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2018.10.12
NSEC and Kyushu University have developed a theoretical method to accurately predict isotopic production cross sections of residual nuclei in the deuteron-induced spallation reactions.
Among radionuclides produced in a nuclear reactor, those with long half-lives require long-term management and hence it is strongly desired to convert them into stable or short-lived ones. Spallation reaction is one of the candidates especially for transmutation of long-lived fission products (LLFPs). In recent years, it has been suggested that the use of deuteron as incident particles improves the efficiency of transmutation compared to other charged particles such as proton.
In the design study of a transmutation system using a deuteron primary beam, accurate cross section data of deuteron-induced reactions on LLFPs are indispensable. Isotopic production cross sections of residual nuclei are especially important. However, conventional theoretical methods are not necessarily adequate for deuteron-induced ones. This is because, although the deuteron is a weakly bound nucleus and easily breaks up by the interaction with a target nucleus, this effect is not considered sufficiently in the conventional methods.
In the present study, we have developed a theoretical method to calculate deuteron-induced spallation reactions taking into account the breakup processes explicitly. The calculated cross sections reproduced the experimental data well over a wide mass number range of residual nuclei.
Research and development on a transmutation system using a deuteron primary beam will make great progress by the present work. In addition, the result of the present work is expected to make a large contribution to various fields related to deuteron-induced reactions, such as production of medical radioisotopes, radioactivity evaluation in deuteron accelerator, and so on.
The study was published in Physical Review C on October 11th, 2018.
JAEA HP Press release (Japanese only)
Kyushu University HP (Japanese only)
JST HP (Japanese only)
2018.8.30
NSEC, JAEA and Takasaki Advanced Radiation Research Institute, QST have clarified the mechanism which determines the light output of scintillation detectors to accurately estimate scintillation light output owing to incidence of protons and heavy ions.
Owing to its high efficiency and low price, scintillators are widely used for measurement of gamma-rays, neutrons, etc. However, theoretical background of the relationship between the light output and the energy deposition by protons and heavy ions has been debated for a long time. Clarification of the light emission mechanism and the mechanism-based prediction of light yield have been desired.
In this study, we developed a numerical model composed of 3 phases; 1: radiation transport calculation to simulate microscopic energy deposition, 2: mechanism to transfer deposited energy between molecules, and 3: the mechanism to dissipate the energy by particular transition without emitting light. This model succeeded in reproducing the light yield of scintillators in irradiation by gamma-rays, beta-rays, alpha-rays, protons and heavy ions. In particular, this model accurately predicted the light yield by protons and heavy ions giving an insight into the mechanism which determines the light yield.
The result of this study can contribute to development of new scintillation detectors for radiation measurement in various environments such as accelerator, and space. The study was published in PLOS ONE on August 30th, 2018.
JAEA HP Press release (Japanese only)
QST HP Press release (Japanese only)
2018.3.26
NSEC developed a numerical simulation code ‘JUPITER’ which estimates the accumulation and distribution of fuel debris in severe accidents (SAs). By using JUPTIER, simulation of the relocation of the fuel debris into the lower part of the primary containment vessel (PCV) become possible. We confirmed that core meltdown behavior in SAs can be evaluated.
In the SAs, it is considered that the high temperature fuels and structures melt and relocate to the inside of the PCV. However, estimation of the composition and distribution of fuel debris, release of fission products from fuel debris and a possibility of re-criticality are difficult and items in evaluations of behavior of the SAs.
In this research, we developed the new numerical simulation code ‘JUPITER’ based on state of the art computational fluid dynamics technique and without artificial assumptions. By JUPITER, we performed melt relocation simulation from the reactor pressure vessel to the lower part of the pedestal, and obtained the following results;
2018.2.16
NSEC, QST and TAT elucidated a new process about modification of the genetic information in DNA due to the irradiation, which causes mutation induction or carcinogenesis, by a computer simulation.
Although most of the radiation damage to genomic DNA could be rendered harmless by repair enzymes in a living cell, it is thought that the localized damage within a few nm (clustered damage) is persistent, resulting in modification of genetic information. However, the precise three-dimensional structure and formation process have still not been fully elucidated for the chemical modification of clustered damage produced by actual irradiation. Therefore, a prediction by a computer simulation was craved.
In this study, we focus on interactions of electrons produced by irradiation in living system. We developed the calculation code that can simulate electron irradiation to a DNA molecule in the nanometer level and succeeded the simulation of the electron behavior which led to clustered damage. From the analysis of those results, we revealed that the clustered damage, which was generated by the electrons, was converted to the double strand breaks of DNA when base excision enzymes process the isolated base lesions induced by the extremely low energy electron. In addition, the termini of the double strand breaks may have some DNA base lesions. This result indicates that a low energy secondary electron is involved in modification of genetic information in the living system and will be significant to understand initial factor of mutation induction or carcinogenesis by radiations.
We will expand our study to quantitative evaluation of the production fraction of complex DNA damage formed by irradiations. This research and its results are published in Physical Chemistry Chemical Physics, edited by the Royal Society of Chemistry.
JAEA HP Press release (Japanese only)
2018.2.5
NSEC, JAEA succeeded in developing a model for estimating the therapeutic Effect of Boron Neutron Capture Therapy (BNCT) considering intra- and intercellular heterogeneity in 10B distribution, under collaboration with Kyoto University, Tsukuba University, and Central Research Institute of Electric Power Industry (CRIEPI). The new model was developed from our previously established stochastic microdosimetric kinetic (SMK) model that determines the surviving fraction of cells irradiated with any radiations. In the model, the probability density of the absorbed doses in microscopic scales is the fundamental physical index for characterizing the radiation fields. A new computational method was established to determine the probability density for application to BNCT using the Particle and Heavy Ion Transport code System PHITS. The parameters used in the model were determined from the measured surviving fraction of tumor cells administrated with two kinds of 10B compounds. The model quantitatively highlighted the indispensable need to consider the synergetic effect and the dose dependence of the biological effectiveness in the estimate of the therapeutic effect of BNCT. The model can predict the biological effectiveness of newly developed 10B compounds based on their intra- and intercellular distributions, and thus, it can play important roles not only in treatment planning but also in drug discovery research for future BNCT. The details of this study are described in T. Sato et al. Sci. Rep. 8: 988, 2018.
JAEA HP Press release (Japanese only)
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