P. C. Kalsi

Neutron-irradiation effects on track etching characteristics of polyester nuclear track detector

The effects of reactor neutron irradiation on the etching characteristics of a locally available Garware polyester film have been studied. The effects in the neutron fluence range of 4.57×1015–1.83×1016 n/cm2 on the fission track registration efficiency and the bulk etch rate are investigated. From the results, it is found that the bulk etch rates increase with the increase in neutron fluence. The increase in etch rates can be explained on the basis of scission of the detector due to neutron irradiation which enhances the dissolution rates. From the measured bulk etch rates at different temperatures, the activation energies for bulk etching at different values of neutron fluence have also been determined. The changes induced by neutron irradiation in the polyester detector have also been studied by UV-visible spectroscopic technique. The neutron irradiation enhances the UV absorbance of the detector, which is a direct consequence of the formation of new chemical species due to scission of the detector.

Measurement of Absolute Fission Yields in the Fast Neutron–Induced Fission of Actinides: 238U, 237Np, 238Pu, 240Pu, 243Am, and 244Cm by Track-Etch-cum-Gamma Spectrometry

Abstract The absolute fission yields of 46 fission products in 238U (99.9997 at.%), 46 fission products in 237Np, 27 fission products in 238Pu (99.21 at.%), 30 fission products in 240Pu (99.48 at.%), 30 fission products in 243Am (99.998 at.%), and 32 fission products in 244Cm (99.43 at.%) induced by fast neutrons were determined using a fission track-etch-cum-gamma spectrometric technique. In the case of highly alpha-active and sparingly available actinides–e.g., 238Pu, 240Pu, 243Am, and 244Cm–a novel recoil catcher technique to collect the fission products on a Lexan polycarbonate foil followed by gamma-ray spectrometry was developed during the course of this work. This completely removed interferences from (a) gamma rays of daughter products in secular equilibrium with the target nuclide (e.g., 243Am-239Np), (b) activation products of the catcher foil [e.g., 24Na from Al(n,α)], and (c) activation products of the target [e.g., 238Np from 237Np(n,γ) and 239Np from 238U(n,γ)] reactions, making the gamma spectrometric analysis very simple and accurate. The high-yield asymmetric fission products were analyzed by direct gamma spectrometry, whereas the low-yield symmetric products (e.g., Ag, Cd, and Sb) as well as some of the asymmetric fission products (e.g., Br) and rare earths (in the case of 238U and 237Np) were radiochemically separated and then analyzed by gamma-ray spectrometry. The neutron spectra in the irradiation positions of the reactors were measured and delineated in the thermal to 10-MeV region using threshold activation detectors. The present data were compared with the ENDF/VI and UKFY2 evaluated data files. From the measured cumulative yields, the mass-chain yields have been deduced using charge distribution systematics. The mass yields, along with similar data for other fast neutron-induced fissioning systems, show several important features: 1. Fine structure in the interval of five mass units in even-Z fissioning systems due to odd-even effects. The fine structure decreases from lighter to heavier even-Z actinides, in accordance with their odd-even effect. 2. Higher yields in the mass regions 133 to 135, 138 to 140, and 143 to 145 and their complementary mass regions, depending on the mass of the fissioning systems due to the presence of 82n-66n, 86n-62n, and 88n-56n shells. 3. For odd-Z fissioning systems having no odd-even effect, the fine structure is very feeble and is due only to shell effects. 4. Unusually high yields observed in the mass region 133 to 139 in the fissioning system 239U* as compared to other U isotopes are explained on the basis of a higher neutron-to-proton ratio (N/Z) of 238U compared to lower-mass uranium isotopes. The [overbar]ν, full-width at tenth-maximum, and ĀL increase with increasing mass of the fissioning systems, whereas AH of ~139 ± 1 remains constant throughout due to the strong preference for the formation of the deformed 88n shell, which is also favorable from the N/Z point of view.

Modification of optical properties of polycarbonate by gamma irradiation

A detailed analysis of absorption, transmission, and reflection spectra of virgin and gamma-irradiated (50–800 kGy) polycarbonate polymer reveals that both indirect as well as direct band gap coexist in virgin and gamma-irradiated samples. The indirect band gap has been found to decrease from 3.00 eV (virgin sample) to 2.78 eV at a dose of 800 kGy. The emission behaviour of gamma-irradiated polycarbonate indicates a clear-cut emission peak in the visible region at –466 nm in the samples with a gamma dose of 400 kGy and above. The refractive index has a decreasing tendency as a result of the increasing gamma dose.

Thin extractive membrane for monitoring actinides in aqueous streams.

Alpha spectrometry and solid state nuclear track detectors (SSNTDs) are used for monitoring ultra-trace amount of alpha emitting actinides in different aqueous streams. However, these techniques have limitations i.e. alpha spectrometry requires a preconcentration step and SSNTDs are not chemically selective. Therefore, a thin polymer inclusion membrane (PIM) supported on silanized glass was developed for preconcentraion and determination of ultra-trace concentration of actinides by α-spectrometry and SSNTDs. PIMs were formed by spin coating on hydrophobic glass slide or solvent casting to form thin and self-supported membranes, respectively. Sorption experiments indicated that uptakes of actinides in the PIM were highly dependent on acidity of solution i.e. Am(III) sorbed up to 0.1 molL(-1) HNO₃, U(VI) up to 0.5 molL(-1) HNO₃ and Pu(IV) from HNO₃ concentration as high as 4 molL(-1). A scheme was developed for selective sorption of target actinide in the PIM by adjusting acidity and oxidation state of actinide. The actinides sorbed in PIMs were quantified by alpha spectrometry and SSNTDs. For SSNTDs, neutron induced fission-fragment tracks and α-particle tracks were registered in Garware polyester and CR-39 for quantifications of natural uranium and α-emitting actinides ((241)Am/(239)Pu/(233)U), respectively. Finally, the membranes were tested to quantify Pu in 4 molL(-1) HNO3 solutions and synthetic urine samples.

