Hyperthermia has been applied as one of the remedy for cancer therapy, because cancer cells are commonly more sensitive to heat than normal cells. Recently it has been reported that the mutant p53 (p53-121F), substituted serine121 by phenylalanine, induces apoptosis efficiently in various cancer cells. In this study, we aimed to establish a new strategy of hyperthermic cancer therapy combined with gene-therapy. For this purpose, we applied the HSP70B promoter, which is activated only after heat treatment, and constructed the plasmid by ligating the p53-121F gene downstream the promoter. The resulted plasmid, pHSp53-121F, was transfected into H1299 carcinoma cells, which have deletion in the p53 gene, and the expression of the p53-121F was determined by western blotting after heat treatment. We confirmed that heat treatment at 43 degrees for 2hr induced p53-121F protein in H1299 cells containing pHSp53-121F and induced apoptosis manifested by cleavage of caspase 3 and 7, and PARP, as well as DNA ladder formation. Cell survival determined by colony-formation assay revealed that lethal effect of hyperthermia at 43 degrees for 2hr was enhanced approximately 70 folds in H1299 cells containing pHSp53-121F compared with the parental H1299 cells. From these results, we propose that hyperthermia combined with the p53-121F gene therapy can be applied as a novel strategy for cancer therapy.

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Electrochemistry cancer therapy (ECT) is a promising new method to cause involution of a tumor by canceling direct current in carcinoma tissue. We study a cell level in an anti-tumor effect of ECT and mechanism of a DNA level, and there is it for the purpose of provided data in fundamental researches of ECT. We used ICR and C3H male mice. And we used cancer cell (Sarcoma-180, Scc-7, Ehrlich) for five weeks. In study of a histological level, we did ECT in the tumor that we inoculated into an upward department of a right foot of C3H mice and resected a tumor after 6, 12, 24hr after each group ECT. Changes of pH in an organization or outbreak of gas occur. That pH value in a tumor became strong alkalinity in the cathode side in strong acid nature in the anode side in this experiment was confirmed. Environmental change in a cell, alteration of protein, apoptosis and necrosis are caused by changes of this pH. In addition, therapy effect by ECT was recognized in a tumor growth measurement experiment, a tumor weight measurement experiment. As for ECT, we think that effective as cancer therapy method than these experiment results.

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As for the chemotherapies and the radiotherapy, a side effect is big, and degradation of immunisation activity and degradation of stamina suffer from a problem. By this study, we used mouse as radioprotector for a side effect in cancer therapy of radiation whether Ganoderma Lucidum and propolis were partial response whether there was not it and reviewed it. We did intra abdominal Ganoderma Lucidum of 100mg/kg and them of propolis in combination more than two weeks. The dosage of preparation reached to the experiment end. We measured white blood cells, lymphocytes, and a monocyte count alike. In addition, we measured anti-oxidation activity. Furthermore, with C57BL laboratory mouse, we did CD 4 and analysis of CD 8. A blood cell count change revealed a white blood cell, a lymphocyte, and increase of a monocyte. In anti-oxidation activity, anti-oxidation action was confirmed by each preparation dosage. CD 4 and CD 8 increased in each administrated group. In addition, CD 4 in Ganoderma Lucidum administrated group and large increase of CD 8 were seen when we looked at the radiation exposure back. It was these, and shell, Ganoderma Lucidum and a radiation protection effect by the propolis dosage were suggested. We can expect it for an immunological enhancement effect in radiation cancer therapy and side effect prevention by taking in Ganoderma Lucidum and propolis.

