Modification of WS2thin film properties using high dose gamma irradiation.

The tunability of the transition metal dichalcogenide properties has gained attention from numerous researchers due to their wide application in various fields including quantum technology. In the present work, WS2has been deposited on fluorine doped tin oxide substrate and its properties have been studied systematically. These samples were irradiated using gamma radiation for various doses, and the effect on structural, morphological, optical and electrical properties has been reported. The crystallinity of the material is observed to be decreased, and the results are well supported by x-ray diffraction, Raman spectroscopy techniques. The increase in grain boundaries has been supported by the agglomeration observed in the scanning electron microscopy micrographs. The XPS results of WS2after gamma irradiation show evolution of oxygen, carbon, C=O, W-O and SO4-2peaks, confirming the addition of impurities and formation of point defect. The gamma irradiation creates point defects, and their density increases considerably with increasing gamma dosage. These defects crucially altered the structural, optical and electrical properties of the material. The reduction in the optical band gap with increased gamma irradiation is evident from the absorption spectra and respective Tauc plots. TheI-Vgraphs show a 1000-fold increase in the saturation current after 100 kGy gamma irradiation dose. This work has explored the gamma irradiation effect on the WS2and suggests substantial modification in the material and enhancement in electrical properties.

Isomeric cross sections of the (n, α) reactions on the 90Zr, 93Nb and 92Mo isotopes measured for 13.73 MeV-14.77 MeV and estimated for 10 MeV-20 MeV neutron energies.

Isomeric cross sections for the 90Zr(n, α)87Srm, 93Nb(n, α)90Ym and 92Mo(n, α)89Zrm reactions were measured at five neutron energies over the range 13.73 MeV-14.77 MeV using the activation technique in combination with high resolution γ-ray spectrometry. In the present work, the cross sections are measured for the 90Zr(n, α)87Srm and 93Nb(n, α)90Ym reactions are referenced to the 27Al(n, α)24Na standard reaction cross section whereas those measured for 92Mo(n, α)89Zrm reaction are referenced to the 56Fe(n, p)56Mn standard reaction cross section. The cross sections for these reactions were also theoretically estimated using the EMPIRE-3.2 and TALYS 1.8 codes over the neutrons energy range of 10 MeV-20 MeV and matched with the experimental cross sections by making a proper choice of the model parameters. A minimum eight different sets of these statistical model calculations were performed by using the consistent sets of model parameters along with the pre-equilibrium mechanism in addition to the direct-reaction and the statistical Hauser-Feshbach (HF) compound nucleus ones. The measured cross sections for these three reactions increase with the increase in neutron energy from 13.73 MeV to 14.77 MeV. As the proton number increased by one when we go from zirconium to niobium or from niobium to molybdenum, the probability of alpha particle emission also increases at each corresponding neutron energy. The present results indicate that the measured cross section at each neutron energy for the 92Mo(n, α)89Zrm reaction is found to be the highest as compared to the other two reactions whereas, for the 90Zr(n, α)87Srm reaction, the measured cross section is found to be the lowest as compared to the other two reactions studied. The results obtained from the present measurement are found to be in good agreement with the calculated reaction cross section based on theoretical models and also with the work reported by earlier authors.

Excitation functions for 209Bi reactions induced by threshold to 50 MeV energy alpha particles.

Excitation functions for 209Bi(α,2n)211At, 209Bi(α,3n)210At and 209Bi(α,4n)209At reactions were calculated using TALYS-1.95 nuclear code from threshold to 50 MeV by invoking suitable options for level densities, nucleon-nucleus optical model potentials and alpha optical model potentials. Statistical factors were used to verify the quality of matching between theoretical model calculations and the experimental data from the EXFOR database. The TTY of 211At calculated using the excitation function of 209Bi(a,2n)211At reaction is compared with existing experimental studies from literature The results of the present study are important for the validation of nuclear model approaches with increased predictive power for 209Bi(α,xn) reactions for the production of 211At.

The flux weighted cross sections of 179Hf(γ,γ')179mHf and natHf(γ,x)179mHf reactions at 8 MeV and 15 MeV bremsstrahlung end point energies.

For the hafnium element, the cross sections of 179Hf(γ,γ')179mHf and natHf(γ,x)179mHf reactions were measured at 8 MeV and 15 MeV bremsstrahlung end point energies respectively using activation method and off-line gamma-ray spectroscopy. The bremsstrahlung radiation spectra were generated by bombarding a 0.1 mm tungsten target with 8 MeV and 15 MeV electrons at 5 µA beam current and also theoretically simulated by GEANT4 computer code. The flux weighted average cross sections of 179Hf (γ,γ')179mHf and natHf(γ,x)179mHf reactions were measured by using 115In(γ,γ')115mIn and 197Au(γ,n)196Au as flux monitor reactions at 8 MeV and 15 MeV bremsstrahlung radiation respectively. The measured cross sections are found close to the corresponding theoretical cross sections estimated by TALYS 1.95 and TENDL 2019 computer codes. These hafnium cross sections at 8 MeV and 15 MeV bremsstrahlung radiation will be new additions to the EXFOR library, as so far not reported in literature.

