R.H. Mahat

Investigation of some commercial TLD chips/discs as UV dosimeters

Using a deuterium UV source, we have investigated the response of a number of commercially available thermoluminescence (TL) dosimeters (TLDs) to UV radiation (UVR), including LiF : Mg, Cu, P (TLD-100 H), CaF2 : Dy (TLD-200), CaF2 : Mn (TLD-400), Al2O3 (TLD-500), 7LiF : Mg, Cu, P (TLD-700 H) and CaSO4 : Dy (TLD-900). The intrinsic method was used to detect UVR, while trap depth and frequency factors were estimated using the initial rise method. We have studied TL intensity as a function of exposure time, observing high sensitivity of TLD-500 to UVR. Conversely, TLD-400 displays weak sensitivity to these same radiations. Although TLD-900 and TLD-200 are both less sensitive to UVR than TLD-500, they each provide a linear response to UVR. The possible use of these phosphors as UV dosimeters has been further appraised, examining thermal fading effects and fading due to light exposure.

UV-VIS and FTIR spectral studies of CR-39 plastics irradiated with X-rays

Abstract A study has been made on the UV-VIS and FTIR spectra of CR-39 plastics irradiated with 50 kVp tube X-rays in the dose range 0ndash;45 MR. The optical transmittance over the wavelength region of 200–1000nm decreases with the X-ray exposure, much greater decrease being observed in the UV region. The IR absorption spectra of the irradiated samples show the presence of two new strong absorption bands at the frequencies 655 and 2340 cm −1 , indicative of the gas CO 2 produced inside the plastic.The absorbance of these bands increases linearly with the X-ray dose.

Soil-to-root vegetable transfer factors for 226Ra, 232Th, 40K, and 88Y in Malaysia

Soil-to-plant transfer factors (TFs) are of fundamental importance in assessing the environmental impact due to the presence of radioactivity in soil and agricultural crops. Tapioca and sweet potato, both root crops, are popular foodstuffs for a significant fraction of the Malaysian population, and result in intake of radionuclides. For the natural field conditions experienced in production of these foodstuffs, TFs and the annual effective dose were evaluated for the natural radionuclides (226)Ra, (232)Th, (40)K, and for the anthropogenic radionuclide (88)Y, the latter being a component of fallout. An experimental tapioca field was developed for study of the time dependence of plant uptake. For soil samples from all study locations other than the experimental field, it has been shown that these contain the artificial radionuclide (88)Y, although the uptake of (88)Y has only been observed in the roots of the plant Manihot esculenta (from which tapioca is derived) grown in mining soil. The estimated TFs for (226)Ra and (232)Th for tapioca and sweet potato are very much higher than that reported by the IAEA. For all study areas, the annual effective dose from ingestion of tapioca and sweet potato are estimated to be lower than the world average (290 μSv y(-1)).

Radionuclide emissions from a coal-fired power plant

Current study concerns measurement of radioactivity levels in areas surrounding a 2420 MW thermal power plant fueled predominantly by bituminous coal. The concentrations of (226)Ra, (232)Th and (40)K in onsite bottom-ash were found to be 139 Bq/kg, 108 Bq/kg and 291 Bq/kg, respectively, the levels for these radiolnuclides in soil decreasing with distance from the power plant. At the plant perimeter the respective radionuclide concentrations were 87 Bq/kg, 74 Bq/kg and 297 Bq/kg. In a nearby town, the corresponding concentrations were 104 Bq/kg, 52 Bq/kg and 358 Bq/kg, suggestive of use of TENORM affected soils. The mean radium equivalent activities (Raeq) in soil and ash sample in the town were 205 Bq/kg and 316 Bq/kg, respectively. The Kapar plant ash/slag appears to contain a higher level of TENORM than the world average. The degree of contamination is much higher inside the town where slag has been mixed with topsoil as landfill or as simple domestic waste. For the prevailing levels of exposure and a worst case senario, the predicted committed effective dose due to ingestion and inhalation for intake durations of 1- and 30 years would be 4.2 μSv and 220 μSv, respectively.

The effect of humidity on the accuracy of measurement of an electret radon dosimeter

Abstract Test has been conducted for the response of electret radon dosimeters with varying levels of humidity. At a constant value of radon concentration, measured values have been found to increase linearly with increasing humidity, from 30% RH up to a value of ∼85% RH. On this basis we argue for the establishment of a humidity-dependent calibration factor.

The presence of natural radioactivity and 137Cs in the South China Sea bordering peninsular Malaysia.

The presence of natural radioactivity and (137)Cs has been investigated in fresh media obtained from South China Sea locations off the coast of peninsular Malaysia. The media include seafood, sea water and sediment. The samples were collected some weeks prior to the devastating 2011 Tōhoku earthquake and associated tsunami, the occurrence of which precipitated the Fukushima incident. All samples showed the presence of naturally occurring (226)Ra, (228)Ra and primordial (40)K, all at typically prevailing levels. The concentrations of natural radioactivity in molluscs were found to be greater than that of other marine life studied herein, the total activity ranging from 337 to 393 Bq kg(-1) dry weight. The total activity in sea water ranged from 15 to 88 Bq l(-1). Sediment samples obtained at deep sea locations more than 20 km offshore further revealed the presence of (137)Cs. The activity of (137)Cs varied from ND to 0.5 Bq kg(-1) dry weight, the activity increasing with offshore distance and depth. The activity concentrations presented herein should be considered useful in assessing the impact of any future radiological contamination to the marine environment.

Thermoluminescence dating analysis at the site of an ancient brick structure at Pengkalan Bujang, Malaysia

Bujang Valley is a well-known historical complex found in the north-west of peninsular Malaysia; more than 50 ancient monuments and hundreds of artefacts have been discovered throughout the area. The discovery of these suggests Bujang Valley to have been an important South East Asian trading centre over the period from the 10th to 14th centuries. Present work concerns thermoluminescence (TL) dating analysis of shards collected from a historic monument located at Pengkalan Bujang in Bujang Valley. All the shards were prepared using the fine grain technique and the additive dose method was applied in determining the paleodose of each shard. The annual dose rate was obtained by measuring the concentration of naturally occurring radionuclides (U, Th and K) in the samples and their surroundings. The TL ages of the shards were found to range between 330±21 years and 920±69 years, indicative of the last firing of the bricks and tiles from which the shards originated, some dating back to the period during which the historical complex remained active.

Diurnal Variation of Indoor Radon Concentration in Malaysia

This paper reports time continuous measurement of radon in a sub-basement room in order to show the hourly diurnal variation in indoor radon concentration. The variation in temperature and humidity was also recorded.

Concentration of Ra‐226 in Malaysian Drinking and Bottled Mineral Water

The concentration of the radionuclide 226Ra was determined in the drinking water which was taken from various sources. It was found that the concentration varies from non‐detectable (ND) to highest value of 0.30 Bq per liter. The concentration was found to be high in mineral water as compare with surface water such as domestic pipe water. Some of these values have exceeded the EPA (Environmental Protection Agency) of America regulations. The activity concentrations obtained are compared with data from other countries. The estimated annual effective doses from drinking the water are determined. The values obtained range from 0.02 mSv to about 0.06 mSv per year.