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Purpose: We analyzed threshold of radiation effects on cortical and posterior subcapsular opacities among A-bomb survivors, in which significant associations with radiation have been observed. Subjects: 873 persons who underwent ophthalmologic examinations in the RERF Adult Health Study during 2000 - 2002. We diagnosed cataract according to the Lens Opacity Classification System II. Methods: Worse eye represented individual opacity for those with different grade opacities. For probability of grade increase of lens opacity using proportional odds model, goodness of fit (log- likelihood) of main effect model using explanatory variables, such as city, sex, age at bombings, and radiation dose (DS86) with threshold was tested. Significance of threshold was determined if the lower confidence interval of obtained best fit threshold (estimated threshold) exceeded 0Sv. Results: Estimated threshold and 90 % and 95 % confidence intervals for cortical opacity were 0.5Sv, (0, 1.1) and (0, 1.3), respectively. Those for posterior subcapsular opacity were 0Sv, (0, 1.1) and (0, 1.5), respectively. Furthermore, similar analyses were conducted on 387 persons with normal visual acuity (0.7 or more) and 486 persons with low visual acuity (less than 0.7) and the lower confidence intervals of the threshold did not exceed 0 Sv in both groups. Conclusion: Lower threshold confidence intervals both in cortical and posterior subcapsular opacities did not exceed 0Sv, suggesting that there is no threshold in both opacities.

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The objective of the present study was to investigate the association of living conditions and health status with feeling of satisfaction in daily life among atomic bomb survivors in Nagasaki. The subjects were 3526 atomic bomb survivors (1261 men and 2265 women) who responded to the self-administered questionnaire mailed in August 1997. The questionnaire included the questions about demographic and lifestyle factors, living conditions, feeling of satisfaction in daily life, presence of chronic disease, self-rated health status. The mental health status was assessed using the 12-item version of General Health Questionnaire (GHQ-12). The frequency of those who were not satisfied with daily life was higher in those who had more chronic diseases, those who rated their health as bad and those with high GHQ-12 score (exceeding 3), as compared with respective controls. Among the men, the frequency of those who were not satisfied with daily life was higher in those who were living alone compared with those who were living with their family members, although among the women, the frequency was almost the same between them. It was indicated that somatic and mental health status affected atomic bomb survivors' feeling of satisfaction in daily life.

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The fetus is known to be radiosensitive. Vergouwen et al (1995) reported that the radiosensitivity of the gonocytes was increased with fetal age when pregnant mice were exposed to single doses of X rays. Fetuses are also very sensitive to environmental endocryn distruptors. In the present study, we examined whether low dose radiation exposure at fetal period caused similar antiandrogenic effects such as feminized males and change of androgen receptor (AR) mRNA expression in epididymis etc. in offspring male mice or not. Pregnant mice were orally administered HTO (10.9kBq/g body weight) or exposed to 137Cs gamma rays (0.3Gy/h) at gestational day 14, and then body weight, ano-genital distance, survival rate, ability of reproduction and organ weight of its offspring were determined, and quantitative AR mRNA expression in caudal epididymis at day 82 of male offspring by using competitive RT-PCR. As fort each measurement items and AR mRNA expression in caudal epididymis, no significant effects of HTO or gamma ray exposure were observed.

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As a standard biodosimeter, scoring chromosomal aberrations is widely used because the preparing and scoring chromosomes is a simple and well established method (cytogenetic biodosimeter). However, when cells are irradiated with large doses (i.e. over 10 Gy), most cells arrest in G2 phase and do not enter mitosis and it is thus difficult or even impossible to obtain chromosomes using conventional colcemid block. Therefore, this problem has limited the use of cytogenetic biodosimeter for estimate the irradiation dose over 10 Gy. Recently, Gotoh and Asakawa (1996) first overcame this limitation using their developed drug-induced premature chromosome condensation (PCC) method (1995). We previously reported that the total number of Giemsa-stained prematurely condensed chromosomes well correlates to the irradiation dose, and it seems to be an adequate index for the irradiation dose (The 46th Annual Meeting of JRRS, Kyoto, Oct, 2003). Here we report that the maximum/minimum length ratio of chromosome fragments of Giemsa-stained prematurely condensed chromosomes well correlates to the irradiation dose up to 40 Gy, and it seems to be an another adequate index for the irradiation dose Therefore, we propose this simple protocol for a new cytogenetic biodosimeter, in particular for determine the irradiation dose of the victims of emergency accidents.

