Short-lived Nuclei Research Articles

Actinide transmutation properties of thermal and fast fission reactors including multiple recycling

To decrease the long-term radiotoxicity risk from nuclear waste, investigations were performed to transmute long-lived radwaste nuclides: actinides, in particular isotopes of Pu, Np, Am, and fission products, to short-lived or stable nuclei. First, from neutron spectra and resulting neutron reaction cross-sections, transmutation half-lives, and fission-to-capture ratios, the priority of fast over thermal reactors with respect to transmutation is derived. Second, transmutation calculations for a park of PWRs and fast CAPRA burner reactors show the ability of CAPRAs to reduce Pu and minor actinides with homogeneous multiple recycling of Pu and Np and heterogeneous multiple recycling of Am. Accumulation of 1st generation PWR-Pu is stopped. Because of Pu deterioration, reactivity requirements and Pu≤45 % in (U,Pu)-MOX, 58 % of `bad quality' and proliferation-resistant Pu from reprocessing of spent CAPRA fuel has to be excluded from recycling. Homogeneous 5 % admixing of Np results in a constant-level Np park inventory. The relatively large consumption of Am is counteracted by a significant in-core production of Am, resulting in a net increase of park Am.

Interdisciplinary regions of nuclear physics studied by use of spin-polarized short-lived nuclei

The creation of nuclear spin polarization is the first step for correlation-type experiments in which correlations between the polarization and out going radiations is detected. Of particular interest is to extract clear non-nucleonic degrees of freedom and to test the conservation laws in weak nuclear currents.

Measurement of (n, p) cross-sections for shortlived products by 13.4–14.9 MeV neutrons

The 28 (n, p) activation cross-sections that lead to short-lived nuclei with half-lives of between 20s and 18 min were measured in the energy range 13.4–14.9 MeV using an activation method. The measured isotopes were 19F, 28,29Si, 37Cl, 50Ti, 52,53,54Cr, 60,62Ni, 66,68Zn, 86,88Sr, 97Mo, 101,102,104Ru, 104,105, 108Pd, 107Ag, 116Cd and 119,120Sn. The intense 14 MeV neutron source facility (OKTAVIAN) at Osaka University was used for irradiation. The γ-rays emitted from the irradiated samples were measured with high-purity germanium (HPGe) detectors. All cross-section values were obtained relative to the standard reaction cross-section of 27Al (n, α) 24Na. The present results were compared with previous data and the evaluated data of JENDL-3 and ENDF/B-VI. Ten reactions were obtained at multi-point-energies for the first time. By using intense neutron sources and making careful corrections, reliable results could be obtained. Most of the data obtained previously at multi-point-energies have shown reasonable agreement within 25%. In comparing 10 experimental reactions with the evaluated data, significant discrepancies of more than 25% were seen for three reactions.

TOF-Mass-Measurements of exotic nuclei at the ESR of the GSI

We plan to measure masses of very shortlived exotic nuclei far from β-stability by using the Experimental Storage Ring (ESR) of the GSI as an energy isochronous Time-of-Flight (TOF) mass-spectrometer which requires a special ion-optical setting of the quadrupoles in the ESR. Via projectile fragmentation a large variety of exotic nuclei can be produced. which can be separated in flight by the Fragment Separator (FRS) prior to being injected into the ESR. A special time-pick-off-detector has been developed, which uses secondary electron emission from a thin foil, which is penetrated by the ions under investigation. This detector has been designed for use in the ESR-vacuum of 10 −11 mbar and has an intrinsic time-resolution of ≈ 85ps. Also a Time Recording System (TRS) with a time-jitter of only ≈ 50ps has been build. The TRS is capable of recording time-marks for a few ions over a large number (> 500) of turns.

