查看更多>>摘要：Recently peaceful use of the nuclear energy and radioactive nuclides has increased the radiation pollution factor in the world and radiation safety problems have become actual ones. The development of the nuclear power engineering, protection and processing of radioactive wastes of nuclear reactors, the use of radioactive isotopes in national economy, nuclear explosion, industrial wastes and etc. may cause the radioactive pollution of the environment. In the case of such pollution the environment as well as living organisms are exposed to radioactive radiation (a-, P-, y- etc.). Radioactive substances emit radioactive rays and as their decay time varies for natural and artificial radioactive substances the time of their environmental effect ranges from some years to million years. In consequence of radiation effect new specific properties - ecological, psycological, biological and so on are observed. It's necessary to determine the harmful effect of radioactive pollution areas on the environment as well as human life and radiation dose in order to protect the area, foods and people from this effect. It is of great importance to make dosimeters capable of registering y-radiation dose in a wide energy range and with high effectiveness and radiation-resistant devices to reveal the singularities of radioactive radiation and assess its safety risks in order to protect environment and living organisms from these effects [1-4]. The dosimeters made on this purpose can be used during environmetal control, radioecological service at sanitary-and-epidemiologic stations, detection of radioactive materials and plants at customs service, emergency cases and military dangers. The pollution areas, radiation type and nature, equivalent dose of y-rays and exposure dose rate is determined by dosimeters and the prospecting for radiactive materials and ionizing sources are realized. A scintillation method of the registration and the spectrometry of ionizing radiation is a more developed one among the different methods of detection. This is conditioned to a high extent by the fact that scintillation materials differ for their high registration efficiency, sufficient temporal and energy resolution. The demand for scintillation detectors rises for their sensitivity and registration efficiency of ionizing radiation, space resolution and high-performance, lack of hygroscopicity, capacity to be applied under extreme climatic conditions (temperature stability, high radiation field) due to the development and creation of the new generation of high-sensitive and high-performance radiation equipment (including nuclear power engineering, space researches under extreme conditions, geophysical instrument engineering). In comparison with other crystals A~3B~6 semiconductor crystals are much more radiation-resistant, have high sensitivity and anisotropic properties in ultraviolet (UV) spectrum region. Scintillation semiconductor detectors (SD) on the base of metal-A~3B~6 lamellar semiconductors are perspective materials for electron, x- and y-irradiation. High photoconductivity in UV-spectral region exceeding marginal region is observed in these semiconductors[5]. One of the main parameters of electron, x- and y-irradiation SDs is a collection efficiency of charge carriers. In the given work the collection of charge carriers in the detectors on the base of metal-GaSe, GaS and InSe lamellar semiconductors has been investigated. The mode of SDs functioning is based on the generation of electron-hole pairs in contact to a metal-semiconductor and their collection at applying reverse bias voltage. The optimal values of sample thickness, the voltage of electric field applied on contacts and photon energy in incident light have been theoretically determined which supplies effective functioning of the detector. The photoconductivity (PC) has been calculated depending on electric field voltage and light absorption. A spatial distribution of non-equilibrium electrons Δn(x) along the crystal thickness during their excitation at several values of the absorption coefficient: a=lcm~(-1), α=10 cm~(-1), α=100cm~(-1) has been theoretically investigated. During the generation of the electrons at a= 1 cm"1 non-equilibrium electrons are distributed at zero bias (V=0 ) more or less uniformly along the crystal thickness. At imposing external field photoexcited electrons may pass into the crystal depth. The bias voltage is applied at so high values that all excited electrons reach back electrode (the opposite one) for efficient functioning of the detector. It has been theoretically determined that PC in the region of low energy values on negatively charged irradiated surface during rise in voltage increases but at an opposite polarity of the applied voltage decreases. PC decreases up to a limiting value in the region of high energy values during rise in voltage, after which the marginal PC increases in four orders. Besides, during rise in voltage the margin of PC moves to a short-wave region. By this way, the optimal values of the parameters have been determined at which a PC maximum is observed in the given structure. The obtained theoretical results agree with the experimental data. The investigated n-InSe samples with ρ ~10~6 Ohm-cm specific resistance at room temperature have been grown by the Bridgman method. The surface-barrier structure has been formed by the vacuum deposition of Au film with 2-2.5mcm thickness on a freshly cleaved InSe surface. Ohmic contacts have been pasted on the opposite surface of the crystal by a silver paste. In a wide range of direct (U=0.05-100V) and reverse bias voltages the current of the investigated structure follows the I～U~n power law. Besides, n power exponent for direct and reverse currents in the voltage region up to U≤5V turns out to be close to the unit which is usually connected with tunneling of the charge carriers or is explained by the current restricted by a space charge. The typical spectral dependence of the obtained structures' PC at 300K temperature has been studied. During the illumination of the structure by the side of Au, PC is observed in 0.36-1.8 mem spectral region. At the values of U=0.05-lV reverse bias photosensitivity increases which can be explained by an exciton decay at hv=1.6eV quantum energies. The dependence of a PC maximum on the electric field has been formulated. On the base of the conducted investigations we have come into conclusion that x- and γ-irradiation detectors can be constructed on the base of metal - GaSe, GaS or InSe semiconductor which will have high sensitivity and differ according its speed.
NETL
NSTL
Trans Tech Publications Ltd