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There were radioactive accidents in the South Ural, former Soviet Union, between 1949 and 1956. The most serious one was the chemical explosion of radioactive waste tank in Mayak. This region was contaminated mainly by ⁹⁰Sr. We sampled cow teeth from this region and measure them with Fuji Imaging plates (IP) to investigate the amount and the distribution of the nuclei in the teeth. The Fuji Imaging plate accumulates trapped electrons created by beta rays from the radioactive nuclei. Laser stimulates the electrons so that they emit UV. By observing the emitted lights, the distribution and the amount of beta emitter are visualized.

Cow teeth were cut in half and the section was placed on the IP for one week before it was measured by BAS-1500 (Fuji). The concentration of ⁹⁰Sr was 10 Bq/g at maximum in the teeth, compared with standard samples, being concentrated in central part of dentin. When a thin slice of 1mm in thickness was placed on the IP, the resolution was better than the half-cut sample but with lower sensitivity. Results of ESR dosimetry of those teeth together with the correlation with soil contamination levels will be presented.

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Recently,IVR techniques advanced remarkably. On the other hand,radiation ulcer as a late effectdue to IVR procedure has been sometimes reported. We experienced 8 cases of radiation dermatitis/ulcer,due to CAG, PTCA or other IVR techniques. Case1-7 represented radiation ulcer mainlydue to CAG or PTCA. Case 8 revealed serious radiation dermatitis,due to four times of TAE. Irradiated dose with IVR procedure is not so small,and these examinations are tend to returnagain and again many times in a short range, we must take care radiation dermatitis/ulcer due to these examinations. To avoid these accident due to IVR methods, radiologists should educate and enlighten thedoctors of other department and carefully measure the irradiated dose in each examination.

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We analysed pathological findings of the skin, digestive tracts, and lungs in a victim in the Tokaimura criticality accident. The patient received 17-24GyEq, and died on day 82. The skin showed wide erosions on the anterior side of the total body. On the chest wall, the epidermis was lost with necrosis and hemorrhage in the dermis. The epidermis on his posterior side was preserved, but the skin colored dark purple. The dose of the irradiation at the back was one eighth of that at the anterior side. Histologically, the epidermis and sweat glands were preserved. It was a sharp contrast to the anterior skin. The gastrointestinal tract showed diffuse erosion and hemorrhage from the esophagus to rectum at autopsy. Contents were bloody, 2040g in the stomach and 2680g in the intestine. The stomach was dilated and its whole mucosa showed erosion. The mucosa of the small intestine and colon was also diffusely hemorrhagic and erosive. Histologically, there was total loss of the epithelial cells from the stomach to descending colon, but the epithelium still remained sparesely in the sigmoid colon and rectum. Both lungs were heavy with edema and congestion. Hemorrhage was also seen in the posterior side. The anterior segment of the middle lobe of the right lung, segment 5, showed more severe congestion and edema, compared with the left S1+2. Lung fibrosis was not observed.

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We have continued epidemiologic research for potential radiation risks of the public near a nuclear power plant (NPP) in Japan. Superficial increase by ecological studies can raise a social concern even for small radiation risks due to NPP routine operations. Japanese geographical pattern of temporal area variation was examined for digestive cancer mortality in 1972-1997 using Poisson regression. Mortality variation in municipalities was assumed to be determined by a geographical hierarchical structure with six local area blocks, prefectures and areas of medical and health planning. About 64.4% of all solid cancers were digestive cancers of esophagus, stomach, colon, gallbladder, pancreas, liver and others. Relative area variation divided into six local area blocks was large for liver and esophagus cancers although it was small for all digestive cancers combined. The geographical mortality pattern for digestive cancers may confound little the risk assessment of areas near NPPs in contrast with the pattern associated with ATL for leukemia and malignant lymphoma.

