The primary X-ray energy distributions from a diagnostic unit were measured with a lithium drifted silicon detector of room temperature type. A pair of wedge shaped collimator was used to reduce the intensity of X-rays to measurable level. The resolution of the system with the detector was improved from 20 keV to 5.0keV for 122 keV gamma rays by a simple cooling apparatus and nitrogen vapor. Measured results for 241Am,57 C o, a n d 1 00 kVp X-rays with WKe, WKf 3 peaks are shown. The response matrix for the system, which is needed in estimating real energy distributions by correcting Gaussian broadening, energy dependence of photopeak efficiency and other effects, was mede by a computer from data of photopeak efficiency, measured FWHM and energy calibrations. Measured spectrum data were smoothed by regressions to second order polynomials on the basis of the least squares method. Corrections for the response of measuring system were performed by the inverse matrix method. The processes are described along with some lines of Fortran program.

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X-ray CT scanner, Half-value-layer, Effective energy A simple technique was described for the evaluation of the half-value-layer of x-ray CT scanner. Detector diagnostic program was found useful to determine the HVL in the normal scanning condition. It does not require to stop the motion of x-ray tube nor detectors. Measurement was performed for the tube voltage of 80 to 130 kV. Spectrum homogeneity was studied with and without x-ray absorber.

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A beam flattening technique for heavy charged particle radiotherapy has studied using a double scatterer method. In order to calculate flux distributions for the double scatterer system, we have introduced three parameters on the geometrical scaling factors of the system. The flux distributions at the therapeutic site were calculated on the various combinations of the scatterers and the beam stopper using the parameters. From these results, it is possible to deduce an optimum solution of the uniform dose distribution and the efficient beam delivery for any heavy charged particle radiotherapy facilities. As typical examples, we have tried to apply this method to NIRS proton radiotherapy facility and to PARMS proton radiotherapy facility of the University of Tsukuba.

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The attenuation and scattering of fast neutrons ranged from 0.5 to 14 MeV by various shielding materials have been studied for the purposes of design of the protective barriers and the collimators. The transmitted and scattered neutrons were measured with a conventional rem counter. The neutrons used were produced by bombarding light nuclide targets with accelerated beams of protons or deuterons using a Van de Graaff accelerator and a neutron generator. The attenuation curves for lead, iron, heavy concrete, ordinary concrete, water, paraffin and borated paraffin were determined under broad beam geometry. Scattering ratios, which were defined as the ratios of scattered neutron dose equivalent to incident neutron dose equivalent on the scatterer, were determined for the scattering angles of 45°,90° and 135° using the monoenergetic neutron beams of 0.5 to 5 MeV. The attenuation characteristics and scattering ratios obtained are tabulated in order to make it easy to use these data.

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