[en] A sensitive device phototransistor has been used as a radiation monitor which measures the dosages in the range of 10² rads to 10⁶ rads. The main measured characteristics of the phototransistor was the variation in the collector current (I_C) with collector to emitter voltage (V_CE). These parameters were measured before and after irradiation. Calibration was carried out by measuring collector current for each value of V_CE for different 1 MeV electron fluences. It was observed that collector current decreases with an increase in radiation dose received by the phototransistor. The outer advantage in the use of this technique is that the transistor current can be changed by varying the incident light intensity which can also be used as a measure of radiation dose. Appropriate calibration of the phototransistor was made with the help of a pocket dosimeter

[en] Published in summary form only

[en] In the present work, an ion accelerator is used to produce a beam of deuterons that strikes the target to produce neutrons with 14 MeV energy. Elemental distribution are obtained by measuring gamma ray spectrum after the beam of 14 MeV neutrons pass through the chemical composition (Sugar, Urea etc.). The characteristic gamma rays emitted due to fast neutron interaction with the elements present in the chemical compositions are being used to determine the respective elemental densities or concentrations

[en] n-channel depletion MOS devices were irradiated with 50 and 80 MeV phosphorous ions, with different fluences varying in the range from 10¹¹ to 10¹³ ions/cm². The pre and post irradiation I-V characteristics were measured and the corresponding threshold shift ΔV_TH was estimated. In both the cases, the drain current I_D and the threshold voltage V_TH were found to decrease with the ion fluence. The increase in the threshold voltage shift ΔV_TH with the ion fluence, was greater for the devices irradiated with 80 MeV ions than those irradiated with 50 MeV ions. The interface and oxide state densities were determined through the subthreshold voltage measurements. To separate the contributions of oxide and interface states towards the threshold voltage shift, the ion irradiated MOS devices were annealed at 150 deg. C. The threshold shift during annealing initially decreased and later increased with increasing annealing period. The rate of change of the interface states during annealing was higher than that of the oxide states. It was also found that depletion mode (normally ON) MOSFETs switched operation to enhancement mode (normally OFF)

[en] A simple and controllable method to synthesize nanoparticles in the surface region of polymers was used by low energy electron irradiation. Using this method, gold nanoparticles have been synthesized by irradiating gold coated PVA (Polyvinyl Alcohol) sheets. This method was easy in operation and even period of few minutes was sufficient to obtain the nanoparticles. The coatings (∼10 μm) made from a mixture of ethanol and HAuCl₄ on PVA sheets (∼150 μm) by simple drop cast method were irradiated with 30 keV electrons, at room temperature and 10⁻⁶ mbar vacuum level. The electron fluence was varied from coating to coating in the range of 0 to 24×10¹⁵ e/cm². The irradiated samples were characterized by the UV–Vis, XRD, SEM and RBS techniques. The plasmon absorption peak at ∼539 nm in UV–Vis spectra was an evidence for the initiation of the growth of gold nanoparticles. The X-ray diffraction results and the blue shift in the plasmon absorption peak reveal that the size of nanoparticles could be tailored in the range from 58 to 40 nm by varying the electron fluence. The diffusion of gold in the PVA was confirmed by the Rutherford backscattering spectroscopy and scanning electron microscopy techniques. This method of synthesis of metal nanoparticles by low energy electron beam irradiation has the key importance in the development of new fabrication techniques for nanomaterials. - Highlights: • The results indicate that low energy electrons can effectively be used for the synthesis of nanoparticles of different sizes. • This study leads to a definite conclusion that gold nanoparticles have been synthesized in surface region of the PVA sheet. • The size of nanoparticles decreases with increasing electron fluence. • The depth of diffusion of Au atoms at maximum fluence was found to be ∼1.5 μm

[en] A comparative study is made on the radiation damage caused by 14 MeV neutrons and 1 MeV electrons in crystalline silicon by measuring Hall mobility, carrier concentration, energies of defect centres and minority carrier lifetime. For both electrons and neutrons the energies of defect centres are found to be almost identical but the observed degradation in Hall mobility is large in neutron-irradiated and marginal in electron-irradiated silicon. The coefficient of radiation damage for 14 MeV neutrons is higher by almost three orders of magnitude compared with that for 1 MeV electrons. (author)

