No abstract

The results of a comparative study of heavy particles of interest in radiotherapy, with peaks spread over a depth of 10 cm, are reported in four parts. The introduction to this study and the depth-dose distributions of the particles, (n, pi-, p, He, C, Ne, and Ar ions) are reported herein. The results indicate that protons give the best localization of dose. The degree of localization of dose with heavy ions is reduced with increasing charge on the ion. For ranges less than 15cm, heavier ions such as neon and argon still have favourable dose localization; however, for ranges in excess of 15 cm, heavy ions such as argon are unfavourable but superior to fast neutrons because penetration can be controlled by modulation of energy or range.

Based on over 5 years of experience in fast neutron radiotherapy, the activation radiation source origins and magnitudes are discussed and the staff radiation exposures reviewed. Source magnitudes were determined using ionization chamber survey instruments and staff doses by commercial TLD and film badge service reports. It is concluded that while staff doses exceed those obtained in conventional therapy, the levels received are well within published guidelines for occupational exposure.

Zero-degree neutron energy spectra for the p(41)-Be and d(49)-Be reactions were measured by time-of-flight for neutrons with energies above 1.9 and 1.4 MeV, respectively. Spectral changes resulting from the addition of copper, aluminum, and polyethylene filters to unfiltered beams were determined. Integral yields, average energies, filter material attenuation coefficients, and kerma fractions were computed for these spectra. Calculated spectra for neutron beams filtered by various thicknesses of polyethylene compared favorably with experimental results

Measurements of the neutron polarization in the P-d breakup reaction are reported. The polarization of breakup neutrons from H(p, n) has been measured at E& =21.4 MeV, el,b =18', as a function of neutron energy with an accuracy of approximately +0.01. The measurement is consistent with zero from 8 to 13 MeV, but shows a small but significant positive polarization from 14 to 18 MeV. A similar measurement of the breakup neutrons from the~H(d, n)2P reaction at the same center-of-mass momentum (E"=42. 8 MeV), also at 0 ""=18, shows nonzero polarization over the neutron energy region 8 to 25 MeV, reaching a maximum of about -0.05+ 0.01. In both cases, the polarization of the breakup neutrons is opposite in sign to that expected if the dominant process is simple quasifree scattering.