A high current, high speed pulser for the beam pulsing of a linear accelerator is described. It uses seven avalanche transistors in cascade. Design of a trigger circuit to obtain fast rise time is discussed. The characteristics of the pulser are : (a) Rise time ≤ 1ns, (b) Peak current ≤ 50A, (c) Pulse width ≥ 0.9ns (FWHM) and (d) Life time ≃ 2000 ～ 3000hr (at 50Hz).

  Microdosimetric measurements for gamma-rays, neutrons and accelerated protons were carried out using two types of tissue-equivalent(TE) proportional counters, an LET-1 inch wall-less counter and an LET-1/2 inch single-wire counter.

The TE gas employed was the propane based mixture, and a pressure of 33.9 torr provided an effective sphere diameter of 2 μm for LET-1-wall-less counter by the special gas flow system. Alpha particles emitted from Am-241 have an energy of approximatery 5.48 MeV, and the energy loss in a 2 μm pathlength of propane based TE gas was calculated to be 84.6 keV/μm. For the improvement of S/N ratio, the input stage of a FET circuit was incorporated into the counter base and the separated-type charge sensitive preamplifier was operated by battery.

Electronic signals were amplified and processed by a homemade logarithmic amplifier with DC servo feedback. This spectroscopy system made it possible to measure the dose distributions in lineal energy from 50 eV/μm to 2000 keV/μm at the same time.