JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY
Year:2012 | Volume:- | Issue:4 (58)|Papers Count:9

In this paper, the behavior of temperature, density, velocity and pressure of the plasma shock front produced by the interaction of a focused Nd: YAG laser beam on a copper target, with an average pulsewidth of 30ns and 140mJ laser energy, have been studied using shadowgraphy technique. For this purpose, the plasma was examined in air at the pressure from 760 to 2x 10-4 Torr by a laser probe beam of 10ns pulsewidth at the wavelength of 532 nm. The results obtained from the measurements and by using the hydrodynamical model indicated that at atmospheric pressure the temperature and plasma pressure near the target surface increase up to 30 eV and 7x104 atm, respectively. The relative plasma density during the interaction time was found to be about 6 times of the air density at the normal atmospheric pressure. By decreasing the pressure from 760 Torr to 50 Torr the shock wave gradually converts to a rarefaction wave. For the pressure less than 0.1 Torr, only a dense region with an electron density higher than »3.94x1021 cm-3 near the target surface was observed.

The study of micro seismicity and monitoring the micro seismic for the purpose of surveying the existing faults treatments and recognition of blind faults and other active tectonic structures in various phases of constructing the important structures, specially nuclear power plants, is unavoidable. According to IAEA safety guides and US-NRC regulatory guides, suitable instrumentation must be provided so that the seismic response of nuclear power plant features importantly from the safety point of view. According to R.G. 1.165 seismic monitoring by a network of seismic stations in the site area should be established as soon as possible after the site selection. Also, it is necessary to shutdown the nuclear power plant if vibratory ground motion exceeds the operating basis earthquake (OBE). The current research demonstrates the field works and studies for locating the local seismograph network in Darkhovein nuclear power plant. After the official studies and the primary visit of the old seismograph stations it was found that the mentioned network doesn’t cover completely the geological structures around the power plant. Therefore, new locations have been introduced through the field investigation and computational methods of optimization. In positioning the new stations, places with the least amount of noise and the best coverage for seismic sources were selected. The modeling with considering an imaginative station at the selected places shows that the thresholds of the complete records of earthquakes around Darkhovein site is under the magnitude 1 (about 0.8).

One of the most requirement for the neutron flux measurement is to use detectors with the response independent of neutron energy. Also, detectors should be directional and insensitive to the gamma radiation. Long-Counter detectors are considered to be in this catagory. In this paper, this type of detector has been designed by the MCNPX code. The counter used in this detector is a gas proportional counter which is filled with BF3 of 400 Torr gas pressure. The effective length and diameter of the counter are 31.1 cm and 2.4 cm, respectively. When the counter is placed in a moderator, its efficiency grows for fast neutron counting. The moderators optimum dimensions (internal and external) and the depth of track in the internal moderator, according to the calculation, are determined to be 8 cm, 8 cm, and 10 cm, respectively. We found a good literature agreement between the calculated response profile up to 20 MeV and the curves appeared in the literature, where all are showing the detector response up to 20 MeV. In this paper, however, it is calculated up to 100 MeV for the first time and in the energy interval of 40 MeV to 100 MeV with the detector response profile smoother then the other reports. In addition, to avoid entering the scattered neutron from the surroundings a 1 mm cadmium absorber is placed between the external and the internal polyethylen moderator. The angular responses for the energies of 2.5 MeV, 5 MeVand 19MeV and also their effect on the detector efficiency have been investigated. The maximum value of the counter response has been obtained when the neutron source is placed along the detector axis.

Cloud-point extraction (CPE) was used with lipophilic chelating agent to extract uranium(VI) from aqueous solutions. The applied methodology was based on formation of metal complexes soluble in a micellar phase of a non-ionic surfactant, Triton X-114. The metal ions complexes, then, were extracted into a surfactant-rich phase at a temperature above the cloud-point temperature. The influence of different parameters including the pH of the solution, surfactant concentration, concentration of the chelating agent, incubation time, equilibrium temperature, centrifugation time, initial concentration of U (VI) and interfering ions on the extraction efficiency was studied. A high extraction efficiency was observed and the calibration graphs were found to be linear in the range of 6.25x 10-4 to 0.1 mg L-1) of uranium (VI) ion. The detection limit (DL) of the applied method was 0.015 mg L-1). The pre-concentration factor was obtained to be 48.5. The interference of the some cations was also tested and in this respect no significant influence was obtained.