A five-HPGe detector system for γ−γ angular correlation measurements for mass-separated short-lived nuclei

A multiple-detector system for γ−γ angular correlation measurements has been constructed to study low-spin states populated via the β-decay of mass-separated short-lived nuclei using an isotope separator on-line. The system consists of five-HPGe detectors which are configured at fixed angles to provide ten correlation angles of 90°, 100°, 110°, 120°, 130°, 130°, 140°, 150°, 160° and 170° simultaneously, and with short source-to-detector distance to enlarge the detection efficiencies. The performance of the system was studied with an 152Eu source in off-line experiments. The contribution of finite solid angle of detectors, random coincidences and Compton-scattered γ-rays were appropriately corrected. Difference in the coincidence efficiency among various detector pairs was experimentally evaluated, and it was concluded that this difference was almost negligible in this system. In an on-line experiment, low-spin states in 126Ba populated via the β +-decay of 126La were investigated with this system.

Spallation reactions in27Aland56Feinduced by 800 MeV protons

Spallation of ${}^{27}\mathrm{Al}$ and ${}^{56}\mathrm{Fe}$ by 800 MeV protons was investigated at the WNR facility of the Los Alamos National Laboratory. Production cross sections for a considerable number of residual nuclei were determined for both targets by use of three different methods. Because of the specific time structure of the WNR beams it was possible to observe both the prompt \ensuremath{\gamma} radiation resulting from the final stage of the spallation reaction and the \ensuremath{\gamma} radiation due to the decay of short-lived residual nuclei by delayed \ensuremath{\gamma}-ray spectroscopy. The activity of long-lived residual nuclei was measured several weeks after the irradiation with a calibrated high-purity Ge \ensuremath{\gamma}-ray detector. In the prompt \ensuremath{\gamma}-ray spectrum it was possible to observe the transitions from the first excited ${2}^{+}$ state to the ground state for all even-even nuclei strongly populated in the spallation reactions and, from these data, to deduce the production cross sections of these mostly stable nuclei in addition to the short- and long-lived residual nuclei mentioned before. In this way production cross sections for 36 nuclides from the proton interactions with ${}^{56}\mathrm{Fe}$ and for 12 nuclides in the case of ${}^{27}\mathrm{Al}$ could be measured; in addition, meaningful upper limits were obtained for a number of further nuclides in both cases. The results are in reasonable agreement with previous measurements obtained by different methods; for a number of nuclides, production cross sections were determined for the first time. The present data as well as the results of all previous measurements are compared with the predictions of the semiempirical systematics and with quantum molecular dynamics calculations.

Gamma-ray solid laser: ion-optical system for fasthigh-quality focusing of powerful non-paraxial ion beams of largeformat enriched with excited nuclei

An ion-optical system (IOS) for fast high-quality focusing of powerful paraxial ion beams of large format is suggested. Such beams could be enriched in excited short-lived (10-4-10-6 s) laser-active nuclei (ELAN). To increase the beam power, ions are collected from the visible surface (10-104 cm2) of an intermediate target (converter). The full converter surface is enhanced by a factor of 102-104 by a special micro-relief and achieves 103-107 m2. The toms containing ELAN are created in the converter by a powerful radiation source using neutrons, γ quanta, charged particles, etc. Those ELAN atoms are emitted from the converter surface and selectively ionized by a dye laser just above the surface. Using a specially chosen emitter (converter) shape, a paraxial ion beam is formed. This is due to the micro-relief structure of the emitter surface, its high-quality orientation, and cylindrical (instead of spherical) ion optics. In the vicinity of an active medium (AM) for a gamma-ray laser, the ions are decelerated so that they can penetrate only into 1-3 outer layers of the host matrix, e.g., diamond. This makes heating of the AM by the ion beam negligible in comparison to self-heating due to internal conversion. Analytical and numerical estimation of the IOS aberrations have shown that the compression of the ion beam exceeds105-106, and that a considerable part (10%) of the ELAN reach the AM in a time as short as10-7 s. This ensures the rapid and controllable deposition of ELAN into an AM within a gamma-laser system based on existing techniques without using nuclear explosions.

