T.B. Clegg

Polarization measurements and phase shifts for p-4He scattering between 3 and 18 MeV

Abstract Angular distributions of the polarization in proton elastic scattering from 4 He were measured at laboratory energies near 4.6, 6.0, 7.9, 9.9 and 11.9 MeV. A phase-shift analysis of available cross-section and polarization angular distributions between 3.0 and 17.5 MeV was performed. The energy dependence of the phase shifts was represented by an effective-range expansion. The phase shifts determined from this expansion permit calculation of the p- 4 He polarization with an accuracy of better than ± 0.02 in this energy range.

The cross section and vector analyzing power for the elastic scattering of 15.0 MeV deuterons from 10B, 12C, 13C, 14N and 16O

Abstract Angular distributions of the cross section and vector analyzing power have been measured for the elastic scattering of polarized 15.0 MeV deuterons from 10B, 12C, 13C, 14N and 16O. The general features of the cross section σ/σR and analyzing power iT11 are reproduced by optical-model calculations obtained by fitting either cross-section and analyzing power data individually or by fitting the cross-section data and the product (σ/σR)(iT11). The optical-model parameters obtained are seen to change in a consistent manner for the nuclei studied.

Analyzing power and differential cross section at 9.9, 11.9 and 13.9 MeV for Ca(n, n)Ca

Abstract The analyzing power and differential cross section for elastic neutron scattering from calcium have been measured at 9.9, 11.9 and 13.9 MeV using the 2 H(d, n) 3 He source reaction and neutron time-of-flight (t.o.f.) techniques to detect the scattered neutrons. Polarized neutron beams were produced via the polarization transfer reaction 2 H( d , n ) 3 He at θ = 0°. The data have been corrected for finite geometry and multiple scattering effects. None of the global neutron-nucleus optical model parameter sets usually referred to in the literature reproduces the present cross-section and analyzing power data. Individual as well as energy-averaged fits of the data resulting from new optical model searches are presented. It is shown that the quoted uncertainties of a recent empirical determination of the real part Δ V c of the Coulomb correction term are probably underestimated. Our imaginary Coulomb correction term Δ W c agrees quite well with both a very recent empirical determination and theoretical studies. Although the quality of the fits to the data can be improved by adding l -dependent potentials to the general optical potential, no definite conclusions can be drawn from the present data as to whether or not l -dependent potentials are important in neutron-calcium scattering in the energy range investigated. The data have also been analyzed using a Fourier-Bessel series description of the real central optical potential. Comparing the X 2 values, the experimental data are better reproduced by the Fourier-Bessel method than by our Woods-Saxon optical model analyses. The Fourier-Bessel potentials obtained show strong deviations from the standard Woods-Saxon shape but are in good agreement with calculations using the nuclear structure approach.

Proton scattering from 9Be between 6 and 30 MeV and the structure of 9Be

Abstract Differential cross-section excitation functions at lab scattering angles 86.9°, 120.0°, 140.0° and 160.0° were measured for 9Be(p, po)9Be, 9Be(p, p2)9Be and 9Be(p, d0)8Be at proton lab energies from 6 to 15 MeV in 100 keV steps. A broad anomaly was observed in the 9Be(p, p0)9Be excitation functions. Differential cross-section angular distributions were measured for 9Be(p, p0)9Be and 9Be(p, p2)9Be at lab energies of 13.0, 14.0, 15.0, 21.35 and 30.3 MeV and for 9Be(p, d0)8Be at 13.0, 14.0, 15.0 and 21.35 MeV. Angular distributions of polarization analysing powers for 9Be( p ,p0)9Be, 9Be(p, p2)9Be and 9Be( p , d0)8Be were measured at 8.0, 11.0, 12.0, 13.0 and 15.0 MeV. A spherical optical-model (SOM) analysis of the elastic scattering angular distribution data from 13.0 to 30.3 MeV showed that an energy dependence of only VR and Ws (volume real and surface imaginary depths) is sufficient to reproduce the measurements. Coupled-channels (CC) analyses were made with a quadrupole-deformed optical-model potential and strong coupling of 3 2 − , 5 2 − and 7 2 − levels of a K = 3 2 ground-state rotational band of 9Be. The 9Be(p, p0)9Be and 9Be(p, p2)9Be data from 13.0 to 30.3 MeV were analyzed simultaneously at each energy, varying only VR and Ws with energy, for a potential deformation of β = 1.1. Both SOM and CC analyses indicated the same energy dependence in VR, while Ws averaged 3.5 MeV lower in CC than in SOM, with both energy dependences consistent with previous analyses of nucleon scattering from 1p shell nuclei.