Study of optically stimulated luminescence and calculation of trapping parameters of K2Ca2(SO4)3:Eu nanophosphor.

K2Ca2(SO4)3:Eu nanophosphor was synthesized by chemical coprecipitation method and annealed at different temperatures from 400 to 900 °C. The nanophosphor annealed at 600 °C showed cubic structure with crystallite size ~25 nm. TEM shows morphology of K2Ca2(SO4)3:Eu nanophosphor was in the form of nanorods having diameter ~20 nm and length of ~100-200 nm. These samples were irradiated with gamma radiation for the doses varying from 10 mGy to 10 kGy and their Thermoluminescence (TL) and continuous-wave optically stimulated luminescence (CW-OSL) have been studied. CW-OSL response was found to be maximal for the sample annealed at 600 °C. The TL glow curve of the nanophosphor apparently showed a major peak at around 160 °C accompanied by three low intensity peaks at ~75, 215 and 285 °C. The traps responsible for all the TL peaks in K2Ca2(SO4)3:Eu were also found to be OSL sensitive. The qualitative correlation between TL peaks and CW-OSL response suggested that the traps associated with low temperature peaks are responsible for fast decay and the traps associated with the higher temperature peaks are responsible for slow decay of the OSL signal. OSL response showed linear behavior up to 1 kGy and saturated with further increase in the gamma dose. The wide OSL response makes studied K2Ca2(SO4)3:Eu nanophosphor a good candidate for high dose measurement.

Effect of size variation and gamma irradiation on thermoluminescence and photoluminescence characteristics of CaSO4:Eu micro- and nanophosphors.

Microcrystalline CaSO4:Eu phosphor particles prepared by the acid re-crystallization method were grinded by ball-milling method and reduced to small particles of sizes ~50 nm, 200 nm, 400 nm and 5 µm. For comparison, nanocrystalline CaSO4:Eu phosphor of size ~20 nm was also prepared by chemical coprecipitation method. The recorded photoluminescence emission and excitation spectra revealed that Eu is doped in CaSO4:Eu in the form of Eu2+ and Eu3+ in all the samples of microcrystalline and nanocrystalline powders. The samples of CaSO4:Eu, with different particle sizes, were irradiated with gamma rays over a range of doses ranging from 1 Gy to 100 kGy. The results of characterization by thermoluminescence method show that the intensity of the thermoluminescence peak for a given dose of gamma-rays decreases with the decrease in the particle size of CaSO4:Eu. A comparison shows that CaSO4:Eu of size 50 nm exhibited linear response between the thermoluminescence peak and the gamma-ray dose in the range of 1 Gy-10 kGy. This phosphor can, therefore, be used for the measurement of gamma ray dose in medical and industrial applications. A comparative study also showed that the sensitivity of thermoluminescence to gamma ray dose for the nanophosphor prepared by the ball milling technique is better than that of the nanophosphor prepared by chemical co-precipitation method.

Analysis of neutron induced (n,γ) and (n,2n) reactions on 232Th from reaction threshold to 20 MeV.

Excitation functions for 232Th(n,γ) and 232Th(n,2n) reactions from reaction threshold to 20 MeV were calculated using TALYS-1.9 nuclear code by invoking suitable options for the level densities, optical model potentials, pre-equilibrium effects and γ-ray strength functions. In earlier studies, theoretical plots for 232Th(n,γ) and 232Th(n,2n) reaction cross-sections were obtained by using EMPIRE 3.2 and TALYS 1.9 codes with default parameters, however none of the reported plots could match with the corresponding experimental cross-sections reported in EXFOR data particularly between 14-20 MeV. The results of the present study reveal that by using a combination of specific input parameters in TALYS 1.9 code, the theoretical evaluation of the cross sections favour a higher pre-equilibrium rate for the harder spectrum. Moreover the estimated cross-sections match fairly well with the corresponding experimental data (EXFOR database) as well as with the evaluated data files (ENDF/VII.0, JENDL-4.0). The results of the present study are important for the validation of nuclear model approaches with increased predictive power for (n,xn) cross-sections and particularly for the application of thorium based fuel in Accelerator-Driven Sub-critical System.

Thermoluminescence studies of CaSO4:Dy nanophosphor for application in high dose measurements.