Beams of short lived nuclei produced by selective laser ionization in a gas cell

An on-line laser ion source has been developed for the production of elemental and isobaric pure beams of radioactive ions. It is based on selective resonant laser ionization of nuclear reaction products thermalized and neutralized in a noble gas at high pressure. The ion source has been tested in a wide range of recoil energies going from 1.3 MeV to ∼ 90 MeV. Efficient schemes of two step laser ionization through autoionizing states have been found for nickel, cobalt and rhodium. Residence times of the reaction products in a gas cell have been measured for helium and argon as buffer gas. Elementally pure beams of 54,55Ni and 54Co, produced in a light-ion induced fusion-evaporation reaction, and of 113Rh, produced in proton-induced fission of 238U, were obtained. An efficiency of the ion source of 6.6% for fusion reactions and of 0.22% for fission reactions has been obtained. A selectivity of the ion source of 300 for fusion and 50 for fission reactions has been achieved.

Molecular Dynamics Study of the Freezing of Clusters of Chalcogen Hexafluorides

Because knowledge about homogeneous nucleation in supercooled molecular liquids is largely indirect, a molecular dynamics investigation of the freezing of liquid clusters was initiated to furnish a plausible account of the molecular behavior involved. Results of the first stage of research are reported. Clusters with free boundaries were chosen instead of bulk systems in order to avoid the interference introduced by periodic boundary conditions. Systems of 150-molecule clusters of SF6, SeF6, and TeF6 were examined. Analyses of Voronoi polyhedra in the warm systems prepared confirmed that the clusters were genuinely liquid, containing no crystalline seeds capable of initiating freezing. As the clusters cooled, random structural fluctuations created short-lived embryonic nuclei. At deeper supercooling, a nucleus of critical size ultimately appeared in each cluster and freezing began. When cooled at a rate of 2 × 1010 K/s or more slowly, all clusters froze to bcc single crystals and these transformed to monoclinic single crystals upon further cooling. Voronoi polyhedra gave much more delicate and definitive analyses of the presence of solid nuclei than did other common indices such as the Lindemann δ. The polyhedra, however, were quite blind to the solid-state transition to monoclinic. It was found that the threshold value of the Lindemann index for freezing decreased systematically with increasing size of the molecules. The reported failure of similar systems to freeze in prior molecular dynamics simulations may have been due to the faster cooling rates adopted.

ISOLTRAP: a tandem Penning trap system for accurate on-line mass determination of short-lived isotopes

The tandem Penning trap mass spectrometer ISOLTRAP has been set up at the on-line mass separator ISOLDE at CERN/Geneva for accurate mass measurements of short-lived nuclei with T 1 2 ≥ 1 s . The mass measurement is performed via the determination of the cyclotron frequency of an ion in a magnetic field. The design of the spectrometer matches the particular requirements for on-line mass measurements on short-lived isotopes. With the ISOLTRAP spectrometer masses of more than 70 radioactive nuclei have so far been determined with resolving powers exceeding one million and an accuracy of typically 10 −7.

Physics Characteristics of Nuclear Power Systems with Reduced Long-Term Radioactivity Risk

This paper considers ways to approach radiologically clean nuclear power (RCNP), i.e., an energy production technology based on a natural nuclear fuel transmutation with a simultaneous fission product transformation into stable or short-lived nuclei. Ways to limit the long-term radiotoxicity accumulation in the fuel cycle, both related to actinides and to long-lived fission products, and to limit the radiological risk related to the in-core nuclear fuel inventory are defined. Criteria and guidelines are defined in that perspective, and they are applied to the evaluation of different options such as open or closed fuel cycles, burnup extension, type of neutron spectrum, use of thorium or uranium fuel cycle, and subcriticality in the multiplying region. Meanwhile, understanding the physics implications of the requirements for an RCNP reveals that there are promising ways to improve current systems. Ideal systems, which are defined to exploit all the desirable physics features to make them better in terms of environmental impact, show potential advantages, but they are never so spectacular--and certainly are to be taken extremely carefully--in view of the need of complementary technological feasibility and cost and safety analyses. Moreover, the problem of radiation doses, which is essential for fuel cycle management and could appreciablymore » influence the choice of the appropriate fuel cycle, have not yet been taken into account. This last aspect and more specific safety analyses, together with cost-benefit evaluations, will be the subject of future investigations.« less

