A high pressure xenon-filled muitiwire proportional chamber is described. It can be used as balloon-borne hard X-ray telescope or hard X-ray detector in other nuclear techniques over the energy range of 10 to 200 keV.

It has a sensitive area of 700 cm

2

with a filling gas of 95% Xe+5% CH

4

at 3 atomospheres pressure. Its energy resolution (FWHM) for single anode is 10% for 59.5 keV (

241

Am radiation source) and 19% for 29.8 keV (the escape peak of 59.5 keV photons in xenon)

and it becomes 17% and 20% respectively if all anodes are connected together. It can keep good energy resolution for three monthes after each gas purification.