Chirag K. Vyas

A novel nanometric DNA thin film as a sensor for alpha radiation

The unexpected nuclear accidents have provided a challenge for scientists and engineers to develop sensitive detectors, especially for alpha radiation. Due to the high linear energy transfer value, sensors designed to detect such radiation require placement in close proximity to the radiation source. Here we report the morphological changes and optical responses of artificially designed DNA thin films in response to exposure to alpha radiation as observed by an atomic force microscope, a Raman and a reflectance spectroscopes. In addition, we discuss the feasibility of a DNA thin film as a radiation sensing material. The effect of alpha radiation exposure on the DNA thin film was evaluated as a function of distance from an 241Am source and exposure time. Significant reflected intensity changes of the exposed DNA thin film suggest that a thin film made of biomolecules can be one of promising candidates for the development of online radiation sensors.

A 2D DNA lattice as an ultrasensitive detector for beta radiations.

There is growing demand for the development of efficient ultrasensitive radiation detectors to monitor the doses administered to individuals during therapeutic nuclear medicine which is often based on radiopharmaceuticals, especially those involving beta emitters. Recently biological materials are used in sensors in the nanobio disciplines due to their abilities to detect specific target materials or sites. Artificially designed two-dimensional (2D) DNA lattices grown on a substrate were analyzed after exposure to pure beta emitters, (90)Sr-(90)Y. We studied the Raman spectra and reflected intensities of DNA lattices at various distances from the source with different exposure times. Although beta particles have very low linear energy transfer values, the significant physical and chemical changes observed throughout the extremely thin, ∼0.6 nm, DNA lattices suggested the feasibility of using them to develop ultrasensitive detectors of beta radiations.

Development of optical monitor of alpha radiations based on CR-39.

Fukushima accident has highlighted the need to intensify efforts to develop sensitive detectors to monitor the release of alpha emitting radionuclides in the environment caused by the meltdown of the discharged spent fuel. Conventionally, proportional counting, scintillation counting and alpha spectrometry are employed to assay the alpha emitting radionuclides but these techniques are difficult to be configured for online operations. Solid State Nuclear Track Detectors (SSNTDs) offer an alternative off line sensitive technique to measure alpha emitters as well as fissile radionuclides at ultra-trace level in the environment. Recently, our group has reported the first ever attempt to use reflectance based fiber optic sensor (FOS) to quantify the alpha radiations emitted from (232)Th. In the present work, an effort has been made to develop an online FOS to monitor alpha radiations emitted from (241)Am source employing CR-39 as detector. Here, we report the optical response of CR-39 (on exposure to alpha radiations) employing techniques such as Atomic Force Microscopy (AFM) and Reflectance Spectroscopy. In the present work GEANT4 simulation of transport of alpha particles in the detector has also been carried out. Simulation includes validation test wherein the projected ranges of alpha particles in the air, polystyrene and CR-39 were calculated and were found to agree with the literature values. An attempt has been further made to compute the fluence as a function of the incidence angle and incidence energy of alphas. There was an excellent correlation in experimentally observed track density with the simulated fluence. The present work offers a novel approach to design an online CR-39 based fiber optic sensor (CRFOS) to measure the release of nanogram quantity of (241)Am in the environment.

A novel approach for preferential recovery of Sr from (Sr, Th)O2.

Quantitative leaching of Sr from homogeneous and calcined (Th,Sr) O(2) in dilute perchloric acid medium suggests the possibility of reducing the hazardousness of discharged nuclear fuel by separation of (90)Sr, a prominent fission product at dissolution stage itself rather than the conventional approach of its recovery from high level nuclear waste. Apart from mitigating the radiotoxicity of the nuclear waste, recovered (90)Sr can be employed as a compact heat source and as parent radionuclide for (90)Y (used in therapy radiopharmaceuticals), provided it can be made available at desired high purity. Leaching behavior of few other fission products was also investigated to quantify their contamination in leached Sr. Feasibility of employing extraction chromatography using Sr selective resin was explored in perchloric acid medium. In this context, the distribution coefficients of (85)Sr(II), Th (IV), Zr(IV), Y(III), Pd(II) as well as (152)Eu(III) and (137)Cs (I) were determined under varying nitric acid/perchloric acid concentration and under varying loading conditions of metal ions. Perchloric acid medium appears better than nitric acid medium for preferential leaching of Sr from (Th,Sr)O(2) as well as for uptake of Sr by Sr selective chromatographic resin.

