Download or read book High resolution Neutron Capture and Transmission Measurements and the Stellar Neutron Capture Cross Sections Of sup 116 120 n written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Improved astrophysical reaction rates for[sup 116,120]Sn(n, [gamma]) are of interest because nucleosynthesis models have not been able to reproduce the observed abundances in this mass region. For example, previous s-process calculations have consistently underproduced the s-only isotope[sup 116]Sn. Also, these studies have resulted in residual reprocess abundances for the tin isotopes which are systematically larger than predicted by reprocess calculations. It has been suggested that these problems could be solved by reducing the solar tin abundance by 10-20%, but there is no experimental evidence to justify this renormalization. Instead, it is possible that the problem lies in the (n, T) cross sections used in the reaction network calculations or in the s-process models. One reason to suspect the (n, [gamma]) data is that previous measurements did not extend to low enough energies to determine accurately the Maxwellian-averaged capture cross sections at the low temperatures (kT=6-8 keV) favored by the most recent stellar models of the s process. Also, the two most recent high-precision measurements of the[sup 120]Sn(n, [gamma]) cross section are in serious disagreement. Because of its small size, this cross section could affect (via the s-process branching at[sup 121]Sn) the relative abundances of the three s-only isotopes of Te.
Download or read book High resolution Neutron Capture and Transmission Measurements and the Stellar Neutron Capture Cross Sections of sup 116 120 Sn written by and published by . This book was released on 1997 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: Improved astrophysical reaction rates for {sup 116,120}Sn(n, [gamma]) are of interest because nucleosynthesis models have not been able to reproduce the observed abundances in this mass region. For example, previous s-process calculations have consistently underproduced the s-only isotope 116Sn. Also, these studies have resulted in residual reprocess abundances for the tin isotopes which are systematically larger than predicted by reprocess calculations. It has been suggested that these problems could be solved by reducing the solar tin abundance by 10-20%, but there is no experimental evidence to justify this renormalization. Instead, it is possible that the problem lies in the (n, T) cross sections used in the reaction network calculations or in the s-process models. One reason to suspect the (n, [gamma]) data is that previous measurements did not extend to low enough energies to determine accurately the Maxwellian-averaged capture cross sections at the low temperatures (kT=6-8 keV) favored by the most recent stellar models of the s process. Also, the two most recent high-precision measurements of the 12°Sn(n, [gamma]) cross section are in serious disagreement. Because of its small size, this cross section could affect (via the s-process branching at 121Sn) the relative abundances of the three s-only isotopes of Te.
Download or read book Neutron Cross Sections and Related Measurements written by and published by . This book was released on 1966 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book New Neutron Capture and Transmission Measurements for sup 134 136 Ba at ORELA and Their Impact on S process Nucleosynthesis Calculations written by and published by . This book was released on 1996 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: We have made high-resolution neutron capture and transmission measurements on isotopically enriched samples of 134Ba and 136Ba at the Oak Ridge Electron Linear Accelerator (ORELA) in the energy range from 20 eV to 500 keV. Previous measurements had a lower energy limit of 3 - 5 keV, which is too high to determine accurately the Maxwellian-averaged capture cross section at the low temperatures (kT (almost equal to) 6 - 12 keV) favored by the most recent stellar models of the {ital s}-process. Our results for the astrophysical reaction rates are in good agreement with the most recent previous measurement at the classical {ital s}-process temperature, kT = 30 keV, but show significant differences at lower 40 temperatures. We discuss the astrophysical implications of these differences.
Download or read book Neutron Cross Sections and Technology written by David T. Goldman and published by . This book was released on 1968 with total page 674 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental determination of the stellar neutron capture cross sections of SUP 148 SM and SUP 150 SM and the consequences for the S process written by K. H. Guber and published by . This book was released on 1993 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Conference on Neutron Cross Section Technology written by P. B. Hemmig and published by . This book was released on 1966 with total page 572 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Stellar Neutron Capture Cross Sections of the Nd Isotopes written by and published by . This book was released on 1997 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Neutron Capture Cross Sections and the S process written by and published by . This book was released on 1967 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Neutron Capture Cross Sections for 86Sr and 87Sr at Stellar Temperatures Revision 1 written by and published by . This book was released on 1986 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent work on s-process nucleosynthesis has focused attention on the investigation of capture cross sections for nuclei in the mass region near the N = 50 closed neutron shell. Of special astrophysical interest are (i) the analysis of the s-process branching through 85Kr as a monitor of stellar neutron density and temperature and (ii) the investigation of the possible chronometric pair 87Rb-87Sr as an independent measure of the age of the galaxy. For both problems the capture cross sections of the two pure s-process nuclei 86Sr and 87Sr have to be known to an accuracy of 5% or better. The current investigation of the neutron capture cross sections for 86Sr and 87Sr was undertaken to extend recent measurements by Walter and Beer to energies below 3.5 keV, where strong resonances are known to exist, and to explore the discrepancy in the results of the Maxwellian averaged capture cross section of 87Sr at kT = 30 keV as reported by previous investigators. 9 refs., 1 fig.
