A.A. Tajuddin

Radiation hazard indices of soil and water samples in Northern Malaysian Peninsula.

The radioactivity quantity and quality were determined in soil and water samples in Northern Malaysian Peninsula (NMP) using HPGe spectroscopy and GR-135 spectrometer. The (226)Ra, (232)Th and (40)K concentrations in soil samples are 57±2, 68±4 and 427±17 Bq kg(-1), respectively, whereas in water samples were found to be 2.86±0.79, 3.78±1.73 and 152±12 Bq l(-1), respectively. These concentrations are within those reported from literature in other countries in the world. The radiological hazard indices of the samples were also calculated. The mean values obtained from soil samples are 186 Bq kg(-1), 88 nGy h(-1), 108 μSv y(-1), 0.50 and 0.65 for Radium Equivalent Activity (Ra(eq)), Absorbed Dose Rates (D(R)), Annual Effective Dose Rates (ED), External Hazard Index (H(ex)) and Internal Hazard Index (H(in)) respectively, whereas, for water samples were found to be 20, 10, 13, 0.05 and 0.06, respectively. All the health hazard indices are well below their recommended limits, except in two soil sampling sites which were found to be (*)025 (1.1 H(ex)) and (*)026 (1.1 H(ex), 1.6 H(in)). The calculated and the measured gamma dose rates had a good correlation coefficient, R=0.88. Moreover, the average value radon is 20 (in the range of 7-64) Bq m(-3), a positive correlation (R=0.81) was observed between the (222)Rn and (226)Ra concentrations in samples measured by the SNC continuous radon monitor (model 1029, Sun Nuclear Corporation) and HPGe detector, respectively. Some soils in this study with H(in) and H(ex)<1 are suitable for use in agriculture and as building materials. Also, in this study H(in) and H(ex)<1 for water samples, therefore, water after processing and filtration is safe and suitable for use in household and industrial purposes.

Photon attenuation studies on tropical hardwoods

Abstract Linear attenuation coefficients of a range of tropical hardwoods have been determined at a photon-energy of 59.54 keV. Good accord with mass-density linear dependence is demonstrated. At 60 Co energies seasoned Rhizophora spp, with a mass-density of 1040 kg m −3 , provides percentage depth-doses that are in agreement to within 2% with those tabulated for water.

Measurement of mass attenuation coefficients of Rhizophora spp. binderless particleboards in the 16.59–25.26 keV photon energy range and their density profile using x-ray computed tomography

The mass attenuation coefficients of Rhizophora spp. binderless particleboard with four different particle sizes (samples A, B, C and D) and natural raw Rhizophora spp. wood (sample E) were determined using single-beam photon transmission in the energy range between 16.59 and 25.26 keV. This was done by determining the attenuation of K(α1) X-ray fluorescent (XRF) photons from niobium, molybdenum, palladium, silver and tin targets. The results were compared with theoretical values of young-age breast (Breast 1) and water calculated using a XCOM computer program. It was found that the mass attenuation coefficient of Rhizophora spp. binderless particleboards to be close to the calculated XCOM values in water than natural Rhizophora spp. wood. Computed tomography (CT) scans were then used to determine the density profile of the samples. The CT scan results showed that the Rhizophora spp. binderless particleboard has uniform density compared to natural Rhizophora spp. wood. In general, the differences in the variability of the profile density decrease as the particle size of the pellet samples decreases.

Measurement of mass attenuation coefficients of moderate-to-high atomic-number elements at low photon energies

Abstract Mass attenuation coefficients for 12 selected moderate-to-high atomic-number elements have been obtained from good-geometry measurements made at five 241Am photon energies of significant emission intensity. Particular interest focuses on measured values for photon energies close to absorption edges. Comparisons with renormalized cross-section predictions indicate agreement to within stated error limits for the majority of cases. Significant discrepancies (>10%) are noted for Ta at 17.8 and 26.3 keV and W at 59.5 keV. Some support for a discrepancy between measurement and theory for W in the region of 60 keV is found in the reported measurements of others.

Mass attenuation coefficients of natural Rhizophora spp. wood for X-rays in the 15.77–25.27 keV range

The mass attenuation coefficients (mu/rho) of Rhizophora spp. were determined for photons in the energy range of 15.77-25.27 keV. This was carried out by studying the attenuation of X-ray fluorescent photons from zirconium, molybdenum, palladium, silver, indium and tin targets. The results were compared with theoretical values for average breast tissues in young-age, middle-age and old-age groups calculated using photon cross section database (XCOM), the well-known code for calculating attenuation coefficients and interaction cross-sections. The measured mass attenuation coefficients were found to be very close to the calculated XCOM values in breasts of young-age group.

