Analysis of outputs from a helium-filled proportional counter at liquid helium temperature

We have formulated output currents from helium-filled proportional counter (HFPC) cooled at low temperatures near 4.2 K, taking account of primary ele ctrons produced by incident radiation and secondary electrons emitted from cathode; according to a simple model for the HFPC operation, the secondary electrons are originated by collision of four active particles with cathode , i.e. low-energy (0-5 eV) photons from excited helium atoms He*, helium io n clusters He-n(+), high-energy (10-20 eV) photons from excited helium mole cules He-2(*) (A(1)Sigma (+)(u)) and metastable helium molecules He-2(m) (a (3)Sigma (+)(u)). In order to determine secondary electron emission probabi lity for each active particle, output pulses and electric discharges from t he HFPC have been analyzed with the theoretical formulation. The present an alysis has made clear the roles of low- and high-energy photons and the ion clusters quantitatively. However, the role of triplet metastables, He-2(m) (a(3)Sigma (+)(u)) or He-m (2(3)S), is still not clear. The formulation an d some results of the analysis are described in detail. A possible applicat ion of the HFPC to a new neutron position detector is also proposed. (C) 20 01 Elsevier Science B.V. All rights reserved.