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The high energy neutron generation facilities worldwide uses the Li(p,n) system for production of the quasi mono-energetic neutrons from epithermal to few hundreds of MeV. Among the facilities either self-standing thick Li target or Li foil supported on a target assembly is used. In case of a supported Li target, either low or high mass supporting substrates like Al, C, Au, Ta etc. can be used. However, the neutron emission from the supporting substrate can interfere with the Li(p,n) reaction neutrons. In the present study neutron yields from a thin natural Li target supported on the thick natural Ta (high Z) and C (low Z) targets were measured at incident proton energies between 8-20 MeV. The proton irradiation of targets were performed at the Pelletron accelerator Facility, Mumbai and the emitted neutrons were measures at both forward (0°) and lateral (90°) directions with respect to the incident beam. The neutron yield was estimated using the CR-39 detectors and dual scintillator based active neutron spectrometer. A neutron dose equivalent (NDE) meter was also used to measure the neutron ambient dose equivalent at the measurement point. Experimentally measured neutron yields and ambient neutron dose equivalent estimates indicated higher Li(p,n) neutron yield with carbon as the supporting substrate. This is due to fewer self-emissions from natC compared to natTa target. Carbon supporting substrate also ensures improved spectral features of the Li(p,n) emission neutrons and lesser neutron fluence around the source location. This ensures efficient implementation of radiation protection practices with carbon target due to lower neutron fluence around the source compared to tantalum target. Carbon is a favorable supporting substrate compared to high Z-metal targets like Ta for emission neutron studies on Li target at proton energies between 8-20 MeV. [ABSTRACT FROM AUTHOR]

natLi(p, n) reaction is a versatile system for the generation of quasi mono-energetic neutrons from epithermal to few hundreds of MeV. The mono-energetic epithermal neutrons serve as a promising alternative source for boron-neutron capture therapy applications for cancer treatment, whereas the high energy reference neutron fields are used as calibration source for high energy physics instrumentations. However, the quasi mono-energetic nature gets disturbed at incident proton energies between 5 and 20 MeV, where different de-excitation modes contribute to the neutron emissions. So, the emission neutron studies at this intermediate proton energy range have not been covered extensively. The present work focuses on the estimation of the relative fraction of different emission neutron groups, along with the neutron spectra and angular distributions for incident proton energies between 8 and 20 MeV. The contribution of different emission neutron groups from natLi(p, n) system were calculated using the nuclear reaction model code TALYS and with FLUKA simulations. The results were validated with experimental measurements. The ambient dose equivalents were also estimated from the spectra using the ICRP-116 dose conversion coefficients and compared with the estimates obtained from a neutron dose equivalent meter. [ABSTRACT FROM AUTHOR]

In this work, electron induced modifications on the bulk etch rate, structural and optical parameters of CR-39 polymer were studied using gravimetric, FTIR (Fourier Transform Infrared) and UV-vis (Ultraviolet-Visible) techniques, respectively. CR-39 samples were irradiated with 10MeV electron beam for different durations to have the absorbed doses of 1, 10, 550, 5500, 16 500, and 55 000 kGy. From the FTIR analysis, the peak intensities at different bands were found to be changing with electron dose. A few peaks were observed to shift at high electron doses. From the UV-vis analysis, the optical band gaps for both direct and indirect transitions were found to be decreasing with the increase in electron dose whereas the opacity, number of carbon atoms in conjugation length, and the number of carbon atoms per cluster were found to be increasing. The bulk etch rate was observed to be increasing with the electron dose. The primary objective of this investigation was to study the response of CR-39 to high electron doses and to determine a suitable pre-irradiation condition. The results indicated that, the CR-39 pre-irradiated with electrons can have better sensitivity and thus can be potentially applied for neutron dosimetry. [ABSTRACT FROM AUTHOR]

Tauc analysis is popularly used for the determination of optical band gap by extrapolating the linear portion of the Tauc's plot and finding its intersection point at energy axis. In most of the studies, the data points in the linear portion of the Tauc's plot are selected manually, which is time-consuming and the reproducibility in the selection process gets affected. To overcome this, an automated determination of band gap has been proposed for ensuring the reproducibility as well as for faster selection process. In this work, we report the development of an efficient algorithm which can provide the information of the optical band gap by Tauc analysis. The algorithm is based on finding the linear portion around maximum slope of the Tauc's plot. A computer program (autoTauc) based on the algorithm was written and was validated through CR-39 irradiated to four different alpha fluences. The extrapolated linear line obtained through linear regression (using the program) was observed to pass through the linear portion of the Tauc's plot. The optical band gap was found to be decreasing linearly with the alpha fluence for both direct and indirect transitions. Also the direct band gap was found to be higher than the indirect band gap. [ABSTRACT FROM AUTHOR]

