B. Zeidman

Precision Rosenbluth measurement of the proton elastic form factors

We report the results of a new Rosenbluth measurement of the proton electromagnetic form factors at Q2 values of 2.64, 3.20, and 4.10 GeV2. Cross sections were determined by detecting the recoiling proton, in contrast to previous measurements which detected the scattered electron. Cross sections were determined to 3%, with relative uncertainties below 1%. The ratio mu(p)G(E)/G(M) was determined to 4%-8% and showed mu(p)G(E)/G(M) approximately 1. These results are consistent with, and much more precise than, previous Rosenbluth extractions. They are inconsistent with recent polarization transfer measurements of similar precision, implying a systematic difference between the techniques.

Measurements of Deuteron Photodisintegration up to 4.0 GeV

The first measurements of the differential cross section for the d(γ,p)n reaction up to 4.0 GeV were performed at the Continuous Electron Beam Accelerator Facility (CEBAF) at Thomas Jefferson Laboratory. We report the cross sections at the proton center-of-mass angles of 36°, 52°, 69°, and 89°. These results are in reasonable agreement with previous measurements at lower energy. The 89° and 69° data show constituent-counting-rule behavior up to 4.0 GeV photon energy. The 52° and 36° data disagree with the counting-rule behavior. The quantum chromodynamics (QCD) model of nuclear reactions involving reduced amplitudes disagrees with the present data.

Search for the tetraneutron by the double-charge-exchange of negative pions

Abstract The momentum spectrum for double-charge-exchange of π − on 4 He has been measured at 0° and T π − = 165 MeV. A 1σ upper limit of 22 nb/sr is set on the cross section for transitions leading to bound tetraneutrons. The cross section in the continuum region is shown to be inconsistent with a four-neutron phase space distribution, while a model including final state interaction effects gives better agreement with experiment.

A high-resolution mass-identification system for heavy ions

Abstract A ΔE − E surface-barrier detector time-of-flight telescope in heavy-ion reactions yields 150 keV energy resolution and 84 ps time resolution in routine operation. Fast analog circuitry, pile-up rejection, and direct computer-memory access allow high count rates that are desirable for the study of heavy-ion transfer reactions at extreme forward angles.

The reaction 25Mg(3He,d)26 Al at 12 MeV

Abstract The 25 Mg( 3 He,d) 26 Al reaction was studied at E( 3 He ) = 12 MeV by use of the Argonne tandem Van de Graaff and a broad-range magnetic spectrograph. All known states up to 4.2 MeV were observed in this experiment; but the doublets at 2.07 MeV and 4.20 MeV have not been resolved. For the 15 strongest transitions, angular distributions between 5° and 25° were measured. They all have characteristic l = 0, l = 2 or l = 0+2 stripping patterns. The l = 0 admixtures in the angular distributions limit spins and parities to 2 + or 3 + for the states at 2.55, 2.92, 3.59, 3.68 and 3.75 MeV, for which no spins and parities were previously known. Spectroscopic factors have been extracted with the Oak Ridge DWBA code Julie. The results are discussed in the framework of the unified model.

Scattering of alpha particles by Zn64 and Zn68

The elastic and inelastic scattering of 43-MeV alpha particles by Zn64 and Zn68 has been studied. Low-lying groups, with angular distributions in phase with elastic scattering, were found at 1.79 and 2.30 MeV in Zn64 and at 1.66 and 1.89 MeV in Zn68. These groups are presumably from two-phonon levels. The two-phonon groups from Zn64 have about the same cross sections as those from Ni60, while those from Zn68 have only about a quarter of this value.

Nuclide distributions in deep inelastic reactions

Abstract The mass and charge of fragments produced in deep inelastic reactions induced by 236 MeV 40 Ar on targets of 42, 48 Ca, 50 Ti. 50 Cr, 56 Fe and 60 Ni were identified by using a time-of-flight ΔE - E detector telescope. The measured nuclide distributions are very broad along the mass asymmetry coordinate, but narrow along the charge asymmetry coordinate. A detailed description of the variations of the mass and charge distributions as a function of target neutron excess is obtained by calculating primary distributions assuming a diffusion-like mass transfer in a two-dimensional potential energy surface determined by liquid drop energies of two touching spheres and folding this primary distribution with the secondary particle decay pattern calculated in the statistical model. Exotic nuclei are produced with comparatively large cross sections.

Laser-driven source of spin-polarized atomic hydrogen and deuterium

Abstract A laser-driven source of spin-polarized hydrogen (H) and deuterium (D) that relies on the technique of optical pumping spin exchange has been constructed. In this source, H or D atoms and potassium atoms flow continuously through a drifilm-coated spin-exchange cell where potassium atoms are optically pumped with circularly-polarized laser light in a high magnetic field. The H or D atoms become polarized through spin-exchange collisions with polarized potassium atoms. High electron polarization ( ≈ 80%) has been measured for H and D atoms at flow rates ≈ 2 × 1017 atoms/s. Lower polarization values are measured for flow rates exceeding 1 × 1018 atoms/s. In this paper, we describe the performance of the laser-driven source as a function of H and D atomic flow rate, magnetic field strength, alkali density and pump-laser power. Polarization measurements as a function of flow rate and magnetic field suggest that, despite a high magnetic field, atoms within the optical-pumping spin-exchange apparatus evolve to spin-temperature equilibrium which results in direct polarization of the H and D nuclei.

Test of the Barshay-Temmer theorem for the reaction 10B + α → 7Li + 7Be

Abstract The Barshay-Temmer theorem has been tested via the reaction 10B(α,7Lig.s.)7Beg.s.and 10B(α,7Beg.s.)7Lig.s. at Eα=46 MeV. In order to minimize experimental uncertainties, angular distributions for both reactions were measured simultaneously; the symmetry required by the theorem was shown by the fact that the ratio between the intensities of the outgoing particles at a fixed angle is unity within the experimental uncertainties. This implies an extreme similarity of the wave functions of the ground-state isobaric doublet 7Li-7Be and provides a simple test of the charge independence of nuclear forces.

(α, d) reactions on N14 and Li6

Angular distributions of the emergent deuterons from the reactions Li/ sup 6/( alpha ,d)Be/sup 8/and N/sup 14/( alpha ,d)O/sup 16/ were obtain ed for an incident alpha-particle energy of 43 Mev. The experiment was performed in the 60-in. scattering chamber, the deuterons being selected by a system employing a double NaI(Tl) crystal dctector. The distributions, which cover the angular range between approximately 15 and 90 in the center-of-mass system, exhibit oscillatory behavior and forward peaking. Attempts to fit the data were made. In the case of N/sup 14/ a satisfactory fit can be obtained using spherical Bessel functions. Inclusion of some heavy-panticle stripping improves the fit to the data. In the case of Li/sup 6/ it was not possible to obtain a satisfactory fit. (auth)