In order to use negative pions for the treatment of large deep-seated tumors in radiotherapy, it is necessary to produce depth-dose distributions tailored to specific shapes. We present here a method of beam shaping which utilizes a fluid-filled piston having a programmable, computer-controlled, time-dependent thickness. The fluid alters the residual range of the pions such that predetermined depth-dose distributions can be obtained. Changing from one distribution to another can be accomplished simply and rapidly without access to the treatment room. Depth-dose distributions which are flat over a range in depth up to 10 cm have been produced. Distributions tailored to produce flat "effective dose" versus depth have also been obtained.
A measurement of the P spectrum of Kr was undertaken to resolve some discrepancies in recently reported values of the branching of the p decay to the ground state of YRb. Sources of mass-separated~Kr, provided by the TRISTAN on-line isotope separator, were investigated with a high-resolution 7t 42 magnetic spectrometer. Using constraints based on previous y-ray decay schemes, the measurement yielded a Q value of 3.888 +0.007 MeV and a ground-state P intensity of (30.5 +2.2)%. In addition, the intensity ratio for an unresolved y-ray doublet at 2555 keV was independently determined on the basis of P-branch intensities to the levels at 2555 and 2960 keV.
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