STUDY OF EFFECTIVENESS OF SHELTERING FROM RADIATION EXPOSURE DUE TO ACCIDENTAL RELEASE OF RADIOACTIVITY.

Sheltering is one of the important protective actions as a part of emergency response during the early phases of an accident-mostly precautionary in nature. Sheltering via structural shielding reduces the direct exposure from plume/cloud shine and ground shine doses as well as the airborne radioactivity concentration and hence inhalation dose. The present study was aimed at estimating the shielding factor in the case of Indian houses for external exposure pathways using the FLUKA Monte Carlo based radiation transport code. Furthermore, the dose reduction factor due to exposure from the inhalation pathway was estimated using an indoor aerosol model. These factors were assessed for the three major types of dwellings, and they provided important inputs for decision-making for sheltering or evacuation in case of any sudden release of radionuclides into the environment.

Temporal evolution of activation products in a zircaloy-4 guide tube and the estimation of its external gamma dose rate for decommissioning activities.

The dismantling of structural objects during the decommissioning of nuclear facilities needs radioactive source characterisation for the planning of decommissioning strategies in compliance with the ALARA (as low as reasonably achievable) principle. The sources may arise from neutron activation of the structural components in the reactor core as well as contamination due to the radioactive release from the fuel occurred during normal operation or unplanned events in a nuclear power plant (NPP). In a pressurised heavy water reactor (PHWR), various in-core components are predominantly made of either zircaloy-2 or 4. The nuclides present as impurities in the zircaloy, playing a crucial role in the activity inventory due to neutron activation of those nuclides, which in turn determine the external gamma dose rate. The activity of the activation products depend on the neutron flux seen by the component, duration of irradiation and cooling period, half-lives of the daughter products and the amount of the impurities present in the structural components. To illustrate this, a guide tube made up of zircaloy-4 has been considered. A guide tube assembly is a part of the primary shut down system (PSS) which guides the movement of absorber elements in the upward and downward direction in the calandria. This study has identified and quantified the activity inventory in a guide tube at the end of the operation of the reactor using the ORIGEN2 code, and then estimated the associated external gamma dose rate using the FLUKA Monte Carlo code. The findings will help the management of radioactive waste, cost optimisation and collective dose budgeting during the decommissioning stage of a typical PHWR.

Effective dose conversion coefficient for gamma ray exposure from an overhead plume.

The external radiation exposure from an overhead plume containing gamma emitting radionuclides can contribute substantial dose to the ground receptor during normal operations as well as accidental release conditions of nuclear facilities. In order to estimate the effective dose conversion coefficients (DCCs) directly, a finite plume Monte Carlo model along with the reference phantom at the ground receptor location needs to be implemented. In the present study, a comprehensive simulation of radiation transport from the Gaussian plume source to the ICRP reference adult voxel phantoms (receptor) is carried out using the FLUKA Monte Carlo code. The organ absorbed doses as well as the effective DCCs of the adult reference phantom are computed for different meteorological parameters and downwind distances. To illustrate the application of this model, an overhead Gaussian plume containing two different gamma emitting radionuclides, 135Xe and 41Ar are considered. From these simulations, the ratio of the effective dose rate to the kerma rate are estimated as 0.6 Sv Gy-1 and 0.65 Sv Gy-1 for the exposure from 135Xe and 41Ar, respectively. This ratio is constant irrespective of the meteorological conditions and cloud models. Further results show that the effective DCCs as a function of the downwind distance vary by an order of magnitude for an unstable weather category; however, the variations are very small in the case of a stable category. This study demonstrates an accurate method for calculating the effective dose to the ground receptor from an external plume which can be further applied for any radionuclide under any meteorological condition.

Er3+-Tm3+-Yb3+:CaMoO4 phosphor as an outstanding upconversion-based optical temperature sensor and optical heater.

