Competition Effects in Charged Particle Induced Reactions

Citation

Zyskind, John Lehrer (1979) Competition Effects in Charged Particle Induced Reactions. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/dtne-cd02. https://resolver.caltech.edu/CaltechTHESIS:10092018-083946154

Abstract

Absolute cross sections have been measured for 14 reactions: ⁵⁴Cr(p,γ)⁵⁵Mn for 0.83 MeV ≤ E_p ≤ 3.61 MeV, ⁵⁴Cr(p,n)⁵⁴M_n for 2.23 MeV < E_p < 3.61 MeV, ⁵¹V(p,γ)⁵²Cr for 0.93 Mev, < E_p < 4.47 MeV, ⁵¹V(p,n)⁵¹Cr for 1.58 MeV < E_p < 4.47 MeV, ⁶⁸Zn(p,γ)⁶⁹Ga for 1.67 MeV ≤ E_p ≤ 4.97 MeV, ⁶⁸Zn(p,n)⁶⁸Ga for 3.77 MeV ≤ E_p ≤ 5.03 MeV, ⁶⁸Zn(p,α)⁶⁵Cu for 3.36 MeV ≤ E_p ≤ 5.48 MeV, ⁴⁸Ca(p,γ)⁴⁴Sc for 0.58 MeV ≤ E_p ≤ 2.67 MeV, ⁴⁸Ca(p,n)⁴⁸Sc for 0.96 ≤ E_p ≤ 2.67 MeV, ³⁷Cl(a,γ)⁴¹K for 2.90 Mev ≤ E_α ≤ 5.23 MeV, ⁶²Ni(α,γ)⁶⁶Zn for 5.07 MeV ≤ E_α ≤ 8.64 MeV, ⁶²Ni(α,n)⁶⁵Zn for 6.95 MeV ≤ E_α ≤ 8.76 MeV, ⁶⁴Ni(α,γ)⁶⁸Zn for 4.50 MeV ≤ E_α ≤ 7.45 MeV, and ⁶⁴Ni(α,n)⁶⁷Zn for 5.29 ≤ E_α ≤ 7.44 MeV. Substantial drops in cross sections, by factors from three to five, were observed above the neutron thresholds for all of the radiative capture reactions except ⁴⁸Ca(p,γ)⁴⁹Sc. These “competition cups” are caused by competition from the neutron channel. In the ⁴⁸Ca(p,γ)⁴⁹Sc and ⁶⁸Zn(p,α)⁶⁵Cu reactions, significant though smaller neutron competition effects were observed. The measured cross sections have been compared with cross sections calculated using global Hauser-Feshbach models. It was thus established that: (i) isospin mixing should be assumed to be complete in these nuclear reaction models, (ii) width fluctuation corrections should be included in the treatment of the competition effects, and (iii) black nucleus strength functions for the neutron channels lead to inadequate neutron transmission functions, and should be replaced by more realistic strength functions which include the effects of size resonances. Cross sections calculated with current versions of global Hauser-Feshbach models, which incorporate these modifications, agree with those measured for the fourteen reactions studies to within a factor of two in almost all cases, and to within a factor of three in all cases.

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