A fluctuation analysis of the reaction 31P(p, α)28Si

doi:10.1016/0375-9474(68)90151-6

Nuclear Physics A

Volume 108, Issue 1, 29 January 1968, Pages 150-176

https://doi.org/10.1016/0375-9474(68)90151-6 Get rights and content

Abstract

The reaction ³¹P(p, α)²⁸Si has been investigated for alpha particles detected at 13 angles in the proton energy range 8.50–12.30 MeV, corresponding to excitations in the compound nucleus ³²S of between 17.36 and 21.16 MeV. The excitation functions were measured in ten keV steps. The two α-particles groups α₀ and α₁ were recorded.

All of the data, i.e. 26 excitation functions each of 380 points, are quantitatively in agreement with the Hauser-Feshbach statistical assumptions including statistical fluctuations. No evidence is found for direct interaction or for doorway states.

The mean level widths of the compound nucleus for decay to the ground and first excited states of ²⁸Si have been found to be 47±7 keV and 42±5 keV, respectively. The statistical dependences of these values on the range of data n and on the experimental values of the auto-correlation are discussed and found to be important considerations.

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An excitation function for the ²⁷Al(n, α) reaction has been measured in steps of about 15 keV throughout most of the energy range between 13.45 and 14.91 MeV in an effort to observe structure in the cross section. The insulated core transformer (ICT) neutron facility was used as the neutron source; a rotating, tritiated titanium target, capable of handling ion beams with currents up to 10 mA and with energies up to 450 keV, was employed. Using the activation method, a total of about 500 relative cross-section measurements were made at 87 different neutron energies. Fluctuations with magnitudes of about 1.5 % were observed in the cross section after all of the data had been correlated and corrected for the anisotropy and scattering effects that had been determined experimentally. A statistical treatment of the data yielded a compound nucleus level width of about 30 keV, which is reasonable for a ²⁸Al nucleus excited to 20–22 MeV. The observed structure can be explained in terms of Ericson fluctuation theory.
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Absolute differential cross sections have been measured for the elastic scattering of protons from ³¹P. Excitation functions were measured for incident proton energies from 8.0 to 10.0 MeV in 10 keV steps at 14 angles and in 50 keV steps at 13 angles. The energy averaged angular distributions have been analysed using the optical-model and Hauser-Feshbach theories and the excitation functions have been analysed using the statistical theory of fluctuations. The fractions of direct reaction calculated by the two methods have been compared and are in good agreement for values of $Y_{D} ⪆ 0.8$ .
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^†: Now at Australian National Laboratory, Canberra.

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Nuclear Physics A

Abstract

References (27)

Nuclear Physics

Ann. of Phys.

Phys. Lett.

Nucl. Instr.

Phys. Lett.

Nuclear Physics

Phys. Lett.

Nuclear Physics

Phys. Lett.

Advan. Phys.

Bull. Am. Phys. Soc.

Cited by (9)

Structure in the total <sup>27</sup>Al(n, α)<sup>24</sup>Na cross section around 14 MeV

Energy levels of A = 21-44 nuclei (V)

Analysis of the reaction <sup>31</sup>P(p, p<inf>0</inf>) in the energy range 8.0-10.0 MeV

Models of reactions - Compound-nucleus (CN) reactions

Comment on the compound-nucleus cross section from nuclear charge-density distributions

Isospin dependence of the nuclear level width