IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY TRANSACTION A- SCIENCE
Year:2008 | Volume:32 | Issue:A3|Papers Count:10

Gafchromic XRCT radiochromic film is a self developing high sensitivity radiochromic film product which can be used for assessment of delivered radiation doses which could match applications such as Computed Tomography (CT) dosimetry. The dose response of Gafchromic XRCT radiochromic film has been measured with reflectance spectrophotometry and desktop scanners. The film automatically changes colour upon irradiation, changing from a yellow to a green/brown colour. Results show a high sensitivity to delivered dose compared to other conventional radiochromic films which is well suited to CT applications where lower applied doses are delivered. Sensitivity is found for this film with a 1cGy applied dose, producing an approximate net optical density change of 0.3 at 636nm and 0.2 net OD using broad band white light. This high sensitivity combined with its relatively energy independent nature around the 100kVp to 150kVp x-ray energy range provides a unique enhancement in dosimetric measurement capabilities over currently available dosimetry films for CT applications.

In the present paper an operator-differential equation of second order in complex domain is considered when the coefficients have singularity of pole type at the point z=0. A theorem of existence of the solution of the equation is proved and the spectral property of the solution is separately investigated when the coefficients are spectral operators.

In this paper, we presented algebroids and crossed modules of algebroids. We also presented pullback crossed module of algebroids and we then define pushout crossed modules of algebroids.

The ionization effects of charged particles produced in neutron interactions for Boron Neutron Capture Therapy are considered here using SRIM Monte Carlo Code. The estimated values of these effects in a Plexiglas acrylic phantom are shown to agree well with the available experimental values in high Boron concentration areas. As expected, the ionization effects from lithium and alpha particles are significant. However in the low Boron areas, proton ionization makes an important contribution and their effect on healthy tissue should not be ignored.

The threshold of weak and strong synchronization in a coupled chaotic Gaussian map is Demonstrated by using the Pyragas’ terminology. However, Vieira and Lichtenberg have shown that the Pyragas’ criteria for weak and strong synchronization cannot be used for all chaotic systems. In this article we demonstrated some interesting synchronization behavior of two coupled chaotic systems with some zero and negative Lyapunov exponents. In such cases the various synchronization behaviors may also depend upon the eigenvalues of a system obtained by subtracting two chaotic systems.

In this paper we demonstrate the existence of a set of polynomials Pi, 1£ i £ n , which are positive semi-definite on an interval [a, b] and satisfy, partially, the conditions of polynomials found in the Lagrange interpolation process. In other words, if a=a1<…<an=b is a given finite sequence of real numbers, then Pi (aj)=dij (dij is the Kronecker delta symbol); moreover, the sum of Pi 's is identically 1.

In this paper we consider a strongly regular relation q on hypermodules so that the quotient is a module (with abelian group) over a fundamental commutative ring. Also, we state necessary and sufficient conditions so that the relation q is transitive, and finally we prove that q is transitive on hypermodules.

Due to many important applications, the group III-Nitride semiconductors have recently attracted remarkable attention among semiconductor researchers and engineers. In this paper, we report on the impact of extrinsic and temporal carriers on the screening of polarization internal fields. The optical efficiency of GaN/AlGaN multiple quantum well (MQW) nanostructures were studied by means of photoluminescence (PL) and time-resolved PL measurements. Extrinsic carriers come from Si doping in the barriers, while temporal carriers originate when the samples are excited by laser beam. The emission peaks of MQWs in PL spectra of the undoped and low-doped samples show a shift towards higher energy levels as excitation intensity increases, while the other samples do not exhibit such a phenomenon due to the dominance of the extrinsic carriers. The transient data confirm the results of the PL measurements.

A lithium borate thermoluminescence dosimeter with 0.3 wt% of manganese impurity concentration was prepared for high dose levels in the range of 1-30 kGy for gamma irradiation applications. The TLD reader was used for read out purposes from ambient temperature to about 400°C with a heating rate of 6oC/sec. The pre- and post- irradiation anneal temperature was 300oC for 1.5 and 1 hours respectively. The effects of absorbed dose, dose rate, storage time, as well as the temperature and humidity versus pre- and post-irradiation storage time have been studied. The main glow peak was found to occur at 375oC, and the dosimeter response in the range of 1-30 kGy was linear. No significant fading effect of the dosimetric peak was observed after 8 weeks of storage, and the effects of ambient temperature and humidity were less than ±5% at 95% confidence level.

As a result of being hydrogenous moderators, several landmine detection methods based on nuclear techniques have been suggested in recent years. Because of elastic scattering and moderating neutrons from hydrogen atoms in landmines, detection of backscattered neutron shows an anomaly in the reflected thermal neutrons count when a detector scans over a mine. On landmine detection using neutron sources, a detector and its shielding play an important role. In this paper, based on the investigations and calculations performed by MCNP code (Monte Carlo N-Particle transport code), detector shielding materials and their thicknesses have been determined. Therefore, the effects of moderators such as graphite, heavy water, beryllium, polyethylene and boric acid on backscattered neutron flux have been investigated.