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Use of a krypton isotope for rapid ion changeover at the Lawrence Berkeley Laboratory 88-inch cyclotron
An isotope of krypton, Kr86, has been combined with a mix of Ar, Ne, and N ions at the electron cyclotron resonance (ECR) source, at the Lawrence Berkeley Laboratory cyclotron, to provide rapid ion changeover in Single Event Phenomena (SEP) testing. The new technique has been proved out successfully by a recent Jet Propulsion Laboratory (JPL) test in which it was found that there was no measurable contamination from other isotopes.
s-process studies - Xenon and krypton isotopic abundances
We propose an analysis of the s-process contributions to the isotopes of xenon and krypton. The object is to aid studies of the possibility that meteorites may contain gas that was carried in presolar grains that were grown in stellar ejecta and that were not degassed prior to incorporation into parent bodies. That model suggests routine interstellar fractionation of s-isotopes from r-isotopes owing to differential incorporation into dust. We show that a deficiency of s-process nuclei cannot yield details of Xe-X, but the gross similarities are strong enough to lead one to think that such a deficiency may play a role in a more complicated explanation. We predict the existence of an s-rich complement somewhere if fractional separation of this type has played a role in Xe-X. We show that the analogous decomposition of krypton is more uncertain, and we call for measurements of neutron-capture cross sections to alleviate these uncertainties.
Harvesting krypton isotopes from the off-gas of an irradiated water target to generate 76Br and 77Br
Abstract A flowing-water target was irradiated with a 150 MeV/nucleon beam of 78 Kr at the National Superconducting Cyclotron Laboratory to produce 77 Kr and 76 Kr. Real-time gamma-imaging measurements revealed the mass transport of the krypton radioisotopes through the target-water processing, or “isotope harvesting”, system. The production rates were determined to be 2.7(1) × 10 –4 nuclei of 76 Kr and 1.18(6) × 10 –2 nuclei of 77 Kr formed per incident 78 Kr ion. Utilizing an off-gas processing line as part of the isotope harvesting system, a total of 7.2(1) MBq of 76 Kr and 19.1(6) MBq of 77 Kr were collected in cold traps. Through the decay, the daughter radionuclides 76 Br and 77 Br were generated and removed from the traps with an average efficiency of 77 ± 12%. Due to the differences in half-lives of 76 Kr and 77 Kr, it was possible to isolate a pure sample of 76 Br with 99.9% radionuclidic purity. The successful collection of krypton radioisotopes to generate 76 Br and 77 Br demonstrates the feasibility of gas-phase isotope harvesting from irradiated accelerator cooling-water. Larger-scale collections are planned for collecting by-product radionuclides from the Facility for Rare Isotope Beams.
On krypton isotopic abundances in the sun and in the solar wind
The Kr isotopic systematics in the meteorite Pesyanoe which is known to contain solar-type gases, are reported. Discrepancies in the isotopic data of fractions released at stepwise increasing temperatures cannot be reconciled with spallation Kr components, although spallation effects are significant. Fractionation mechanisms on the parent body and in the solar wind source region are considered and the implications for solar abundances discussed.
Coulomb excitation of 80,82 Kr and a change in structure approaching N = Z = 40
Nuclei approaching N = Z = 40 are known to exhibit strongly deformed structures and are thought to be candidates for shape coexistence. In the krypton isotopes, 80,82 Kr are poorly characterized, preventing an understanding of evolving deformation approaching N = 40. The present work aims to determine electric quadrupole transition strengths and quadrupole moments of 80,82 Kr in order to better characterize their deformation. Sub-barrier Coulomb excitation was employed, impinging the isotopes of krypton on 196 Pt and 208 Pb targets. Utilizing a semiclassical description of the safe Coulomb-excitation process E 2 matrix elements could then be determined. Eleven new or improved matrix elements are determined in 80 Kr and seven in 82 Kr . The new B(E2;0$^+_1$ → 2$^+_1$ ) value in 82 Kr disagrees with the evaluated value by 3σ , which can be explained in terms of deficiencies in a previous Coulomb-excitation analysis. Conclusions: Comparison of measured Q s ( 2$^+_1$ ) and B(E2; 0$^+_1$ → 2$^+_1$ ) values indicates that neutron-deficient ( N ≤ 42 ) isotopes of krypton are closer to axial deformation than other isotopic chains in the mass region. A continuation of this trend to higher Z may result in Sr and Zr isotopes exhibiting near-axial prolate deformation.
