Nonlinearity of pulse height of recoil helium in 3He proportional counters

The nonlinearity of the pulse height of recoil helium in ³ He proportional counters were measured, as functions of the operating voltage and the counting gas component. The recoil edge in the pulse height distribution was deviated from the ideal edge position to the lower energy even under the condition of optimized voltage. However, in the same experimental condition, the full energy peak of ³He(n,p)T reaction agreed well to the ideal peak position. This may be concluded that the nonlinear effects, such as an initial recombination and a space charge effect, take place more significantly in the energy loss process of recoil helium, because of its higher LET (linear energy transfer) in the counting gas compared to total of p+T. The deviation of the pulse height of recoil helium becomes larger with increasing of average LET. The experimental results suggested that the nonlinear effects are not avoidable for the higher LET gas, even if the operating voltage is changed in the possible range