Radiographic and scattering investigation on the suitability of Rhizophora sp. as tissue-equivalent medium for dosimetric study

Abstract Previous measurements on the Malaysian hardwood Rhizophora sp. support the tissue equivalence of this material at diagnostic photon energies [Bradley, Tajuddin, Che Wan Sudin and Bauk (1991) Appl. Radiat. Isot. 42 , 771]. The present study makes use of a 1.67 GBq 241 Am source and a 5 cm NaI(T1) detector to obtain additional evaluation of scattering intensity for a range of hardwoods, water and modified rubber [Bradley, Ng and Aziz (1988) Appl. Radiat. Isot. 39 , 439] for eight scattering angles covering the range 10°–45°. Samples of Rhizophora sp. and modified rubber have been submersed in water, radiographed and their film optical densities compared with water. Results of this study at diagnostic energies further support the photon-interaction equivalence of modified rubber and Rhizophora sp. with water.

A study of Rhizophora spp wood phantom for dosimetric purposes using high-energy photon and electron beams

Previous scattering and depth-dose investigations involving use of the Malaysian hardwood Rhizophora spp have shown this medium to produce good agreement with measurements made in water. Present study extends the comparison, now including measurements of percentage depth-dose made for photons at 6MV and 5 and 12MeV electron beams. For the 6 MV photon and 5 MeV electron beams, discrepancies between percentage depth-dose for Rhizophora spp and water, at all depths, are found to be within 2.6 and 2.4% respectively. At 12 MeV electron energies, measured percentage depth-doses in Rhizophora spp beyond 3.5cm depth are found to be in significant discord with those for water. The absorbed dose in water measured in Rhizophora spp at d(max) for all three beams produces discrepancies of no more than 1.1% when compared with measurements made in water.

Total differential scattering cross-sections of 59.54 keV photons for elements in the range 29 ≤ Z ≤ 74

Abstract Using the 59.54 keV gamma rays emitted by the radionuclide 241 Am, total differential scattering cross-sections have been determined for eleven moderate to high atomic number elements. Measurements were performed using a standard back-scattering geometry arranged to obtain scattering angles of 145°, 154° and 165° and associated photon momentum transfers, 4.58 ≤ x ≤ 4.76 A −1 . High purity (>99.9%) foils of Cu, Zn, Zr, Nb, Mo, Ag, Cd, In, Sn, Ta and W were used as targets. Measurements have generally been found to be in accord with predictions to within a conservative uncertainty of 10%, predicted values being obtained as total differential scattering cross-sections based upon the tabulations of modified form factors corrected for anomalous scattering (ACMFF) and non-relativistic wave functions for incoherent scattering.

Continuous measurements of radiation levels along the west coast highway of Peninsular Malaysia

Abstract Long baseline continuous measurement of radiation levels, due to cosmic sources, naturally occurring radioactive materials (NORM) and technologically enhanced natural radiation, has been carried out along the west coast highway of Peninsular Malaysia. High sensitivity monitoring was made possible through use of a car-borne facility, based around a large volume (4″ φ × 4″) NaI(Tl) scintillation detector. Count rates have been summarized and converted into dose rate. Results show the highest reading (∼ 1.5 μGy/h) to have been recorded in Bukit Merah, one of the prominent mineral processing areas, where on occasion abundant quantities of heavy mineral residues have been found to be piled up along the sides of the road.

Photon-atom scattering of 26.4 and 59.5 keV gamma rays in Mo, Nb and Zr

Abstract Differential coherent scattering cross-sections have been experimentally determined with 0 (10%) error for the photon energies 26.4 and 59.5 keV, using an annular 100 mCi 241 Am source. The source is housed in a stainless steel holder fabricated to contain heavy tungsten alloy shielding and capped with a beryllium window. The measurements were performed using a standard back-scattering geometry set up to obtain scattering angles of 145° and 165°. Mo, Nb and Zr (Aldrich Chemical Company, Inc.) foils of better than 99.9% purity were used as targets in conjunction with a Hyper-pure Germanium detector. Measurements using another prominent line at 17.8 keV are not presented due to the fact that the intense fluorescence X-ray peaks overlap significantly with the coherent scatter peaks from the Mo and Zr targets and the incoherent peak due to the Nb target. Experimental data have been compared with theoretical predictions.