Long-lived Radioactive Nuclei Research Articles

Threshold effects in the 10B(p,α)7Be, 12C(p,γ)13N and 14N(p,γ)15O reactions

The typical energy range for charge particle interactions in stellar plasmas corresponds to a few 10s or 100s of keV. At these low energies, the cross sections are so vanishingly small that they cannot be measured directly with accelerator based experimental techniques. Thus, indirect studies of the compound structure near the threshold are used in the framework of reaction models to complement the direct data in order to extrapolate the cross section into the low energy regime. However, at the extremely small cross sections of interest, there maybe other quantum effects that modify the such extracted cross section. These may result from additional nuclear interactions associated with the threshold itself or could be due to other processes, such as electron screening. Measurements in plasma environments like at the OMEGA or National Ignition Facility facilities offer an entirely new set of experimental conditions for studying these types of reactions, often directly at the energies of interest. In this paper, we examine three reaction, 10B(p,α)7Be, 12C(p,γ)13N and 14N(p,γ)15O, which have all been measured at very low energies using accelerator based methods. All three reactions produce relatively long-lived radioactive nuclei, which can be collected and analyzed at plasma facilities using a variety of collection and identification techniques.

Direct measurement of the resonance strengths and branching ratios of low-energy (p, γ) reactions on Mg isotopes * *Supported by the National Natural Science Foundation of China (11490563, 11961141003) and the Continuous Basic Scientific Research Project (WDJC-2019-13)

Proton capture reactions on Mg isotopes are significant in the Mg-Al cycle in stellar H-burning. In particular, the resonance strengths and branching ratios of low-energy resonances in 25Mg( )26Al reactions determine the production of 26Al, which is one of the most important long-lived radioactive nuclei in nuclear astrophysics. In this article, we report our first experiment using the intense proton beam of approximately 2 mA provided by the JUNA accelerator ground laboratory and a new technique that can minimize the composition change of targets under intense beam irradiation. The resonance strengths and branching ratios of E = 214, 304, and 326 keV resonances in the reactions of 24Mg( )25Al, 25Mg( )26Al, and 26Mg( )27Al, respectively, were measured with high accuracy. The success of this experiment provides a good calibration for the nuclear astrophysical experiment at the Jinping underground laboratory.

Statistical neutron capture in the limit of low nuclear level density

A major barrier in the study of neutron-induced nuclear reactions is the impossibility of direct measurements with short-lived radioactive isotopes. For these exotic nuclei, theoretical inputs such as the photon strength function (PSF) are poorly constrained. At Los Alamos National Laboratory, the Detector for Advanced Neutron Capture Experiments (DANCE) provides direct measurements of $\ensuremath{\gamma}$-ray cascades following neutron capture reactions on stable or long-lived radioactive nuclei. While Hauser-Feshbach calculations can provide reasonable predictions for neutron capture on heavy nuclei, their application to neutron-rich light nuclei with low nuclear level densities and low neutron separation energies is questionable. In this paper, we report on the $\ensuremath{\gamma}$-ray spectra from individual neutron resonances from the $^{96}\mathrm{Zr}(n,\ensuremath{\gamma})$ reaction, with an emphasis on the sensitivity of of the $\ensuremath{\gamma}$-ray spectra to different PSF models. The comparison of the measured $\ensuremath{\gamma}$-ray spectra with predicted spectra does not support the addition of a low-energy enhancement of the size reported in many charged-particle reaction measurements, but the sensitivity of the $\ensuremath{\gamma}$-ray spectra to different PSF models is weak.

Solar r-process-constrained actinide production in neutrino-driven winds of supernovae

Long-lived radioactive nuclei play an important role as nucleo-cosmochronometers and as cosmic tracers of nucleosynthetic source activity. In particular nuclei in the actinide region like thorium, uranium, and plutonium can testify to the enrichment of an environment by the still enigmatic astrophysical sources that are responsible for the production of neutron-rich nuclei by the rapid neutron-capture process (r-process). Supernovae and merging neutron-star (NS) or NS-black hole binaries are considered as most likely sources of the r-nuclei. But arguments in favour of one or the other or both are indirect and make use of assumptions; they are based on theoretical models with remaining simplifications and shortcomings. An unambiguous observational determination of a production event is still missing. In order to facilitate searches in this direction, e.g.\ by looking for radioactive tracers in stellar envelopes, the interstellar medium or terrestrial reservoirs, we provide improved theoretical estimates and corresponding uncertainty ranges for the actinide production ($^{232}$Th, $^{235,236,238}$U, $^{237}$Np, $^{244}$Pu, and $^{247}$Cm) in neutrino-driven winds of core-collapse supernovae. Since state-of-the-art supernova models do not yield r-process viable conditions ---but still lack, for example, the effects of strong magnetic fields--- we base our investigation on a simple analytical, Newtonian, adiabatic and steady-state wind model and consider the superposition of a large number of contributing components, whose nucleosynthesis-relevant parameters (mass weight, entropy, expansion time scale, and neutron excess) are constrained by the assumption that the integrated wind nucleosynthesis closely reproduces the solar system distribution of r-process elements. We also test the influence of uncertain nuclear physics.

