Long-lived Radioactive Nuclides Research Articles

Secondary gas in debris discs released following the decay of long-lived radioactive nuclides, catastrophic, or resurfacing collisions

ABSTRACT Kuiper-like belts of planetesimals orbiting stars other than the Sun are most commonly detected from the thermal emission of small dust produced in collisions. Emission from gas, most notably CO, highlights the cometary nature of these planetesimals. Here, we present models for the release of gas from comet-like bodies in these belts, both due to their thermophysical evolution, most notably the decay of long-lived radioactive nuclides, and collisional evolution, including catastrophic and gentler resurfacing collisions. We show that the rate of gas release is not proportional to the rate of dust release, if non-catastrophic collisions or thermal evolution dominate the release of CO gas. In this case, care must be taken when inferring the composition of comets. Non-catastrophic collisions dominate the gas production at earlier times than catastrophic collisions, depending on the properties of the planetesimal belt. We highlight the importance of the thermal evolution of comets, including crucially the decay of long-lived radioactive nuclides, as a source of CO gas around young (<50 Myr) planetary systems, if large (10–100 km) planetesimals are present.

Activity Treatment of Some Long-Lived Radioactive Nuclides Using Thermal Neutron Incineration

In the present work, the possibility of treating many types of radioactive sources was examined practically. Six types of sealed radioactive sources were selected: 137Cs, 133Ba, 90Sr, 152Eu, 226Ra, and 241Am. The sources were exposed to a neutron flux emitted from 241Am/Be source for 33 days. The results showed a measurable reduction of activity for 226Ra, 241Am, and 152Eu, while the other radionuclides, 137Cs, 133Ba, and 90Sr, showed less response to neutron incineration.

Transient analysis of the CiADS reactor core loaded with nitride fuel

The China initiative Accelerator Driven System (CiADS) is a nuclear energy system that can perform transmutation of long-lived radioactive nuclides in spent fuel. In this article, the CiADS reactor core loaded with nitride fuel was studied by using SAS4A/SASSYS-1 code. The preliminary simulation results of the unprotected transient over power (UTOP) at BOC (beginning of cycle) and EOC (end of cycle) showed that the maximum reactivity insertion to avoid cladding rupture was 500pcm. For unprotected loss of flow (ULOF), the fuel and cladding failures will not happen in all postulated ULOF cases according to our simulations.

High-precision Nuclear Chronometer for the Cosmos

Nuclear chronometers, which predict the ages of the oldest stars by comparing the present and initial abundances of long-lived radioactive nuclides, provide an independent dating technique for the cosmos. The idea of synchronizing Th/X, U/X, and Th/U chronometers can impose stringent constraints on the astrophysical conditions in the r-process simulations, giving rise to the Th-U-X chronometer. It is found that the astrophysical uncertainties of nuclear cosmochronology are significantly reduced from more than ±2 billion years to about 0.3 billion years. The Th-U-X chronometer is then applied to estimate the ages of the six metal-poor stars with observed uranium abundances, and the predicted ages are compatible with the cosmic age of 13.8 billion years predicted from the cosmic microwave background radiation but contradict the cosmic age of 11.4 billion years from the gravitational lens measurement.

Determination of the Activity Inventory in the Structural Components of the Dalat Nuclear Research Reactor for Its Decommissioning Planning

This report presents the methods and calculated results of the activity inventory in the structural components of the Dalat Nuclear Research Reactor (DNRR). These components include the shielding concrete, the reactor tank, and its inside irradiated facilities; the thermal and thermalizing columns; and the horizontal channels. The MCNP5 code with a three-dimensional neutron transport model was used to calculate the neutron flux distribution, neutron energy spectrum at different locations, and activation cross sections of long-lived radioactive nuclides in activated major materials, including heavy concrete, reflection graphite, and aluminum of the reactor. The calculated results of the energy spectrum and activation cross sections of MCNP5 were used in the ORIGEN2.1 point depletion code to calculate the neutron-induced activity of activated materials at different time points by modeling the irradiation history and radioactive decay. Radioactivity of long-lived key activation products such as 41Ca, 60Co, 55Fe, 63Ni, and 152Eu was modeled, and volumes of radioactive waste mainly of ordinary concrete, graphite, and aluminum in the structural components of the reactor were estimated. Experimental results of neutron flux and specific activities of some typical nuclides such as 60Co, 152Eu, 55Fe, and 63Ni in activated aluminum samples showed good agreement with the calculated results. As part of the national regulation requirements, the obtained data have been used to develop the decommissioning plan for the operational DNRR, with an estimation of about 10 years before its permanent shutdown.

Aminomethylpyridine isomers functionalized cellulose microspheres for TcO4-/ReO4- uptake: Structure-properties relationship and their application in different aquatic systems

Technetium-99 (99Tc) is a long-lived radioactive nuclide that poses great threat to environment, hence selective removal of 99Tc from aquatic system is always an issue. Aminomethylpyridine (AMP) equipped with pyridine and amino, is a promising receptor for TcO4- and its surrogate ReO4-, thus it is of interest to explore and understand the structure-properties relationship of ReO4- adsorption related to n-AMP structure that differ in amino methyl position. In this work, three n-AMP functionalized cellulose microspheres (n-AMPR, n = 2, 3, 4) were synthesized and employed for TcO4-/ReO4- uptake. The effect of aminomethyl position on adsorption properties of n-AMPR for ReO4- were investigated and compared. Adsorption kinetics and adsorption isotherm showed that adsorption speed and adsorption capacity were in order of 3-AMPR > 2-AMPR > 4-AMPR. DFT calculation verified that the adsorption of ReO4- by n-AMPR was attributed to electrostatic interaction and hydrogen bonding interaction, the order of adsorption abilities of n-AMPR was due to that steric effect and hydrogen bond collaborated in stabilizing n-AMPR-ReO4- complexes. The column experiments demonstrated that 3-AMPR can be selectively remove ReO4- from simulated groundwater. More importantly, 99Tc column experiments showed that 3-AMPR had a better ability for actual radioactive TcO4-.

Europium as a lodestar: diagnosis of radiogenic heat production in terrestrial exoplanets

Context. Long-lived radioactive nuclides, such as 40K, 232Th, 235U, and 238U, contribute to persistent heat production in the mantle of terrestrial-type planets. As refractory elements, the concentrations of Th and U in a terrestrial exoplanet are implicitly reflected in the photospheric abundances of the stellar host. However, a robust determination of these stellar abundances is difficult in practice owing to the general paucity and weakness of the relevant spectral features. Aims. We draw attention to the refractory, r-process element europium, which may be used as a convenient and practical proxy for the population analysis of radiogenic heating in exoplanetary systems. Methods. As a case study, we present a determination of Eu abundances in the photospheres of α Cen A and B with high-resolution HARPS spectra and a strict line-by-line differential analysis. To first order, the measured Eu abundances can be converted into the abundances of 232Th, 235U, and 238U with observational constraints, while the abundance of 40K is approximated independently with a Galactic chemical evolution model. Results. Our determination shows that europium is depleted with respect to iron by ~0.1 dex and to silicon by ~0.15 dex compared to solar in the two binary components. The loci of α Cen AB at the low-ends of both [Eu/Fe] and [Eu/Si] distributions of a large sample of FGK stars further suggest significantly lower potential of radiogenic heat production in any putative terrestrial-like planet (i.e. α-Cen-Earth) in this system compared to that in rocky planets (including our own Earth) that formed around the majority of these Sun-like stars. Based on our calculations of the radionuclide concentrations in the mantle and assuming the mantle mass to be the same as that of our Earth, we find that the radiogenic heat budget in an α-Cen-Earth is 73.4−6.9+8.3 TW upon its formation and 8.8−1.3+1.7 TW at the present day, which is 23 ± 5% and 54 ± 5% lower than that in the Hadean Earth (94.9 ± 5.5 TW) and in the modern Earth (19.0 ± 1.1 TW), respectively. Conclusions. As a consequence, mantle convection in an α-Cen-Earth is expected to be overall weaker than that of Earth (assuming other conditions are the same), and thus such a planet would be less geologically active, suppressing its long-term potential to recycle its crust and volatiles. With Eu abundances being available for a large sample of Sun-like stars, the proposed approach can extend our ability to predict the nature of other rocky worlds that can be tested by future observations.