To overcome the limitation of CR-39 at high dose region where large number of tracks are overlapped, the FTIR spectroscopic technique can be implemented for dose estimation. In the present work, CR-39 detectors were irradiated with alpha particles from 239Pu source having known doses up to 5.12 Gy. The detectors were subjected to chemical etching in steps of 1 h and subsequently FTIR spectra were recorded. Three strong bands i.e., 1800–1675 cm−1, 1350–1150 cm−1 and 810–760 cm−1 in the FTIR spectra were analysed to study the effect of etching and dose on the peak absorbance of these bands. The peak absorbance was found to decrease with the dose as well as with etching duration and the saturation effect in the peak absorbance was observed above 3 h etching. Etching duration of 2 h was found to be optimal etching time where the linear response was observed up to 5.12 Gy. Furthermore, the threshold for dose estimation by the FTIR spectroscopic technique was observed to be 0.41 Gy, above which this technique can be used. Empirical relations correlating the peak absorbance and dose were generated which can be used as calibration factors for dose estimation in the range 0.41–5.12 Gy using the peak intensity in FTIR spectrum of CR-39 detector. [ABSTRACT FROM AUTHOR]

Current research in the accelerator technology is focused towards achieving high energy, intense beams by minimizing conversion losses during beam acceleration. In such high current facilities, induced activity in structural materials become primary concern for radiation protection and materials like Ta and Nb, with low induced activity generation, high corrosion resistance characteristics are preferred along with conventional structural materials. In view of significant use of elements like Nb, Ta and Fe in the proton accelerators, a dose rate measurement and decay study has been carried out. The prompt γ- and neutron doses with residual activity profile from short and long lived isotopes were estimated using γ-ray spectrometric method. [ABSTRACT FROM AUTHOR]

Presently accelerator facilities emphasizes on generating charged particles with enhanced energy and flux. The radiation protection practices at these facilities are considered in civil engineering designs and strictly implemented through different administrative, access control measures (Sarkar in Radiat Meas 45:1476–1483, 2010). However, concern arises from induced activities, during maintenance and decommissioning stages, when sections of accelerator and shielding materials become highly radioactive. Major contribution of induced activity arises from stainless steel (SS-304) beam enclosures and Cu-dumps. Present work focuses on the generation of induced radioactivity profiles with delay counting of SS-304 and Cu along with instantaneous gamma and neutron dose rate measurements at various proton energies for source term estimation. [ABSTRACT FROM AUTHOR]

While measuring the neutron dose in accelerator radiation environment using CR-39 detector for radiation protection purpose, LET (linear energy transfer) spectrometry method is implemented when the information about the radiation source term is unknown. In this work, the neutron dose has been measured for p+181Ta reaction at different proton energies i.e. 8–20 MeV by LET spectrometry method using CR-39 detectors. The track density in CR-39 was found to increase exponentially with the proton energy and an empirical relation has been established. The dosimetric quantities viz. absorbed dose (DLET) and dose equivalent (HLET) were determined from the LET spectra and both these quantities were found to be increasing with the proton energy. Empirical relations were generated, which will be useful for predicting dose in similar radiation environment. The dosimetric data generated in this study would be useful for radiation protection of occupational workers working in the accelerator radiation environment. [ABSTRACT FROM AUTHOR]

Microwave induced chemical etching (MICE) has been established as a faster and improved technique compared to other contemporary etching techniques for the development of tracks in a CR-39 detector. However, the methodology could not be applied for LET (linear energy transfer) spectrometry due to lack of a calibration curve using this method. For this purpose, a new LET calibration curve in the range of 12 keV/μm-799 keV/μm was generated considering different ions such as H, Li, C, O, and F on CR-39 having different LETs in water. An empirical relation was established from the obtained calibration curve for determining the value of LET (in water) from the value of V, the ratio of track etch rate to bulk etch rate. For application of this calibration curve in neutron dosimetry, CR-39 detectors were irradiated to neutrons generated from 120 and 142 MeV 16O+27Al systems followed by a similar MICE procedure. The absorbed dose (DLET) and the dose equivalent (HLET) were obtained from the LET spectra and were found to be 13% and 10% higher for 142 MeV 16O+27Al system than those for 120 MeV 16O+27Al system, respectively. The outcome of the study demonstrates the possibility of using the MICE technique for neutron dose estimation by CR-39 via LET spectrometry. [ABSTRACT FROM AUTHOR]