Injection of freshly synthesized Ca-41 in the early solar nebula by an asymptotic giant branch star

view Abstract Citations (82) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Injection of Freshly Synthesized 41Ca in the Early Solar Nebula by an Asymptotic Giant Branch Star Wasserburg, G. J. ; Gallino, R. ; Busso, M. ; Goswami, J. N. ; Raiteri, C. M. Abstract We show that ejecta from the envelope of one asymptotic giant branch star of M is approximately 3 solar mass may account for many of the short-lived nuclei in the early solar system and also for the recent evidence of the presence of Ca-41 (bar-tau41 = 1.50 x 105 yr) in early solar nebular condensates. This would require that the injection into the protosolar molecular cloud took place within a narrow time interval of (5-7) x 105 yr before the formation of the solar system. If true, this places extremely tight constraints on the whole process of injection mixing and collapse. The timescales for both Ca-41 and Al-26 require that the placental medium be a dense molecular cloud (2 x 103 -8 x 103( H/cc. If the observed residual Ca-41 is instead produced by a proton bombardment mechanism within the early solar system, similar to what appears necessary to explain Mn-53, then the time interval is relaxed but would still be (1-2) x 106 yr from consideration of Al-26. Publication: The Astrophysical Journal Pub Date: February 1995 DOI: 10.1086/187771 Bibcode: 1995ApJ...440L.101W Keywords: Abundance; Asymptotic Giant Branch Stars; Calcium Isotopes; Molecular Clouds; Solar System Evolution; Aluminum 26; Nuclear Fusion; Astrophysics; ISM: ABUNDANCES; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; ABUNDANCES; SOLAR SYSTEM: FORMATION; STARS: AGB AND POST-AGB full text sources ADS | data products SIMBAD (1)

Beta-decay intensity distributions for the fission products 139Cs and 140Cs measured with a total absorption γ-ray spectrometer

A total absorption γ-ray spectrometer has been developed on the 252Cf-based INEL ISOL facility and is being used in a program of measurements of β −-decay intensity distributions of short-lived fission-product nuclei. Spectra for 139Cs and 140Cs have been measured and compared with those simulated for the published decay schemes as a test of the completeness and correctness of these schemes. New β −-intensity distributions have been deduced for the decay of these isotopes.

The use of a radiactive beam of fission products for TDPAC experiments

In order to use a wide variety of radioactive nuclei as probes in material research, an on-line isotope separator (ISOL) for fission products has been utilized to produce and accelerate short-lived nuclei suitable for TDPAC experiments. The140Cs isotope (T 1/2=63.7 s) from ISOL has been implanted into YBaCuO compounds to investigate the hyperfine field around a Ba atom. The140Ba-140La source of 3×104 decays/s is obtained for TDPAC experiments on the 329–487 keV γ-γ cascade in140Ce. Another candidate was examined to use the 345–94 keV cascade in the91Rb (T 1/2=58 s) decay. The angular correlation coefficients, however, unfortunately turned out to be fairly small. A tentative result of theg-factor measurement has been given. The details of the present method have been described with emphasis on the application to material research.

