Tritium Β-rays Research Articles

Prolonged effect associated with inflammatory response observed after exposure to low dose of tritium β-rays

Background: The value of relative biological effectiveness of tritium increases at low dose domain, which results in the suspicion of weighting factor of 1 for tritium after low dose exposure. Thus, present study was carried out to analyze the differences in the cellular responses at early and late period between low dose of tritium β-rays and γ-rays radiation.Methods: MCF-10A cells were exposed to low dose of tritium β-rays or γ-rays, then cellular behaviors, such as DNA double strand breaks (DSBs), apoptosis, reactive oxygen species (ROS) level and inflammatory relevant gene expression were analyzed at early and late period post-irradiation.Results: At early period the elimination of DSB foci produced by HTO is longer than γ-rays. High ROS level and a continual change of cell cycle distribution are observed in HTO radiation group. Based on the results of RNA sequencing, Ingenuity Pathway Analysis (IPA) indicates TNFR1 signaling and production of nitric oxide and ROS are activated as an acute response at 24 h post radiation. Moreover, it also shows a disturbance in cholesterol biosynthesis. The results of 30 days point that there is a lasting active inflammatory response, accompanying with a persistent high expression of relevant cytokines, such as TNF and IL1R.Conclusion: Compared to an acute response induced by γ-rays, a persistent inflammatory response exists in HTO-irradiated cells when cultured for 30 days, which might be related to accumulation of tritium in the form of organically bound tritium (OBT) in cellular DNA or lipids.

The low dose effects of human mammary epithelial cells induced by internal exposure to low radioactive tritiated water

Tritium is an important radioactive waste which needs to be monitored for radiation protection. Due to long biological half-life of organically bound tritium (OBT), the adverse consequence caused by chronic exposure of tritiated water (HTO) attracts concern. In this study, fibroblast cells were exposed to 2 × 106 Bq/ml HTO to investigate the cellular behaviors. The dose relationship of survival fraction and γH2AX foci was a “U-shaped” curve. And the results of γH2AX intensity produced by ICCM, which was obtained from different doses, demonstrated bystander signal accounted for the protective effects induced by intermediate dose of 100 mGy. The comparison of temporal kinetics and spatial dynamics of DNA repair between tritium β-rays and γ-rays showed longer time was need for the dephosphorylation of H2AX protein after HTO exposure. It indicated complex cluster DSBs induced by tritium β-rays at the low dose impaired efficient recovery of DNA damage, which bear responsibility for the persistence of residual foci after low dose expsoure. It suggests after exposed to low dose radiation cells prefer to eliminate damage population to avoid DNA damage increasing the mutation potential.

The response of human mesenchymal stem cells to internal exposure to tritium β-rays.

There is no doubt that estimating the exposure risk of external and internal low-dose radiation is an imperative issue in radiobiological study. Human mesenchymal stem cells (hMSCs) are multipotent and self-renewing, supporting the regeneration of damaged tissue, including tissue damaged by radiation. However, the responses of hMSCs to internal exposure to radionuclides are still insufficiently understood. In order to evaluate the adverse effects produced by internal exposure to tritiated water (HTO) at a low dose, hMSCs were exposed to 2 × 107 Bq/ml HTO, and the biological effects after the exposure were examined. Apoptosis and DNA double-strand breaks (DSBs) were assayed to analyze the cellular response to the damage induced by HTO. Slight enhancement of apoptosis was found after treatment, except at the dose of 9 mGy. The number of DSBs at 24 h post-irradiation showed that the DNA damage was able to be efficiently repaired by the hMSCs. Moreover, the increasing proportion of the cell population in S phase proved that the persistence of residual γH2AX foci at lower concentrations of HTO was attributable to the secondary production of DSBs in DNA replication. Our work adds to the available data, helping us understand the risk of stem cell transformation due to internal exposure and its correlation with low-dose radiation–induced carcinogenesis.