Download or read book Measurements of Low Energy Neutron Cross Sections of Non fissile Nuclides and Their written by and published by . This book was released on 1966 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Stellar Nucleosynthesis and the 24 keV Neutron Capture Cross Sections of Some Heavy Nuclei written by and published by . This book was released on 1979 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The neutron capture cross sections of 112Sn, 13°Ba, 146Nd, 148Nd, 186W, 19°Os, and 192Os at 24 keV neutron energy were measured with respect to 197Au by activation in a 24 keV neutron beam at the Brookhaven High Flux Beam Reactor. The reliability of this technique was verified by remeasuring the cross section of 186W and comparing it to previous measurements. This continuing series of measurements will provide a more reliable data base for nucleosynthesis calculations. 12 references.
Download or read book Stellar neutron capture cross sections of the Gd isotopes written by and published by . This book was released on 1995 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book New Neutron Capture and Total Cross Section Measurements On sup 88 r and Their Impact on S process Nucleosynthesis written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The authors have made new and improved measurements of the neutron capture and total cross sections of[sup 88]Sr at the Oak Ridge Electron Linear Accelerator (ORELA). Improvements over previous measurements include a wider incident neutron energy range, the use of metallic rather than carbonate samples, better background subtraction, reduced sensitivity to sample-dependent backgrounds, and better pulse-height weighting functions. Because of its small cross section, the[sup 88]Sr(n, [gamma]) reaction is an important bottleneck during the s-process nucleosynthesis. Hence, an accurate determination of this rate is needed to better constrain the neutron exposure in s-process models and to more fully exploit the recently discovered isotopic anomalies in certain meteorites. They describe the experimental procedures, compare the results to previous data, and discuss their astrophysical impact.
Download or read book Neutron Cross Sections written by Donald J. Hughes and published by Elsevier. This book was released on 2016-01-22 with total page 193 pages. Available in PDF, EPUB and Kindle. Book excerpt: Neutron Cross Sections presents the principles of cross-section measurement and use, as well as sufficient theory so that the general behavior of cross sections is made understandable. This compilation is a direct result of experiences connected with the collection and evaluation of cross-section data during the past eight years at ""Sigma Centre"", Brookhaven National Laboratory. Here, experimental results received from laboratories throughout the world are carefully evaluated and compiled in the curves and tables of the large volume Neutron Cross Sections, The most recent version of the compilation, known as BNL 325, appeared 1 July 1955, and Supplement 1 to BNL 325 was published on 1 January 1957. The compilation itself consists almost completely of cross sections at specific energies, shown in the form of curves or tables, with only brief explanatory texts. The text opens with discussions of the general properties of cross sections and principles of nuclear structure that are important to the understanding of cross-section behavior. Separate chapters follow that describe specific techniques for measuring cross sections along with experimental results involving fast neutrons, resonance neutrons, resonances in fissionable materials, and thermal neutrons.
Download or read book Atlas of Neutron Resonances written by Said F. Mughabghab and published by Elsevier. This book was released on 2018-02-09 with total page 840 pages. Available in PDF, EPUB and Kindle. Book excerpt: Atlas of Neutron Resonances: Resonance Properties and Thermal Cross Sections Z= 1-60, Sixth Edition, contains an extensive list of detailed individual neutron resonance parameters for Z=1-60, as well as thermal cross sections, capture resonance integrals, average resonance parameters and a short survey of the physics of thermal and resonance neutrons. The long introduction contains: nuclear physics formulas aimed at neutron physicists; topics of special interest such as valence neutron capture, nuclear level density parameters, and s-, p-, and d-wave neutron strength functions; and various comparisons of measured quantities with the predictions of nuclear models, such as the optical model. As in the last edition, additional features have been added to appeal to a wider spectrum of users. These include: spin-dependent scattering lengths that are of interest to solid-state physicists, nuclear physicists and neutron evaluators; calculated and measured Maxwellian average 5-keV and 30-keV capture cross sections of importance to astrophysicists involved in nucleosynthesis modeling; s-, p-, and d-wave average radiative widths; and, nuclear level density parameters. Provides a comparison of average resonance parameters with optical model calculations and with the generalized Landau-Fermi model Presents scattering radii for various partial waves from the analysis of total neutron cross sections in the keV to MeV energy region Includes a brief review of sub-threshold fission Examines consistent treatment of average neutron parameters with values from the resolved resonance region
Download or read book Neutron Cross Sections written by Donald James Hughes and published by . This book was released on 1966 with total page 426 pages. Available in PDF, EPUB and Kindle. Book excerpt:
