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Title: Experiments on nuclear structure
Author: Pullen, D. J.
ISNI:       0000 0004 2742 5551
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1963
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Magnetic deflection techniques have been employed to measure proton angular distributions from some (d,p) and (t,p) reactions. In many cases the distributions exhibit typical stripping patterns and their analysis in terms of plane wave and distorted wave theories of stripping has enabled spin and parity assignments to be made for a number of excited nuclear levels. These theories are briefly outlined in Chapter 1 of this thesis and the experimental procedures are described in Chapter 2. The (d,p) reaction has been studied at an incident energy of 3 MeV with target nuclei B10, B11, C12, C14 and O16 and an account of this investigation is given in Chapter 3. Although the plane wave theory gives a good account of the angular distributions corresponding to the low-Q transitions (say Q ≤ 2 MeV) it is not a good approximation for the high-Q transitions. This is in accord with Wilkinson's suggestion that distortion effects should be quite small even at low deuteron bombarding energies providing also that the reaction Q-value is low. Agreement with the high-Q ground state distribution for B11 could only be obtained with distorted wave theory if a cut-off radius were used. This may indicate the need for taking into account finite range effects in this theory. The Se76(d,p)Se77 reaction has been studied at 7.8 MeV bombarding energy and eleven angular distributions corresponding to the ground and ten excited states of Se77 have been analysed using distorted wave theory. This investigation is described in Chapter 4. Deuteron and proton elastic scattering measurements have also been made from Se76 and Se77, respectively. The optical model potentials required to describe the stripping distributions are found to be entirely consistent with those derived from the elastic scattering data. In Chapter 5 an account is given of a systematic study of the (t,p) reaction for target nuclei B10, B11, C12, C14, O18, Si28, Si29 and Ca40. This investigation was carried out at triton energies between 8 and 13 MeV. In the majority of cases the angular distributions are observed to be strongly forward peaked and these have been analysed in terms of Newn's plane wave theory of double stripping. With the exception of the B10(t,p)B12 and C12(t,p)C14 reactions the agreement in general is found to be very satisfactory. In addition to the ground state, nine excited states of B13 were observed and information on the spins and parities of six of them have been obtained. The excitation energies of only four excited states were previously known. C16 had not previously been observed and the present investigation has shown this to be stable by 4.25 MeV against neutron emission, in good agreement with the predicitons of Zel'dovich. The ground state was confirmed to be O+ and the first excited state at 1.753 MeV excitation is probably 2+. The delayed neutron emission for C16 has also been studied and its measured half-life found to be 0.74 ± 0.03 seconds. Angular distributions were measured for the ground and nine excited states of O18 and ground and four excited states of O20. Only one state, at 4.45 MeV excitation in O18, could not be interpreted by a double stripping process. Spin-parity assignments from the reactions Si28(t,p)Si30, Si29(t,p)Si31 and Ca40(t,p)Ca42 are in good agreement with earlier measurements. The Be11 nucleus has been studied using the Be9(t,p)Be11 reaction at 6 and 10 MeV triton energies. This investigation is described in Chapter 6. At the higher bombarding energy six energy levels of Be11 were observed and three of these were found to have natural widths in excess of 10 keV. Proton distributions were measured at both energies for the ground and first excited states. Their interpretation in terms of a double-stripping mechanism is complicated by the presence of large backward peaks but the distributions are not inconsistent with the spins of 1/2 - and 1/2 +, respectively, predicted by Talmi and Unna. Angular distributions from the C12(t,α)B11 reaction at 10 MeV triton energy were also studied in an attempt to obtain information on the spins and parities of some of the states in B11 which are involved in the beta-decay of Be11. In Chapter 7 an account is given of triton elastic scattering measurements made at incident energies 6.4, 6.8 and 7.2 MeV from C12, O16, O18, F19 and Ca40. Only the scattering from F19 and Ca40 can be described by the optical model, although the optical parameters are ambiguous. The scattering distributions from O16 at all three energies exhibit large backward peaks suggestive of compound resonance scattering. Optical model parameters derived from the triton scattering data have been uesd by Rook and Mitra to analyse the proton distributions from Ca40(t,p)Ca42, using distorted wave theory. A brief account of the results is given in Appendix C.
Supervisor: Wilkinson, Denys H. Sponsor: U.K. Department of Scientific and Industrial Research
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Physics ; Nuclear structure theory ; plane wave theory ; distorted wave theory ; double stripping reactions ; light nuclei