyur. In radiological practice (see. Radiation therapy , Radio isotope diagnosis ) - the item serves for calculation of size dosage rates of radiation (see), created by any source gamma radiations (see).

- the item characterizes dozny field (see), created by the gamma radiation of radioisotopes in air at certain reference conditions.

Distinguish differential and full G. - the item. Differential G. - the item. (To γ ) treats a certain monoenergetic line of a gamma range of isotope. Full G. - the item. (To γ ) it develops from differential:

where m — number of lines in a range of gamma radiation of this isotope.

Full G. - the item of this radioisotope can be calculated by a formula:

where 3,7×10 7 — number of disintegrations in 1 sec. at activity of an isotope source (Q), equal 1 mkyur; E i — energy of gamma quanta (in Mev) in this spectral line (i) of this isotope; n γ i — the number of gamma quanta of this energy falling on 1 disintegration; γ i — mass coefficient of true absorption in air of gamma quanta with a certain energy (in cm 2 /г); 1,6×10 - 6 — a power equivalent of 1 Mev (in an erg); 3600 — number of seconds at 1 o'clock; 87,7 — a power equivalent 1 r (in эрг/г×р).

- the item gives the chance to calculate the dozny field created by various isotope sources in air. E.g., for a point source with a certain activity the power of an air dose (R) at this distance (R) is equal

If the isotope source is put into a cover, then into value K γ it is necessary to make allowance for filtering of gamma radiation in a cover. E.g., for 226 Ra, being in balance with decomposition products, To γ it is equal 9,36 without filtering; if drug is put into the filter from platinum 0,5 mm thick, To γ it is equal to 8,4 r-cm 2 / hour-mkyuri. For 60 With, 137 Cs, 192 Ir used at a gamma therapy To γ it is equal (without filtering) respectively 12, 93; 3,1 and 4,65 r-cm 2 / hour-mkyuri.

- the item allows to establish connection between activity of this isotope (Q) and its gamma equivalent (M):

where 8,4 — a gamma and constant 1 mkyur (1 mg) 226 Ra, being in balance with the decomposition products and put in the platinum filter 0,5 mm thick.

Bibliography: Bibergal A. V., Margulies U. Ya. to an ivorobyeva. I. Protection from x-ray and gamma-rays, M., 1960; Gusev N. G. and d river. Protection against ionizing radiation, t. 1, page 309, M., 1969; Ivanov V. I. Course of dosimetry, page 45, M., 1970; Moiseyev A. A. and Ivanov V. I. Reference book on dosimetry and physics health, M., 1974.

U. Ya. Margulies.