Construction details of a 5" diameter 1.7 litre gas scintillation counter are given. The behaviour of the counter when containing He⁴ gas and a mixture of He⁴ and 10% Xe at various total pressures has been investigated. Two 5" photomultiplier tubes and a variety of different gas purifiers were tested in an attempt to obtain the best possible resolution. The pulse height was found to depend sensitively on the purification procedure adopted. A resolution of 10% for the Po²¹⁰ α-peak has been attained in two different chambers containing He⁴ plus 10% Xe. The voltage pulses rose in ≤300 nsec. Intense irradiation of a counter with 6 Mev x-rays caused only a slight increase in the maximum noise level already present from the photomultiplier tube. The behaviour of the counter as a fast neutron detector has been investigated using an uncollimated beam of 4.1 Mev neutrons. Pulses from recoiling protons and C¹² nuclei were observed as well as the He⁴ recoils.