The influence of neutron activated products in BIXS method for tungsten

Tritium β-decay Induced X-ray Spectroscopy (BIXS) is a promising method to obtain tritium retention details both on surface and in bulk of plasma facing materials (PFMs) in magnetic fusion devices. Influence of neutron activated products (NAPs) is one of the primary problems in BIXS, since the energy of Compton scattering photons and characteristic X-rays is close to the range of tritium β-rays. In this paper, Monte Carlo simulation was introduced to evaluate effects of NAPs in BIXS measurements for tungsten. Three steps are included in simulation, neutron flux simulation to reckon the neutron flux in PFMs based on the simplified model of ITER, activated products calculation to compute the distribution of NAPs in PFMs and radiation spectra simulation to calculate the spectra of NAPs in PFMs sample. Six typical nuclides (including W-185, W-181 and Re-188, etc.) produced by neutron irradiation were considered in this study. Finally, influence of NAPs was estimated quantitatively with the assumption that 1% of DT fuel retained in PFMs uniformly. It is found that the intensity of spectrum devoted by NAPs is as much as 10.6 times larger than it by tritium in the same region of interest (ROI) directly after reactor shutdown, while it will reduce to 0.83% after 19 months.

Self-radiolysis of tritiated water. 1. A comparison of the effects of 60Co γ-rays and tritium β-particles on water and aqueous solutions at room temperature

Monte Carlo simulations were used to investigate the chemistry of pure water and aqueous solutions after irradiation with different kinds of radiation: tritium β-rays and high-energy electrons or 60Co γ-rays. The objective of this work was to elucidate the mechanisms involved in the self-radiolysis of tritiated water, and to examine the importance of the effects of higher “linear energy transfer” (LET) by comparing 3H β-electrons (mean initial energy of ∼5.7 keV) with 60Co γ-rays (∼1-MeV electrons). We considered several chemical systems for which experimental data were available. These included pure water, aqueous solutions of sulfuric acid, and aqueous ferrous sulfate solutions in aerated 0.4 M H2SO4 (Fricke dosimeter). Simulations clearly showed quantitatively different yields of radical and molecular products produced by the radiolysis of water with tritium β− particles compared with corresponding yields from γ or energetic electron radiolysis. As a rule, lower radical and higher molecular yields were observed for 3H β-rays. These differences in yields are completely consistent with differences in the nonhomogeneous distribution of primary transient species (i.e., the structure of electron tracks) in the two cases. In the “short-track” (columnar) geometry of tritium β-electron radiolysis, radicals were formed in much closer initial proximity than in the “spur” (spherical) geometry of γ radiolysis. The “short-track” geometry favors radical-radical reactions in the diffusing tracks, which increases the proportion of molecular products at the expense of the radical products. The same trend in yields of radical and molecular products was also found under acidic conditions as well as in the aerated Fricke dosimeter. Unfortunately, comparison with experimental data was rather limited due to the paucity of experimental information for the radiolysis of water by 3H β-particles. Despite this deficiency, our simulations reproduced very well the significant increase observed in the yield of H2 at the microsecond time scale for 3H β-electrons (∼0.6 molecule/100 eV) compared to 60Co γ-rays (0.45 molecule/100 eV). Furthermore, our predicted yield of Fe3+ ions for tritium β-electron radiolysis of Fricke (acidic ferrous sulfate) solutions compared well with the literature values (∼11.9–12.9 molecules/100 eV). In particular, it was shown that the measured yield of the Fricke dosimeter was best reproduced if a single, “mean” or “equivalent” electron energy of ∼7.8 keV was used to mimic the energy deposition by the tritium β-particles (rather than the commonly used mean of ∼5.7 keV that mimics the tritium beta energy spectrum), in full accordance with a recommendation of ICRU Report 17. This decrease in G(Fe3+) compared to the value observed for 60Co γ-rays (15.5 ± 0.2 molecules/100 eV) was mostly due to the decrease in the yield of the escape radical products. Such results, even if fragmentary, corroborate very well with previous experimental and theoretical work, and support a model of tritium β radiolysis mainly driven by the chemical action of short tracks of high local LET.

Ultra-high sensitive study of the identity of β-rays with atomic electrons

Goldhaber and Scharff-Goldhaber have carried out an experiment studying the nature of β-rays emitted by the radioactive nucleus which was based on the Pauli exclusion principle. Davies and Grace have repeated that experiment and reported that less than one captured X-ray was observed for 4 × 10 5 β-rays. But the sensitivities of these experiments were low. The development of experimental techniques including a strong β-ray source and a high resolution X-ray detector enables us to perform an ultra-high sensitive experiment to test the identity of β-rays with atomic electrons. Here we report our experimental result which shows that less than 1.4 × 10 −13 (95% confidence level) of the tritium β-rays stopped in the erbium target are captured into the K shell of these atoms. This limit is about seven orders of magnitude lower than the previous experiment.

