1f:T433,The NIST sealed water calorimeter is intended for direct measurement of absorbed dose to water. This calorimeter was used for a series of approximately 3700 measurements to investigate the so-called heat defect, that is, anomalous endothermic or exothermic effects caused by dissolved gases. The three systems investigated were "high-purity" water saturated with N₂, H₂, and mixtures of H₂/O₂. The repeatability of the measurements of absorbed dose rates for the ⁶⁰Co teletherapy beam was studied with different water fillings and accumulated absorbed dose. Measurements with the H₂/O₂ system varied with accumulated absorbed dose. Based on the measurements and theoretical considerations, it appears that the H₂-saturated system is the best choice for eliminating the heat defect. Measurements with both the N₂- and H₂-saturated systems are in good agreement with those determined with a graphite and graphite-water calorimeter (for which there is no heat defect).20:T521,The Monte Carlo technique has been used to obtain estimates of dose and dose equivalent in a homogeneous tissue slab irradiated by a broad beam of normally incident monoenergetic protons and also for an isotropic flux of protons incident on a homogeneous parallelepiped of tissue. Incident proton energies as high as 400 MeV are considered. The dose is essentially uniform above 200 MeV, where average primary proton ranges become large compared with the mean track lengths of primary protons in the target. At all proton energies the ratio of rem and rad doses is generally about 1.4 if rem dose estimates are based on values of RBE in current use for long-term occupational exposure to ionizing radiation. The contributions to dose from various ranges of LET values which arise in the calculations are presented and discussed. The nuclear interactions considered are cascade and evaporation phenomena. The effect of the presence of pions is assumed to be negligible at incident proton energies not exceeding 400 MeV. An analysis of nuclear interactions is made from the standpoint of dose assessment. From the results of the detailed Monte Carlo calculations a simplified model is derived which permits a rapid and accurate estimation of proton dose. A method of handling RBE in a flexible manner is given also.

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