Abstract
THE energy locally absorbed in a material exposed to γ-radiation has usually been determined indirectly from measurements with an ionization chamber, using the Bragg–Gray formula. The calculation involves the use of two quantities the values of which are not accurately known: W, the average energy required to produce an ion pair, and ρ the ratio of the stopping powers of the material and the gas. The direct measurement of the energy absorbed presents some difficulties due to the small rise of temperature which is produced. If a dose corresponding to 300 r. is given to a sample of water, the temperature will rise by only 6.7 × 10−4 deg. C. However, the development of the thermally sensitive resistors known as thermistors has made possible the detection of a change of temperature of less than 10−5 deg. C.
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References
Whyte, G. N., Nucleonics, 12, No. 2, 18 (1954).
Spencer, L. V., and Attix, F. H., Radiology, 64, 113 (1955).
Valentine, J. M., Proc. Roy. Soc., A, 211, 75 (1952).
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JOHNS, H., BERNIER, J. & CORMACK, D. A Direct Measurement of the Energy Locally Absorbed from a Gamma-Ray Beam. Nature 176, 560 (1955). https://doi.org/10.1038/176560a0
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DOI: https://doi.org/10.1038/176560a0
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