[en] An experimental simulation of a neutron boronometer was performed, reason being that there is hope of improving such a device for use in fission reactors. The importance of a neutron boronometer is heightened during refueling and potential boron dilution episodes. The safety significance is, of course, avoiding inadvertant criticality. The apparatus used was a Pu-Be neutron source suspended in the center of a 4800 ml beaker. A BF₃ filled tube was used as a neutron detector. The beaker was filled with water, and boron conentrations were varied by simple addition of boric acid. The experimental results were compared with ANISN calculations. The calibration of the boronometer would depend on the precision with which ANISN calculations would model experimental results

[en] Neutron energy spectrum measurement in the energy range 50 keV to a few MeV is very important for scientific and medical applications. Neutron dosimetry is very important as well but difficult to achieve. Several methods are generally used for these purposes. None of the methods is adequate in the low energy range. In the present work, a new neutron spectrometer is described. The spectrometer is based on using a BF 3-detector for measuring thermal neutrons and polyethylene moderator of various thicknesses for neutron thermalization. A response matrix was calculated with the MCNP code for a certain distance between neutron source and BF 3-detector. Bach value in the response matrix was obtained as an integral of the product of the neutron spectrum, after thermalization for a given moderator thickness due to a certain neutron source energy at the detector, and the energy response of the detector. The number of thermal neutrons was measured for twenty polyethylene moderator thicknesses with and without Cd-foil between neutron source and moderator. The system was tested with an Am-Be neutron source. The 20 x 20 response matrix allows a neutron spectrum determination in the 0- 10 MeV energy range, with 0.5 MeV steps. Different ways of matrix formation are described and results are presented. A comparison of the present results with those obtained with a liquid scintillator and unfolding method is shown. The neutron dose is obtained from the neutron spectrum . (authors)

No abstract available

[en] A gamma back scatter density gauge using Nai(Tl) detector and 3.5 mCi Cs¹³⁷ source was designed for continuously logging drill holes upto 1500 meters depth and recording the gamma back scatter response on a 0-1mA recorder. This was used to locate aquifer region in two boreholes in Turamdih area, Bihar, using its higher gamma back scatter response for lower density of water as compared to other rock formations. This aquifer region has been confirmed by using a moisture (n,n) logging probe designed for the purpose, which uses a 40 mCi Pu-Be fast neutron source and BF₃ counter as neutron detector. Geological log of these two boreholes shows core loss and limonitisation of the crushed core pieces in the detected aquifer zones, thus confirming the possibility of voids being filled with water. (auth.)

[en] Ideas of two-detector soil density and moisture content measuring techniques have been discussed and prototypes of such gauges constructed in INT Academy of Mining and Metallurgy, Cracow have been described. Two-detector gauges contain two independent detectors (of gamma rays or thermal neutrons respectively) spaced at different distances from source. The ratio of the count rates of these detectors is treated as the probe response. The two-detector probe responses are much less influenced by such factors as: changes of soil composition, changes of casing thickness, disturbance of a soil structure caused by the casing tube. On the other hand, the two detector probes are very sensitive to the changes of the soil density and moisture content, respectively. Results of experiments and methods of the optimization of the source-detector distances have been presented. (author)

No abstract available

[en] Inorganic scintillation detectors have wide applications in nuclear spectroscopy, medical imaging, space science, geological exploration etc. The detectors that are recently attracted to the nuclear and particle physics experimentalists are La-halide, Lu_2SiO_5 (LSO) and BaF_2 because of their superior energy and time resolutions. A BaF_2 detector is known to have very good timing properties because of its ultrafast decay time component (600 ps) but a poor energy resolution (∼10% at 662 keV). On the other hand, La-halide detectors have subnanosecond time resolutions as well as excellent energy resolution because of their high light output and faster scintillation decay time (16 ns). Here, we have performed comparative studies of LaBr_3(Ce) and BaF_2 detectors with same crystal sizes (38 x 25 mm"2)

[en] BF_3 gas is used in neutron proportional counters for reasonable neutron absorption cross section of "1"0B isotope. It is the only stable gaseous form of boron and not available to us in high purity form. Thus BF_3 gas is generated from CaF_2 (BF_3) complex made available by Heavy water Board. Detectors operated in proportional region are sensitive to impurities and loss of electrons in drift region. Interaction of BF_3 with ppm level of moisture and Si can permanently degrade the performance of detector. Large concentrations of negative ions also reduce effective electric field causing recombination and reduction in pulse height. During the process of generation and purification, continuous monitoring of vacuum is necessary. Initially the complex is heated up to 110° C for moisture extraction. Further temperature is gradually raised up to 350°C. Gas is passed through series of impurity traps. A NaF trap for HF and a glass thimble are maintained at -109° C with dry ice and acetone mixture. Gas is condensed at the thimble with LN_2 trap. Collected gas is further purified using distillation process. Gas purification system consists of a spiral stem bulb fitted with a needle valve. Safety precautions, such as enclosure to entire glass system, mounting of gas leakage sensor and maintaining gas at negative pressure, are strictly followed while handling gas

[en] An extension of the single-decaying-source technique was applied to measure the dead time of a delayed-neutron counting system. The three longest half-lives associated with the delayed neutrons emitted in ²³⁵U fission were used in this analysis. A dead time of 6.3 μs was calculated, based on a detector system which obeyed an extendable model for dead-time behavior. (orig.)

[en] The absolute neutronic activity of a ²⁵²Cf source has been measured using a set of eight BF3 counters; each fission was identified, the corresponding detected neutrons were counted for a time equal to the maximum lifetime of these neutrons in the moderator, the number of prompt neutrons was determined and the probability of detection for one neutron in the BF3 counter was measured. After corrections have been completed, the absolute accuracy of measurement is estimated to be 1%