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Glutathione (GSH) is one of low molecular weight antioxidants in a living body to scavenge reactive radicals. In the present study, the radioprotective effect of GSH on DNA damage in human T- lymphocyte leukemia Molt-4 cells induced by gamma irradiation was examined. Molt-4 cells were cultured for 24 h at 37C in GSH containing medium and then exposed to 60Co gamma radiation (2Gy/h) for 1 h. After irradiation, survival rates of the cells were periodically measured by staining with trypan blue and the estimation of DNA damage in the cells by the comet assay were conducted using SCG software. No significant effect of GSH addition was observed on the survival rates of irradiated or non-irradiated Molt-4 cells, while GSH addition decreased DNA damage in the irradiated cells.

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Radon exposure contributes to nearly half of the environmental radiation. However, its molecular nature of the biological effects has not been elucidated. We, therefore, have started the development of the experimental procedure for detecting the biological effects, especially genetic one, caused by radon, if any. In the control experiments, mouse FM3A cells were grown on soft-agar plates, and irradiated with 0, 1, 3, and 10 Gy of X-ray. DNA was extracted from the cells that formed colonies, and was analyzed by Southern blot hybridization technique using hypervariable repeat Pc-1 DNA as a probe. Dynamic mutation at Pc-1 locus was observed in the cells exposed with 10Gy of X-ray. Also the cells growing on soft-agar plates were exposed to 100K-1MBq/cubic-meter of radon, and the Pc-1 locus was analyzed. However, the mutation was not detected in the cells exposed to radon. We also attempted to detect the mutation occurred in the Hprt gene by selecting resistant mutants against 6-thioguanine. The experiments are still on the half way, and we will describe the results and the reliability of this new experimental procedure.

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Chlorinated derivatives of Bisphenol A (chlorinated BPAs) have been detected in wastewater from waste paper recycling plants. These compounds have been reported to show more strongly estrogenic activity than BPA. BPA and chlorinated BPAs are always exposed to UV radiation in environment and consequently various photoproducts might be generated. In this study, we investigated the cytotoxicity, chemical structure and estrogenic activity of photoproducts of BPA and chlorinated BPAs (3-ClBPA, 3,3'-diClBP and 3,3',5-triClBPA) after UV irradiation. The effect of photoproducts on Jurkat cells was determined by alamar Blue assay. The chemical structure of photoproducts was identified using GC/MS.
The cytotoxicity of 3-ClBPA and 3,3'-diClBPA was higher than that of BPA and 3,3',5-triClBPA. The toxicity of chlorinated BPA was increased by irradiation of UVB and UVC at 100J/cm² and decreased at 1000J/cm² in comparison with those at 100J/cm², indicating that their structures were changed. 3-OHBPA was detected in the photoproducts of 3-ClBPA irradiated with UVB and UVC at 100J/cm², and 3-OHBPA and 3-Cl-3'-OHBPA were detected in those of 3,3'-diClBPA. The toxicity of 3-OHBPA has been reported to be higher than that of BPA. Therefore, the formation of hydroxylated BPAs might contribute to the increase of toxicity by UV irradiation. Chlorinated BPAs showed higher estrogenic activity than BPA, whereas their photoproducts after irradiation of UVB (100J/cm²) showed no agonist activity for estrogen receptor.

