Empirical Dose Quality Distributions of Californium-252

LET distributions from 252Cf and 226Ra tube sources have been measured in a sphere of simulated tissue both with and without moderating media surrounding the sphere and as a function of depth in the media. The detector was a tissue equivalent spherical proportional counter of 2 in. diameter. The distributions of absorbed dose in LET were obtained over the respective ranges lying between 0.2 and 1000 keV/μm at effective chamber diameters of 0.7 and 1.9 μm. A single californium source (16.5 fig) and an array of 8 californium sources (93 μg) were used at depths of 1–10 cm from the detector. A 20 mg radium tube also was used. A computer code was used to assimilate the data in a reproducible and objective manner. The measurement of LET distributions provided neutron dose rates, dose average LET values, and insight to the quality changes of the radiation as a function of depth into tissue material.