جستجوی مقالات مرتبط با کلیدواژه « plasma focus » در نشریات گروه « فیزیک »

One of the reasons for the use of PET radioisotopes in medical research is the presence of a series of positron emitters such as 11C, 13N, 15O, and 18F. The detectors combined with them perform a series of processes similar to natural processes in the body. Another advantage of this method is imaging of metabolic function, which causes early detection of dangerous diseases such as cancerous tumors, cardiovascular diseases, neurological diseases such as epilepsy, Parkinson's disease, and allows the doctor to treat the disease before it develops. In this research, in search of radioisotope production devices with short half-lives, to simulate the depth dose received by a phantom cube of water geometries are 20 cm at a distance of 50 cm from the spring and firing one million photons from a point spring with the energy of 25 MeV Cylindrical water with a radius of 7 cm and a height of 3 mm in order to produce radioisotope F18, Geant tool 4.10.7 has been used and to have safe radiotherapy, the received deep dose has been calculated with appropriate results.

The destructive effects of high-energy hydrogen and argon ions irradiated in the MTPF-2 Mather type plasma focus device on the surface and structural properties of graphite were investigated. Raw and irradiated samples were analyzed using a Scanning Electron Microscope. While microscopic images of samples irradiated with hydrogen ions point sputtering, pores are seen on the samples' surface along with spot melts, the predominant phenomenon on the surface of samples irradiated with argon ions is sputtering of particles from the graphite surface. X-ray diffraction analysis was used to investigate the changes caused by the irradiation of high-energy protons and argon ions on the graphite structure. In the X-ray diffraction spectrum of the irradiated samples, the peaks' displacement, and the change in the peaks' intensity compared to the X-ray diffraction spectrum of the reference sample were observed. The peak of the graphite sample's locations irradiated with hydrogen and the sample irradiated with argon have been shifted to smaller angles. The displacement of the peaks in the proton-irradiated sample is higher than that of the argon ions. The argon ion and hydrogen ion beam specifications were calculated using the Lee code.

Damage of tungsten due to helium and argon ions of a PF device was studied. Tungsten samples were irradiated by 20 shots of the plasma focus device with argon and helium as working gases, separately. The tungsten surface was analyzed by SEM, before and after irradiation. SEM revealed dense blisters with diameters of a few hundred nanometers, on the samples which were irradiated by helium ions, while on the samples irradiated by argon, cracks were developed on the surface. XRD analysis was used for crystallography of tungsten, before and after irradiation. Irradiation by helium and argon affects peak location, peak intensity, FWHM, and spacing of planes, which shows that the crystalline structure of tungsten is affected by irradiation.Characteristics of ion beam of the plasma focus device were calculated by the Lee code. The depth profiles of dpa/shot and ion concentration were calculated using the SRIM code. Using the Lee code, the average fluencies of helium and argon ion beams of the PF device were calculated about 7.9×1014 cm-2 and 0.25×1014 cm2 per shot, respectively. SRIM revealed that the maximum DPA was about 1.7 and 0.17 and occur in the depth of 7 nm and 30 nm for argon and helium, respectively. Also, the maximum concentration occurs in the depth of 20 nm and 40 nm for argon and helium, respectively.

In this study, to calculate the radioactivity of radioisotopes such as 11C, 15O, 18F and 123,124I in a focus plasma device for the production of medical radioisotopes, the particles of neutrons and protons with cubic targets of Nitrogen, Xenon, Carbon and a solid natural Boron is used. Particles energy are at the input of the program from 1MeV to 10MeV. Also, the total yield coefficient is considered. In this paper, with the help of MCNPX 2.7 code, the amount of flux and deposited energy of neutron and proton particles is calculated for the production of medical radioisotopes in the focal plasma system. According to the obtained results in this study, it is shown that due to the different absorption and resonance cross sections for the considered targets with the energy of the neutrons and the protons are not a linear increase in the flux of particles. But after an energy of approximately 10 MeV, this slope is almost constant due to the constant cross section. Also, the results of this study show that with increasing energy of protons in these targets, the deposited energy of protons increases linearly, but its maximum value for the nitrogen target and its lowest value for the Xenon target due to different interactions cross-section.

The most important part of neutron therapy treatment (NCT1) is to achieve a beam of neutrons with suitable energy and intensity, as well as the least pollution and damage. In this study, in order to correct the neutron spectrum from D-D fusion and its use in neutron therapy, a set of different materials which are called the Beam Shaping Assembly (BSA) was placed in the direction of energy 2.45 MeV neutrons output in such a way that the neutron beam intensity and energy output were appropriate for treatment. Moreover, the total yield coefficient 109 was considered. In this article IS set for a plasma focus device was designed and optimized by MCNPX2.6 code. The results of this study indicated that, according to BSA3 materials, epithermal neutrons were the best choice for energy range.

The silver activation counters are commonly used for pulsed-neutron yield measurements especially in plasma focus devices. The counter normally consists of a Geiger-Muller tube along with silver foils and polyethylene (as a moderator), which is calibrated against an Am-Be radioisotope neutron source. The neutrons, after being slowed-down in the polyethylene, activate the silver foils. By measuring the foil activity with a Geiger-Muller counter, the neutron yield is determined. In the present paper, the activation counter’s calibration constant calculation using the MCNP4C code is explained. The calculated calibration constant is in good agreement with the experimental results.