Influence of direction of charged particles produced by thermal neutrons on pulse height in 3He proportional counters

The variations of pulse height and energy resolution at a full energy peak depending on the direction of charged particles produced by thermal neutrons in cylindrical ³He proportional counters have been measured using a pulse shape analysis. The difference of peak positions affected by charged particles having mainly “parallel direction” and “any other direction” to the anode wire was found to be 1%, and this difference became larger with increasing bias voltage. It is concluded that, as a result of space charge effect, the direction of charged particles to the anode wire affects the variations of pulse height, energy resolution and the optimum bias voltage in the proportional counter. The experimental results also suggest that by selection of signal pulses produced by the parallel ion track, the full-width-at-half-maximum (FWHM) of the 764 keV full energy peak can be reduced from 4.9% to 3.9%