A.J.P.L. Policarpo

Improved resolution for low energies with gas proportional scintillation counters

Abstract Observation of the light emitted by xenon, when the primary electrons produced by an ionizing particle are accelerated under an electric field, allows the detection of energies, in the ionization chamber region, that, with gas counters, were only previously detectable in the proportional region. For example, for 5.9 keV a full width half maximum of 500 eV was measured. The relative variance of the pulses from the gas proportional scintillation counter is 0.087 E − 1 2 (E in keV ) and can be slightly improved. The possibility of using the counter for fast coincidence work is considered.

Detection of soft X-rays with a xenon proportional scintillation counter

Abstract Soft X-rays were detected with a xenon proportional scintillation counter; for example, full widths at half maximum of 100 eV and 140 eV were obtained for the carbon and oxygen X-rays, respectively. Window sizes up to 100 mm2 were used. The measured value of the Fano factor, 0.170 ± 0.007, implies that the ultimate relative standard deviation of the pulses is 0.06 E − 1 2 (E in keV ) to be compared to the experimental determination 0.087 E − 1 2 .

Coupling the gas scintillation proportional counter to photoionization detectors

Abstract The possibility of detection of the light emitted by gas scintillation proportional counters (GSPC) with photoionization detectors (PID) is considered.

The argon-nitrogen proportional scintillation counter

Abstract The characteristics of a gas proportional scintillation counter are studied for various argon-nitrogen mixtures at total pressures of around 1000 Torr, using α-particles. Measurements of the delay between the primary and the secondary scintillation pulses show that most of the secondary light is produced close to the central anode. The secondary scintillation amplitude increases sharply with the nitrogen concentration reaching a maximum at about 2.5%. Its variation with the anode voltage is studied and it is shown that for large voltages higher order scintillation components appear. The various factors affecting the energy resolution are considered. The experimental resolution is found to be limited by the appearance of the higher order components, the light collection efficiency and the photomultiplier. The extrapolation of the data shows that if the first factor can be eliminated the resolution will be limited by the total number of photons produced and not by a scintillator intrinsic resolution which is found to give a contribution of less than 1%. The spectral analysis of the secondary light (carried out with optical filters) is made for various voltages and nitrogen concentrations. It shows that most of the light is produced within the 3250 A–3800 A region. The importance of nitrogen on the secondary scintillation mechanism is discussed.

The gas proportional scintillation counter under X-rays bombardment: Resolution and pulse correlations

Abstract The resolutions of a proportional scintillation counter (“pill box” geometry) with Xe and Xe−0.75% N 2 and the correspondent charge resolutions are measured for 5.9 keV X-rays. Typical values are 20% for the light pulses and 17.5% for the charge pulses. It is shown that there is a strong correlation between charge and light pulses, implying the same intrinsic resolution, in agreement with the mechanism of light production. The practical light output for the 5.9 keV X-rays was about the same as the light output of a NaI(Tl) crystal for the 137 Cs γ-rays.

Large light output gas proportional scintillation counters

Abstract The scintillating properties of the mixtures Ar-5% Xe and He-42.5% Xe are studied under the influence of a radial electric field. The secondary scintillation pulse, which is slow (∼ 10 μs), has an amplitude that exceeds by a factor of 200–300 the pulse amplitude from standard CsI(Tl) and NaI(Tl) scintillators. This is an order of magnitude larger than the one from the previously reported argon proportional scintillation counter. This study is carried out for different conditions of pressure and electric field intensity, with and without wavelength shifter. The maximum pulse amplitude (with no higher order components) is, for the Ar-5% Xe mixture, independent of pressure. These mixtures have inherent interest for nuclear spectroscopy applications.

Localization of ionizing particles with the gas proportional scintillation counter

Abstract The gas proportional scintillation counter (PS counter) enables localization of tracks of ionizing particles by timing the primary and the secondary scintillation.

Wavelength shifters for xenon proportional scintillation counters

Abstract Relative efficiencies of p-terphenyl, sodium salicylate and p-quaterphenyl, as wavelength shifters for xenon proportional scintillation counters, are reported.

Peak shifts in gas proportional scintillation counters

Abstract A xenon gas proportional scintillation counter working in or very near the ionization chamber region was tested under high X-ray fluxes from a 55 Fe source. Within about 0.4% no intrinsic peak shift was detected up to 90 000 c/s, and practically no resolution deterioration was observed up to 40 000 c/s. Preliminary results concerning the variation of the light output and resolution with pressure are also reported.

IMPROVED ENERGY RESOLUTION WITH X RAY GAS DETECTORS.

Abstract Detection of the light pulses from a xenon counter gives a resolution of 11.2% for 5.9 keV. This value can be further improved.