Dose-response relationship for the induction of structural chromosome aberrations in human spermatozoa after in vitro exposure to tritium β-rays

The effects of tritium (HTO) β-rays on human spern chromosomes were studied using our interspecific in vitro fertilization system between spermatozoa and zona-free hamster oocytes. Semen samples were treated with media containing 1.53–24.3 mCi/ml HTO for about 80 min. 1290 spermatoza from the controls and 1842 spermatozoa from the irradiated groups were karyotyped. The incidence of spermatozoa with structural chromosome aberrations increased linearly with increasing dosage. Breakage-type aberrations occurred far more frequently than exchange-type. Chromosome-type aberrations appeared far more frequently than chromatid-type. All of these types of aberrations showed linear dose-dependent increases. The RBE values of HTO β-rays relative to X-rays were calculated for the above-mentioned 5 indices, respectively. Their RBE values ranged from 1.89 to 3.00 when the absorbed dose was estimated to be the minimum, whereas the values ranged between 1.04 and 1.65 when the abosorbed dose was estimated to be the maximum.

Application of air proportional counters to a tritium-in-air monitor

A tritium-in-air monitor using air proportional counters as a detector has been devised. The detector consists of two layers of identical multiwire counters, and it operates without using any counting gas other than sampled air. The background due to internal α-rays was eliminated by pulse-height discrimination, and that due to external, penetrating γ-rays and cosmic rays was evaluated from the coincidence counting rate of the two counters. The counting rate by tritium β-rays was obtained from the anticoincidence counting rate N a by subtracting the product of the coincidence counting rate N c and a constant ratio k = N a / N c for the background. The ratio k was verified to be independent of the intensity, energy and incident direction of the γ-rays, though it varied with pressure and humidity of the sampled air. A detection efficiency of about 14% was obtained for tritium β-rays, and a detection limit of less than 1 pCi/cm 3 was obtained with a normal background level and a counting time of 30 s.

環境中におけるトリチウムガスのトリチウム水への転換（文献調査）

The literature on conversion of tritium gas to tritiated water in various environments is reviewed. The conversion mechanisms and the conversion rates are as follows.1. In the oxidation with oxygen and the isotopic exchange with water, tritium β-rays and metal catalyst are effective. The oxidation rate is -0.02%/day at initial tritium concentration ≤10-2Ci/l and -2%/day at 1Ci/l. In the presence of oxygen and water, it is not clear whether the exchange reaction occurs or not because of the small amount of data.2. For biological conversion, soil microorganisms contribute significantly. The conversion rate is greater than 10%/hr. The tritium gas deposition velocity, which includes the uptake rate of tritium gas by soil and the conversion. rate, ranges from 0.0025 to 0.11cm/sec and is influenced by temperature and moisture of the soil.3. Tritium gas is converted to the tritiated water througn the reaction with hydroxyl radical produced by sunlight in the atmosphere.

Windowless air proportional counters for detecting tritium β-rays

This paper describes windowless air proportional counters designed to detect low energy β-rays with high sensitivity which are emitted from tritium deposits. When air is used as the filling gas of proportional counters, usually only low efficiency can be obtained for the detection of β-rays, since primary electrons created in air by a β-ray are lost in the main by electron attachment to oxygen molecules in air before they trigger an electron avalanche. To improve this situation multiwire counters are constructed which possess narrow anode-cathode distances of 1–2 mm. The counters were proved to provide high intrinsic efficiency for tritium β-rays and hence will be expected to be used as a detector of the tritium survey meter.

Radiotracer Studies on Adsorption of Surface Active Substance at Aqueous Surface. II. The Effect of Excess Salt on the Adsorption of Sodium Dodecylsulfate

Abstract The adsorbed amount and the surface tension at the air-solution interface of the solution of tritiated sodium dodecylsulfate in the presence of excess common inorganic salt have been accurately measured at 25°C. The radioactivity of tritium β-rays over the solution was counted with a sheet scintillation counter and the surface tension of the solution was measured by a drop volume method. In the sodium dodecylsulfate solution containing sodium chloride of 0.115 mol/l, the adsorbed amount of dodecylsulfate ions was saturated to give 4.33×10−10 mol/cm2 when the bulk concentration was higher than 5.0×10−4 mol/1000 g solution. In the presence of the excess inorganic salt common to the ionic surfactant in solution the Gibbs adsorption isotherm has been experimentally proved to be valid for n=1. Moreover, it was confirmed that the equation of state for the ionic adsorbed film on the salt-free solution proposed previously is also applicable to the ionic surfactant solution with the excess salt.