Nanorods of CaSO4:Dy (having diameter ∼20 nm and length ∼200 nm) were prepared by chemical coprecipitation method and their thermoluminescence (TL) characteristics were studied after annealing at different temperatures in the range 400-1000 °C. Microcrystalline material was also prepared through acid recrystallization method. TL glow curves of the nanocrystalline material annealed at 700 °C showed a major peak at around 283 °C. The effect of annealing temperature on the phase structure/morphology of particles was studied. Phase change was observed when CaSO4:Dy was annealed at different temperatures as confirmed by XRD and TG-DTA. It was observed from the TEM images that the nanomaterial originally in the nanorods form broke into nanoparticles due to strain developed by phase change on annealing at higher temperatures. The combined effect resulted in changes in TL glow curve structure. For better clarity the TL glow curves were further deconvoluted by Computerized Glow Curve Deconvolution (CGCD) method and kinetic trapping parameters were determined. It was found that the values of kinetic parameters also changed for the nanocrystalline material annealed at different temperatures. These were also compared with the corresponding values of the microcrystalline material. It was also observed that the TL intensity saturates at about 100 Gy in case of microcrystalline phosphor, while that in case of nanocrystalline phosphor did not do saturate even up to 5 kGy.

Cross sections for formation of 139mCe radioisotope through the 140Ce (n, 2n) reaction over 13.73-14.77 MeV neutrons.

Cross sections for the formation of metastable state of 139Ce through 140Ce(n, 2n)139mCe reaction were measured at five neutron energies over 13.73-14.77 MeV range using the activation method and off-line gamma-ray spectrometric technique. These cross sections were in agreement with the corresponding theoretical cross sections estimated over 10-20 MeV neutrons by EMPIRE-3.2 code, using LEVEDEN 4 and strength function GSTRFN 0 parameters, and TALYS-1.8 code using ldmodel 5 and preeqmode 4 parameters. The estimated most probable excitation energies of 139Ce were 1.320-3.877 MeV, respectively over 13.73 MeV and 14.77 MeV neutron energies.

Monte Carlo based investigations of electron contamination from telecobalt unit head in build up region and its impact on surface dose.

A Telecobalt unit has wide range of applications in cancer treatments and is used widely in many countries all around the world. Estimation of surface dose in Cobalt-60 teletherapy machine becomes important since clinically useful photon beam consist of contaminated electrons during the patient treatment. EGSnrc along with the BEAMnrc user code was used to model the Theratron 780E telecobalt unit. Central axis depth dose profiles including surface doses have been estimated for the field sizes of 0×0, 6×6, 10×10, 15×15, 20×20, 25×25, 30×30cm2 and at Source-to-surface distance (SSD) of 60 and 80cm. Surface dose was measured experimentally by the Gafchromic RTQA2 films and are in good agreement with the simulation results. The central axis depth dose data are compared with the data available from the British Journal of Radiology report no. 25. Contribution of contaminated electrons has also been calculated using Monte Carlo simulation by the different parts of the Cobalt-60 head for different field size and SSD's. Moreover, depth dose curve in zero area field size is calculated by extrapolation method and compared with the already published data. They are found in good agreement.

Design of 6Mev linear accelerator based pulsed thermal neutron source: FLUKA simulation and experiment.

The 6MeV LINAC based pulsed thermal neutron source has been designed for bulk materials analysis. The design was optimized by varying different parameters of the target and materials for each region using FLUKA code. The optimized design of thermal neutron source gives flux of 3×10(6)ncm(-2)s(-1) with more than 80% of thermal neutrons and neutron to gamma ratio was 1×10(4)ncm(-2)mR(-1). The results of prototype experiment and simulation are found to be in good agreement with each other.

Measurement of angular distribution of neutron flux for the 6MeV race-track microtron based pulsed neutron source.

The 6MeV race track microtron based pulsed neutron source has been designed specifically for the elemental analysis of short lived activation products, where the low neutron flux requirement is desirable. Electrons impinges on a e-gamma target to generate bremsstrahlung radiations, which further produces neutrons by photonuclear reaction in gamma-n target. The optimisation of these targets along with their spectra were estimated using FLUKA code. The measurement of neutron flux was carried out by activation of vanadium at different scattering angles. Angular distribution of neutron flux indicates that the flux decreases with increase in the angle and are in good agreement with the FLUKA simulation.

Synthesis of gold and silver nanoparticles by electron irradiation at 5-15 keV energy.

Thin coatings (∼10 µm) made from a mixture of polyvinyl alcohol (PVA) and HAuCl(4) or PVA and AgNO(3) on quartz plates were irradiated with 5-15 keV electrons, at room temperature. The electron energy was varied from coating to coating in the range of 5-15 keV, but electron fluence was kept constant at ∼10(15) e cm(-2). Samples were characterized by the UV-vis, XRD, SEM and TEM techniques. The plasmon absorption peaks at ∼511 and ∼442 nm confirmed the formation of gold and silver nanoparticles in the respective electron-irradiated coatings. The XRD, SEM and TEM measurements reveal that the average size of the particles could be tailored in the range of 130-50 nm for gold and from 150-40 nm for silver by varying the electron energy in the range of 5-15 keV. These particles of gold and silver embedded in the polymer could also be separated by dissolving the coatings in distilled water.