Observations of galactic gamma-ray activity have challenged the current understanding of nucleosynthesis in massive stars. Recent measurements of (60)Fe abundances relative to ;{26}Al;{g} have underscored the need for accurate nuclear information concerning the stellar production of (60)Fe. In light of this motivation, a first measurement of the stellar (60)Fe(n, gamma)(61)Fe cross section, the predominant destruction mechanism of (60)Fe, has been performed by activation at the Karlsruhe Van de Graaff accelerator. Results show a Maxwellian averaged cross section at kT = 25 keV of 9.9 +/-_{1.4(stat)};{2.8(syst)}mbarn, a significant reduction in uncertainty with respect to existing theoretical discrepancies. This result will serve to significantly constrain models of (60)Fe nucleosynthesis in massive stars.
The radionuclide inventory of a copper beam dump from the 590 MeV proton accelerator of the Paul Scherrer Institute in Switzerland was determined, focusing on radioisotopes with half-lives of more than 60 d, and in particular, of long-lived isotopes with T 1/2 = 10 4 -10 7 years, which are important regarding radioactive waste management. The measurements were carried out using high resolution γ -measurement without sample destruction, as well as liquid scintillation counting (LSC) and accelerator mass spectrometry (AMS) after chemical separation. For the first time, a beam dump from a high power accelerator facility was completely characterized concerning the depth and radial distribution profile of the most hazardous and/or long-lived radionuclides. Moreover, it turned out that some of the investigated radionuclides, like for instance 26 Al, 44 Ti or 60 Fe represent valuable material for application in several scientific fields like nuclear astrophysics, basic nuclear physics research, radiopharmacy and many others. Therefore, based on the analytical results, a special research and development program has been started at PSI objecting on specific preparative extraction of longlived radioisotopes (ERAWAST -exotic radionuclides from accelerator waste for science and technology).
With the development of advanced large-scale accelerator facilities, considerable quantities of activated material are now being produced. From both a scientific and a technological viewpoint, many of these nuclides are of great interest for future research, and in fact cannot be obtained through other means. The Paul Scherrer Institute-operating one of the most powerful proton accelerators in Europe-is able to provide considerable amounts of several exotic long-lived radionuclides. The present report is focused on the separation and application of radionuclides with a special interest on nuclear astrophysics topics.
The bonding of N(2) to the five-coordinate complexes [FeX(depe)(2)](+), X = Cl (1a) and Br (1b), has been investigated with the help of X-ray crystallography, spectroscopy, and quantum-chemical calculations. Complexes 1a and 1b are found to have an XP(4) coordination that is intermediate between square-pyramidal and trigonal-bipyramidal. Mössbauer and optical absorption spectroscopy coupled with angular overlap model (AOM) calculations reveal that 1a and 1b have (3)B(1) ground states deriving from a (xz)(1)(z(2))(1) configuration. The zero-field splitting for this state is found to be 30-35 cm(-1). In contrast, the analogous dinitrogen complexes [FeX(N(2))(depe)(2)](+), X = Cl (2a) and Br (2b), characterized earlier are low-spin (S = 0; Wiesler, B. E.; Lehnert, N.; Tuczek, F.; Neuhausen, J.; Tremel, W. Angew. Chem, Int. Ed. 1998, 37, 815-817). N(2) bonding and release in these systems are thus spin-forbidden. It is shown by density functional theory (DFT) calculations of the chloro complex that the crossing from the singlet state (ground state of 2a) to the triplet state (ground state of 1a) along the Fe-N coordinate occurs at r(C) = 2.4 A. Importantly, this intersystem crossing lowers the enthalpy calculated for N(2) release by 10-18 kcal/mol. The free reaction enthalpy Delta G degrees for this process is calculated to be 4.7 kcal/mol, which explains the thermal instability of N(2) complex 2a with respect to the loss of N(2). The differences in reactivity of analogous trans hydrido systems are discussed.
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