The Experimental Determination by Ionization Methods of the Rate of Emission of Beta-and Gamma-Ray Energy by Radioactive Substances

The Measurement of High-Energy Radiation Intensity

“…This is borne out by experiment although there appears to be a marked increase in W with decreasing energy for electrons with energy less than about 60 kev. For electron energies encountered in this work, the best value for W appears to be 32.5 ev per ion pair, as given by Gray (13).…”

“…The determination of the value of W, the energy required to produce a pair of ions in the gas, has been the subject of several theoretical and experimental investigations, the results of which have been summarized by Gray (13). From theoretical considerations, W should be independent of energy for fast electrons and have a value, in air, of about 32 ev per ion pair.…”

Autoradiography and radioactivity measurements with human neoplasms containing radiophosphorus

“…I n Cases 7 to 9, in which biopsy specimens were available, thin slices of the fresh tissues were cut, and compared under an end-window counter with a simulated P3* standard (Tracerlab-Boston, Mass., U.S.A.). Correction for thickness of sample was made by extrapolating to zero thickness according to an exponential relationship (GRAY 1949) which was found t o fit our observations. I n the last two cases (10, 11), weighed pieces of the tissue were dissolved, made up to a standard volume, and compared with a diluted aliquot of the original radioactive solution given to the patient.…”

Energy per Ion Pair

“…7 MeV and a mean energy of about 0.685 to 0.695 MeV. If a sample of P32 is assayed by a (3-counting technique as, for example, by a 4 n-solid angle Geiger counter or proportional counter, and then a known quantity of the P32 is dispersed uniformly throughout the internal lining of an ionization chamber and the ionization current measured (14), a value of WAil' can be derived. One of the organisations involved, namely, the Radiotherapeutic Research Unit of the Medical Research Council, has determined the ionization produced under such circumstances by a known quantity of a sample assayed independently by 4 n Geiger counter methods by three of the organisations, and has deduced that WAil' for P32 (3-rays lies between 33.0 and 33.5 eV, according to whether the mean energy of the spectrum is taken to be 0.685 MeV or 0.695 MeV.…”

“…The British organisations referred to previously (37) as collaborating in a programme of measurements of radioactive isotopes have dealt with several {3-y emitters which lend themselves to assay by {3-ray counting techniques, by {3-y coincidence measurements, or by the so-called y-ray ionization method (14,29). In the latter, if the number of atoms (N) disintegrating per second is known and also the y energy (E) per disintegration, as indicated by the decay scheme, it is possible, by using wellsupported theoretical values for y-ray absorption coefficients (,u), to calculate the energy absorbed in an air cavity of known volume in an "air-walled" chamber at a known distance from the source.…”