J.A.C. Gonçalves

The performance of low-cost commercial photodiodes for charged particle and X-ray spectrometry

Abstract The energy response of a low-cost commercial silicon photodiodes detectors for alpha particles, fission fragments, internal conversion electrons and X-rays was studied. An alpha energy resolution of 16.7 keV (FWHM) was obtained for 5.486 MeV α-particles from 241 Am which is comparable in performance with the best surface barrier detectors available, that are considerably more expensive.

Rate effects in a proportional counter with resistive cathode

In this work, the rate e⁄ects associated with the gain of detectors with resistive electrodes are considered. To study these e⁄ects it was decided to use the classical proportional counter geometry, with a cylindrical glass tube as the cathode, rather than parallel plate devices. Indeed, the generality of the information obtained is not a⁄ected and the cylindrical proportional counter geometry has several advantages to gather detailed experimental data and to compare it with simple electric field calculations. A self-consistent set of data is presented for the e⁄ects of counting rate from a few tens of Hz up to several hundreds of Hz, using several gas mixtures, di⁄erent anode wires, cathode radii and thickness of the resistive electrodes. Although a few sources of systematic errors can be identified, all the observed experimental data can be quantitatively explained. Indeed, the measured gas amplification, from a few tens up to &5]104 and for the range of counting rates quoted above, depends only on the local electric field as it should be expected. These results are directly relevant to approach the problem of counting eƒciency in resistive plate chambers. ( 1998 Elsevier Science B.V. All rights reserved.

Transient behaviour and rate effects in resistive detectors

Abstract The dependence of the detection efficiency (or charge gain) of a resistive detector on the counting rate has been considered by several authors. The influence of the resistivity of the electrodes, the counter geometry and the gas mixture composition have also been studied. Most of those measurements assume a stationary regime. In the present work we report on studies of the transient behaviour of detectors with a resistive cathode for various counting rates, charge gains and detector geometries. We show that in some cases the time-decay curves can be fitted by a single exponential plus a constant term, while in others (higher charge gains or higher counting rates) a sum of two or even three exponentials plus the constant term is needed to fit the experimental data. A study of the electric properties of the dielectrics used is also presented and a comparison is made between these results and the data obtained under irradiation conditions.

Pressure dependence of secondary NIR scintillation in Ar and Ar/CF/sub 4/

The variation with charge gain of the total number of photons emitted per electron, in the visible and near-infrared (NIR) regions (400</spl lambda/<1000 mm), in Ar/CF/sub 4/, mixtures, is investigated for CF/sub 4/ concentrations below 15%. Measurements were performed in a uniform field configuration and results are presented for charge gains below 100, under X-ray excitation. The maximum number of photons emitted per drifting electron (0.7 and 0.2 ph/e/sup -/ for Ar/sup +/ 2% CF/sub 4/ and Ar+10% CF/sub 4/, respectively) is obtained for a charge gain G/spl sim/4. The spectral distribution of the emitted light in Ar/CF/sub 4/ mixtures is also analyzed. The pressure dependence (1-4 atm) of the secondary light output, in the visible and near infrared regions is studied as a function of the reduced electric field E/P for pure argon and Ar/CF/sub 4/ mixtures. Above the charge multiplication threshold, the maximum number of photons emitted per electron decreases by a factor of about 1.5 when the pressure increases from 1 to 2 atms.

Manufactured silicon diode used as an internal conversion electrons detector

In this work we have studied the direct detection and spectrometric capabilities for internal conversion electrons of an ion-implanted diode, developed in the framework of R&D programs at CERN, envisaging its use in an electron-gamma coincidence system for nuclear parameters measurements. The best energy resolution obtained until now, 12.6 keV (FWHM) for the 133Ba 320.32 keV electron emission, is sufficiently good to justify the use of this diode for spectrometry of low energy electrons.

On the Origin of the Satellite Peaks in Alpha Particle Spectra

In this work we describe the results obtained with S3590-06 and ion-implanted diodes for alpha particle spectrometry. Satellite peaks were also investigated in order to identify not only the origin of these phenomena, but also the importance of the guard ring region on their relative intensities. The preliminary results indicate that the true cause of the spurious satellite peaks might be associated with the weak electric fields around the guard rings region and changes on the entrance window absorption near the edge of the diodes. Further steps are needed to clear up this problem

Pressure dependence of secondary NIR scintillation

The variation with the charge gain of the total number of photons emitted per electron, in the visible and NIR regions (0.4</spl lambda/<1 /spl mu/m), in Ar/CF/sub 4/ mixtures, is investigated for CF/sub 4/ concentrations below 15%. Measurements are performed in a uniform field configuration and results are presented for charge gains below 100, under X-ray excitation. The spectral distribution of the emitted light in Ar/CF/sub 4/ mixtures is also analyzed. The pressure dependence (1-5 atm) of the secondary light output, in the visible and near infrared regions (NIR) is studied as a function of the reduced electric field E/P for pure argon and argon-tetrafluoromethane mixtures. Above charge multiplication threshold, the number of NIR photons decreases with increasing pressure.

Rate effects in radiation detectors with resistive electrodes

Detectors with highly resistive electrodes, particularly RPCs, have been studied extensively in recent years. Several authors considered the effect of rate on the detector response (efficiency) and a few also associated with the rate, in a rather qualitative manner, the charge per event, i.e., the current. Here, without loss of generality of the results obtained, rate effects are studied with a classical cylindrical counter geometry and different gas mixtures. To a high accuracy, the observed behavior, both for the proportional mode and for the transition to streamers, is quantitatively and accurately interpreted as loss of voltage on the dielectric due to the current generated in the detector, with direct consequences for the local electric field in the avalanche region. Results obtained in the self quenching streamer (SQS) mode fail the previous interpretation and clearly need further research.

Determination of the First Townsend Coefficient in Pure Isobutane

In this work studies of the first Townsend coefficient (α) behavior in isobutane for reduced electric fields ranging from l39Td up to 2O8Td are presented. Pure isobutane has been widely used in Resistive Plate Chambers (RPCs) and other gaseous detectors because of its excellent timing properties. Regardless of these characteristics, there is a lack of swarm parameters data in the literature for this gas. The measurements were based on the Pulsed Townsend technique. Considering the ratio between the current, measured in avalanche mode, and the primary ionization current, the first Townsend coefficient can be determined. In order to validate the technique, results for nitrogen are also presented.

Studies of Gaseous Multiplication Coefficient in Isobutane

This work presents the studies of gaseous multiplication coefficient behavior for isobutane, as function of the reduced electric field, by means of signal amplitude analysis. The experimental method used is based on the Pulsed Townsend technique, which follows from Townsend equation solution for a uniform electric field. In our configuration, the anode is made of a high resistivity (2.1012 Ω.cm) glass, while the cathode is of aluminium. In order to validate the technique and to analyze effects of non‐uniformity, results for nitrogen, which has well‐established data available in literature, are also presented.