Energy distributions of neutrons emitted from the interaction of 20 MeV protons incident on a thick Be target were estimated at two angles (0° and 90°) with respect to the incident beam using activation foils as threshold detectors. A recently developed unfolding code GAMCD based on Genetic Algorithm and Monte Carlo methods was used to estimate the neutron spectra by unfolding the counts obtained from the activation foils. These results were compared with the unfolding codes, MAXED and GRAVEL. In the GAMCD code, a guess spectrum as a-priori information need not be provided as input unlike in MAXED and GRAVEL. Results obtained from all these codes matched each other reasonably well. Out of 30 reactions studied experimentally only the selected 15 were found sufficient to generate acceptable spectra in the case of neutrons emitted from the p+Be reaction at 20 MeV. A peak in the energy distributions around 3 MeV at both the measured angles is contributed by the three body breakup process while a broad hump between 6 MeV and 10 MeV only in the forward direction suggests contribution from the pre-equilibrium emissions from the 9Be(p, n)9B channel, which also contributes to the small peak observed around 15 MeV. The code GAMCD was found to perform satisfactorily for the present data set. [ABSTRACT FROM PUBLISHER]

Monte Carlo simulations have been carried out using the FLUKA code to improve the neutron ambient dose equivalent [H*(10)] response of the ZReC (zirconium-lined portable neutron counter responding satisfactorily to neutrons up to 1 GeV) by introducing various neutron absorbers in the system such as cadmium, gadolinium, natural boron, enriched 10B and borated polythene. It was found that ZReC can be effectively used as a portable neutron monitor by introducing any one of the following perforated layers: 5 mm thick natural boron, 0.5 mm thick enriched 10B or 1 cm high-density polythene mixed with 50 % boron by weight. The integral response of the instrument was also calculated for some typical reference neutron fields. The relative ambient dose equivalent response of the said system is also found comparable with that of the existing LINUS neutron monitor. [ABSTRACT FROM AUTHOR]

CR-39 detectors, widely used for neutron dosimetry in accelerator radiation environment, have also been applied in tissue microdosimetry by generating the linear energy transfer (LET) spectrum. In this work, the neutron dose has been estimated via LET spectrometry for 9Be (p, n) reaction which is useful for personnel monitoring around particle accelerators and accelerator based therapy facilities. Neutrons were generated by the interaction of protons of 6 different energies from 4-24 MeV with a thick Be target. The LET spectra were obtained from the major and minor radii of each track and the thickness of removed surface. From the LET spectra, the absorbed dose (DLET) and the dose equivalent (HLET) were estimated using Q-L relationship as given by International Commission on Radiological Protection (ICRP) 60. The track density in CR-39 detector and hence the neutron yield was found to be increasing with the increase in projectile (proton) energy. Similar observations were also obtained for absorbed dose (DLET) and dose equivalents (HLET). [ABSTRACT FROM AUTHOR]

A systematic study on the measurement of neutron spectra emitted from the interaction of protons of various energies with a thick beryllium target has been carried out. The measurements were carried out in the forward direction (at 0° with respect to the direction of protons) using CR-39 detectors. The doses were estimated using the in-house image analyzing program autoTRAK_n, which works on the principle of luminosity variation in and around the track boundaries. A total of six different proton energies starting from 4 MeV to 24 MeV with an energy gap of 4 MeV were chosen for the study of the neutron yields and the estimation of doses. Nearly, 92% of the recoil tracks developed after chemical etching were circular in nature, but the size distributions of the recoil tracks were not found to be linearly dependent on the projectile energy. The neutron yield and dose values were found to be increasing linearly with increasing projectile energies. The response of CR-39 detector was also investigated at different beam currents at two different proton energies. A linear increase of neutron yield with beam current was observed. [ABSTRACT FROM AUTHOR]

The directional distribution of the ambient neutron dose equivalent from 145-MeV 19F projectiles bombarding a thick aluminium target is measured and analysed. The measurements are carried out with a commercially available dose equivalent meter at 0°, 30°, 60° and 90° with respect to the beam direction. The experimental results are compared with calculated doses from EMPIRE nuclear reaction code and different empirical formulations proposed by others. The results are also compared with the measured data obtained from an earlier experiment at a lower projectile energy of 110 MeV for the same target–projectile combination. [ABSTRACT FROM PUBLISHER]

While antiretroviral drugs, those approved for clinical use and others under evaluation, attempt in lowering viral load and boost the host immune system, antiretroviral drug resistance acts as a major impediment in the management of human immune deficiency virus type-1 (HIV-1) infection. Antiretroviral drug resistance testing has become an important tool in the therapeutic management protocol of HIV-1 infection. The reliability and clinical utilities of genotypic and phenotypic assays have been demonstrated. Understanding of complexities of interpretation of genotyping assay, along with updating of lists of mutation and algorithms, and determination of clinically relevant cut-offs for phenotypic assays are of paramount importance. The assay results are to be interpreted and applied by experienced HIV practitioners, after taking into consideration the clinical profile of the patient. This review sums up the methods of assay currently available for measuring resistance to antiretroviral drugs and outlines the clinical utility and limitations of these assays. [ABSTRACT FROM AUTHOR]