The Path to Krypton and Xenon Isotopic Measurements from Few-Micron Sized Samples: III Kr Calibration and First Applications of the RIS-TOF System
We describe progress towards the micron-scale analysis of krypton isotopes in extraterrestrial material.
Analysis of 85Kr: a comparison at the 10-14 level using micro-liter samples
The isotopic abundance of 85Kr in the atmosphere, currently at the level of 10211, has increased by orders of magnitude since the dawn of nuclear age. With a half-life of 10.76 years, 85Kr is of great interest as tracers for environmental samples such as air, groundwater and ice. Atom Trap Trace Analysis (ATTA) is an emerging method for the analysis of rare krypton isotopes at isotopic abundance levels as low as 10214 using krypton gas samples of a few micro-liters. Both the reliability and reproducibility of the method are examined in the present study by an inter-comparison among different instruments. The 85Kr/Kr ratios of 12 samples, in the range of 10213 to 10210, are measured independently in three laboratories: a low-level counting laboratory in Bern, Switzerland, and two ATTA laboratories, one in Hefei, China, and the other in Argonne, USA. The results are in agreement at the precision level of 5%.
Nuclear Data Sheets for A = 93
Nuclear structure data pertaining to all nuclei with mass number A=93 (Se, Br, Kr, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag) have been compiled and evaluated and incorporated into the ENSDF data file. This publication for A=93 supersedes the previous publication by C.M. Baglin, Nuclear Data Sheets80, 1 (1997) (literature cutoff date November 1996) and subsequent revisions by C.M. Baglin of the ENSDF files for 93Br and {sup 93}Kr (literature cutoff 26 February 2001) and for {sup 93}Rh (literature cutoff 27 February 2001); it includes all data available prior to 15 December 2010. Significant changes since prior evaluations include the following: 2010Hw03 identified several high-spin states in {sup 93}Kr in {sup 252}Cf SF decay; in addition to the many low-spin levels already known in {sup 93}Rb from {beta}{sup -} decay, several higher-spin states have now been identified in a {sup 252}Cf SF decay study (2009Hw03); this SF decay has also been used to identify additional states in {sup 93}Sr (2003Hw01) and the {sup 238}U({sup 82}Se,X{gamma}) reaction (2007Bu35) has provided new information on {sup 93}Y. (HI,xn{gamma}) reaction studies have expanded our knowledge of the structure of {sup 93}Zr (2002Fo03, 2005Pa48), {sup 93}Nb (2007Wa45), {sup 93}Mo (2005Fu01), {sup 93}Tc (2003Ha22) and {sup 93}Pd (2004So04,2004Ru02). Considerable information on {sup 93}Nb was provided by a (p,2n{gamma}) study (2010Or01, 2006Or09, 2007Or01). The level schemes of {sup 93}Ru, {sup 93}Rh and {sup 93}Pd have undergone the most extensive revision thanks to studies of {sup 93}Rh {epsilon} decay (2004De40), {sup 94}Ag {epsilon}p decay (2004Mu30) and {sup 94}Ag p decay (2005Mu15, 2005Mu30), respectively. The half-life of the Zr member of this chain is of particular interest because of {sup 93}Zr's large contribution to long-term activity of nuclear reactor waste and also due to its potential as a supernova chronometer. During 2010, two new well-documented measurements of T{sub 1/2}({sup 93}Zr) were published (2010Ya01 and 2010Ca01); one agrees well with an earlier, undocumented measurement but, unfortunately, the other is many standard deviations lower for reasons which are not immediately apparent.
