Result of alpha track detection of radon in soil gas in the Khlong Marui Fault Zone, Southern Thailand: A possible earthquake precursor

Measurements of radon concentration in soil gas were conducted at ten stations (ST1-ST10), located mainly in theKhlong Marui Fault Zone, Thap Put District, Phang Nga Province over a period from 28 January to 25 April, 2007. The resultsof the radon concentration were presented as the variation of cumulative alpha track over a week period. At Station ST10 theradon concentrations are in general higher than those at other stations for every week. Two significant radon anomalies werefound to have the concentration above the mean value plus one standard deviation. During the period of monitoring thelocal and regional earthquake activities were observed showing patterns consistent with the occurrence of the radon anomalies.The maximum radon concentration is interpreted to be related to a possible influence of the pressure and stress increasedin the subsurface. An increase in the number of earthquakes is observed correlating to a lower radon concentration when thesubsurface pressure dropped due to tectonic stress release by seismic activities. Therefore, it would be possible to use thevariation of soil gas radon concentration as an earthquake precursor in the Khlong Marui Fault Zone

Monte Carlo simulation of 6 MV flattening filter free photon beam of TrueBeam STx LINAC at Songklanagarind Hospital

In this study, 6 MV photon beam of TrueBeam STx Varian LINAC with Flattening Filter Free (FFF) was simulated using PRIMO code. The depth dose profiles for various jaws open fields and cross beam profiles for various depths inside water phantom were determined using Monte Carlo (MC) simulation technique and validated with experimental result. The experiments were performed using the Source to Surface Distance (SSD) technique with a 100 cm distance from target to the surface of water. Simulation used 109 histories with the same configurations with experiments. The depth dose profiles and cross beam profiles of 6 MV FFF photon beam was determined using MC simulations and compared with experimental results. The results showed that depth dose profiles and cross beam profiles by MC simulation accurately matched with experimental results. The best result of depth dose profile was obtained at 10×10 cm2 jaws open field with 98.53% passing criterion whereas cross beam profile was obtained at 10 cm depth inside water phantom with 88.96% passing criterion.The discrepancies were caused by scatter of particle and incompatibility of primary beam in PRIMO with experiment

Construction of a dead-end type micro- to R.O. membrane test cell and performance test with the laboratory- made and commercial membranes

A dead-end type membrane stirred cell for an RO filtration test has been designed and constructed. Magnetic stirring system is applied to overcome a pressure-induced concentration polarization occurred over a membrane surface in the test cell. A high pressure N2 tank is used as a pressure source.Feed container is designed for 2.5 l feed solution and a stirred cell volume is 0.5 l . The test cell holds a magnetic stirrer freely moved over the membrane surface. All units are made of stainless steel. A porous SS316L disc is used as a membrane support. The dead-end stirred cell is tested to work properly in an operating pressure ranged 0 - 400 psi. It means that the dead-end cell can be used to test a membrane of different filtration modes, from micro- to Reverse Osmosis filtration. Tests performed at 400 psi for 3 hours are safe but tests at a 500 psi increase leakage possibility. The cell is used to test the performance of both commercial and laboratory-made membranes. It shows that the salt rejection efficiency of the nano- and RO membranes, NTR759HR and LES90, determined by using the new test cell, is closely similar to those reported from the manufacture. Result of the tests for our own laboratory-made membrane shows a similar performance to the nanofiltration membrane LES90

Magnetic Characterization of the Thung-Yai Redbed of

A total of 57 standard specimens are prepared from 31 oriented core samples drilled from the Thung-Yai redbed of Upper Jurassic - Lower Cretaceous age. All specimens are characterized magnetically. Results show that distributions of the magnetic susceptibility (73.5 - 144.7 SI), natural remanent magnetization (3.19-13.59 mA/m) and Kenigsberger ratio (0.96-3.65) of the specimens are similar to those of the Khorat redbeds. Low anisotropy degree Pj of 1 - 7 % indicates a low degree of deformation in the Thung-Yai redbed. Distribution of the principal axes of susceptibility indicates an imbrication of the minimum axes (K 3 ) toward the West which is interpreted as the palaeo-current direction during deposition of sediments. There are probably gravitational and hydrodynamic forces of flowing water that affect the Thung-Yai redbed at the time of deposition. Analyses of magnetic data and fluorescent X-ray images indicate that magnetite and haematite are the predominant magnetic minerals in the Thung-Yai redbed. This shows a non-marine environment during sedimentation. Remanent magnetization derived from a high temperature range of 530 - 630 C directed at Dec/Inc = 32.6/18.8 is considered to be primary remanent magnetization and its pole position is at Plat/Plon = 57.8N/ 184.6E. This pole overlaps well with the pole position derived from the Khorat redbeds (Plat/Plon = 60.7N/181.0E). This indicates that the Shan-Thai block, the parent block of southern Thailand and Indochina block, the parent block of the Khorat plateau, have not moved with reference to each other since the Upper Jurassic -- Lower Cretaceous