DISTRIBUTIONS OF LONG-LIVED RADIOACTIVE NUCLEI PROVIDED BY STAR-FORMING ENVIRONMENTS

Radioactive nuclei play an important role in planetary evolution by providing an internal heat source, which affects planetary structure and helps facilitate plate tectonics. A minimum level of nuclear activity is thought to be necessary --- but not sufficient --- for planets to be habitable. Extending previous work that focused on short-lived nuclei, this paper considers the delivery of long-lived radioactive nuclei to circumstellar disks in star forming regions. Although the long-lived nuclear species are always present, their abundances can be enhanced through multiple mechanisms. Most stars form in embedded cluster environments, so that disks can be enriched directly by intercepting ejecta from supernovae within the birth clusters. In addition, molecular clouds often provide multiple episodes of star formation, so that nuclear abundances can accumulate within the cloud; subsequent generations of stars can thus receive elevated levels of radioactive nuclei through this distributed enrichment scenario. This paper calculates the distribution of additional enrichment for $^{40}$K, the most abundant of the long-lived radioactive nuclei. We find that distributed enrichment is more effective than direct enrichment. For the latter mechanism, ideal conditions lead to about 1 in 200 solar systems being directly enriched in $^{40}$K at the level inferred for the early solar nebula (thereby doubling the abundance). For distributed enrichment from adjacent clusters, about 1 in 80 solar systems are enriched at the same level. Distributed enrichment over the entire molecular cloud is more uncertain, but can be even more effective.

Development of resonance ionization in a supersonic gas-jet for studies of short-lived and long-lived radioactive nuclei

High-resolution resonance ionization spectroscopy (RIS) is required for laser spectroscopy and trace analysis of short-lived and long-lived radioactive nuclei. We have proposed high-resolution resonance ionization spectroscopy in a gas jet combined with a narrow band-width injection-locked Ti:Sapphire laser. Resonance ionization of stable 93Nb in a gas jet was demonstrated using a broad bandwidth Ti:Sapphire laser. In addition, a setup for high-resolution RIS in a gas-jet was designed using numerical simulations of the gas-jet conditions based on computational fluid dynamics.

Nucleosynthesis of Heavy Elements in Supernova Explosions and Nucleocosmochronology

We review recent progress in theoretical studies of r-process nucleosynthesis in supernova (SN) explosions. We found suitable physical conditions for a successful r-process and that particle and nuclear reactions on light neutron-rich nuclei as well as heavy nuclei play the significant roles in primary r-process. We also review astronomical observations of the neutron-capture elements detected in extremely metal-deficient halo stars. These stars are presumed to be the second generation, and their chemical composition consists of freshly synthesized heavy elements in the first generation exploding SNe in the Galaxy. We discuss cosmochronology by the use of long-lived radioactive nuclei like 232Th (half life τ1/2 = 14.05 Gyr) and 238U (half life τ1/2 = 4.468 Gyr). We found theoretical reason for the universality of r-process abundance pattern for 56 ≤ Z ≤ 70, but that it is not simply extended to 70 < Z including actinides. We propose that the U/Th cosmochronometer is a roburst cosmic clock although Th/Eu is not reliable.

Transmutation of239Pu and other nuclides using spallation neutrons produced by relativistic protons reacting with massive U- and Pb-targets

SummaryExperimental studies on the transmutation of some long-lived radioactive waste nuclei, such as129I,237Np, and239Pu, as well as on natural uranium and lanthanum were carried out at the Synchrophastron of the Laboratory for High Energies at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. The radioactive targets (I, Np and Pu) were contained in weld-sealed aluminium holders produced by the Institute of Physics and Power Engineering, Obninsk, Russia. Spallation neutrons were produced by relativistic protons with energies in the range of 0.5 GeV≤Ep≤1.5 GeV interacting with 20 cm long uranium or lead target stacks. The metallic targets were surrounded by 6 cm thick paraffin moderators. The uranium and lanthanum samples were positioned on the outside of the moderator surface and typically contained approximately 0.5 to 1.0 gram of uranium or lanthanum. The highest fluence of spallation neutrons was observed in the region of 5 to 10 cm downstream the entrance of the primary beam into the metallic target, rather independent of the target material or the proton energy. The results obtained by nuclear chemistry methods were supplemented by SSNTD (Solid State Nuclear Track Detector) studies. Consistent and systematic results ofB-values and spectral distributions for neutrons have been found. From the experimentally observed transmutation rates one can extrapolate that in a subcritical nuclear power assembly (or "energy amplifier") using a 10 mA proton beam of 1 GeV onto a Pb-target as used here, one can transmute within one month in one gram of sample about 3 mg129I, 21 mg237Np, 3.3 mg238U, and 200 mg239Pu. Rather similar results have been found by another group for129I and239Pu. Observations show that the transmutation rates increase almost linearly with the proton energy in the energy interval 0.5 GeV up to 7.4 GeV. These findings are largely confirmed by model calculations using the LAHET- and DCM/CEM-codes.

