R. Müller

PHOTOPEAK EFFICIENCY AND RESPONSE FUNCTION OF VARIOUS NaI(Tl) AND CsI(Tl) CRYSTALS IN THE ENERGY RANGE UP TO 11 Mev

Abstract The photopeak efficiency for gamma-rays of energy ranging from 661 keV to 10.83 MeV, for scintillation counters with NaI(Tl) crystals of dimensions 2″ × 2″, 3″ × 3″, 5″ × 4″ and a CsI(Tl) crystal of 2 3 4 ″ × 2 3 4 ″ was determined. The measurements were carried out with a narrow collimated and a broad parallel gamma-ray beam, using the (n,γ)-reaction as a gamma source. The effect of the energy of the gamma quanta on the shape of the response function was also measured for the same crystals and energies.

Large angle elastic scattering of 9Be ions on carbon isotopes

Abstract The differential cross sections for elastic scattering of 9 Be on the carbon isotopes 12 C and 13 C were measured at two different energies (11.4 and 14.9 MeV c.m.). The anomalously high cross sections for backward angles are explained as contributions of 3 He and 4 He exchange processes. The calculations were performed with an optical model for potential scattering and a finite range DWBA model for the transfer processes.

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.

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%.

Deuteron break-up in the field of the nucleus

Abstract The break-up of deuterons in Coulomb and nuclear fields is calculated in the framework of a distorted-wave Born approximation (DWBA). The matrix element in the post-interaction formulation is evaluated using a partial-wave decomposition. The results are in very good agreement with recent experiments, but only if nuclear forces are included. In addition, other theoretical models for the disintegration of deuterons are reviewed critically.

Energy dependence of proximity scattering

Abstract The dependence of proximity scattering on the energy of the incident particles has been investigated in the reaction 7 Li(d, nα) 4 He.