F. Abu-Jarad

Determination of radon exhalation rates from tiles using active and passive techniques

Abstract Measurements of radon exhalation rates for selected samples of tiles used in Saudi Arabia were carried out using active and passive measuring techniques. These samples were granite, marble and ceramic. In the active method, a PC-based radon gas analyzer with emanation container was used, while, in the passive method, PM-355 nuclear track detectors with the “can technique” were applied for 180 days. A comparison of the exhalation rates measured by the two techniques showed a good linear correlation coefficient of 0.7. The granite samples showed an average radon exhalation rate of 0.7 Bq m −2 h −1 , which was higher than that of marble and ceramic by more than twofold. The radon exhalation rates measured by the “can technique” showed a non-uniform exhalation from the surface of the same tile.

Indoor radon measurements in dwellings of four Saudi Arabian cities

Abstract An indoor radon survey of a total of 269 dwellings, with one dosimeter per house, distributed in four Saudi Arabian cities was carried out. The objective of this survey was to carry out indoor radon measurements of two cities in the Eastern Province, Khafji and Hafr Al-Batin and to compare this with two cities in the Western Province, Al-Madina and Taif. The survey provides additional information about indoor radon concentrations in Saudi Arabia. The results of the survey in these cities showed that the overall minimum, maximum and average radon concentration were 7,137 and 30 Bq m −3 , respectively. The lowest average radon concentration (20 Bq m −3 ) was found in Hafr Al-Batin, while the highest average concentration was found in Khafji (40 Bq m −3 ) .

Performance tests of external moderators of a PGNAA setup

Performance tests of external cylindrical moderators of an accelerator-based prompt gamma ray neutron activation analysis (PGNAA) setup have been carried out through thermal neutrons and prompt gamma-ray yield measurements. The PGNAA setup is to be used for analysis of cement samples. This study was conducted to investigate the effects of geometry of cylindrical moderator on yield of thermal neutrons and prompt gamma-rays for two different types of moderator assemblies. One of the moderators was to be used with a small sample and the other to be used with a large sample. Fast and thermal neutron yield was measured inside the sample volume as a function of the front moderator thickness as well as sample length. Neutron yield measurement was carried out at the King Fahd University of Petroleum and Minerals 350 keV pulsed beam accelerator using nuclear track detectors. The pulsed 200 keV deuteron beam with 5 ns pulse width and 31.25 kHz frequency was used to produce 2.8 MeV neutrons via D(d,n) reaction. Neutron yield measurements showed that the large sample moderator has a smaller yield of thermal neutrons as compared to the small sample moderator, which is in complete agreement with the results of Monte Carlo yield calculations of the thermal and fast neutrons from both the moderators. Finally, the prompt gamma-ray yield from a Portland cement sample was measured using the two moderators and was compared with each other. As predicted by Monte Carlo simulations, in spite of a smaller yield of thermal neutrons, the large sample moderator has a higher yield of prompt gamma-rays.

Indoor radon survey in dwellings of some regions in Yemen

Abstract Indoor radon survey in a total of 241 dwellings, distributed in some regions of Yemen was performed, using CR-39 based radon monitors. The objective of this radon survey is to get representative indoor radon data of three regions, namely Dhamar, Taiz and Hodeidah, situated at different altitudes above sea level. The radon concentrations varied from 3 to 270 Bq m −3 with an average of 42 Bq m −3 . It was found that the average radon concentration in the surveyed areas increases with altitudes. The highest average radon concentration of 59 Bq m −3 was found in Dhamar city while the lowest average concentration of 8 Bq m −3 was found in Hodeidah city.

Experimental and Monte Carlo simulation studies of open cylindrical radon monitoring device using CR-39 detector

There are several methods of measuring radon concentrations but nuclear track detector cylindrical dosimeters are widely employed. In this investigation, the consequence of effective volumes of the dosimeters on the registration of alpha tracks in a CR-39 detector was studied. In a series of experiments an optimum radius for a CR-39-based open cylindrical radon dosimeter was found to be about 3 cm. Monte Carlo simulation techniques have been employed to verify the experimental results. In this context, a computer code Monte Carlo simulation dosimetry (MOCSID) was developed. Monte Carlo simulation experiments gave the optimum radius of the dosimeters as 3.0 cm. The experimental results are in good agreement with those obtained by Monte Carlo design calculations. In addition to this, plate-out effects of radon progeny were also studied. It was observed that the contribution of radon progeny (218Po and 214Po) plated-out on the wall of the dosimeters increases with an increase of dosimeter radii and then decrease to 0 at a radius of about 3 cm if a point detector has been installed at the center of the dosimeter base. In the code MOCSID different types of random number generators were employed. The results of this research are very useful for designing an optimum size of radon dosimeters.

