نشریه تابش و فناوری هسته ای
سال دوم شماره 4 (زمستان 1394)

Explosives include elements such as H, C, N and O with specific the amount and ratio. Nitrogen and oxygen are more abundant than others and the amount of nitrogen is an excellent characteristic to detect explosives. The Probability of existing explosives in an environment could be found out by acquiring the amount of nitrogen accumulated in the environment. In this paper, the prompt gamma neutron activation analysis (PGNAA) technique has been used in order to detection and identification of explosives. Using this method, one could detect suspicious packages and bags containing explosives and they are prevented to entry into government agencies, military facilities, airports, ports, embassies, banks, power plants, major organizations and sensitive companies. The nitrogen nucleus emits the thermal neutrons and gamma radiation spectrum 10.83 MeV almost at the same time as it absorbs them. In the designed system, the source and NaI detector has been used as neutron generator and emitted gamma receiver respectively. MCNPX2.6 code has been exploited to simulate neutron - photon transport In this system. To design this system, different thickness of paraffin and lead have been utilized to moderate neutrons and comply with shielding principles and health physics respectively. The designed system is capable of detecting NG explosive with a weight of 323 g and 1023 g for 10 minutes and one minute respectively.

Thomas-Fermi model is one of the oldest models produced to study different properties of nuclei. Density is a major variable to present both dynamical and statically properties of nuclei in this model. Also, there is no limitation for considering any deformation for nuclei. In This investigation, some major properties of heavy deformed nuclei are investigated using Liquid Drop and Thomas-Fermi model. Considering Quadruple and Hexagonal deformations along with energy improved terms in to nuclear matter, Liquid-Drop parameters containing surface, volume and asymmetry parameters are calculated. Using these parameters, fission barrier high for some heavy deformed nuclei in different temperatures are evaluated. The obtained results compared with experimental data. Comparison indicates that fission barrier high is satisfactory for heavy deformed nuclei. Also, using developed version of this model the precise liquid-drop parameters are obtained so these parameters used to study thermodynamic properties of hot deformed nuclei. Such studies improve knowledge of nuclear physics.

Today hadrontherapy is progressing as a modern treatment technique for different types of hard and radioresistent tumor. The advantage of the high accuracy of the dose deposition resulting from the physical properties of hadrons and the higher radiobiological effectiveness make this kind of radiation a promising tool for cancer treatment. However, the new modalities of dose delivery for this radiation imply a high technology development, and type of accelerator plays a crucial role for a successful treatment. Compared with the conventional radiation therapy in which photons are mainly used, In order to overcome the physical and biological limitations of the conventional radiotherapy, proton and carbon ion employed in hadrontherapy can spare healthy tissues more effectively because of the optimal distribution of their doses in tissue. In addition, radiobiological advantages associated with hadron therapy give the technique an unique position among the conventional treatment methods. However, following the new technological developments and the advantages of hadrons over conventional radiation therapy the number of hospital based centers provided with equipments completely dedicated to clinical activity is increasing, the demand for the use of this treatment methode is increasing worldwide and since most of the treatment centers are now hospital-based, they need to be built as small as possible in size while maintaining their clinical advantages and reducing related costs as much as possible. Accordingly, choosing the appropriate accelerators has always been of utmost importance to achieve this goal.

In this study a dose simulation system was constructed based on the FLUKA Monte Carlo code to simulate proton dose distribution in homogeneous and CT phantoms. Conversion from Hounsfield unit of a patient CT image set to material information necessary for Monte Carlo simulation is based on Schneider’s approach. We used the NEU codes package to design a nozzle of proton therapy system, and we used FLUKA to simulate the transport of protons in the nozzle and a water phantom. Depth dose and SOBP dose distributions for homogeneous and CT head Phantoms for a 80 MeV proton beams were compared. Bragg peak in homogeneous and CT head phantoms were different about 6 mm. The result showed while for large fields these might be local effects, for very small fields in the head region these effects can potentially affect the majority of the treatment volume. Therefore treatment planning programs in proton therapy that water environment is considered, the results are less accurate for small field sizes. Also the simulation results showed that NEU code is a powerful tool in the design of passive-double scattering systems that constitute the basis of Proton therapy nozzles.

In this research by utilization the reaction(_1^1)H(n,γ)(_1^2)H was determined the heavy water enrichment. For this mean used the thermal neutron source obtained from Am-Be and moderating system that there is in nuclear physics laboratory in the Arak University. Moderator included a cubic of paraffin with dimension 50×50×50 cm3 and two outside layer included Boric acid with 2.5 cm thickness and 5 cm lead. The HPGe GCD30195 BSI detectors with 30% relative efficiency and corresponding electronic system MCB were used for registration of prompt γ- ray spectra. Heavy water samples with known enrichment as 0.01233%,13.5%, 35.2% and 58.2% were used to determine the linear calibration plot. In this research correlation coefficient obtained as R2= 0.99. Using the corresponding linear plot, were determined unknown enrichment heavy water as 57. 64 ± 0.02 mol%. The enrichment of D2O in this sample determined using FT-FR method that obtained 56.11±0.02 mol% which shows 1.53% disagreement.