a.a. mowlavi

Detecting the charge particles at Giga hertz rate is one of the applications of UFSD (Ultra-Fast Silicon Detectors). The UFSD test in front of the proton beam to count the beam particles and use it for a more precise Dose Delivery System for the treatment of the cancerous tumor by charge particles can become an effective step for the development of cancer treatment. In fact, this assessment is a prerequisite and guarantees the use of these detectors in the dose delivery system. In this regard, the best method for time measurement, which was CFD, was chosen. MATLAB software was used to measure and analyze the UFSD output signals. The results of the 50-μm-thick UFSD test and the various geometries that we performed in several different experiments at the CNAO Cancer Treatment Center in Italy, as well as the data obtained at the laboratory of CERN accelerator in Germany, were analyzed by the CFD method. The results of many different runs of programs in MATLAB for many registered signals show: 1- These sensors are reliable to count the proton particles in Giga hertz rate. 2-The CFD devices could be used to record the UFSD output signals. Therefore, they can be used in the correction of the dose delivery system as a counter for the proton number of the proton beam.

Some different time measurement methods have been presented for similar signals with the same trigger that one can choose by considering signal conditions. Finding the best time measurement method for the output signals from the UFSD (Ultra Fast Silicon Detectors) is our goal because we wanted to use these sensors to detect protons in the proton therapy system to treat cancerous tumors. Some different methods include Constant Fraction Discriminator (CFD), Cross-Correlation (CC), and Time over Threshold (TOT) by different data. These kinds of data include Data from Weightfield2 which is a UFSD signal simulator, Data from simulated signals in practice inside the laboratory, and experiment data, which are real data from the UFSD test in front of a Pico laser beam. Several programs in MATLAB software have been written and run to analyze and compare the different methods. The results are shown that CFD is the best method for time measurement finally

In the present study, we have systematically studied the role of surface energy coefficient as well as temperature dependence in the fusion hindrance phenomenon of the heavy-ion reactions using the proximity potential formalism. To this end, we have performed the calculations of the interaction potential using the original proximity potential 1977 (Prox. 77) and the fusion cross sections are calculated based on the coupled-channels (CC) approach. The considered fusion systems are including the heavy-ion reactions 11B+197Au, 12C+198Pt, 16O+208Pb, 28Si + 64Ni, 28Si + 94Mo, 58Ni+58Ni, 32S+89Y,34S+89Y, 12C+204Pb and 36S + 64Ni with conditions of Q <0 and charge product of the participant nuclei 392≤ Z1Z2 ≤784. Our preliminary calculations show the Prox. 77 model predicts the theoretical values ​​of the fusion cross-sections less than the corresponding experimental data especially in the energy regions below the fusion barrier. However, the imposing of the mentioned physical effects increases the calculated values of the fusion cross sections and thus improves their agreement with the experimental cross sections for the selected reactions. In addition, by considering the energy dependence on the surface energy constant γ0 of the proximity formalism at the low energy region we are able to reproduce well the fusion cross sections, the astrophysical factor S(E) as well as the logarithmic derivative L(E) in these regions.‎

Considering the importance of photoneutron production in linear accelerators, it is necessary to describe and measure the photoneutrons produced around modern linear accelerators.

The aim of the present research is to study photoneutron production for the 18 MV photon beam of a Siemens Primus Plus medical linear accelerator.

This study is an experimental study. The main components of the head of Siemens Primus Plus linac were simulated using MCNPX 2.7.0 code. The contribution of different components of the linac in photoneutron production, neutron source strength, neutron source strength and photon and electron spectra were calculated for the flattening filter and flattening filter free cases for the 18 MV photon beam, and was scored for three fields of 5 × 5 cm2, 10 × 10 cm2 and 20 × 20 cm2 in size.

The results show that the primary collimator has the largest contribution to production of neutrons. Moreover, the photon fluence for the flattening filter free case is 8.62, 6.51 and 4.62 times higher than the flattening filter case for the three fields, respectively. The electron fluences for the flattening filter free case are 4.62, 2.93 and 2.79 times higher than with flattening filter case for the three fields under study, respectively. In addition to these cases, by increasing the field size, the contribution of neutron production related to the jaws is reduced, so that when the field size increases from 5 × 5 cm2 to 20 × 20 cm2, a 17.93% decrease in photoneutron production was observed.