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To investigate the dose response relationship of mutagenicity by exposure to static magnetic fields, point mutation frequency on lys1-1/lys1-1 and gene conversion/recombination on arg4-4/arg4-17 was investigated up to a 5Tesla (T) static magnetic field in S. cerevisiae XD83. It was found that gene conversion/recombination frequency was slightly but significantly increased by exposure to a 5T static magnetic field for 5 days at 30Cº. On the other hand, this effect did not observed in 2T, decrease of mutation frequency was observed in 1T and the effect disappeared in 0.5T. In all experimental condition, point mutation frequency was unchanged. This suggests that exposure to a strong static magnetic field cause specifically increase of gene conversion/recombination and its dose relationship is J-shape. In gene expression analysis, induction of several genes that related to TCA cycle was observed by exposure to a 14T static magnetic field but not in a 5T after stationary incubation in YPD medium for 24hr in S. cerevisiae 4338 using cDNA microarray and real time RT-PCR. However, specific gene cascade was not detected and also change in expression of DNA repair or stress response genes was not observed. These results suggest that effects of magnetic field are very small even in a 14T in S. cerevisiae.

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DNA double strand breaks (DSBs) are often induced by ionizing radiation such as cosmic rays. Fidelity of DSB repair is a important factor that determines quality of genomic stability. It is known that the most of DSBs are properly repaired on the earth, however, little is known whether those are rejoined at the same fidelity even under the space environment. One of the DSB repair pathway, homologous recombination (HR), allows the cells to repair their DSBs with error free. Therefore, the efficiency of HR is a good index to assess the fidelity of DSB repair. In order to clarify the effect of gravity stress on HR pathway, we established a cell line that can detect a site-specific DNA repair via HR. The cells carrying a reporter construct for HR were incubated under hyper-gravity condition (30G) for 12 h after induction of site specific DSB. Our results suggest that the gravity stress may affect the HR efficiency. Further analysis on HR pathway under hyper-gravity condition is in progress.

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Omura bay located in Nagasaki Pref., Japan is restrictedly isolated from the outer sea. Contaminants supplied to the enclosed embayment system are expected finally to be accumulated together with the bottom sediment. In recent years, red tide occurrence is increasing, and mutations are frequently found in the bottom organisms in Omura bay, and these are suspected to be due to the human activities, but it have not sufficiently been verified. So we studied the bottom sediment to reveal the present state of the bay.
We evaluated accumulation rates of the sediments by the activities of ²¹⁰Pb. And we analyzed vertical and horizontal distributions of 44 elements including heavy metals to estimate chronological change and regional difference of the sediment composition.
We found content of some heavy metals of the bottom sediment including Cd larger than the average content in the earth's crust. And there was the tendency that the chronologically newer sediment contains the larger amount of Cd, Pb, Zn and Cu. The accumulation rates of the whole sediment along the coast were found faster than that of the middle of the bay. But those of the heavy metals showed a relatively uniform distributions.

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Nagasaki is located in the western end of Japan, and receives aerosol factors from the Eurasian Continent such as Asian dusts first in Japan and directly with almost no mixing of the domestic factors. With attention to this geographical situation of Nagasaki area and for the environmental study of Omura bay, we have measured the aerosol size and the concentration of ²¹⁰Pb and ⁷Be adhering to the aerosol. Seasonal variation of these data was analyzed combined with the weather data, of the rainfall and the wind direction. We observed simultaneously at two points, in city and in the suburbs, to estimate refloat and the effects of human. We analyzed elements in rainfall and atmosphere. We will present and discuss some result from the analysis.

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Concentration of organically-bound tritium and carbon-14 in the tree-ring cellulose of a pine tree grown in Shika-machi, Ishikawa prefecture, Japan(37.1^oN, 136.5^oE), was measured during the ring-years from 1949 to 1999, and compared with those of a pine tree grown in Tatsunokuchi-machi, Ishikawa prefecture, Japan (36.4^oN, 136.5^oE). The annual variation of tritium in tree rings demonstrated two differences between the Shika-machi tree and the Tatsunokuchi-machi tree: No secondary peak appeared in the period after the maximum peak of 1963 for the Shika-machi tree, while two peaks appeared in 1966 and 1970 for the Tatsunokuchi-machi tree. In addition, the height of the 1963 peak was 30% higher for the Shika-machi tree than for the Tatsunokuchi-machi tree. These differences are considered to be caused by the influence that the underground water in the root zone of the Tatsunokuchi-machi tree was strongly affected by water which was transported to the tree site from mountain regions as compared to the Shika-machi tree. On the contrary, the annual variations of carbon-14 concentration in tree rings agreed well with each other. This fact suggests that there was no local variation of the annual average levels of carbon-14 concentration in atmospheric CO₂.

