J. Lang

Measurement of T20 in Elastic Electron-Deuteron Scattering

The authors report on a measurement of the tensor analyzing power T{sub 20} in elastic electron-deuteron scattering in the range of four-momentum transfer from 1.8 to 3.2 fm{sup {minus}1}. Electrons of 704 MeV were scattered from a polarized deuterium internal target. The tensor polarization of the deuterium nuclei was determined with an ion-extraction system, allowing an absolute measurement of T{sub 20}. The data are described well by a non-relativistic calculation that includes the effects of meson-exchange currents.

Search for cold-fusion events

Abstract In a recent electrochemical investigation M. Fleischmann and S. Pons [1] found some excess heat, which — according to the authors — was due to the cold fusion of deuterium nuclei. Using a very similar experimental arrangement we looked for the characteristic neutrons and gamma rays from the dd fusion reaction. None were found. In addition, LaNi5, a substance which is known to absorb a very large amount of hydrogen, was loaded with deuterium gas. Again no nuclear fusion processes could be observed.

Direct determination of a short nuclear lifetime (≈10−20s) by the proximity scattering method

Abstract A nuclear reaction with three outgoing particles can proceed in two sequential stages, one of the product particles (R) of the first step being unstable. Under certain conditions, two of the three particles in the final state can undergo a further nuclear (“proximity scattering”). The probability for such a process to occur depends on the lifetime of the unstable particle R, as shown by a simple classical analysis. A quantal estimate of the proximity scattering cross section is presented and an experiment described in which the correlations between the protons and neutrons of the reaction 12C(d, pn)12C at a deuteron energy of 5.39 MeV were measured. A lifetime of τ = 0.7 × 10−20s can be assigned to the level group at 3.5 MeV in 13N.

Elastic scattering of 9Be on heavy target nuclei

Abstract The elastic scattering of 9 Be ions on Mg, Al, Si, Ca, Ni, Ag and Au target nuclei has been studied at 14, 20 and 26 MeV projectile energy. Excitation curves on Si were measured at four angles in the energy range of 14–20 MeV. A universal optical potential fitting all these angular distributions was found and ambiguities of the parameters are discussed. For each target the interaction distance, the strong absorption distance and the sensitive regions were calculated.

Fusion and direct reactions for strongly and weakly bound projectiles

Abstract The interaction of 6 Li, 9 Be and 12 C projectiles with a 28 Si target was investigated by measuring the angular distributions of the elastically scattered projectiles and of the emitted protons, deuterons and α-particles. The experiment was performed in order to deduce direct and compound nucleus process contributions to the total reaction cross section and to study the influence of the projectile structure on the relative importance of these two mechanisms. Optical model parameters and therefore the total reaction cross section are strongly influenced by the binding energy of the projectile. The parameters of the Glas-Mosel model describing the fusion reaction vary smoothly with the atomic number. In the system 9 Be + 28 Si around 50% of all reactions are direct processes even at energies near the Coulomb barrier, whereas in the other systems the direct part amounts to 15 % ( 12 C) and 30 % ( 6 Li) only.

Positron polarization in the decay of polarized N-12: a precision test of the Standard Model

The longitudinal polarization of positrons emitted along and opposite to the nuclear spin direction has been measured in the decay of polarized N-12. The results are consistent with the Standard Model prediction. In manifest left-right symmetric models this measurement provides a lower bound of 310 GeV/c(2) at 90% CL on the mass of a possible right-handed gauge boson contributing to the electroweak interaction. In generalized versions of this model our measurement provides constraints complementary to those set by high-energy experiments

Performance of a Polarized Deuterium Internal Target in a Medium-Energy Electron Storage Ring.

Abstract A polarized deuterium target internal to a medium-energy electron storage ring is described in the context of spin-dependent (e,e′d) and (e,e′p) experiments. Tensor polarized deuterium was produced in an atomic beam source and injected into a storage cell target. A Breit-Rabi polarimeter was used to monitor the injected atomic beam polarization. An electrostatic ion-extraction system and a Wien filter were utilized to measure on-line the atomic fraction of the target gas (71 ± 2%) in the storage cell. A target thickness t ⋍ 2 × 10 13 2 H/cm 2 was achieved. The target tensor polarization was varied from P zz + = 0.49(3) to P zz − = −0.89(6) while keeping the vector polarization P z at zero. The luminosity was ∼ 2 × 10 31 e − · 2 H · cm −2 s −1 at a beam current of 120 mA. The performance was stable over a fiv running period. A large acceptance non-magnetic detector system was used for the electron-proton (deuteron) coincidence measurement. It is demonstrated that these techniques result in low backgrounds due to scattering from species other than the polarized target gas and allow for fast and flexible orientation of the target spin. Specific issues such as interfacing the experiment to the storage ring and monitoring the performance of the target system are discussed in detail.

Search for right-handed weak currents in the beta-asymmetry-polarization correlation from N-12 decay

Abstract The polarization of positrons emitted along and opposite to the nuclear spin direction has been measured in the decay of polarized 12 N. The results are consistent with the Standard Model prediction. In manifest left-right symmetric models this measurement provides a lower limit of 220 GeV/c 2 at 90% CL on the mass of an eventual right-handed gauge boson contributing to the electroweak interaction.

Cross section and analyzing power A y in the breakup reaction H 2 ( p →, pp ) n at 65 MeV: Collinearity configurations

Kinematically complete breakup cross section and proton analyzing power data for four different collinearity configurations (neutron at rest in the c.m. system) have been measured in the reaction [sup 2]H([ital [rvec p]],[ital pp])[ital n] at [ital E][sub [ital p]][sup lab]=65 MeV. The experimental data are compared with rigorous solutions of the Faddeev equations using the Argonne AV14, Bonn B, Nijmegen, and Paris potentials. While the overall agreement is quite good there exist distinct discrepancies between theoretical and experimental cross section and analyzing power data in some regions of phase space.

A quantitative monitor for beam intensity and polarization profiles

Abstract A beam profile monitor is described which permits a rapid quantitative determination of the beam intensity profiles I(x), I(y) in two directions (x, y) perpendicular to the beam, as well as the proton beam-polarization profiles Py(x), Py(y), Px(y) and Px(x) for a 50 MeV proton beam. The device consists of two wheels which move thin strips of graphite through the beam. Four scintillation detectors are used to detect protons elastically scattered from the graphite targets. An encoder digitizes the position of the targets associated with each detected proton. The scanner is interfaced with a computer. Performance figures for the scanner are given. Typically, when a 0.1 μA beam of 3 mm diameter is interrupted by the targets during 10% of the time, a 1 min measurement suffices to determine the center of the beam to ±4 μm and the beam polarization to ±0.3%.