Asymptotic Giant Branch stars as a source of short-lived radioactive nuclei in the solar nebula

We carried out a theoretical evaluation of the contribution of Asymptotic Giant Branch (AGB) stars to some short-lived (10<SUP>6</SUP> less than or equal to Tau-bar less than or equal to 2 x 10<SUP>7</SUP> yr) isotopes in the Interstellar Medium (ISM) and in the early solar system using stellar model calculations for thermally pulsing evolutionary phases of low-mass stars. The yields of s-process nuclei in the convective He-shell for different neutron exposures tau<SUB>0</SUB> were obtained, and AGB stars were shown to produce several radioactive nuclei (especially Pd-107, Pb-205, Fe-60, Zr-93, Tc-99, Cs-135, and Hf-182) in diferent amounts. Assuming either contamination of the solar nebula from a single AGB star or models for continuous injection and mixing from many stars into the ISM, we calculate the ratios of radioactive to stable nuclei at the epoch of the Sun's formation. The dilution factor between the AGB ejecta and the early solar system matter is obtained by matching the observed Pd-107/Pd-108 and depends on the value of tau<SUB>0</SUB>. It is found that small masses M<SUB>He</SUB> of He-shell material (10<SUP>-4</SUP>-10<SUP>-7</SUP> solar mass) enriched in s-process nuclei are sufficient to contaminate 1 solar mass of the ISM to produce the Pd-107 found in the early solar system. Predictions are made for all of the other radioactive isotopes. The optimal model to explain several observed radioactive species at different states of the proto-solar nebula involves a single AGB star with a low neutron exposure (tau<SUB>0</SUB> = 0.03 mbarn<SUP>-1</SUP>) which contaminated the cloud with a dilution factor of M<SUB>He</SUB>/solar mass approximately 1.5 x 10<SUP>-4</SUP>. This will also contribute newly synthesized stable s-process nuclei in the amount of approximately 10<SUP>-4</SUP> of their abundances already present in the proto-solar cloud. Variations in the degree of homogenization (approximately 30%) of the injected material may account for some of the small general isotopic anomalies found in meteorites. It is also found that Fe-60 is produced in small but significant quantities that may be sufficient to explain the observations if the time elapsed delta from the contamination of the ISM to the formation of protoplanetary bodies is not higher than delta = 5 x 10<SUP>6</SUP> yr. If delta is longer, up to 10 x 10<SUP>6</SUP> yr, this would require the single AGB star to experience enhanced neutron densities (n<SUB>n</SUB> approximately 3 x 10<SUP>9</SUP>n/cu cm) in the s-processing zone in order to compensate for the branching at Fe-59. The alternative model of long-term continuous ejection of matter from many AGB stars does not appear to match the observations. We also estimate the Al-26 production from the H-shell and find that the Al-26 abundance in the early solar system may be readily explained in a self-consistent manner. Moreover, Al-26 from AGB stars may contribute substantially to the galactic Al-26 gamma-source, while no significant gamma-flux from Co-60 (deriving from Fe-60 decay) is to be expected.

Theoretical estimate of the fast-neutron fission cross sections of235,238U

The cross sections for fissioning of {sup 235,238}U by fast neutrons have been studied experimentally in greater detail and with higher accuracy than the same cross sections for other actinide nuclei. As a result, they are used as neutron standards in the range of neutron energies E{sub n} from several hundreds of keV up to 20 MeV. They are widely employed in relative measurements of other cross sections, primarily the fission cross sections of less-studied nuclei. This methodological solution considerably expanded the possibilities for performing systematic investigations of {sigma}{sub f}(E{sub n}, Z, A) for many nuclei that play an appreciable role in nuclear technology. However, the requirements of nuclear technology cannot be solved by measurements alone, especially in the case of highly active short-lived target nuclei. Attempts are being made to eliminate the associated deficiencies and problems in the experimental information by means of theoretical calculations.

Mass and charge distribution in232Th(?, f) reaction in the projectile energy range 28 to 72 MeV

The cumulative yields for 13 short-lived neutron rich nuclei in the mass rangeA=99 toA=118, produced via the232Th (α, f) reaction were determined at four incident beam energies covering the range from 28 to 72 MeV usingγ-spectroscopy of fission products. The charge distribution parameter Z p was determined for theA=99 mass chain at all the four incident beam energies of 28.5, 39.7, 50.8 and 71.4 MeV and was found to fit into a description of fission process with unchanged charge division (UCD). The measured cumulative yields were converted into chain yields assuming UCD and the yieldmass distribution was obtained at all the above energies. The mass distribution remains asymmetric even at 71.4 MeV, the highest energy studied in this work. The excitation energy dependence of the mass and the charge distribution and of the cumulative yields indirectly suggests that the fission has predominantly proceeded from a relatively low level of excitation allowing most of the excitation energy to be carried away by light particles prior to scission.