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The genus of green algae, Bryopsis showed a unique chemical composition; they accumulated alkali earth elements, especially of large mass number including naturally occurring radium. Radioactivity concentrations of ²²⁶Ra in algae ranged from 40 to 92 Bq/kg-wet, whereas those of ²²⁸Ra varied widely from location to location, ranging from 28 to 211 Bq/kg-wet. The site dependence of ²²⁸Ra concentration in algae would reflect the extent of the burden of terrestrial radioactivity in the adjacent coastal environment, while ²²⁶Ra concentration was rather uniform in the sea owing to its long half-life. It was suggested that species of Bryopsis be useful as a biological monitor for monitoring the influence of natural background radioactivity in the marine environment. The hypothetical intake of the algae as foodstuff would result in radiation dose of 0.06 - 0.29 mSv to humankind altogether for ²²⁶Ra and ²²⁸Ra. The intake of algae could be one of the most critical pathways delivering dose due to naturally occurring radionuclides as well as to artificial radionuclides such as ⁹⁰Sr. Observed concentrations of radium provided the estimates of dose rate of 110 - 260 nGy/h to the algae themselves, using the coefficients values of the internal dose rate per unit concentration given by the UNSCEAR. Care should be directed to a so-called hyperaccumulator like species of Bryopsis, from the radiation protection point of view.

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For nuclear safety assessment, it is required to know the behavior of radiocesium and radiostrontium in the environment because cesium has affinity to be concentrated in muscle and strontium in bone. We have already estimated the soil-to-plant transfer factors (TFs) of radiocesium and radiostrontium using Andosol, the most abundant soil types in Japan. TF showed the concentration ratio of the nuclide between crop and soil at harvest. It is, however, necessary to obtain the plant/soil ratio at different growth stages in order to understand the uptake pattern during the cultivation. Therefore, we have carried out radiotracer experiments on the transfer of Cs and Sr from Andosol to radish. This experiment on Mn, which showed similar tendency to Sr in previous study, was carried out for comparison. The concentration ratio (on a wet weight basis) of Cs and Mn for roots (tubers) of radish decreased with time. Contrary to these, the concentration ratios of Sr and Mn observed for leaves of radish increased with time.

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In order to eliminate atmospheric HT released from tritium handling apparatus, we intended to use HT oxidizing ability (enzyme:hydrogenase) of bacterial strains isolated from various soils obtained at home and abroad. Among the isolated strains with high HT oxidation activity, several strains were selected to develop a tritium elimination (detritiation) system. Bioreactors were made of the bacterial cells grown on agar medium fixed on filter and stored in a refrigerator until use. The detritiation ability of bioreactors at room temperature was investigated in the intentional tritium release experiments carried out in the Cassion Assembly for Tritium Safety Study (CATS) in TPL/JEARI. When a part of HT contaminating air from the CATS was introduced into the biological detritiation system, in which three small bioreactors were connected in series, about 85% of HT in air (200Bq/cm³) was removed as HTO in these bioreactors during once through mode of the detritiation system at a flow rate of 100cm³/min.

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Low dose radiation acts on activation of an immunity function. Moreover, it is reported that it exerts a useful effect on a living thing. Irradiation of 0.01 to 0.5Gy radiation raises SOD activity in erythrocyte with a dose, and cell multiplication of the number of cells of marrow or CFU-GM is activated, and it is reported to irradiation of a high dose after that that the probability of survival increases. Present study examined the radiation hormesis effect which irradiation of the low dose for one month brings about. Evaluation of the damage of DNA was quantified by the comet assay method. When a mouse is exposed to the radiation of a low dose for one month, the DNA damage for comet image of bone marrow exposed by 8Gy gamma ray irradiation decreased.