Weak decay rates for neutron-deficient Kr isotopes relevant for the rp process
Weak interaction rates under stellar density and temperature conditions relevant for the rp process are studied in neutron-deficient Kr isotopes. The nuclear structure part of the problem is described within the deformed Skyrme Hartree-Fock+BCS+QRPA, which reproduces not only the beta-decay half-lives but also the available Gamow-Teller strength distributions, measured under terrestrial conditions. The various sensitivities of the decay rates to both density and temperature are discussed. In particular, we study the contributions coming from excited states in the parent nucleus, which are thermally populated, and the competition between beta-decays and continuum electron captures.
Exotic structures near the drip lines
In our recent study of the isotope shifts of Kr isotopes near rp-process path in the framework of the RMF theory, we have found that due to large shell gaps in the deformed space, several N = Z nuclei exhibit the double magicity of protons and neutrons. These nuclei are known to contribute to large abundances in the rp-process nucleosynthesis and have been shown to be the waiting-point nuclei. In another study of the shell effects at N = 126 near the neutron drip line, we have found that nuclei exhibit additional stability beyond the neutron drip line.
Alpha-particle capture reactions in inverse kinematics relevant to p-process nucleosynthesis
The first feasibility study of an {alpha}-particle capture reaction in inverse kinematics at energies relevant to the p process was performed at the Wien Filter of the LISE spectrometer at GANIL. Hereby, the {sup 4}He({sup 78}Kr,{gamma}){sup 82}Sr reaction was investigated using as target an {sup 4}He-implanted thin Al foil. The analysis of the data has shown that the determination of ({alpha},{gamma}) reaction cross sections at rather low energies around 2 MeV/u in inverse kinematics is indeed feasible regarding the high rejection rate of the primary beam, which in the present work was better than a factor of 10{sup 9}. However, the expected position of the recoils of interest was completely masked by particles of currently unknown origin that could hardly be attributed to scattering of the primary beam. The most probable explanation for the origin of these 'pollutants' could be microscopic dust particles of 10 {mu}m diameter and less, that are extremely difficult to avoid in standard experimental conditions. Hence, the use of a gas-jet target instead of a solid one is compulsory.
TYPE Ia SUPERNOVAE AS SITES OF THE p-PROCESS: TWO-DIMENSIONAL MODELS COUPLED TO NUCLEOSYNTHESIS
Beyond Fe, there is a class of 35 proton-rich nuclides, between {sup 74}Se and {sup 196}Hg, called p-nuclei. They are bypassed by the s and r neutron capture processes and are typically 10-1000 times less abundant than the s- and/or r-isotopes in the solar system. The bulk of p-isotopes is created in the 'gamma processes' by sequences of photodisintegrations and beta decays in explosive conditions in both core collapse supernovae (SNe II) and in Type Ia supernovae (SNe Ia). SNe II contribute to the production of p-nuclei through explosive neon and oxygen burning. However, the major problem in SN II ejecta is a general underproduction of the light p-nuclei for A < 120. We explore SNe Ia as p-process sites in the framework of a two-dimensional SN Ia delayed detonation model as well as pure deflagration models. The white dwarf precursor is assumed to have reached the Chandrasekhar mass in a binary system by mass accretion from a giant/main-sequence companion. We use enhanced s-seed distributions, with seeds directly obtained from a sequence of thermal pulse instabilities both in the asymptotic giant branch phase and in the accreted material. We apply the tracer-particle method to reconstruct the nucleosynthesis by the thermal histories of Lagrangian particles, passively advected in the hydrodynamic calculations. For each particle, we follow the explosive nucleosynthesis with a detailed nuclear reaction network for all isotopes up to {sup 209}Bi. We select tracers within the typical temperature range for p-process production, (1.5-3.7) x 10{sup 9} K, and analyze