MICRODOSIMETRY OF MONOENERGETIC NEUTRONS

Tissue spheres 0.25, 0.5, 1.0, 2.0, 4.0 and 8.0 mu m in diameter were simulated using a wall-less spherical counter filled with propane-base d tissue-equivalent gas, Microdosimetric spectra corresponding to thes e site sizes were measured for five neutron energies (0.22, 0.44, 1.5, 6 and 14 MeV) and the related mean values (y(F)) over bar and (y(D)) over bar were calculated for several site sizes and neutron energies, An elaborate calibration technique combining soft X rays, an Fe-55 pho ton source and a collimated Cm-244 alpha-particle source was used thro ughout the measurements. The spectra and their mean values are compare d with theoretically calculated values for ICRU standard tissue. The a greement between the calculated and the measured data is good in spite of a systematic discrepancy, which could be attributed, in part, to t he difference in elemental composition between the tissue-equivalent g as and plastic used in the counter and the ICRU standard tissue used i n the calculations. (C) 1996 by Radiation Research Society