Production of noble gas isotopes by proton-induced reactions on lead
ABSTRACT We measured integral thin target cross sections for the proton-induced production of He-, Ne-, Ar-, Kr- and Xe-isotopes from lead from the respective reaction threshold up to 2.6 GeV. The production of noble gas isotopes from lead is of special importance for design studies of accelerator driven nuclear reactors and/or energy amplifiers. For all experiments with proton energies above 200 MeV a new mini-stack approach was used instead of the stacked-foil technique in order to minimise the influences of secondary particles on the residual nuclide production. About 420 cross sections for 23 nuclear reactions were determined. The phenomenology of the determined excitation functions enables us to distinguish between the different reaction modes fragmentation, hot and cold symmetric fission, asymmetric fission and deep spallation. Cross sections for the production of 21Ne and 38Ar measured below 100 MeV and 200 MeV, respectively, enable us to study nuclide production below the nominal Coulomb-barrier. The experimental data are compared to results from the theoretical nuclear model code INCL4/ABLA. While the model describes the production of 4He reasonably well, it underestimates the cross sections for Ne- and Ar-isotopes produced via deep spallation and/or multifragmentation by up to two orders of magnitude. For the Kr- and Xe-isotopes the agreement between modelled and measured data strongly depends on the reaction mechanisms. While INCL4/ABLA describes the production of n-poor Kr-isotopes via hot-symmetric fission and the production of Xe-isotopes via asymmetric fission reasonably well, i.e. within a factor of 2, the discrepancies between modelled and measured cross sections for the n-rich Kr-isotopes produced via cold symmetric fission are significantly larger. For the Xe-isotopes produced via spallation, i.e. at energies higher than about 600 MeV, the model completely fails to describe the experimental data. Therefore, the comparison of measured and modelled thin target cross sections clearly indicates that experimental data are still needed because the predictive power of nuclear model codes, though permanently improving, does still not allow to reliably predict the cross sections needed for most applications and irradiation experiments remain indispensable.
Book: Table of isotopes[show abstract] [hide abstract]
ABSTRACT: The table is ordered by mass number and subordered by atomic number. For each mass number there is an abbreviated mass-chain decay scheme, showing the adopted half-lives, spin-parity assignments, and decay energies (Q-values) for the isobars, and the decay relationships between them. Following the mass-chain decay scheme, tabulated data and detailed nuclear level schemes are given for individual isotopes. Tabulated data entries are included for each ground state or isomer with half-life >1 s. A few shorter-lived isomeric species are also included, e.g., fission isomers and a few ''historic'' isomers, such as /sup 24//sup m/Na. The data include natural abundance, mass excess, nuclear spin, thermal neutron cross sections, all categories of data on radioactive decay, and excited-state half-lives. Data categories are shown. Each entry under a given data category concludes with the reference code or codes. Detailed level schemes are given for each isotope (A,Z) for which there is information beyond that shown on the mass-chain decay scheme. The schemes are separated into a ''decay-level'' scheme, showing levels and transitions observed in the decay of all parent isotopes and isomeric states, and a ''reaction'' scheme, summarizing the information derived from nuclear reaction studies. Decay-level schemes include all levels established in radioactive decay studies. Reaction schemes include most levels observed in nuclear reactions. Not included are most neutron-capture resonances and other unbound states (e.g., giant resonances); these states are generally outside the scope of the present compilation, with a few exceptions in the light-element region. Some references to unbound levels other than neutron resonances are included. Uncertainties are included in tabular data listings whenever they were given in the original literature.12/1977;
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ABSTRACT: Ever since their first discovery in 1960, the origin of the relatively short-lived radionuclides, now extinct but alive in the early solar system, has been under debate. Possible scenarios are either nucleosynthetic pro-duction in stellar sources, e.g., asymptotic giant branch stars, Wolf-Rayet stars, novae, and supernovae, with subsequent injection into the solar nebula, or the production by spallation reactions in the early solar system. Here we present model calculations for the second scenario, the production of the relatively short-lived radio-nuclides by solar energetic particle events at the start of the solar system. The model is based on our current best knowledge of the nuclear reaction probabilities. In addition, the modeling depends on the relative flu-ence contribution of protons, 3 He, and 4 He in the solar particle events as well as on their energy distribution. The relative fluence contribution is the only free parameter in the system. Finally, the modeling depends on the chemical composition assumed for the irradiated target. The model simultaneously describes the observed solar system initial ratios 7 Be/ 9 Be, 10 Be/ 9 Be, 26 Al/ 27 Al, 41 Ca/ 40 Ca, 53 Mn/ 55 Mn, and 92 Nb/ 93 Nb. In the framework of the local production scenario, the concordance of measured and modeled data for nuclides with half-lives ranging from 53 days up to 36 Myr enables us to put some stringent constraints on possible calcium-aluminum–rich refractory inclusion (CAI) production and its timing. One important requirement in such a scenario is that the material forming most of the CAIs must have experienced a surpris-ingly homogenous particle fluence. CAIs showing evidence for live 10 Be, 26 Al, 41 Ca, 53 Mn, and 92 Nb close to the inferred solar system initial ratios would have to have been irradiated within $1 Myr. Much more strin-gent would be the time constraint for the one CAI for which formerly live 7 Be has been reported. Such CAIs would have to have been irradiated for less than about 1 yr. Such a short timescale requires flux densities as high as $10 16 cm À2 s À1 . To allow further tests of the local production scenario, we also predict solar system initial ratios for 14 C/ 12 C, 22 Na/ 23 Na, 36 Cl/ 35 Cl, 44 Ti/ 48 Ti, 54 Mn/ 55 Mn, 63 Ni/ 60 Ni, and 91 Nb/ 93 Nb, whose correlated shifts in the daughter isotopes would help to further test the local production scenario.The Astrophysical Journal 01/2003; 594(1). · 6.73 Impact Factor