Naslov
Statistical fluctuations in gas amplification factor of a low-pressure proportional counter

Autori
Krajcar Bronić, Ines ; Grosswendt, Bernd

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Book of Abstracts / Obelić, B; Ranogajec-Komor, M; Miljanić, S; Krajcar Bronić, I - Zagreb, 2001

Skup
IRPA Regional Congress on Radiation Protection in Central Europe, Radiation Protection and Health

Mjesto i datum
Dubrovnik, Hrvatska, 20.05.2001. - 25.05.2001

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
gas amplification; proportional counter; statistical fluctuations

Sažetak
The electron avalanche formation in low-pressure argon-based gas mixtures at strong non-uniform electric fields was studied by a proportional counter. Concentration of admixtures (propane, DME, isobutane) varied between 1% and 80% and total pressures from 2 kPa to 90 kPa. Gas amplification M and energy resolution R were measured by the 55Fe source as a function of admixture concentration and total gas pressure. The relative variance f of the avalanche size distribution was determined by measuring single-electron (SE) spectra. In pure gases and in mixtures with high content of the admixture, the SE spectra have always a peaked distribution, f<1, although f increases with M. In "thin" mixtures the SE spectra change the shape to the over-exponential distribution, f>1. The f value depends on the partial pressure p of the admixture and on M. Over-exponential increase of gas gain with high voltage above a certain gas gain, M0, was determined in all mixtures. The gas gain where the SE spectra change their shape, f~1, is roughly equal to M0. Both effects in M and f are caused by avalanche chain formation due to insufficient quenching of the admixture. Energy resolution is directly determined by the f value, therefore, in "thin" mixtures above M0 it degrades very quickly. Since this limiting value M0 depends on p, we conclude that partial pressure should be above ~10 kPa to assure good quenching even at the highest gains obtained in the present experiment.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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