RESUMO
Silicon Photo-Multipliers (SiPMs) are increasingly becoming popular for discrete photon counting applications due to the wealth of advantages they offer over conventional photo-detectors such as photo-multiplier tubes and hybrid photo-diodes. SiPMs are used in variety of applications ranging from high energy physics and nuclear physics experiments to medical diagnostics. The gain of a SiPM is directly proportional to the difference between applied and breakdown voltage of the device. However, the breakdown voltage depends critically on the ambient temperature and has a large temperature co-efficient in the range of 40-60 mV/°C resulting in a typical gain variation of 3%-5%/°C [Dinu et al., in IEEE Nuclear Science Symposium, Medical Imaging Conference and 17th Room Temperature Semiconductor Detector Workshop (IEEE, 2010), p. 215]. We plan to use the SiPM as a replacement for PMT in the cosmic ray experiment (GRAPES-3) at Ooty [Gupta et al., Nucl. Instrum. Methods Phys. Res., Sect. A 540, 311 (2005)]. There the SiPMs will be operated in an outdoor environment subjected to temperature variation of about 15 °C over a day. A gain variation of more than 50% was observed for such large variations in the temperature. To stabilize the gain of the SiPM under such operating conditions, a low-cost, multi-channel programmable power supply (0-90 V) was designed that simultaneously provides the bias voltage to 16 SiPMs. The programmable power supply (PPS) was designed to automatically adjust the operating voltage for each channel with a built-in closed loop temperature feedback mechanism. The PPS provides bias voltage with a precision of 6 mV and measures the load current with a precision of 1 nA. Using this PPS, a gain stability of 0.5% for SiPM (Hamamatsu, S10931-050P) has been demonstrated over a wide temperature range of 15 °C. The design methodology of the PPS system, its validation, and the results of the tests carried out on the SiPM is presented in this article. The proposed design also has the capability of gain stabilization of devices with non-linear thermal response.
RESUMO
Deformity in leprosy is a major problem causing serious socio-economic and psychological consequences to the patients and their families, as well as for the programmers. This paper examines the nature and extent of social and economic problems of leprosy-affected families having patients with and without deformities and their strategy to cope with those problems. The data were collected from 500 sampled families in two monotherapy districts in Tamilnadu in 1989-1990. About 20% of the families reported facing socioeconomic problems. The proportion of families having patients with deformities facing problems was ten times higher (57.3%) than those having patients with no deformities (5.7%). Majority of the problems of the affected families were economic. The major strategy adopted to deal with economic problems was to adjust within the earnings of other family members to make up the loss or reduction in income from the patient. The major social problem faced was denial of participation in the community. While families with deformed patients adopted "acceptance of their existing situation," families with non-deformed patients adopted "avoidance" as their coping strategy. Appropriate rehabilitation programmes to restore economic security to the patients and their families is called for. There is also the need to educate the community about the disease in order to dispel the myths and fears associated with leprosy.