Systematics of 8Li-induced radioactive beam reactions: E=13-20 MeV.

Elastic and inelastic scattering, one-nucleon transfers [mostly ${(}^{8}$Li, $^{7}\mathrm{Li}$)] and the ${(}^{8}$Li,\ensuremath{\alpha}) fusion-evaporation reaction have been studied on a variety of targets (A=1--58) at E${(}^{8}$Li)\ensuremath{\approxeq}13--20 MeV using the University of Michigan--University of Notre Dame radioactive nuclear beam (RNB) facility. The latter, which produces an energy-resolved (\ensuremath{\sim}500 keV FWHM), focused beam with intensity \ensuremath{\gtrsim}${10}^{6}$ $^{8}\mathrm{Li}$/s, permitted measurements to selected nuclear levels with cross sections down to approximately 1 mb/sr. Based on the systematics of the measured $^{8}\mathrm{Li}$ elastic scattering an appropriate $^{8}\mathrm{Li}$ optical potential was deduced. Large inelastic scattering cross sections (and B[E2\ensuremath{\uparrow}]) are observed for $^{8}\ensuremath{\rightarrow}^{8}$${\mathrm{Li}}_{0.98}^{\mathrm{*}}$. Large cross sections are also observed for the ${(}^{8}$Li${,}^{7}$Li) transfer reaction corresponding to quasielastic (viz., Q\ensuremath{\approxeq}0) neutron transfer to selected high spin excited levels in the residual nucleus. The ${(}^{8}$Li,\ensuremath{\alpha}) fusion-evaporation reaction also appears to be significant and can produce very-high-energy \ensuremath{\alpha} particles, viz., ${\mathit{E}}_{\mathrm{\ensuremath{\alpha}}}$\ensuremath{\gg}${\mathit{E}}_{\mathrm{beam}}$. Although observed using $^{8}\mathrm{Li}$, these features appear to be important for many RNB-induced reactions and they must be considered, for example, in nucleosyntheis calculations involving $^{8}\mathrm{Li}$ and other short-lived radioactive nuclei.

RF-coupling and cooling techniques of stored heavy ions

A tandem Penning trap system, the ISOLTRAP, is now used at the on-line mass separator ISOLDE at CERN, Geneva, for accurate mass measurements of short-lived nuclei. The mass of the stored ions is measured by the determination of the cyclotron frequency ωc=qB/m in theB=6 T magnetic field of the trap. A new technique has been developed and implemented to allow reliable high-efficiency loading of the trap with radioactive heavy ions.

Time-resolved and time-integral on-line nuclear orientation measurements of neutron-deficient Hg−Au−Pt−Ir nuclei

The methods of time-resolved and time-integral on-line nuclear orientation have been applied to study short lived nuclei with the NICOLE facility (Nuclear Implantation into Cold On-Line Equipment) at ISOLDE-3 in CERN using beams of182–186Hg. The half-lives in these decay chains are of the order of seconds and therefore comparable to the spin-lattice relaxation times of the nuclei in iron. As the relaxation rate depends strongly on the g-factor, g-factors of nuclei in the decay chains can be deduced from the observation of the time evolution of γ-ray anisotropy. Using this technique the existence of an isomer in184Au has been found and the g-factors of184Au,184mAu and182Au have been determined. Accurate half-lives have been extracted from the data.Time-integral nuclear orientation has been observed for short lived as well as longer lived isotopes of the Hg decay chains. From these measurements, after proper correction for incomplete relaxation, the magnetic moments of183mPt,183Ir and182Ir have been derived.The applicability of the time-resolved nuclear orientation technique for nuclei far from stability and its possible limitations is discussed.