The effect of mineral particle size on the bioleaching of uranium from Saghand mine (anomaly 1&2) by acidophilic mesophile Acidithiobacillus ferrooxidans was investigated in a shake flask. The findings are indicating that this strain is suitable for the uranium recovery from the mentioned ore. In the range of our studies the uranium recovery is faster in the case of d80=108 micron from anomaly 1, while, a comminution level of d80=160 micron was obtained as an appropriate size for the anomaly 2. The results showed that the particle size distribution of the mineral in this range did not considerably influence the microbial activity. Also, based on the results of bacterial oxidation, the negative effects and toxicity due to the presence of solid and solute components do not put a limit on the microbial activity, and at the tested parameters range, the grown microbial population is performing the desired process excelently.

Interaction of energetic ion beam with matter results in atomic excitation and ionization of matter which consequently leads to occurance of the characteristic X-rays fluorescence. In the interaction of energetic molecular beam with matter, the unique phenomena of “Vicinage effect” and “Coulomb explosion” have already been observed and reported. In this research work, the interaction of molecular ion beam with targets of different atomic numbers was investigated. For this purpose, the yields of characteristic X-rays due to interaction of H2+ molecular ion beam with the selected targets were compared with those due to interaction of H+ atomic beam with the same targets. To accomplish this, atomic and molecular beams in the energy range of 1 to 1.4 MeV/u were used to irradiate targets of different atomic numbers, including Cu, Mn and AI. For Mn and Cu. The measured yields of the characteristic X-rays due to the irradiation by the atomic and molecular beams were found to be approximately the same. However, for the Al target, a significant difference was observed for the X-ray characteristic yields due to the irradiation by the atomic and molecular beams.

Blue mold caused by Penicillium expansum causes most of the losses during the storage period in the world. In this study, the inhibition effect of different doses of gamma radiation on spore germination and mycelial growth of Penicillium expansum was investigated. As a result, the Penicillium expansum was recovered from infected apple fruits. In order to evaluate the gamma radiation effect on the spore germination, spore suspension (104 spore/ml) exposed to 0, 100, 300 and 600 grey, using Co-60 gamma cell with a dose rate of 0.2 Gy/Sec. Also, a disk of mycelium (0.5 cm2) was removed from the edge of a three-days colony and transferred to PDA plates and irradiated to 0, 1500, 2000, 2500, 3000 and 3500 Gy. The results showed that, the irradiation has completely inhibited the spore germination at 600Gy. While, a dose of 3000Gy completely inhibited the mycelial growth of Penicillium expansum.

The event of the initiator neutron source damage in the Tehran Research Reactor (TRR) caused to release a significant amount of radioactive materials in the primary cooling system of the TRR. The event caused the impuritie level to exceed beyond the allowed limit and to an extent that the present water purification system was not able to function effectively. Hence, elimination of radioactive pollutions was found to be a necessary task for the safe operation of the reactor. It was realized, initially that the contamination is due to very small particles size. Thus, the method of water treatment for the small-size particle elimination was found to be essential. For this purpose, the efficiency of fiber filters was studied for selecting the most efficient sample. In spite of implementation of a high particle removal efficiency, however, the effectiveness of the fiber filters in this process was found to be low, and consequently, it was concluded that contamination particles are ranged in a very small-size and in the dimensions of molecular size. Based on this investigation, the method of purification of molecular size impurities were examined. Our examinations showed that utilizing a carbon active filter is the best approach for purifiying the reactor primary cooling system. The laboratory results have also shown that the efficiency of carbon active filter of 40cm deeps is about 76% for removing the alpha emitter particles. By considering these results, we set up a filtration system for water purification with granular charcoal of 100 cm deeps. After the successful purification of the polluted primary cooling system, the reactor was able to operate safely.