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To predict radionuclide concentrations in marine organisms under short term radionuclide introduction to coastal water, the simple time series ¹³⁷Cs transfer both from seawater and food chain to marine organisms were studied. The model was developed for typical Japanese coastal water including benthic food chain and planktonic food chain, with transfer parameter data set, such as uptake rate constant, excretion rate constants, gut transfer rates, food ingestion rates. For the development of the modeling technique in prediction of the temporal concentrations in marine biota, the time and space distributions of ¹³⁷Cs concentrations in marine organisms are important. We developed a 3 dimension model being composed of nuclide transfer both from seawater and food chain in imaginary coastal area, expressing the temporal ¹³⁷Cs concentrations in marine organisms accompanied with the habitat location. The result of 3D modeling in case of short term introduction to exhibit the following information; 1) The introduced ¹³⁷Cs in seawater is diluted and disappeared quickly under normal current conditions, while ¹³⁷Cs in organisms slowly increased even after the seawater is cleared, mainly from the contribution from ¹³⁷Cs transfer through food chain. 2) The ¹³⁷Cs concentration in fish of higher trophic level appears approximately 100 days later, and the concentration ratio (¹³⁷Cs in organism / ¹³⁷Cs in seawater) reaches only 1 - 10 even using the maximum concentrations in organism and seawater.

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Telomerase is a reverse transcriptase that elongates telomere sequence. Normal cells have very low telomerase activity and a limited life span. On the other hands, most cancer cells have telomerase activity and an unlimited life span. Therefore, proliferation of cancer cells may be inhibited specifically by inhibiting telomerase activity. In this experiment, we screened marine bacteria that produce the telomerase inhibitor from library of marine bacteria. We screened telomerase activity by TRAP assay, and found a novel marine bacterium that inhibits telomerase activity. Its molecular weight is over 50,000 and it is denatured by heat treatment. Cancer cells were treated with medium supplemented with 5% supernatant for 14days. This suppressed the telomerase activity of cancer cells down to 60% of untreated cancer cells. These results suggest that supernatant of a novel marine bacterium is hopeful for anti-cancer drugs.

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Monte Carlo particle transport codes, MCNP and PHITS, were utilized to analyze the energy deposition processes in the body for the neutron incidence. Various secondary particles are produced via nuclear reactions in the body. The results of the simulation codes show that electrons play more dominant role than other heavy charged particles as decreasing the incident neutron energy or increasing the volume of the receptor. Secondary photons are produced by H(n, γ)D thermal neutron capture reaction and the photon kicks out the electron from the orbit. The relative contribution of electrons, therefore, increases in the situations described above. In our poster presentation, we will exhibit the relative contribution of each charged particle (i.e. electron, proton, deuteron, alpha particle etc.) at various incident energies and sizes of the receptor volume.

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The contribution of OH radicals to cell death by low-energy photons and heavy ions with high LET nature was evaluated by competition kinetics analysis using DMSO. Reciprocal of the degree of protection by DMSO was plotted against reciprocal of DMSO concentration. >From the linear relationship, maximum protection level at infinite concentration of DMSO and the slope that corresponds to scavenging capacity of cellular molecules responsible for cell death. These two parameters were summarized for X-rays whose energy ranges from 12.4keV to 1.25MeV, and for C, Si and Fe ions whose LET ranges from 20 to 440keV/μm. The maximum protection level decreased with decreasing photon energy or increasing ion LET, and reached about 60% for both radiations. These results showed that indirect action still plays a major role in cell death by low-energy X-rays and high-LET heavy ions. Scavenging capacity defined as the product of the reaction rate constant and the concentration of the cellular molecules increased with increasing LET for heavy ions, while it was nearly constant for X-rays with energies examined. The results may reflect the production density of OH radicals in these radiations.

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