in detail their behavior, exploring the influence of different s-process distributions on the p-process nucleosynthesis. In addition, we discuss the sensitivity of p-process production to parameters of the explosion mechanism, taking into account the consequences on Fe and alpha elements. We find that SNe Ia can produce a large amount of p-nuclei, both the light p-nuclei below A = 120 and the heavy-p nuclei, at quite flat average production factors, tightly related to the s-process seed distribution. For the first time, we find a stellar source able to produce both light and heavy p-nuclei almost at the same level as {sup 56}Fe, including the debated neutron magic {sup 92,} {sup 94}Mo and {sup 96,} {sup 98}Ru. We also find that there is an important contribution from the p-process nucleosynthesis to the s-only nuclei {sup 80}Kr, {sup 86}Sr, to the neutron magic {sup 90}Zr, and to the neutron-rich {sup 96}Zr. Finally, we investigate the metallicity effect on p-process production in our models. Starting with different s-process seed distributions for two metallicities Z = 0.02 and Z = 0.001, running two-dimensional SN Ia models with different initial composition, we estimate that SNe Ia can contribute to at least 50% of the solar p-process composition. A more detailed analysis of the role of SNe Ia in Galactic chemical evolution of p-nuclei is in preparation.
Role of angular momentum in the production of complex fragments in fusion and quasifission reactions
The influence of angular momentum on the competition between complete fusion followed by the decay of compound nucleus and quasifission channels is treated within the dinuclear system model. The charge distributions of the products in the reactions {sup 28}Si+{sup 96}Zr, {sup 4}He+{sup 130}Te, and {sup 40}Ca+{sup 82}Kr are predicted at bombarding energies above the Coulomb barrier. The results of calculations for the reactions {sup 93}Nb+{sup 9}Be,{sup 12}C,{sup 27}Al; {sup 84}Kr+{sup 27}Al; {sup 86}Kr+{sup 63}Cu; {sup 139}La+{sup 12}C,{sup 27}Al; and {sup 45}Sc+{sup 65}Cu are compared with the available experimental data.
The atmosphere of Mars - Detection of krypton and xenon
Krypton and xenon have been discovered in the Martian atmosphere with the mass spectrometer on the second Viking lander. Krypton is more abundant than xenon. The relative abundances of the krypton isotopes appear normal, but the ratio of xenon-129 to xenon-132 is enhanced on Mars relative to the terrestrial value for this ratio. Some possible implications of these findings are discussed.
Predicted versus observed cosmic-ray-produced noble gases in lunar samples - Improved Kr production ratios
New sets of cross sections for the production of krypton isotopes from targets of Rb, Sr, Y, and Zr have been constructed primarily on the bases of experimental excitation functions for Kr production from Y. These cross sections were used to calculate galactic-cosmic-ray and solar-proton production rates for Kr isotopes in the moon. The paper reports spallation Kr data obtained from ilmenite separates of rocks 10017 and 10047. Production rates and isotopic ratios for cosmogenic Kr observed in ten well-documented lunar samples and in ilmenite separates and bulk samples from several lunar rocks with long but unknown irradiation histories were compared with predicted rates and ratios. The agreements were generally quite good.
S-process krypton of variable isotopic composition in the Murchison meteorite
Data are reported which, for the first time, permit the derivation of the full isotopic spectrum of s-process krypton with reasonable precision. It is shown that this s-Kr in a residue from the Murchison meteorite did not originate in one single s-process but rather is a mixture of contributions from stellar environments where the density of free neutrons was not the same. The astrophysical conditions under which this krypton was produced were distinct from those that have been invoked to explain the solar system s-process abundance. Similar to the C-13-rich carbon component in an aliquot of the same residue, the s-process Kr from different astrophysical sites has retained its identity during the accumulation and subsequent history of the meteorite.