S. P. Wells

An in-beam polarimeter for intermediate energy protons using p + d elastic scattering

The importance of high quality spin-observable data in intermediate energy nuclear physics requires that techniques be developed for obtaining accurate and reliable measurements of incident beam polarizations in a nondestructive manner. For this purpose, we have constructed, installed, and calibrated two transmission-type polarimeters at IUCF, in which p+d elastic scattering is used to determine the two transverse polarization components of a high energy proton beam. In this report, we discuss some of our experimental design considerations, and provide technical details on the actual implementation schemes chosen. Representative spectra are shown, and typical performance capabilities are described. We have also completed a calibration of the effective analyzing power of the polarimeter (Apol) as a function of the incident (beam) proton energy, and find Apol ≈ 0.51 over the entire proton energy range studied in this work ( ∼ 150–200 MeV) when θdlab = 42.6°.

Fragmentation of ‘‘stretched’’ 6− strength in 28Si(p↘,p↘′)28Si

Using a 198.3 MeV polarized proton beam, measurements have been made of the dσ/dΩ, A and DNN′ for the 28Si(p↘,p↘′)28Si reaction to locate the 6− strength for comparison with large basis shell model calculations. Based on both dσ/dΩ and A data, six states above 15 MeV were determined to carry 6− strength. The measurements of & were used as a meter of isospin mixing. The shell model calculations do not match the experimental results.

A calibration of the IUCF K600 focal plane polarimeter

We have carried out a precise determination of the effective analyzing power of the K600 focal plane polarimeter at IUCF for incident proton energies extending from 200 MeV down to 120 MeV. Two different calibration techniques, and several analyzer thicknesses, were used over this range. As the energy decreases, the effective analyzing power falls almost linearly. The polarimeter efficiency, however, rises rapidly, thus maintaining a reasonable figure‐of‐merit.

A measurement of the spin transfer observable DNN′ for p+p elastic scattering at Tp=200 MeV

Recent analyses of NN and {pi}N scattering data have resulted in values for the {pi}NN coupling constant which are significantly smaller than those obtained prior to 1987. These controversial results prompted us to investigate the usefulness of high-quality spin measurements towards resolving this issue. We found that the normal component spin transfer observable D{sub NN{prime}} for p+p elastic scattering is very sensitive to {ital g}{sup 2}{sub 0}, particularly at small angles. We have therefore determined precise values of D{sub NN{prime}} for this reaction for {theta}{sub {ital lab}}=5.0{degree}, 7.2{degree}, 8.4{degree}, 9.7{degree}, 11.8{degree}, 14.6{degree}, 18.8{degree}, 24{degree}, 30{degree}, and 38{degree} at an incident beam energy of 200 MeV. The forward-going proton was detected in the IUCF K600 spectrometer and the coincident recoil proton was detected in a Si/CsI detector telescope. Our preliminary D{sub NN{prime}} values are reproduced reasonably well by Arndt`s C200 solution, the Nijmegen PWA93, and the Nijmegen I potential, but differ severely from both Arndt`s SM94 global solution and the predictions of the Bonn potential.