[en] The energy distributions of neutral atoms ejected from the polycrystalline Cu target, the Si(1 1 1)-7x7 surface, and the Si(1 1 1)-''5 x 5''-Cu surface by 5 keV Ar⁺ ion bombardment have been measured with very high efficiency by means of the multi-photon resonance ionization spectroscopy, in order to obtain the surface binding energies. The energy distributions for Cu from polycrystalline Cu target, Si from the Si(1 1 1)-7x7 surface, and Cu from the Si(1 1 1)-''5 x 5''-Cu surface have been found to have a peak at energies of around 3.0, 5.0 and 1.5 eV, and the function shapes of high energy tails to be proportional to E^-1.9, E^-1.2 and E^-1.3, respectively. Based on the linear collision cascade theory, the surface binding energies are determined to be 5.7, 6.0 and 2.0 eV, and the power factor m in the power law approximation to the Thomas-Fermi potential are determined to be 0.1, 0.4 and 0.3 for Cu from the Cu polycrystalline, Si from the Si(1 1 1)-7x7 surface, and Cu from the Si(1 1 1)-''5 x 5''-Cu surface, respectively. In conclusion, the results indicate that the energy distributions of ejected particles are well characterized by the linear collision cascade theory developed by Sigmund

[en] Bunches of 1 MeV electrons were made to fall normally on surfaces of graphite, aluminium, copper, silicon and silver and in each case the yield of backscattered electrons was measured using a special type of Faraday cup. The average beam current was kept low enough to avoid any surface heating and also to match the radiation levels that exist in some regions of space. The measured values of backscattering ratios and coefficients are found to be close to the values derived using an empirical relation but slightly higher than those reported earlier for relatively high beam currents. (author)

[en] In the Department of Physics, University of Pune, Pune, a 200 keV ion accelerator and a 6 to 8 MeV electron accelerators were developed using mostly indigenous components, and being used since 1980 onwards for research and teaching work. The ion accelerator can provide gaseous ions such as hydrogen, deuterium, argon, etc over energy range 30 keV to 200 keV at a current level of ∼ 150 microampere. The gaseous ions from this accelerator are used in research work related to ion irradiation, ion implantation, etc. Most of the time, this ion accelerator is used as a 14 MeV neutron generator involving D-T reaction. The 14 to 14.8 MeV neutrons with flux ∼ 10⁸ n/cm²-sec are used for research work in the fields of nuclear reactions, elemental analysis, etc. The other accelerator facility is an electron accelerator called Race-Track Microtron, unique in the country. This accelerator can provide electrons over two energy ranges; 0.5 MeV to 1 MeV and 6 to 8 MeV. The electron beam is being used for different studies such as Bremsstrahlung production, gamma-ray radiography, and radiation damage in semiconductor devices, polymers, and space quality materials. Recently, a new irradiation system has been developed to simulate space radiation environment. This system has facility to irradiate a sample with hydrogen ions of energies up to 50 keV, and electrons of energy up to 30 keV simultaneously under exposure of UV radiation. All these indigenously developed facilities have contributed significantly in the accelerator based research and teaching programmes. The 6.5 MeV electrons from the Race-Track Microtron were successfully used in tailoring the switching characteristics of a number of thyristors and diodes made by BHEL, Bangalore. Similarly, the 14 MeV neutrons have been used for the analysis of explosive class materials. (author)

[en] The energy spectra of positively charged and neutral species ejected from the Si(1 1 1) surfaces by keV Ar impact have been measured by means of a combined technique of the time-of-flight (TOF) analysis with the multi-photon resonance ionization spectroscopy (MPRIS). It is shown that positively charged species of Si⁺, Si²⁺ and SiO⁺ are ejected from the as-cleaned 7x7 surface by 11 keV Ar impact. It is also shown that Ar sputter cleaning of the as-cleaned 7x7 surface for 14 min at the flux of 2x10¹³/cm²s removes completely the oxygen impurity and the yields of Si²⁺ is comparable to that of Si⁺. Moreover, the ionization probability of Si atoms sputtered is shown to be expressed as an exponential function of the inverse of their velocity. The production mechanism for the doubly charged Si ion is discussed based on the L-shell ionization of Si atoms due to quasi-molecule formation in the collisions of the surface atoms with energetic recoils and subsequent Auger decay of the L-shell vacancy to doubly ionized Si ions