Measurement of Adsorbed Amount of Sodium Dodecylsulfate at Gas-Solution Interface by Radiotracer Method Using Tritium-Labeled Compounds

Abstract Sodium dodecyl-2,3-3H,3Hsulfate (SDS) was synthesized from non-radioactive dodecanol, and the adsorbed amount of SDS at the gas-water interface, Γ, was directly measured by the radiotracer method with the use of 2π gas-flow windowless counter and humidified propane as a flow-gas. Because of a very soft nature of tritium β-rays, surface radioactivity is exclusively due to the solute adsorption compared with the large contribution from the bulk of the solution as in the case of 14C or 35S labeled detergents. Therefore the use of 3H labeled compounds enables the determination of the amount of adsorption in high accuracy, even in the region of high concentration beyond the critical micelle concentration (CMC) of SDS solution. However, no reliable reports have appeared as yet on the studies of adsorption of surfactant at gas-solution interface using 3H labeled compounds. Our measurement was carried out under exactly specified conditions, namely using chemically and radiochemically pure sample and under the condition free from evaporation. It was confirmed that Γ increased with the increase of SDS concentration and approached the saturation value of 5.9×10−10 mol/cm2 or 28.2 Å2/molecule at the concentration higher than 6×10−3 mol/1000 g solution and beyond CMC. Furthermore, Γ proved to be independent of the acidity of solution above pH 4, while it increased with increasing acidity below pH 4. The phenomenon is explained by the presence of hydrolytically formed dodecylsulfuric acid whose surface activity is higher than that of SDS.

Consecutive ionic reactions in propylene and cyclopropane

Ion-molecule reactions occurring in propylene and cyclopropane have been studied, up to a pressure of 0.9 torr, inside a mass spectrometric source where ionization is provided by tritium β-rays. Consecutive ion-molecule reactions leading to the formation of polymeric ions up to C13H+25 have been detected. The pattern of reactions appears to be similar in the two isomers.

Consecutive ionic reactions in gaseous butenes

Ion-molecules reactions occurring in the four isomeric butenes have been studied up to a pressure of 0.5 torr inside a mass spectrometric source, where ionization is produced by tritium β-rays. Long-chain processes have been recognized, leading to the formation of polymeric ions. In isobutene, the predominant chain, which involves alkyl carbonium ions, has been followed up to C16H+33. This chain, although with a lower yield, has also been found in the other isomers. Minor chains and branching reactions complicate the mass-spectra at the highest pressures investigated, and lead mainly to CnH+2n–1 and CnH+2n–3 ions. Peculiar to the 2-butenes are extensive chains of odd-electron CnH+2n ions.

Calibration of the Ferrous Sulphate Dosimeter by Ionometric and Calorimetric Methods

THE ferrous sulphate dosimetric system was proposed in 1927 (ref. 1) and has since been extensively investigated and applied in a number of dose estimation problems. Shalek et al.2 showed that reliable and precise calibration factors ( values) have not been well established over a wide range of radiation energies. Individuals or groups of workers have in the past given values for only a few radiation energies with rather poor agreement for the low-energy X-rays; β-rays have also received insufficient coverage in the literature. In the work described here, dosimetric calibrations have been carried out by ionometric, particle counting, and microcalorimetric methods, and values established with a reasonable degree of accuracy from tritium β-rays to 14 MeV X-rays.

Emission Characteristics of ZnS-phosphors Excited by Tritium β-rays

トリチウムガス刺激による螢光体の励起発光について, 2種の螢光体の発光強度特性を測定し, トリチウム量と発光強度の関係を検討した。ガラス管球内壁に螢光体結晶を1層になるよう塗布し, この中にトリチウムガス2キュリーを導入して, トリチウムガス圧に対する発光強度を測定した。トリチウムガス圧に対する発光効率は, ガス圧が上がると次第に減少する。これは, トリチウムガス自体によるβ線の自己吸収として説明され, 実験結果とよく一致する関係を導き出した。この自発光光源は, 標示用光源のほかに, 比較標準光源としても利用できると期待される。