A Comparative Study of Indoor Radon Concentrations between Dwellings and Workplaces in the Ko Samui District, Surat Thani Province, Southern Thailand

The Ko Samui district of Surat Thani province is located in the high amounts of equivalent uranium in the ground surface that is the source of radon. Our research in the Ko Samui district aimed at comparing the indoor radon concentrations between dwellings and workplaces. Measurements of indoor radon concentrations were carried out in 46 dwellings and 127 workplaces, using CR-39 alpha-track detectors in closed-cup. A total of 173 detectors were distributed in 7 sub-districts. The detectors were placed in bedrooms of dwellings and workrooms of workplaces. All detectors were exposed to airborne radon for 90 days. After exposure, the alpha tracks were made visible by chemical etching before they were manually counted under an optical microscope. The track densities were assumed to be correlated with the radon concentration levels. We found that the radon concentrations could be well described by a log-normal distribution. Most concentrations (37%) were found in the range between 16 and 30 Bq.m-3. The radon concentrations in dwellings and workplaces varied from a minimum of 11 Bq.m-3 to a maximum of 305 Bq.m-3. The minimum (11 Bq.m-3) and maximum (305 Bq.m-3) values of indoor radon concentrations were found in a workplace and a dwelling, respectively. Only for four samples (3%), the indoor radon concentrations were found to be higher than the reference level recommended by the WHO (100 Bq.m-3). The overall geometric mean in the surveyed area was 32.6±1.65 Bq.m-3, which was lower than the worldwide average (39 Bq.m-3). The statistic comparison of the geometric mean indoor radon concentrations between dwellings and workplaces showed that the geometric mean in dwellings (46.0±1.55 Bq.m-3) was significantly higher than in workplaces (28.8±1.58 Bq.m-3) at the 0.05 level. Moreover, our study found that the majority of the bedrooms in dwellings had a closed atmosphere, resulting in poorer ventilation than in most of the workplaces that had access to air flow through open doors and windows at daytime. We consider this to be the main reason for the higher geometric mean indoor radon concentration in dwellings compared to workplaces

Monte Carlo simulation using PRIMO code as a tool for checking the credibility of commissioning and quality assurance of 6 MV TrueBeam STx varian LINAC

AimTo validate and implement Monte Carlo simulation using PRIMO code as a tool for checking the credibility of measurements in LINAC initial commissioning and routine Quality Assurance (QA). Relative and absolute doses of 6MV photon beam from TrueBeam STx Varian Linear Accelerator (LINAC) were simulated and validated with experimental measurement, Analytical Anisotropic Algorithm (AAA) calculation, and golden beam.Methods and MaterialsVarian phase-space files were imported to the PRIMO code and four blocks of jaws were simulated to determine the field size of the photon beam. Water phantom was modeled in the PRIMO code with water equivalent density. Golden beam data, experimental measurement, and AAA calculation results were imported to PRIMO code for gamma comparison.ResultsPRIMO simulations of Percentage Depth Dose (PDD) and in-plane beam profiles had good agreement with experimental measurements, AAA calculations and golden beam. However, PRIMO simulations of cross-plane beam profiles have a better agreement with AAA calculation and golden beam than the experimental measurement. Furthermore, PRIMO simulations of absolute dose agreed well with experimental results with ±0.8% uncertainty.ConclusionThe PRIMO code has good accuracy and is appropriate for use as a tool to check the credibility of beam scanning and output measurement in initial commissioning and routine QA

Nuclear track-etched pore membrane production using neutrons from the Thai research reactor TRR-1/M1

This work presents the results of the nuclear pore membrane production using the neutrons from the Thai research reactor TRR-1/M1 for pore piercing process on the polycarbonate thin film. With our experimental design, the fast neutron provides better results in pore piercing comparing with thermal neutron bombardment. This can be explained by most of the latent tracks produced by thermal neutron bombardment not penetrating through the thin film. Chemical etching process using NaOH solution with appropriate time, concentration and temperature is employed to enlarge the latent tracks in the bombarded film. Fast neutron bombardment with 5, 10 and 20 minutes bombarding time successfully produces the nuclear track membrane. Pore size and pore density of the produced membranes examined by SEM are 0.24 – 1.01 μm and 4.7 – 245 × 106 pore/cm2, respectively. Bubble point tests show the maximum pore diameter of the produced membrane ranged between 1.18 – 3.25 μm