Calculations of Proton Induced Reactions on Lead in Energy Region up to 300 MeV

Various cross sections of the p+natPb reaction are calculated in the 5- to 300-MeV energy region based on nuclear reaction models, i.e., the optical, evaporation, and exciton models, and direct reaction theory. Comparison of the calculated results with the experimental data shows that our calculations are quite reasonable. Excitation functions of some long-lived radioactive nuclei and neutron multiplicity are predicted. For medium-energy proton-induced natPb fission, an empirical formula is developed.

Setting new constraints on the age of the Universe

There are three independent techniques for determining the age of the Universe: via cosmochronology of long-lived radioactive nuclei, via stellar modelling and population synthesis of the oldest stellar populations, and, most recently, via the precision cosmology that has become feasible with the mapping of the acoustic peaks in the cosmic microwave background. We demonstrate that all three methods give completely consistent results, and enable us to set rigorous bounds on the maximum and minimum ages that are allowed for the Universe. We present new constraints on the age of the Universe by performing a multiband colour analysis of bright cluster ellipticals over a large redshift range (0.3<z<0.9), which allows us to infer the ages of their stellar populations over a wide range of possible formation redshifts and metallicities. Applying a prior to Hubble's constant of H-0 = 72 +/-8 km s(-1) Mpc(-1) we find the age of the Universe to be 13.0(-2.0)(+3.0) Gyr (1 sigma), in agreement with the estimates from Type Ia supernovae, as well as with the latest uranium decay estimates, which yield an age for the Milky Way of 12.5 +/-3 Gyr. If we combine the results from cluster ellipticals with the analysis of the angular power spectrum of the cosmic microwave background and with the observations of Type Ia supernovae at high redshift, we find a similar age: 13.2(-0.8)(+1.2) Gyr. Without the assumption of any priors, universes older than 18 Gyr are ruled out by the data at the 90 per cent confidence level.

Recent results of radioactive beam experiments at ATLAS

Various beams of short- and long-lived radioactive nuclei have recently been produced at the ATLAS accelerator at Argonne National Laboratory, using either the so-called In-Flight or the Two-Accelerator method. With these beams many questions which are of interest in the areas of nuclear structure and nuclear astrophysics can be addressed. In this contribution first results from experiments with 44Ti (T 1 2 60y) and 17F (T 1 2 64s) beams are discussed, which are of interest to the nucleosynthesis in supernovae and X-ray bursts.

Nucleocosmochronology

Nucleocosmochronology is the use of the abundances of radioactive nuclear species and their radiogenic decay daughters to establish the finite age of the elements and the time scale for their formation. The long-lived radioactive nuclei 232Th, 235U, and 238U, formed in the astrophysical r-process of nucleosynthesis, play an important role in this regard. Observational studies of the heavy element abundance patterns in metal deficient stars have provided critical input: (1) the presence of r-process abundances in the oldest stars provides evidence that we are indeed dating the entire epoch of stellar nucleosynthesis in the Galaxy, and (2) the extraordinary agreement of the abundance pattern characteristic of low metallicity stars with the r-process abundance distribution in solar system matter confirms the robustness of the r-process mechanism for the production of nuclei of mass A≳140. We discuss the implications of these abundance studies for nucleocosmochronology and briefly survey recent age determinations.

Theoretical Calculations of Proton Reaction Cross Sections in a Lead Target with Energy Ep ≤ 300 MeV

Various cross sections of the p+natPb reaction are calculated in the 5- to 300-MeV energy region based on nuclear reaction models, i.e., the optical, evaporation, and exciton models, and direct reaction theory. Comparison of the calculated results with the experimental data shows that our calculations are quite reasonable. Excitation functions of some long-lived radioactive nuclei and neutron multiplicity are predicted. For medium-energy, proton-induced natPb fission, an empirical formula is developed.