In all of the accelerators, the neutron strength also increases with increasing energy. The calculated neutron strength was equal to 0.83×1012 neutron Gy −1 at the isocenter.

The total yields of direct Single-Strand Breaks (SSBs) and Double-Strand Breaks (DSBs) in proton energies varying from 0.1 to 40 MeV were calculated. While other studies in this field have not used protons with energy less than 0.5 MeV, our results show interesting and complicated behavior of these protons.

The simulation has been done using the Geant4-DNA toolkit. An atomic model of DNA geometry was simulated. Simulations were performed with a source in the Z-axis direction at the cell nucleus entrance with protons at energies of 0.1-1 MeV in 0.1 MeV steps, 5 MeV, and 10-40 MeV in 10 MeV steps.

The calculated SSB yields decreased from 60.08 (GbpGy)−1 for 0.1 MeV proton energy to 49.52 (GbpGy)−1 for 0.5 MeV proton energy, and then it increased to 54.35 (GbpGy)−1 in 40 MeV. The DSB yields decreased from 4.32 (GbpGy)−1 for 0.1 MeV proton energy to 1.03 (GbpGy)−1 for 40-MeV protons. The DSB yields for energies less than 0.5 MeV was about 56%, and for the other energy levels, it was 44%. As for SSB yields, 35% of the breaks arose from protons with an energy of fewer than 0.5 MeV and 65% from higher energies.

It was found that the proton ranges with an energy less than 0.5 MeV are smaller than the cell size (10 μm), and 100% of the energy is deposited in the cell region. Then protons with these energies are the best choice to increase the number of DSBs.

Bachground: Hadron therapy is a novel technique of cancer radiation therapy which employs charged particles beams, 1H and light ions in particular. Due to their physical and radiobiological properties, they allow one to obtain a more conformal treatment, sparing better the healthy tissues located in proximity of the tumor and allowing a higher control of the disease. As it is well known, these light particles can interact with nuclei in the tissue, and produce the different secondary particles such as neutron and photon. These particles can damage specially the critical organs behind of thyroid gland. In this research, we simulated neck geometry by MCNPX code and calculated the light particles dose at distance of 2.14 cm in thyroid gland, for different particles beam: 1H, 2H, 3He, and 4He. Thyroid treatment is important because the spine and vertebrae is situated right behind to the thyroid gland on the posterior side. The results show that 2H has the most total flux for photon and neutron, 1.944E-3 and 1.7666E-2, respectively. Whereas 1H and 3He have best conditions, 8.88609E-4 and 1.35431E-3 for photon, 4.90506E-4 and 4.34057E-3 for neutron, respectively. The same calculation has obtained for energy depositions for these particles. In this research, we investigated that which of these light particles can deliver the maximum dose to the normal tissues and the minimum dose to the tumor. By comparing these results for the mentioned light particles, we find out 1H and 3He is the best therapy choices for thyroid glands whereas 2H is the worst.

The most common intravascular brachytherapy sources include 32P, 188Re, 106Rh and 90Sr/90Y. In this research, skin absorbed dose for different covering materials in dealing with these sources were evaluated and the best covering material for skin protection and reduction of absorbed dose by radiation staff was recognized and recommended. Four materials including polyethylene, cotton and two different kinds of plastic were proposed as skin covers and skin absorbed dose at different depths for each kind of the materials was calculated separately using the VARSKIN3 code. The results showed that for all sources, skin absorbed dose was minimized when using polyethylene. Considering this material as skin cover, maximum and minimum doses at skin surface were related to 90Sr/90Y and 106Rh, respectively. polyethylene was found the most effective cover in reducing skin dose and protecting the skin. Furthermore, proper agreement between the results of VARSKIN3 and other experimental measurements indicated that VRASKIN3 is a powerful tool for skin dose calculations when working with beta emitter sources. Therefore, it can be utilized in dealing with the issue of radiation protection.

In this paper, an algorithm base on Monte Carlo simulation for pileup effect in gamma spectrum of a detection system is presented whose its code was written in FORTRAN language. The code can be run in paralayzable and nonparalazable mode to obtain the pileup distortion and value of pulses pileup for any detection system. The result show, that the computed spectrum of 137Cs is in good agreement with the experimental spectrum in NaI(Tl) detector. The free of pileup free spectrum and sub-spectra with different degrees of pulses of pileup are calculated. Also, we can apply it to different sources and detectors for pileup correction.