Optical temperature sensing in Er3+-Tm3+-Yb3+codoped CaMoO4 phosphor prepared by chemical co-precipitation route based on the near infrared (NIR) to green upconversion emission from Er3+ ion is reported. The variation with respect to external temperature in emission intensity ratio of the green emissions around 530 nm and 552 nm, corresponding to the 2H11/2 â†’ 4I15/2 and 4S3/2 â†’ 4I15/2 transitions respectively, under 980 nm excitation has been studied in detail, to report the sensing property of the prepared material; the maximum sensor sensitivity ∼0.0182 K-1 was attained at 413 K. The laser induced optical heating within the prepared phosphor has been explored and the heat generation caused by the laser effect has been verified by comparison of experimental and calculated data.

pH controlled Ho³âº-Yb³âº codoped Y2O3 nanowires for display devices.

The wire like structure with particle size in the nanometer range of Ho(3+)-Yb(3+) codoped Y2O3 phosphors have been synthesized through hydrothermal synthesis route by controlling the pH value. The Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) analysis of the synthesized phosphor powders have been studied which confirms the formation of nanowires in the prepared materials and the formation of proper crystalline structure respectively. The frequency upconversion emission spectra under 980 nm excitation have been recorded and an efficient green emission has been observed. The excitation energy corresponding to the NIR photon seems to be fully utilized for the emission lying in the green region. The Fourier transform infrared (FTIR) spectroscopic analysis for existence of the impurities in the developed material has also been performed. The experimental observation proves the utility of the prepared material in the display devices and diagnosis purposes.

The Er3+-Yb3+ codoped La2O3 phosphor in finger print detection and optical heating.

The presence of impurities and morphological information about the Er(3+)-Yb(3+) codoped La2O3 phosphors prepared by two different synthesis techniques have been obtained with the help of Fourier transform infrared (FTIR) spectroscopy and Scanning electron microscopy (SEM) respectively. The effect of synthesis process on the frequency upconversion (UC) emission with an excitation at 980 nm from laser diode radiation has been performed. The use of codoped phosphor in latent finger print detection and laser induced heat generation has also been explored.

Yb3+ sensitized Er3+ doped La2O3 phosphor in temperature sensors and display devices.

The frequency upconversion emissions in the Er(3+)/Er(3+)-Yb(3+) doped/codoped hexagonal shaped La2O3 phosphor characterized by X-ray diffraction (XRD) upon excitation with 980 nm and 800 nm CW lasers have been investigated. The upconversion emissions corresponding to the (2)H(9/2) → (4)I(15/2), (2)H(11/2) → (4)I(15/2), (4)S(3/2) → (4)I(15/2) and (4)F(9/2) → (4)I(15/2) transitions peaking at 409 nm, 523 nm, 548 nm and 660 nm have been observed under 980 nm excitation whereas 523 nm, 548 nm and 660 nm upconversion emission bands have been visualized under 808 nm excitation. The upconversion emission intensity of Er(3+) ions is enhanced by several times due to the codoping with Yb(3+) ions, under 980 nm excitation while there is a reduction in intensity in the codoped sample under 808 nm excitation. The decay curve analysis for the green UC emission band corresponding to the (4)S(3/2) → (4)I(15/2) transition in the Er(3+)/Er(3+)-Yb(3+) doped/codoped La2O3 phosphor upon 980 nm excitation has been done. The colour coordinate of the phosphor sample has been calculated at different pump powers and its value is observed to be almost similar to that of the standard green colour and also independent of the excitation power density. The effect of temperature on the upconversion emission intensity of the green emissions has been determined and noted that the present phosphor material can be used in making temperature sensing device upto 600 K.

Green upconversion emission in Nd³âº-Yb³âº-Zn²âº:Y2O3 phosphor.

The Y(2)O(3) phosphor powder codoped with Nd(3+):Yb(3+) ions have been synthesized through optimized combustion route. Crystalline structures of the prepared samples have been investigated by powder X-ray diffraction technique. Efficient upconversion emission in the green region upon 980 nm NIR CW diode laser excitation has been reported. The maximal enhancement in the intensity of the green upconversion emission band has been observed on codoping with Zn(2+) ions in the Nd(3+):Yb(3+) codoped sample. The processes responsible for such an enhancement in the green upconversion emission band which can be used for the localization and diagnosis of cancer has been explained in detail.