Studies on irradiated photovoltaic cells by proton beam in a plasma focus device.

In this study, the effects of irradiation by proton beam of a plasma focus device with 5 kJ discharge energy on photovoltaic (PV) cells were investigated. Before and after irradiation, the I-V curve of the cells was measured. Changes in Voc and Isc of silicon-type PV cells were recorded. After 1, 2, 4 and 8 shots, on average compared to the initial conditions, the voltage decreased by 76.81%, 76.70%, 84.94% and 83.74% respectively, and the current decreased by 43.18%, 54.91%, 67.49% and 58.07% respectively. The behavior of the plasma focus device was simulated by the LEE code, and the damage caused by the protons of the plasma focus device in each shot was evaluated by SRIM & TRIM software. For each shot of the plasma focus device, on average, about 3.82% of the atoms were displaced. The recovery time of the crystal structure, and the improvement of photovoltaic cells' properties after irradiation were investigated experimentally. After 10 days of irradiation, the open circuit voltage of the cells that were irradiated by 1, 2 and 4 shots were increased by 22.81, 18.00 and 35.10%, respectively. Also, the short-circuit current of the cells were increased by 7.37, 8.91 and 27.89%, respectively.

Damage study of irradiated tungsten and copper using proton and argon ions of a plasma focus device.

The destructive effects of proton and argon ions produced in a low energy plasma focus device on the surface of tungsten and copper were investigated. Optical microscopy, SEM, EDX, XRD and ERD analysis were performed for initial and irradiated samples. The results showed that total thermal impact under the irradiation by argon is much more significant than that by hydrogen. Sub-micrometer blisters, clusters of joined bubbles and rupture patterns were observed on the surface of copper after irradiation by argon. Micro-cracks were observed on the tungsten samples irradiated by argon, which indicate fast annealing of the molten surface. Many dense blisters and evidence of ion sputtering were observed on the surfaces irradiated by protons. Results of ERD analysis showed that the highest concentration of hydrogen is 24% in the second layer and at a depth of 20-55 nm from the tungsten surface. In the copper sample, the highest density of hydrogen was found to be 23% in the second layer and at a depth of 28-68 nm. Also, the highest penetration depth of protons into the tungsten and copper samples was 118 nm and 160 nm, respectively.

Micro-dosimetry calculation of Auger-electron-emitting radionuclides mostly used in nuclear medicine using GEANT4-DNA.

A large number of nuclear medicine radionuclides are Auger-electron-emitters and internal conversion electrons which can transmit significant doses to the patient during diagnosis. Therefore, the dosimetry of these radioisotopes is necessary for the evaluation of their biological effects and their use for treatment and targeted-radiotherapy. In this study, dosimetry calculation of a number of widely used radioisotopes in nuclear medicine was performed on a cellular scale using Geant4-DNA simulation. S-values of some of the diagnostic radioisotopes, including 123I, 125I, 99mTc, 67Ga, 201Tl, and 111In, were evaluated in a homogeneous spherical geometry model with unit density in which the cell and nucleus were concentric. The results revealed that S-values of these diagnostic radioisotopes were mainly greater than S-values of the radioisotope 131I, which emits ß-particles; they were lower but can be compared with 211At (emitter of alpha particles) in the cellular scale. It shows better the importance of dosimetry calculation of diagnostic Auger-electron-emitting radioisotope in a cellular scale and their applicability in treatment. It should be noted that the S-values obtained out of the Geant4-DNA simulation are in line with the values of the other codes and the MIRD technique.

Measurement of the effective energy of pulsed X-rays emitted from a Mather-type plasma focus device.

The current study examined the effective energy of pulsed x-rays emitted from a Mather-type plasma focus device with copper anodes at an energy range of 2-3kJ using x-ray transmission radiography. Aluminum filters of different thicknesses and dental x-ray film were used. When air gas was used at a constant voltage of 21kV at 0.3, 0.6, 0.9 and 1.2 mbar, the effective energy of pulsed the x-ray was 10.9, 10.7, 17.3 and 15.8keV, respectively. At 0.6 mbar of air, as the operating voltage increased to 19, 21 and 23kV, the effective energy of the x-ray radiation was 10.6, 10.7 and 12.4keV, respectively. Comprehensive investigation of the characteristics of x-ray emission from plasma focus devices makes it feasible to use this device as an intensive x-ray generator for medical and industrial purposes. The present study is a part of a program which is planned to realize these applications.