The present work looks into the aspect of thermal modifications induced in polymers by proton irradiation. The kinetics of thermal decomposition of polymers is investigated by using the thermogravimetric (TG) technique. It has been observed that the degradation of polymers is a multi-step process that involves sequential and competing processes, and obeys the Arrhenius kinetics which allows us to connect the rate constant with the absolute temperature and the activation energy. The activation energy of thermal decomposition has been calculated from the TG curves, and its variation with different irradiation doses has been derived. [ABSTRACT FROM AUTHOR]

The ion irradiation of polymeric solids induces numerous modifications in the polymer properties thus increasing their applicability in various fields. The present work looks into the aspect of thermal modifications induced in the irradiated polymers. The kinetics of thermal decomposition of polymers is investigated by using the thermogravimetric (TG) technique, It has been observed that the degradation of polymers is a multi-step process that involves sequential and competing processes, and obeys the Arrhenius kinetics which allows us to connect the rate constant with the absolute temperature and the activation energy. The activation energy of thermal decomposition has been calculated from the TG curves, and its variation with different irradiation doses has been derived. [ABSTRACT FROM AUTHOR]

Thin films of polypropylene have been irradiated with different doses of gamma radiation from a 60 Co source. IR, UV-VIS spectra of this polymer before and after irradiation have been recorded and from the spectral data some modifications in the properties have been investigated. The spectra indicated that polypropylene film was oxidised at the dose of 10 6  Gy. Due to the removal of additives, total destruction of the polymer takes place at this dose. Isotactic arrangement of the polymer is no longer present after irradiation. Growth of carbon cluster takes place above a gamma dose of 10 2  Gy. Thermal stability of the polymer changes due to irradiation and the polymer seems to decompose in four different steps at the highest dose of 10 6  Gy. [ABSTRACT FROM AUTHOR]

A systematic investigation of 62 MeV proton irradiated Poly(ethylene terephthalate) (PET) has been carried out using Fourier Transformed Infrared Spectroscopy, thermogravimetric analysis, differential scanning calorimetry and X-ray diffraction spectroscopy. The experiments revealed a restoration of the crystalline matrix and simultaneous decrease in thermal stability in the irradiated polymer as a function of dose, indicating that PET underwent both degradation and cross-linking by proton irradiation. [ABSTRACT FROM AUTHOR]

A systematic investigation of 62 MeV proton irradiated Poly(ethylene terephthalate) (PET) has been carried out using Fourier Transformed Infrared Spectroscopy, thermogravimetric analysis, differential scanning calorimetry and X-ray diffraction spectroscopy. The experiments revealed a restoration of the crystalline matrix and simultaneous decrease in thermal stability in the irradiated polymer as a function of dose, indicating that PET underwent both degradation and cross-linking by proton irradiation. [ABSTRACT FROM AUTHOR]

The aim of our study is to describe the dose dependent proton induced modifications in Polytetrafluoro ethylene (PTFE) by using Fourier Transform Infra-red spectroscopy (FTIR), Thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC) and X-ray diffraction analysis (XRD). The shifting of the main peak along with a decrease in its intensity, the decrease in thermal stability and melting point and the formation of stable free radicals were observed in the polymer by proton irradiation. [ABSTRACT FROM AUTHOR]

Sulphadimidine acetylation studies were undertaken in 103 patients, 52 of whom had been classified as slow and 51 as rapid inactivators of isoniazid by a standard microbiological assay method. Each patient received sulphadimidine by mouth in a dose of 44 mg./kg. body weight, and free and total sulphadimidine were estimated in blood and urine collected at six hours. The findings suggest that patients may be classified as slow inactivators of isoniazid if the proportion of acetylated sulphadimidine (total minus free) is () less than 25% in blood or () less than 70% in urine. The sulphadimidine test is easy to perform and the result is available the same day; urine specimens for the test can be stored at room temperature for over a week without any loss of drug. [ABSTRACT FROM PUBLISHER]

It is well recognized all over the world that inhalation of indoor radon (222Rn), thoron (220Rn) and their progeny contribute a major fraction of the total radiation dose to human beings from natural sources. In the present work, an attempt has been made to assess the levels of radon and thoron in some dwellings of the seismic-prone North-Eastern region of India, using a special type of twin-chamber dosimeter. The results show a non-significant increase inradon and thoron concentration during the winter season compared to summer of nearly 1.6 times and 1.3 times, respectively. [ABSTRACT FROM AUTHOR]