Acid resistant zirconium phosphate for the long term application of 68 Ge/ 68 Ga generator system

The 68Ge/68Ga generator system is an excellent source for producing ready-to-use Ga-68 in clinical Positron Emission Tomography (PET) applications. The column adsorbent is the key component for the 68Ge/68Ga generator system. Therefore, several studies have been conducted to identify column materials with a stable and superior elution yield in an acidic eluent (0.1 N HCl solution). In this study, four different zirconium phosphates were synthesized with a particle size of 200-800nm, pore-size of 55∼190Å and surface area of 0.72-268m2g-1. Synthesized and studied amorphous zirconium phosphate (ZrP-1) exhibited excellent acid resistant properties for the 0.1 N HCl eluent and a large surface area of 268m2g-1. Amorphous ZrP-1 showed a good Ga-68 elution yield of 74% in 0.1 N HCl eluent accompanying extraordinary low breakthrough of Ge-68 (0.007%).

Phosphonates as alternative to tributyl phosphate for the separation of actinides from fission products

Abstract The present work investigates the role of increase in the basicity of organophosphorus extractant (dialkylalkyl phosphonates) on the uptake of actinides and fission products vis-à-vis tributyl phosphate (TBP), currently employed as a universal extractant. Two dialkylalkyl phosphonates viz. dibutylpropyl phosphonate (DBPrP) and dibutylpentyl phosphonate (DBPeP) were synthesized, characterized and evaluated for their solvent extraction behavior towards U(VI), Th(IV), Eu(III) and Tc(VII) in nitric acid medium ranging from 0.01–6 M. It was observed that increasing the basicity of the phosphoryl oxygen enhanced the uptake of the actinides and the distribution coefficient values were significantly larger as compared to TBP. The limiting organic concentration (LOC) value was estimated for Th(IV) for these extractants and compared with the TBP system. The separation factors of actinides with phosphonates over Tc(VII) are distinctly better than that with TBP.

ADS Research Activities at Sungkyunkwan University

Thorium-based accelerator-driven system (ADS) technology for future nuclear energy is being developed at Sungkyunkwan University. Our research activities include research on computational modeling, partitioning and transmutation, detector development, and life cycle assessment analysis. A brief overview is given here.

A Novel Approach for Preferential Recovery of 90Sr from Irradiated ThO2

Thorium is likely to play a pivotal role in the sustained use of nuclear energy as uranium reserves dwindle in the next few decades. This outlook is a result of thorium’s abundant supply (3–4 times that of uranium), favorable neutronic and physico-chemical properties (as a fuel material), intrinsic proliferation resistance (owing to the presence of 232U along with 235U), the lower content of minor actinides in the spent fuel, and better long-term behavior of its waste in geological repositories. Its high η factor makes 233U the best fissile isotope, of all existing fissile isotopes, for thermal neutrons, but it produces significant amounts of 90Sr. If this 90Sr can be recovered, it can be used as a valuable radionuclide for 90Y—a potential radionuclide for therapeutic applications, such as treating lung cancer, melanoma, and renal cell carcinoma.

Preferential leaching of Sr from mixed (Th/Sr) oxide

AbstractPreferential leaching of Sr from irradiated thorium may play an important role to facilitate the management of high level waste as well as provide a new route to recover valuable fission product 90Sr which has potential applications as (a) compact heat source and (b) as parent radionuclide for 90Y, used in therapeutic radiopharmaceuticals. In the present work, leaching of Sr from (Th,Sr)O2 in nitric acid and perchloric acid medium has been investigated as a function of acidity as well as refluxation time. It was interesting to observe that quantitative leaching of Sr(II) is possible even at 0.01 M HClO4 where leaching of Th is negligible (∼0.01%). Leaching behavior of other metal ions, like Pd(II), Y(III), and Zr(IV), representing few major fission products was also investigated.

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.