Polarization transfer in the 2H(d,n)3He reaction at θ = 0°

Abstract The vector polarization transfer coefficient K y y ′ and the tensor analyzing power A zz have been measured for the 2 H( d n ) 3 He reaction at θ = 0° over an incident deuteron energy range from 1 to 15 MeV in 0.5 MeV steps. The results agree with the previous 2 H( d n ) 3 He measurements of Simmons et al. and are nearly identical to the 2 H( d n ) 3 H measurements of Clegg et al. in the region of overlap. The present results provide an accurate and complete set of the observables necessary to use the 2 H( d , n ) 3 He reaction as a source of polarized neutrons.

Global parameterization of the nucleon-nucleus scattering potential

Abstract A new parametirization of the nucleon-nucleus optical model potential for 16⩽ E p ⩽65 MeV, 10⩽ E n ⩽26 MeV, and 40⩽ A ⩽209 is summarized, emphasizing features that differ from previous parameterizations and significant uses of this potential.

Isospin-forbidden T = 32 resonances in 25Al, 29P and 33Cl, and the systematics of isospin mixing☆

Abstract The two lower T = 3 2 states in 25Al and the lowest T = 3 2 states in 29P and 33Cl were observed as isospin-forbidden proton elastic-scattering resonances. The widths of these states were deduced by combining polarisation analysing-power data in the vicinity of these resonances with high-resolution cross-section data in an analysis incorporating the effects of finite beam resolution (≈ 650 eV), Doppler broadening, and straggling of the incident beam in the target. A new estimate of Γ for the lowest T = 3 2 state in 21Na was obtained by re-analysing previously measured data. The elastic-proton reduced widths γp2 of the T = 3 2 states observed in scattering from T = 0 nuclei with 8 ≦ A ≦ 40 are well represented by the formula γp2 = cA2.4 where c = 0.128 ± 0.007 eV for target nuclei with A = 8n + 4 and c = 0.023 ± 0.009 eV for A = 8n, where n is integral. Possible mechanisms for this behavior of γp2 which is not predicted by previous calculations, are discussed.

A high efficiency bunching system for polarized beams

Abstract A three-stage bunching system has been constructed for use with a Lamb-shift polarized ion source. The first stage consists of a linear voltage ramp of approximately 100 V peak-to-peak applied to the anode of the duoplasmatron. This voltage ramp prebunches the beam at 4 or 2 MHz into bursts approximately 70 ns wide. The beam is compressed further with a two-stage double-drift buncher system. With this system we have been able to transport 75% of the dc beam to the target and bunch up to 90% of this beam into pulses approximately 2.0 ns wide (fwhm). Average pulsed currents of up to 150 nA have greatly enhanced our capability to perform ( p , n ), ( d , n ), ( n , n ) and ( n , γ) experiments.

The polarization of 3He particles elastically scattered from 9Be, 12C and 16O

Abstract The polarization of 3 He particles scattered from 9 Be, 12 C and 16 O has been measured at 18 MeV (and 20 MeV for 12 C) over an angular range θ c.m. = 20°–60°. Cross-section angular distributions out to 170° have also been obtained. The polarization distributions for the three nuclei appear similar and compare reasonably well with optical-model calculations. A spinorbit well epth greater than 3 MeV is required in the calculations to predict polarizations having the magnitudes of the measured values. Comparisons are made between the data and predictions which use optical-model parameter families related by the discrete and continuous ambiguities.

Four-nucleon studies: (III). Measurement of the 2H(d, p)3H polarization via the 3H(→, d)2H reaction and comparison to polarization in 2H(d, n)3He

Abstract Accurate angular distributions of the analyzing power in the 3 H ( p , d ) 2 H reaction were measured at eight energies from 6.7 to 14.7 MeV. By reciprocity, these analyzing powers are the same as the proton polarizations of the 2 H ( d , p ) 3 H reaction from 2.0 to 14.0 MeV. The products P1 (θ)σ(θ) were fitted with a series of even-order associated Legendre functions, and two terms in the series were found to be sufficient to describe the reaction up to 14 MeV. Comparisons are made with the polarizations from the mirror reaction 2 H ( d , n ) 3 He , and good agreement is found when the reactions are compared at the same exit-channel energies. The implications of this are discussed in the light of other recent comparisons which suggest that differences in these mirror reactions may be a violation of charge symmetry of nuclear forces.