F. Malik

Swelling in CR-39 and its effect on bulk etch-rate

Abstract The effect of swelling in CR-39, during the etching process has been studied using ‘thickness-measurement’ method. The values of the bulk etch-rate ( V B ) determined by this method have been corrected in the context of irreversible swelling produced in various CR-39 samples. The results have been compared with those obtained using the ‘mass-measurement’ as well as the ‘fission fragment track diameter’ methods. The values of experimental V B have been obtained by taking the arithmetic average as well as by fitting the Gaussians to the results of a number of CR-39 samples. It is shown that the ‘thickness-measurement’ method is as good as the other methods of determining the bulk etch-rate provided sufficiently large number of CR-39 samples are used for obtaining the mean value from the Gaussian fit of the experimental data.

Measurement of natural radioactivity in sand samples collected along the bank of rivers Indus and Kabul in northern Pakistan

Radioactivity is a part of the natural environment. The presence of natural radioactivity in sand and other building materials results in internal and external exposure to the general public. Therefore, it is desirable to determine the concentration of naturally occurring radionuclides, namely (232)Th, (226)Ra and (40)K in sand, bricks and cement which are commonly used as building materials in Pakistan. In this context, sand samples were collected from 18 different locations covering an area of ∼1000 km(2) along the banks of river Indus (Ghazi to Jabba) and river Kabul (Nowshera to Kund) in the northern part of Pakistan, whereas bricks and cement samples were collected from local suppliers of the studied area. In order to measure the specific activities in these samples, a P-type coaxial high-purity germanium-based gamma-ray spectrometer was used. In sand samples, the average specific activities of (226)Ra, (232)Th, and (40)K were found to be 30.5±11.4, 53.2±19.5 and 531±49 Bq kg(-1), whereas in brick samples, specific activities of 30±14, 41±21 and 525±183 Bq kg(-1) were observed, respectively. In cement samples, measured specific activity values were 21±5, 14±3 and 231±30 Bq kg(-1), respectively. Radium equivalent activities were calculated and found to be 143.8±38.6, 124±49.8 and 56.69±7 Bq kg(-1) for sand, brick and cement samples, respectively. The annual mean effective dose for the studied sand samples was found to be 0.40 mSv. External and internal hazard indices were less than unity for all the studied samples. The present results have been compared with those reported in the literature.

Monitoring of Indoor Radon Levels Around an Oil Refinery Using CR-39-Based Radon Detectors

Contribution of radon and its decay products towards the total effective dose has been reported to be more than 50% and is a second leading cause of the lung cancer after cigarette smoking. It is an established fact that besides soil and rocks, naturally occurring radio nuclides are also associated with the petroleum extracted from the sedimentary deposits. Therefore, radon measurement around oil refineries is desirable. In this regard, an indoor radon measurement study was carried out in 40 dwellings which were situated in the vicinity of an oil refinery in the Rawalpindi district using CR-39-based radon detectors. For comparison, indoor radon levels were also measured in 40 dwellings situated at a greater distance (>2 km) from the refinery. The maximum measured indoor radon concentration was found to be 190 ± 6 Bq·m−3 whilst the minimum recorded concentration was 12 ± 7 Bq·m−3. The mean radon concentration in the dwellings surveyed was 57 ± 29 Bq·m−3. No significant difference was observed in the average indoor radon levels in the dwellings situated near the oil refinery premises when compared with those further away. From the measured radon concentrations, an annual effective dose was calculated to be 0.9 ± 0.1 mSv which is below the ICRP recommended value.

Assessment of Annual Effective Dose due to the Indoor Radon Exposure in Districts Bagh and Kahuta of the Azad Kashmir, Pakistan

In continuation to our earlier studies concerning generation of the baseline indoor radon data, an indoor radon measurement survey was carried out in the districts Bagh and Kahuta, state of the Azad Jammu and Kashmir. In this context, 150 houses were selected in the aforesaid districts and CN-85-based box-type radon detectors installed in bedroom and living room of each house. The detectors were exposed to indoor radon for 3 months. After etching CN-85 detectors in 6 M NaOH at 70°C for 3 h, the observed track densities were related to the indoor radon concentration using calibration factor of 0.0092 tracks cm−2·h−1 per Bq·m−3. The measured indoor radon concentration ranged from 56 to 124 Bq·m−3 and 61 to 106 Bq·m−3 in the studied areas of districts Bagh and Kahuta, respectively. The mean annual effective dose ranged from 1.42 ± 0.15 to 3.12 ± 0.10 mSv·y−1 with an average of 2.16 ± 0.13 mSv·y−1 in the district Bagh and 1.54 ± 0.14 to 2.68 ± 0.12 mSv·y−1 with an average of 2.17 ± 0.13 mSv·y−1 in the district Kahuta. These values are within the safe limits recommended by the World Heath Organization.

A quick method for maintaining the molarity of NaOH solution during continuous etching of CR-39

Abstract A series of experiments have been performed to investigate the physio-chemical changes that occurred in the 6 M NaOH solution after etching CR-39 (Pershore and Homalite) detectors, each for 3, 6, 9, 12 and 15 h . Various physical parameters like concentration, electrical conductivity (EC) and density of the solutions have been measured after each etching interval. Results have been discussed in the light of stoichiometrical equation for the interaction of CR-39 with NaOH. It is found that the concentration, EC and the density of the solution, in which CR-39 has been etched, increase linearly with respect to the etching time. The inter-relationship of EC–concentration and density–concentration suggest that the concentration of the etchant can be maintained at certain desired value by adjusting the corresponding value of EC or density, measured through non-destructive and quick methods.