Application of multiple γ-ray detection to long-lived radioactive nuclide determination in environmental samples

ABSTRACT Gamma-gamma coincidence measurement utilized in γ-ray spectroscopy experiments is well known to be effective for the improvement of signal-to-noise ratio in a γ-ray spectrum. We study its applicability to the determination of long-lived radioactive nuclides in environmental samples. The γ-ray simulation code Geant 4.10.2 was used. A conventional and effective detector system comprising five Ge detectors was assumed. We took up 38 nuclides which need to be determined for the evaluation of fission product leakage at the nuclear accident in the Fukushima nuclear power plants in Japan. Among them 12 nuclides emit γ-rays and five nuclides of 60Co, 94Nb, 134Cs, 152Eu, and 154Eu can be the objectives of the multiple γ-ray detection methods. The simulation results indicate that the signal-to-noise ratio can be improved by a factor between 9.84 and 283, and the detection limit by a factor between 2.71 and 8.53 relative to the singles measurement, implying that the method can be well applied to the determination of the long-lived radioactive nuclides and will provide a quick and non-destructive analysis method.

Sensitivity of charged particle activation analysis for long-lived radioactive nuclide determination

ABSTRACT Charged Particle Activation Analysis (CPAA) utilizing an 8-MeV proton beam has been studied for determination of 35 long-lived radioactive nuclides. We accumulated the reaction cross section and nuclear decay data by referring to nuclear database supplied by National Nuclear Data Center in Brookhaven National Laboratory. We also calculated the reaction cross sections by using statistical model code ALICE. By using the nuclear data, we have derived determination sensitivity of the radioactive nuclides relative to unit weight and specific radioactivity. The result indicates that several hardly measurable nuclides with long half-lives such as 135Cs, 244Pu, 129I, 126Sn, 93Mo, 107Pd, 236U, 248Cm, and 237Np have high sensitivity. It may be concluded that CPAA can be applied to determination of several long-lived nuclei and will provide a quick and non-destructive analysis method.

Prediction of activation products and resulting dose rates for the magnetic septum in heavy-ion medical accelerator

In high-energy heavy-ion medical accelerator facility, the induced activity due to primary and secondary interactions of the lost beams is the most concerned issue in view point of nuclear safety because long-lived radioactive nuclides cause problems of radiation exposure for staff involved in the repair or maintenance work and in decommissioning the facility. This paper presents activation of a thick magnetic septum by modeling the copper coils which are heavily showered by the lost carbon ion beams with the energy of 430 MeV/u. The activation takes place by all possible interaction modes which include direct interaction of the carbon ion beam with the elements, the interaction of backscattered neutrons from the concrete walls, and isotope production as a result of the decay of other isotopes produced in these interactions. The prediction of the radionuclide inventory and induced activation are performed by using the combination of MCNPX2.7.0 and CINDER’90 codes.

Li2TiO3 powder synthesis by solid-state reaction and pebble fabrication for tritium breeding material

The tritium breeding materials require small particle size to reduce the diffusion distance of generated tritium in the intercrystalline. In addition, the essential resource, especially enriched Li-6, has to be recovered from the used tritium breeding material. For the hands-on operation during the recovery process, the activation level of the used breeder is strictly limited in order to reduce the impurities of long-lived radioactive nuclides in the tritium breeding material. In this study, lithium oxide (Li2O) and titanium dioxide (TiO2) were used as starting materials in the synthesis of Li2TiO3 powder. The starting materials were mixed by wet ball-milling process. The mixed powders were synthesized by heat treatment. The average particle size of synthesized Li2TiO3 powder was approximately 150nm. And, the long-lived radioactive nuclides, such as aluminum (Al) and cobalt (Co), were not accumulated in the synthesized Li2TiO3 powder during the synthesis process. The Li2TiO3 pebbles were fabricated by slurry droplet wetting method using the synthesized Li2TiO3 nano-powder. The particle size, crush load, and porosity of fabricated Li2TiO3 pebbles using the synthesized nano-powder were investigated.

Analysis of Genetic Damage in Lymphocytes of Former Uranium Processing Workers

The frequency of cells containing micronuclei (MN) and the presence of centromeres in these MN were analyzed in lymphocytes of 98 men from Southern Bohemia. Forty-six of them had worked at the uranium processing plant ‘MAPE Mydlovary' which was closed in 1991, and 52 men were controls from the same area. FISH using human pan-centromeric chromosome paint was employed to detect centromere-positive (CEN⁺) and -negative (CEN^-) MN. A total of 1,000 binucleated cells (BNC) per participant were analyzed after cytochalasin B treatment. All BNC with MN (CEN⁺ or CEN^-) were recorded. No differences were found between formerly exposed workers and the control group, neither in the total frequency of cells with MN per 1,000 BNC (mean levels ± SD, 9.1 ± 3.1 and 9.8 ± 2.5, respectively) nor in the percentage of CEN^- MN, which were equal (50 ± 18 and 49 ± 17, respectively). Also, there was no difference between individuals living in the 3 villages closest to the uranium processing plant and those living further away. Considering the fact that effective doses of the workers at MAPE Mydlovary were overall similar to those of former uranium miners in whom higher frequencies of CEN^- MN have been found more than 10 years after they had finished working underground, these results are somewhat surprising. A more detailed analysis of the exposures indicates that uranium miners received a greater percentage of their effective dose from the inhalation of radon and its daughters, whereas uranium processing workers received it from the incorporation of long-lived radioactive nuclides such as uranium. If, as has been suggested before, the higher level of DNA damage in miners is due to induced genomic instability, then this phenomenon may be related to radon exposure rather than exposure to uranium.

Application of neutron activation analysis to micro gram scale of solid samples

An instrumental neutron activation analysis (INAA) procedure for analyzing extremely small samples was developed and applied to two kinds of extraterrestrial samples. A few mg of the Allende meteorite as well as the JB-1 basalt can work well as a reference sample for a relative method. To evaluate the applicability of this INAA procedure, detection limits are presented and compared with the elemental contents in a potential sample to be analyzed. The possibility of reuse of neutron-irradiated samples for mass spectrometry was noted by indicating degree of increase in isotopic abundance for noble gas and long-lived radioactive nuclides.

DRAGON用于嬗变MA的计算研究

长寿命高放废物MA作为核电站乏燃料中的重要组成部分，由于其特殊的物理化学性质，对生态有很强的危害性，一直是各国研究的重要课题之一。目前处理MA最安全有效的方法，是中子嬗变技术，而压水堆又是我国目前投入商业运行的主要的堆型，因此开展压水堆嬗变MA的研究在我国具有重要的意义。本文利用DRAGON程序建立了简化的AP1000燃料组件模型，模拟计算了在可燃毒物内均匀混合MA、在可燃毒物外镀层引入MA两种方式对燃料组件有效增殖因子(keff)、堆芯燃耗、燃料周期以及堆芯寿期的影响。结果表明：MA以上述两种方式添加到可燃毒物中后，燃料组件的燃耗深度会减少，从而延长了堆芯的燃料周期，同时也会对燃料组件的keff值产生影响，燃料组件维持在临界以上的时间也会延长，在一定程度上也会对整个堆芯的寿期产生有利影响。 The Minor Actinides (MA), a sort of long-lived and high-level radioactive nuclides is one of the most important part in the nuclear spent fuel. The MA is harmful to the ecological system because of its peculiar physical and chemical property. How to handle the MA in the spent fuel has always been one of the most important issues in nuclear waste management all over the world. The MA can be transmuted into stable or short-lived nuclides by neutron irradiation, and this is the most effective way to manage those high-level wastes. The PWR is the main reactor type at commercial operation in China, and the MA has a larger capture and fission cross section in the thermal reactor, therefore the study on the transmutation of the MA in the PWR has an important significance in China. This paper has used the DRAGON to build a simplified model of the AP1000 PWR fuel assembly and calculated the impacts on the k-effective of the fuel assembly, the fuel burnup, the fuel cycle and core lifetime when the MA uniformly mixed with the burnable poison or cladded on the burnable poison. The results show that: when the MA is added to the burnable poison in the above two methods, burnup level of the fuel assembly decreases and the fuel cycle of the core lengthens. It also has an impact on the k-effective of the fuel assembly, extending the time of the fuel assembly maintaining above the critical and has a favorable impact on core lifetime.

THE LIGHT CURVE OF SN 1987A REVISITED: CONSTRAINING PRODUCTION MASSES OF RADIOACTIVE NUCLIDES

We revisit the evidence for the contribution of the long-lived radioactive nuclides 44Ti, 55Fe, 56Co, 57Co, and 60Co to the UVOIR light curve of SN 1987A. We show that the V-band luminosity constitutes a roughly constant fraction of the bolometric luminosity between 900 and 1900 days, and we obtain an approximate bolometric light curve out to 4334 days by scaling the late time V-band data by a constant factor where no bolometric light curve data is available. Considering the five most relevant decay chains starting at 44Ti, 55Co, 56Ni, 57Ni, and 60Co, we perform a least squares fit to the constructed composite bolometric light curve. For the nickel isotopes, we obtain best fit values of M(56Ni) = (7.1 +- 0.3) x 10^{-2} Msun and M(57Ni) = (4.1 +- 1.8) x 10^{-3} Msun. Our best fit 44Ti mass is M(44Ti) = (0.55 +- 0.17) x 10^{-4} Msun, which is in disagreement with the much higher (3.1 +- 0.8) x 10^{-4} Msun recently derived from INTEGRAL observations. The associated uncertainties far exceed the best fit values for 55Co and 60Co and, as a result, we only give upper limits on the production masses of M(55Co) < 7.2 x 10^{-3} Msun and M(60Co) < 1.7 x 10^{-4} Msun. Furthermore, we find that the leptonic channels in the decay of 57Co (internal conversion and Auger electrons) are a significant contribution and constitute up to 15.5% of the total luminosity. Consideration of the kinetic energy of these electrons is essential in lowering our best fit nickel isotope production ratio to [57Ni/56Ni]=2.5+-1.1, which is still somewhat high but is in agreement with gamma-ray observations and model predictions.

Studies on Production of Neutrons in the Spallation Reactions Using the Monte Carlo Code MCNPX

The accelerator-driven system (ADS) is an innovative reactor that is being considered as a dedicated high-level-waste burner in a double-strata fuel cycle. (“Double-strata fuel cycle” means a partitioning and transmutation system for long-lived radioactive nuclides.) The target is the physical and functional interface between the accelerator and the subcritical reactor in the ADS, so it is probably the most innovative component of the ADS. Key parameters of ADS are the number of neutrons emitted per incident proton, the neutron multiplicity (n/p), the mean energy deposited in the target for neutrons produced, the neutron energy spectrum, and the spallation product spatial distribution. This paper focuses on the production of neutrons in the spallation reactions. The neutrons produced in the spallation reactions can be characterized by their energy and spatial distributions and multiplicity. The present calculations have been performed using the Monte Carlo code MCNPX. The Monte Carlo simulations have been performed to investigate the neutron multiplicity as a function of incident proton beam energy, as well as a function of target material and target size. Neutron flux distributions at the target surface are calculated and compared with different target materials and proton energies. A comparison of MCNPX with experimental results is made.

Radiation safety management of residual long-lived radioactivity distributed in an inner concrete wall of a medical cyclotron room

The depth distribution of residual long-lived radioactivity in the inner concrete wall of a medical cyclotron room was measured by assaying concrete cores. Seven long-lived radioactive nuclides ((46)Sc, (60)Co, (65)Zn, (134)Cs, (152)Eu, (22)Na and (54)Mn) were identified by gamma-ray spectrometry of the concrete samples. It was confirmed that the gamma-ray-emitting radionuclides induced by thermal neutrons through the (n, γ) reaction are dominant, and that the activity induced by thermal neutrons is greater at a depth of 10-30 cm, rather than at the surface of the concrete, and decreased exponentially beyond a depth of ~40 cm. Although the specific activity at the surface was greater than the clearance level for radioactive waste indicated in IAEA RS-G-1.7, the mean specific activities in the walls and floor were less than the clearance level.

The Galactic Cosmic Ray Intensity over the Past 106–109 Years as Recorded by Cosmogenic Nuclides in Meteorites and Terrestrial Samples

