Estimation of alpha exposure on CR-39 detector using a UV-VIS spectrophotometer.

This work is dedicated to study the possibility of using UV-VIS spectrophotometer, a non-invasive technique with a versatile applications that is being used to determine the optical properties of matter, to estimate the CR-39 exposure to alpha particles. CR-39 detectors were exposed to alpha particles from two different alpha sources: 241Am and radon gas. Tracks densities on CR-39 were determined using the traditional counting method by an optical microscope. The transmittances of CR-39 detectors were measured using UV-VIS spectroscopy in the range of 400-1000 nm, and results were correlated with measured tracks densities. The comparison showed that this method is effective in estimating exposure of CR-39 to alpha particles, and that its efficiency has increased by increasing the etching time of the detectors.

ESTIMATION OF SCATTERED NEUTRONS CONTRIBUTION IN A NEUTRON CALIBRATION BUNKER USING A MONTE CARLO SIMULATION.

The contribution of scattered neutrons is inevitable in neutron calibration facilities. This contribution complicates the measurements of neutron radiation, therefore, it should be estimated to correct the response of neutron probe instruments. In the present work, Monte Carlo simulation was performed for a neutron calibration bunker using the MCNP-4C code. This simulation aimed to calculate the contribution ratio of scattered neutrons to the neutron field. To simulate the neutron field, 241Am-Be neutron source defined in the ISO 8529-1 was used. The results of the simulation reported in this work were found to be consistent with those found experimentally in previous work. Additionally, the distribution of both the ambient dose equivalent rate and the contribution ratio of scattered neutrons in the bunker were mapped using this simulation.

Estimation of photoneutron intensities around radiotherapy linear accelerator 23-MV photon beam.

CR-39 solid-state nuclear track detectors (SSNTDs) were used to study the variations of fast neutron relative intensities around a high-energy (23MV) linear accelerator (Varian 21EX) photon beam. The variations were determined on the patient plane at 0, 50, 100, 150 and 200cm from the isocenter of the photon beam. In addition, photoneutron intensities and distributions at isocenter level with field size of 40×40cm(2) at Source Axis Distance (SAD)=100cm around 23MV photon beam were also determined. The results showed that the photoneutron intensities decreased rapidly by increasing the distance from the center of the x-ray beam towards the periphery, for the open fields.

A simplified technique to determine random coincidence summing of gamma rays and dead time count loss corrections.

The loss in counts rate under the peak in gamma spectrum was studied using two techniques (complex spectrum and high active single isotope). The results showed that the loss was occurred when the integrated counting rate was more than 400 counts per second (CPS) up to 10(4)cps, for energy range 20-2,500 keV. This was mainly due to the random summing effect in the detector's volume. It was found that the probability of random summing has increased with the increase of the volume of detector's crystal. The correction factor F(Ct) for the counts rate under the peak was determined experimentally.

Variation of radon exposure in Damascus dwellings.

In the present work, activity concentrations of (222)Rn in air and (222)Rn and (226)Ra in drinking water were measured in Damascus city covering its old and modern parts. It was found that the average air radon activity concentration in the old part was higher than in the modern part, and in drinking water, radon was found to be 60 ± 3 Bq/l, and less than 0.13 Bq/l for radium, which were lower than the recommended levels set by WHO.

Diffusion of radon through varying depths of cement.

Portland cement was mixed with different concentrations of radium chloride (1200, 2400 and 3600 Bq) to produce radioactive sources. These sources were surrounded with cement of different thickness (1, 2 and 4cm). The release of radon from these sources (before and after being surrounded) was studied. The results showed that radon release from the sources itself was less then its release from the same source after being surrounded by cement, and the release did not change with the thickness of cement. Samples were covered with a thin layer of polyethylene before being surrounded with cement. It was found that this additional layer reduced the radon exhalation. This thin layer stopped any reaction between the source and the surrounding cement during solidification of the cement layers. These reactions are thought to be the reason for the increase of radon exhalation from the sources surrounded by cement.