Cosmic rays from the Galactic center - Electron and positron fluxes in a modified model

view Abstract Citations (1) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Cosmic Rays from the Galactic Center: Electron and Positron Fluxes in a Modified Model Wibig, Tadeusz Abstract A model of cosmic-ray (CR) production applied to the Galactic center to describe secondary-to-primary ratios and Galactic gradient data is extended to describe electron and positron fluxes. Parameters from the model by Said et al. (1981) modified by Wibig (1991) are fitted to experimental CR data to propose a modified CR propagation mechanism. Specific attention is given to the assumption that particles remain in the galactic halo for a long time. Assumptions are used to predict the proton spectrum and the primary electron spectrum, and the extra electron-positron component is assumed to be a power law to reconcile the two spectra. Observational data on the fraction of long-lived radioactive nuclei support the analytical predictions, and the results do not change if the CRs are produced around the Galactic center and not just in the center. Publication: The Astrophysical Journal Pub Date: October 1992 DOI: 10.1086/171874 Bibcode: 1992ApJ...398..507W Keywords: Electrons; Galactic Nuclei; Milky Way Galaxy; Positrons; Primary Cosmic Rays; Secondary Cosmic Rays; Computational Astrophysics; Interstellar Magnetic Fields; Radioactive Isotopes; Space Radiation; ELEMENTARY PARTICLES; GALAXY: CENTER; ISM: COSMIC RAYS full text sources ADS | data products SIMBAD (1)

Explosive nucleosynthesis in SN 1987A. II - Composition, radioactivities, and the neutron star mass

The 20 solar mass model of Nomoto and Hashimoto (1988) is utilized with a 6 solar mass. He core is used to perform explosive nucleosynthesis calculations. The employed explosion energy of 10 to the 51st ergs lies within the uncertainty range inferred from the bolometric light curve. The nucleosynthesis processes and their burning products are discussed in detail. The results are compared with abundances from IR observations of SN 1987A and the average nucleosynthesis expected for Type II supernovae in Galactic chemical evolution. The abundances of long-lived radioactive nuclei and their importance for the late light curve and gamma-ray observations are predicted. The position of the mass cut between the neutron star and the ejecta is deduced from the total amount of ejected Ni-56. This requires a neutron star with a baryonic mass of 1.6 + or - 0.045 solar mass, which corresponds to a gravitational mass of 1.43 + or - 0.05 solar mass after subtracting the binding energy of a nonrotating neutron star.

Fusion reactor materials to minimize long-lived radioactive waste

Abstract This paper examines, in relation to the norms and practices now applied in different countries, the prospects for the storage and disposal of the radioactive wastes to be expected from future fusion power plants. There is at present no regulation in Europe that defines the treatment and the allowed concentration of the possible long-lived nuclides of waste to be disposed of in shallow land burial. There are a few sites of this type, each one having different acceptability criteria. In the USA the norms applicable are those of the Code of Federal Regulation (10CFR61) which could be logically and consistently extrapolated to fusion materials. The knowledge of the acceptability index of the elements appears to be quite useful in improving the composition of fusion reactor materials, in particular for the first wall and the breeding blanket. These indices, or waste disposal ratings, have been computed either with reference to the UK site norms, which are at present the most restrictive in Europe, or with reference to be extrapolated US norms. The conclusion is relatively optimistic in the second case and less so in the first. The state of the activation cross sections is also examined and recent progress, particularly in the data needed for long-lived radioactive nuclei, is reported.

Nuclear gamma-rays from energetic particle interactions

view Abstract Citations (268) References (118) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Nuclear gamma-rays from energetic particle interactions. Ramaty, R. ; Kozlovsky, B. ; Lingenfelter, R. E. Abstract Gamma-ray line emission due to nuclear deexcitation following energetic particle interactions with abundant constituents of cosmic matter is studied. Reactions induced by energetic protons and alpha particles in ambient nuclei (He, C, N, O, Ne, Mg, Al, Si, S, Ca, and Fe) are considered, along with inverse reactions in which energetic nuclei interact with ambient H and He. Line-production cross sections are evaluated by analyzing a large body of laboratory nuclear data. Both prompt gamma rays, produced by direct excitation of nuclear levels and by spallation reactions that leave the secondary nucleus in an excited state, and delayed emission from long-lived radioactive nuclei also produced in the energetic particle reactions are investigated. A line list is provided, and the shapes of the gamma-ray lines are determined. Gamma-ray line production in the interstellar medium is evaluated in detail. Publication: The Astrophysical Journal Supplement Series Pub Date: July 1979 DOI: 10.1086/190596 Bibcode: 1979ApJS...40..487R Keywords: Energetic Particles; Gamma Ray Astronomy; Nuclear Reactions; Particle Interactions; Astronomical Spectroscopy; Cross Sections; Gamma Ray Spectra; Interstellar Matter; Line Spectra; Photons; Protons; Solar Radiation; Space Radiation; Galactic Center:Gamma Rays; Gamma Rays:Interstellar Matter; Gamma Rays:Nuclear Reactions full text sources ADS |