Some Nuclear Reaction Rates of Importance for Nucleosynthesis around Mass 45

Details Some Nuclear Reaction Rates of Importance for Nucleosynthesis around Mass 45 Some Nuclear Reaction Rates of Importance for Nucleosynthesis around Mass 45

Jun 1985

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985phdt.......162m&link_type=abstract

Thesis (PH.D.)--UNIVERSITY OF MELBOURNE (AUSTRALIA), 1985.Source: Dissertation Abstracts International, Volume: 47-04, Section:

Astronomy and Astrophysics

Astrophysics

Astrophysics

Scientific paper

This thesis describes the measurement of absolute cross sections and the determination of thermonuclear reaction rates for a series of reactions which are of importance in stellar nucleosynthesis. The yield of (gamma)-rays from the reaction ('42)Ca(p,(gamma))('43)Sc has been measured as a function of bombarding energy over the range 0.63 - 3.01 MeV, from ('44)Ca(p,(gamma))('45)Sc over the range 0.775 - 4.00 MeV, from ('42)Ca((alpha),(gamma))('46)Ti over the range 3.62 - 5.62 MeV, from ('42)Ca((alpha),p(gamma))('45)Sc over the range 4.06 - 5.92 MeV, from ('44)Ca(p,p'(gamma))('44)Ca over the range 1.90 - 5.03 MeV and from ('42)Ca(p,p'(gamma))('42)Ca over the range 2.24 - 3.01 MeV. High resolution Ge(Li) detectors have been used for all meas- urements. The cross section of the reaction ('44)Ca(p,n)('44)Sc has been measured from threshold up to a bombarding energy of 5.05 MeV by observation of the 1157 keV (gamma)-ray associated with the residual 3.93 h ('44)Sc activity, and the cross section of ('45)Sc(p,n)('45)Ti has been measured from threshold to a bombarding energy of 4.00 MeV both by observation of the annihilation radiation associated with the residual 3.09 h ('45)Ti activity and by measurement of the total neutron yield with a wide angle BF(,3) tube and paraffin detector. The cross section for the ('42)Ca((alpha),p(,0,1))('45)Sc reaction has been measured over the range 4.78 - 5.92 MeV by observing the emitted protons with a surface barrier detector. Experimental procedures for these measurements are detailed in the thesis, and in particular the efficient preparation of calcium targets with very low levels of ('19)F contamination is discussed. Data from all reactions are compared with the predictions of the statistical model code HAUSER*4, which employs global optical model parameters in the calculation of transmission coefficients and includes width fluctuation corrections. Satisfactory agreement is achieved, being better than a factor of 2 for all reactions except ('45)Sc(p,n)('45)Ti, for which the prediction is higher than the data by a factor of (TURN)2.3. Thermonuclear reaction rates have been calculated from the experimental cross section data for the temperature range 5 x 10('8) - 10('10)K, and the significance of the results for explosive nucleosyn- thesis in stars in discussed. The rates have been parameterized for. use in nucleosynthesis network calculations according to the scheme of Woosley et al. (Wo78). Reference. S. E. Woosley, W. A. Fowler, J. A. Holmes and B. A. Zimmerman. \At. Nucl. Data Tables 22 (1978) 371.

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