A novel approach of using thin epitaxial silicon PIN detectors for thermal neutron measurements with reduced gamma sensitivity has been presented. Monte Carlo simulations showed that there is a significant reduction in the gamma sensitivity for thin detectors with the thickness of 10-25 mu m compared to a detector of thickness of 300 mu m. Epitaxial PIN silicon detectors with the thickness of 10 mu m, 15 mu m and 25 mu m were fabricated using a custom process. The detectors exhibited low leakage currents of a few nano-amperes. The gamma sensitivity of the detectors was experimentally studied using a 33 mu Ci, 662 keV, Cs-137 source. Considering the count rates, compared to a 300 mu m thick detector, the gamma sensitivity of the 10 mu m, 15 mu m and 25 mu m thick detectors was reduced by factors of 1874, 187 and 18 respectively. The detector performance for thermal neutrons was subsequently investigated with a thermal neutron beam using an enriched B-10 film as a neutron converter layer. The thermal neutron spectra for all three detectors exhibited three distinct regions corresponding to the He-4 and Li-7 charge products released in the B-10-n reaction. With a B-10 converter, the count rates were 1466 cps, 3170 cps and 2980 cps for the detectors of thicknesses of 10 mu m, 25 mu m and 300 mu m respectively. The thermal neutron response of thin detectors with 10 mu m and 25 mu m thickness showed significant reduction in the gamma sensitivity compared to that observed for the 300 mu m thick detector. Considering the total count rate obtained for thermal neutrons with a(10)B converter film, the count rate without the converter layer were about 4%, 7% and 36% for detectors with thicknesses of 10 mu m, 25 mu m and 300 mu m respectively. The detector with 10 mu m thickness showed negligible gamma sensitivity of 4 cps, but higher electronic noise and reduced pulse heights. The detector with 25 mu m thickness demonstrated the best performance with respect to electronic noise, thermal neutron response and gamma sensitivity.

Detection of threatening objects and materials using X-ray line scan images is important part for security inspection. In X-ray Baggage Inspection Systems (XBIS), line scan images of objects are obtained by measuring the transmitted X-rays through the objects using pixelated detectors. A standard dual energy machine comprises of about 640 pixels each of high energy (HE) and low energy (LE) detectors to generate two images. Depending on the atomic number of the material, the low energy detectors and high energy detectors give different contrast and information about the nature of objects can be obtained. The XBIS also needs to qualify certain criteria in terms of spatial resolution, wire resolution in air, contrast for thin objects, penetration through thick objects, and discrimination between inorganic and organic materials.

Prototype single crystal diamond detectors with different types of metallization and post metallization treatment were fabricated for the applications requiring fast neutron measurements in the Indian Test Blanket Module (TBM) at the International Thermonuclear Experimental Reactor (ITER) Experiment. The detectors were characterized by leakage current measurements to ascertain that the leakage currents are low and breakdown voltages are higher than the voltage required for full charge collection. The detector response to charged particles was evaluated using a 238+239 Pu dual energy alpha source. The detectors showed an energy resolution of about 2% at 5.5MeV. In order to study their suitability for the operation at higher temperatures, leakage current variation and alpha response were studied up to 300°C. At 300°C, peaks corresponding to 5.156MeV and 5.499MeV alphas could be separated and there was no significant degradation of energy resolution. Finally, the detector response to fast neutrons was evaluated using a Deuterium-Tritium (D-T) neutron generator. The observed spectrum showed peaks corresponding to various channels of n-C interactions with a clear isolated peak corresponding to ~8.5MeV alphas. The detectors also showed high sensitivity of 3.4×10−2cps/n/(cm2s)–4.5×10−2cps/n/(cm2s) and excellent linearity of response in terms of count rate at different neutron flux in the observed range of 3.2×105n/(cm2s) to 2.0×106n/(cm2s).

Double sided DC-coupled silicon strip detectors with geometry of 65mm×65mm have been developed in India for nuclear physics experiments. The detectors have 64 P+ strips on the front side and 64 N+ strips on the backside with a pitch of 0.9mm. These detectors were fabricated using a twelve mask layer process involving double sided wafer processing technology. Semiconductor process and device simulations were carried out in order to theoretically estimate the impact of important design and process parameters on the breakdown voltage of detectors. The performance of the first lot of prototype detectors has been studied using static characterization tests and using an alpha source. The characterization results demonstrate that the detectors have low leakage currents and good uniformity over the detector area of about 40cm2. Overview of the detector design, fabrication process, simulation results and initial characterization results of the detectors are presented in this paper.