2488 IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 49, NO. 5, OCTOBER 2002 A Large Area Gas Proportional Scintillation Counter for Balloon Born Solar X-ray Spectrometry H. Natal da Luz, J. F. C. A. Veloso, J. M. F. dos Santos, C. A. N. Conde, Rui M. C. Silva, H.-R. Pan, Z.-Y. Li, and H.-A. Lin Abstract—A compact xenon filled gas proportional scintillation counter (GPSC) having a window area of 12.5 cm coupled to low weight, low volume and low power associated electronics is de- scribed to be used in a balloon gondola to fly at high altitudes (30 to 40 km) and measure X-ray spectra in the 20 to 80 keV energy range, arising from solar flares. The detector has an energy reso- lution of 4.3% at 59.6 keV for the full window opening, and 2.7% for a 2-mm-diameter collimated X-ray beam. Index Terms—Gas proportional scintillation counters, solar flares, space instrumentation, X-ray detectors. I. INTRODUCTION T HE latest efforts toward development of a solar X-ray detector using a large area gas proportional scintillation counter (GPSC) are described in this work together with associated compact electronics. The GPSC is designed for solar X-ray spectrometry measurements in the 20 to 80 keV energy range. Charged particles, originating in solar flares that reach the earth produce effects such as increased atmospheric drag in satellites and radio interference in communications [1]. It has been shown that these charged particles take about 20–40 h to reach the earth, while the X-rays produced by the same solar flares take only about 8 min [2]. In [3], [4], and [5] a statistical relation between the proton and high energy X-ray fluxes is presented. By observing these X-rays one is thus able to study each solar flare in order to find its “signature,” and predict the harmful effects of the charged particles that may later follow. For this, an X-ray detection system with a good energy resolution and stability is required. GPSCs are preferred to other kinds of room temperature detectors with large collection area such as Proportional Counters or NaI(Tl) counters due to superior energy resolution for hard X-rays [6]. State of the art technology allows the use of low-cost and low-power consumption high-voltage modular supplies, while at the same Manuscript received November 25, 2001; revised April 3, 2002 and June 19, 2002. This work was supported in part by Fundação para a Ciência e a Tecnologia – Lisboa through the project POCTI/CTAE/1920/95-21920. The work of H. Natal da Luz was supported by Fundação para a Ciência e a Tecnologia (FCT) – Lisboa under Grant PRAXIS XXI/BTI/22314/99. The work of J. F. C. A. Veloso was supported by FCT. This work was carried out in the Grupo de Instrumentação Atómica e Nuclear, Centro de Instrumentação (Unit 217/94), Departamento de Física da Universidade de Coimbra, Portugal, and was supported by Project CTAE/1920/95-2190-Fase II. H. Natal da Luz, J. F. C. A. Veloso, J. M. F. dos Santos, C. A. N. Conde, and R. M. C. Silva are with the Departamento de Física da Universidade de Coimbra, P-3000 Coimbra, Portugal. H.-R. Pan, Z.-Y. Li, and H.-A. Lin are with the Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100080, China. Digital Object Identifier 10.1109/TNS.2002.803888 Fig. 1. Schematic of the xenon filled gas proportional scintillation counter with the ellipsoidal grid. time allowing improved GPSC functionality relative to earlier GPSCs. An experiment using a GPSC to study solar flares will be done in collaboration between the Physics Department, Uni- versity of Coimbra and the Chinese Academy of Sciences, in Beijing, with the detector flying in the gondola of a high alti- tude balloon. The launch of the balloon is expected to take place in about one year’s time. If funds are available, the planned X-ray spec- trometry experiment will be upgraded to a satellite experiment, which will allow a continuous monitoring of solar flares. To meet these requirements the GPSC was built as described in the following section. II. EXPERIMENTAL SYSTEM The GPSC has been designed as shown in Fig. 1, built and filled with xenon at 900 torr. It has a xenon absorption depth of 70 mm. The laboratory prototype has a 75- m-thick polyimide (Kapton) window which has approximately the same transmission as the 300 m Be window used in the flight prototype [7]. The calculated overall detection efficiency of the detector for X-rays incident normally to the window is shown 0018-9499/02$17.00 © 2002 IEEE