Concentrations of stable and radioactive nuclides produced by cosmic ray particles in meteorites allow us to track the long term average of the primary flux of galactic cosmic rays (GCR). During the past ∼10 Ma, the average GCR flux remained constant over timescales of hundreds of thousands to millions of years, and, if corrected for known variations in solar modulation, also during the past several years to hundreds of years. Because the cosmic ray concentrations in meteorites represent integral signals, it is difficult to assess the limits of uncertainty of this statement, but they are larger than the often quoted analytical and model uncertainties of some 30%. Time series of concentrations of the radionuclide 10Be in terrestrial samples strengthen the conclusions drawn from meteorite studies, indicating that the GCR intensity on a ∼0.5 million year scale has remained constant within some ±10% during the past ∼10 million years. The very long-lived radioactive nuclide 40K allows to assess the GCR flux over about the past one billion years. The flux over the past few million years has been the same as the longer-term average in the past 0.5–1 billion years within a factor of ∼1.5. However, newer data do not confirm a long-held belief that the flux in the past few million years has been higher by some 30–50% than the very long term average. Neither does our analysis confirm a hypothesis that the iron meteorite data indicate a ∼150 million year periodicity in the cosmic ray flux, possibly related to variations in the long-term terrestrial climate.

A photo-neutron source for time-of-flight measurements at the radiation source ELBE

The radiation source ELBE ( Electron Linear accelerator with high Brilliance and low Emittance) at Forschungszentrum Dresden-Rossendorf uses the high brilliance electron beam from a superconducting LINAC to produce various secondary beams. Electron beam intensities of up to I e - = 1 mA at energies up to E e - = 40 MeV can be delivered with a pulse width of less than 10 ps. With these parameters the electron beam allows to generate sub-ns neutron pulses by stopping the electrons in a heavy (high atomic number) radiator and producing neutrons by bremsstrahlung photons through (γ, n)-reactions. In order to enable measurements of energy resolved neutron cross sections like (n, γ), (n, n′γ), (n, p), (n, α), and (n, f) at a time-of-flight arrangement with a short flight path of only a few meters it is necessary to keep the volume of the radiator for neutron production as small as possible to avoid multiple scattering of the emerging neutrons, which would broaden the neutron pulses. It is the primary physics objective of this neutron source to measure neutron cross sections firstly for construction materials of fusion and fission reactors, for which it is important to select materials with low activation cross sections, and secondly for the handling of waste from such reactors, especially in order to find processes which transmute long-lived radioactive nuclides into short-lived and finally stable ones. Furthermore experiments can be performed which address problems of nuclear astrophysics. The power deposition of the electron beam in the small neutron radiator volume of 1 cm 3 reaches up to 25 kW. This is such a high power density that any solid high Z number material would melt. Therefore, the neutron radiator consists of liquid lead circulated by an electromagnetic pump. The heating power introduced by the electrons is removed through the heat exchanger in the liquid lead circuit. Typical flow velocities of the lead are between 1 m/s and 5 m/s in the radiator section. From the thermal and mechanical point of view, molybdenum turned out to be the most suited target wall material in the region where the electrons impinge on the neutron radiator. To reduce the radiation background at the measurement position, the neutrons are decoupled from the radiator at an angle of about 90° with respect to the impinging electrons. Particle transport calculations using the Monte Carlo codes MCNP and FLUKA predict a neutron source strength in the range of 7.9 × 10 12 n / s to 2.7 × 10 13 n / s for electron energies between E e - = 20 and 40 MeV. At the measuring place 3.9 m away from the radiator, a neutron flux of about 1.5 × 10 7 n / ( cm 2 s ) will be obtained. The short beam pulses allow for a neutron energy resolution of better than 1% for neutron energies between E n = 50 keV and 5 MeV. The usable energies range up to about 10 MeV.

Long-lived activation products in TRIGA Mark II research reactor concrete shield: calculation and experiment

In this paper, a process of long-lived activity determination in research reactor concrete shielding is presented. The described process is a combination of experiment and calculations. Samples of original heavy reactor concrete containing mineral barite were irradiated inside the reactor shielding to measure its long-lived induced radioactivity. The most active long-lived (γ emitting) radioactive nuclides in the concrete were found to be 133Ba, 60Co and 152Eu. Neutron flux, activation rates and concrete activity were calculated for actual shield geometry for different irradiation and cooling times using TORT and ORIGEN codes. Experimental results of flux and activity measurements showed good agreement with the results of calculations. Volume of activated concrete waste after reactor decommissioning was estimated for particular case of Jožef Stefan Institute TRIGA reactor. It was observed that the clearance levels of some important long-lived isotopes typical for barite concrete (e.g. 133Ba, 41Ca) are not included in the IAEA and EU basic safety standards.