Application of alpha track registration technique for plutonium estimation in bioassay samples

Bioassay monitoring is carried out for occupational workers handling plutonium (Pu) in nuclear facilities. In India, presently Pu estimation in bioassay samples is done by alpha spectrometry. The minimum detectable activity (MDA) of alpha spectrometry is 0.5mBq for a counting period of 1 day. To reduce the load of sample counting on alpha spectrometry, an alternative method based on alpha track registration in solid state nuclear track detectors (SSNTDs) is developed in the present paper. For this purpose, few urine samples of normal subjects spiked with known amounts of Pu in the range of 0.5-5.5mBq were exposed to CR-39 SSNTDs. The total number of alpha tracks seen in the CR-39 films of the sample and the standard were used to calculate the amount of Pu in the sample. The results of alpha track registration technique were also compared with that obtained by the well-established alpha spectrometry and were found to agree well within +/-30%. The minimum amount of Pu that can be analyzed by this method is 0.18mBq for an exposure period of 45 days.

γ-Ray modifications of optical/chemical properties of a PVC polymer

Polyvinyl chloride (PVC) films are subjected to high doses of γ -radiation up to 800 kGy. The modifications in the optical properties, the structural and chemical changes are investigated by recording the ultraviolet–visible (UV–VIS) and the Fourier transform infrared (FTIR) spectra of unirradiated and irradiated PVC films. The UV–VIS data show an increase in absorbance and shift of the absorption edge towards the visible region from the UV region with the increase in the γ -radiation dose. This may be attributed to the formation of conjugated system of bonds. The direct and the indirect optical energy band gaps are determined as a function of the γ -exposure dose. The results show that both the direct and the indirect energies of transitions decrease with the increasing γ -absorbed dose. Also the direct energy band gap has higher values when compared with the corresponding values of the indirect energy band gap. The intensity of the different infrared bands in the FTIR spectra of irradiated PVC indicates the presence of the hydroxyl group, release of volatile gases and polyene formation. A total destruction of the structure is observed at a very high γ -radiation dose.

Nuclear analytical techniques for quantification of uranium for its recovery from seawater

Nuclear analytical techniques namely fission track technique using solid state nuclear track detector (SSNTD) and instrumental neutron activation analysis (INAA) have been standardized and applied for quantification of low uranium concentrations in liquid samples such as feed, elute and brine and solid sorbent samples respectively. The quantification of uranium is required for its recovery study from seawater, which is one of the potential sources of uranium. The uranium concentration of a liquid sample obtained by SSNTD method was compared with the other well established conventional techniques like ICP-MS, ICP-AES, adsorptive stripping voltametry and alpha spectrometry. INAA was applied for uranium concentration determination in the radiation grafted polyamidoxime sorbent samples.

Track revelation and optical properties of pentaerythritol tetrakis (allyl carbonate) plastic for application as nuclear track detector: effects of gamma radiations

ABSTRACT The etching conditions of an indigenously prepared thin film of pentaerythritol tetrakis(allyl carbonate) (PETAC) were standardised for the use as a nuclear track detector. The optimum etching times in 6 N NaOH at 70°C for the appearance of fission and alpha tracks recorded in this detector from a 252Cf solid source were found to be 30 min and 1.50 h, respectively. The experimentally determined values for the bulk and track-etch rates for this detector in 6 N NaOH at 70°C were found to be 1.7 ± 0.1 and 88.4 ± 10.7 µm/h, respectively. From these results, the important track etching properties such as the critical angle of etching, the sensitivity and the fission track registration efficiency were calculated and compared with the commercially available detectors. The activation energy value for bulk etching calculated by applying Arrhenius equation to the bulk etch rates of the detector determined at different etching temperatures was found to be 0.86 ± 0.02 eV. This compares very well with the value of about 1.0 eV reported for most commonly used track detectors. The effects of gamma irradiation on this new detector in the dose range of 200–1000 kGy have also been studied using bulk etch rate technique. The activation energy values for bulk etching calculated from bulk etch rates measurements at different temperatures were found to decrease with the increase in gamma dose indicating scission of the detector due to gamma irradiation. The optical band gap of this detector was also determined using UV–visible spectrometry and the value was found to be 4.37 ± 0.05 eV.

Determination of alpha activity in organic solvents using CR-39.

Solid State Nuclear Track Detector (SSNTD) like CR-39 offers a unique opportunity to measure alpha radiations in a complex matrix like high level nuclear waste due to its sensitivity to only alpha radiations in the presence of intense beta-gamma radiation field. There is however a concern about the lower sensitivity of SSNTD when the radiation source is present in solution vis-à-vis solid medium. The sensitivity of CR-39 toward detection of alpha particles homogenously distributed in n-hexane, n-dodecane and n-octanol has been investigated and was found to be better than that obtained in 3 M HNO3.