Fast and thermal neutron intensity measurements at the KFUPM PGNAA setup

Abstract Fast and thermal neutron intensity distributions have been measured at an accelerator based prompt gamma ray neutron activation analysis (PGNAA) setup. The setup is built at the 350 keV accelerator laboratory of King Fahd University of Petroleum and Minerals (KFUPM). The setup is mainly designed to carry out PGNAA elemental analysis via thermal neutron capture. In this study relative intensity of fast and thermal neutrons was measured as a function of the PGNAA moderator assembly parameters using nuclear track detectors (NTDs). The relative intensity of the neutrons was measured inside the sample region as a function of front moderator thickness as well as sample length. Measurements were carried out at the KFUPM 350 keV accelerator using 2.8 MeV pulsed neutron beam from D(d,n) reaction. The pulsed deuteron beam with 5 ns pulse width and 30 kHz frequency was used to produce neutrons. Experimental results were compared with results of Monte Carlo design calculations of the PGNAA setup. A good agreement has been found between the experimental results and the calculations.

Comparison and limitations of three different bulk etch rate measurement methods used for gamma irradiated PM-355 detectors

Abstract Samples of Nuclear Track Detectors (PM-355) were exposed to high gamma doses from 1×10 5 Gy (10 Mrad ) up to 1.2×10 6 Gy (120 Mrad ) at an incremental dose of 1×10 5 Gy (10 Mrad ). The gamma source was a 9.03 PBq ( 244 kCi ) Co-60 source used for sterilization of medical syringes. The bulk etch rate ( V b ) was measured for various high gamma doses by three different methods: 1—thickness change method; 2—mass change method; 3—fission track diametric method. The study gives a comparison and limitations of these three methods used for bulk etch rate measurements in the detectors as a function of high gamma doses. The track etch rate ( V t ) and the sensitivity ( V ) of the detector were also measured using the fission track diametric method. It was observed that V b increases with the increase of the gamma absorbed dose at a fixed etching time in each bulk etch measuring method. The bulk etch rate decreases exponentially with the etching time at a fixed gamma absorbed dose in all three methods. The thickness change and mass change methods have successfully been applied to measure V b at higher gamma doses up to 1.2×10 6 Gy (120 Mrad ). The bulk etch rate determined by the mass change and thickness change methods was almost the same at a certain gamma dose and etching time whereas it was quite low in the case of the fission track diametric method due to its limitations at higher doses. Also in this method it was not possible to measure the fission fragment track diameters at higher doses due to the quick disappearance of the fission tracks and therefore the V b could not be estimated at higher gamma doses.{

Effect of high gamma dose on the PADC properties

Abstract The effect of the properties of PADC nuclear track detectors after exposure to high doses of gamma absorbed doses up to 5×10 5 Gray (50 Mrad) were studied. The gamma source was a 9.03 PBq (244 KCi), Co-60 source. Results indicate that each of the bulk etch rate (V b ), the tracks etch rate (V t ) and the sensitivity (V) of the detectors increases with the high gamma absorbed dose, but there is a drop in these parameters at the low gamma absorbed dose. Signs of surface roughness were observed by increasing the gamma absorbed doses and changes in color observed for doses larger than 2×10 5 Gray. The temperature of detectors during irradiation time reached 41°C. The fission fragment tracks (from Cf-252 source) disappeared quickly within the etching time (minutes) for total absorbed doses greater than 3×10 5 Gray due to their high bulk etch rate.

CO2 pulsed laser effect on CR-39 registration properties

Abstract The effect on alpha and fission fragment tracks of CR-39 nuclear track detectors exposed to a 10.6 μm CO2 pulsed laser has been studied in the energy range 60 mJ/P to 2 J/P for different exposure times. It has been found that the surface structure did not change if exposed to energies below 180 mJ/P and for total energies up to 3600 J. The surface shows significant changes in terms of track sizes, shapes and chain-like structures when exposed to energies greater than 450 mJ, independent of the exposure time. The circular annealed central area around the laser pulses increased by increasing the energy/pulse from 1 J to 2 J/P, where the radius of the circular annealed area increased from 900 μm up to 3500 μm, respectively. Both alpha and fission fragment tracks disappeared from this area. From 450 mJ/P up to 1 J/P, only fission fragment tracks are annealed from the central area. Circular laser diffraction patterns appeared on the surface at energies > 450 mJ/P. The width of these diffraction patterns decreases with increasing distance from the center of the pulse. At the center of each diffraction pattern, chain structures appeared due to the high temperature of the laser and evaporation to a depth of 20 μm occurred.

The use of nuclear track detectors as an environmental solar ultraviolet radiation dosimeter

Investigation of using CR-39 nuclear track detectors as solar ultraviolet radiation (SUVR) dosimeter was studied. The nuclear track detectors were irradiated with Cf-252 (alpha and fission fragments) before exposure to sun light. The exposure of nuclear track detectors to SUVR were carried out under two different conditions (i) the detector was mounted on a solar tracker mechanism which always rotate towards the sun, and (ii) fixed on a horizontal surface. The measurements were performed for different periods extended from one to eight weeks continuously at Dhahran - Saudi Arabia. The period extended from the middle of July to middle of September: the hottest months in Saudi Arabia. The weekly integrated SUVR measured by Eppley sensor was ranged from 2400 W. h. m−2 for one week up to 21000 W.h.m−2 for eight weeks. The results indicate linear correlation between both the track diameters of alphas and fission fragments and the total exposure to SUVR. The results clearly demonstrate that it is possible to use the nuclear track detectors as an environmental and personal SUVR dosimeters.