NATURAL RADIOACTIVITY AND ASSESSMENT OF HAZARD INDICES OF THE SOIL FOUND AT SUNG VALLEY, MEGHALAYA.

In this work, the variation of the radioactivity at different depth of the soil found at the Sung Valley in West Jaiñtia Hills District of Meghalaya in India is estimated by using the gamma-ray spectroscopy. The average activity concentration of 226Ra, 232Th and 40K for soil samples at different depths are measured to be 57, 156 and 352 Bq kg-1, respectively. The radiological hazard indices for the soil samples are calculated using standard models in order to determine the safe utility of these materials that are being used to manufacture domestic products by the locals. Values of all the radiological hazard indices are observed to be within the internationally recommended values as proposed by the European Commission and the United Nations Scientific Committee on the Effects of Atomic Radiation. The present study ensures that the soil analysed presents a negligible radiation hazard, and produced poetries and artefacts radiological incidence will stay within the allowed natural limit.

Neutron emission and dose distribution from natural carbon irradiated with a 12 MeV amu-1 12C5+ ion beam.

Measured neutron energy distribution emitted from a thick stopping target of natural carbon at 0°, 30°, 60° and 90° from nuclear reactions caused by 12 MeV amu-1 incident 12C5+ ions were converted to energy differential and total neutron absorbed dose as well as ambient dose equivalent H *(10) using the fluence-to-dose conversion coefficients provided by the ICRP. Theoretical estimates were obtained using the Monte Carlo nuclear reaction model code PACE and a few existing empirical formulations for comparison. Results from the PACE code showed an underestimation of the high-energy part of energy differential dose distributions at forward angles whereas the empirical formulation by Clapier and Zaidins (1983 Nucl. Instrum. Methods 217 489-94) approximated the energy integrated angular distribution of H *(10) satisfactorily. Using the measured data, the neutron doses received by some vital human organs were estimated for anterior-posterior exposure. The estimated energy-averaged quality factors were found to vary for different organs from about 7 to about 13. Emitted neutrons having energies above 20 MeV were found to contribute about 20% of the total dose at 0° while at 90° the contribution was reduced to about 2%.

Detector system dose verification comparisons for arc therapy: couch vs. gantry mount.

The aim of this study was to assess the performance of a gantry-mounted detector system and a couch set detector system using a systematic multileaf collimator positional error manually introduced for volumetric-modulated arc therapy. Four head and neck and esophagus VMAT plans were evaluated by measurement using an electronic portal imaging device and an ion chamber array. Each plan was copied and duplicated with a 1 mm systematic MLC positional error in the left leaf bank. Direct comparison of measurements for plans with and without the error permitted observational characteristics for quality assurance performance between detectors. A total of 48 different plans were evaluated for this testing. The mean percentage planar dose differences required to satisfy a 95% match between plans with and without the MLCPE were 5.2% ± 0.5% for the chamber array with gantry motion, 8.12% ± 1.04% for the chamber array with a static gantry at 0°, and 10.9%± 1.4% for the EPID with gantry motion. It was observed that the EPID was less accurate due to overresponse of the MLCPE in the left leaf bank. The EPID always images bank-A on the ipsilateral side of the detector, whereas for a chamber array or for a patient, that bank changes as it crosses the -90° or +90° position. A couch set detector system can reproduce the TPS calculated values most consistently. We recommend it as the most reliable patient specific QA system for MLC position error testing. This research is highlighted by the finding of up to 12.7% dose variation for H/N and esophagus cases for VMAT delivery, where the mere source of error was the stated clinically acceptability of 1 mm MLC position deviation of TG-142.

Light charged particle emission from neutron and alpha-induced reactions.

Emissions of protons and alpha-particles from neutron and alpha-induced reactions have been estimated using two nuclear reaction model codes ALICE91 and PRECO-2000. Calculated results have been compared with available energy differential and double differential emission cross sections from experimental measurements. Analysis of the data based on different nuclear reaction mechanisms revealed the relative importance of these mechanisms as well as predictive capabilities of the codes used. These results are useful in accelerator-driven systems, radioactive ion beam facilities and space dosimetry.

Measurement and unfolding of neutron spectra using Bonner spheres.

Neutron spectra from Am-Be, 252Cf sources and 2H + 2H and 2H + 3H reactions have been measured using a Bonner sphere system in conjunction with a 4 x 4 mm2 LiI(Eu) detector, and unfolded using the two codes BUNKI and MAXED. The BON unfolding algorithm is used with BUNKI. It has been observed that end test percentage between 1 and 3 and smoothing factor between 0.05 and 0.1 are optimal choices for the BUNKI code. A temperature parameter 1.0 is used for MAXED. Comparison with standard spectra shows that the shape of the spectra is fairly well reproduced. A coupling between the two codes is made and the solution spectrum from BUNKI is used as the default spectrum in MAXED.