J. David Bowman

A novel zero time detector for heavy ion spectroscopy

Abstract The design, construction and test of a heavy ion time pick-off system are described. The detector presents a homogeneous foil of a few μg/cm 2 thickness to the beam. Secondary emission electrons are isochronously transported to a channel plate electron multiplier by crossed electric and magnetic fields. A time resolution of (230±30) ps has been measured using natural alpha particles and a time coincidence between a surface barrier silicon detector and the foil time pick-off system. Sources of the measured time dispersion are discussed.

Search for time reversal invariance violation in neutron transmission

Time reversal invariance violating (TRIV) effects in neutron transmission through a nuclear target are discussed. Here, we demonstrate the existence of a class of experiments that are free from false asymmetries. We discuss the enhancement of TRIV effects for neutron energies corresponding to p-wave resonances in the compound nuclear system. Finaly, we analyze a model experiment and show that such tests can have a discovery potential of 102-104 compared to current limits.

A 207Bi light pulser for stabilization of scintillation and lead glass Cherenkov detectors

Abstract The design, fabrication techniques, and performance parameters are presented for a light pulser consisting of radioactive 207Bi embedded in capsulses of various types of plastic scintillator material. A typical resolution of 16% (fwhm) for the 0.974 MeV conversion electron line was obtained. A method whereby the contribution to the resolution due to photoelectron statistics can be separated from the total measured resolution is described. An application of these pulsers to the stabilization of an array of 60 lead glass counters is described.

The pion single charge exchange reaction

Abstract We report on the pion single charge exchange program at LAMPF. The LAMPF π° spectrometer is described and its successful performance in this first data run is discussed. Results on the excitation of the isobaric analog state (IAS) in pion single charge exchange at forward angles are presented. The IAS was observed for nuclei throughout the periodic table. The mass and energy dependence of the forward angle differential cross section is discussed. An angular distribution for the reaction 3 He( π − , π °) 3 H at angles from 0° to 84° at a bombarding energy of 200 MeV is presented. The data indicate a substantial contribution from the spin-flip amplitude. An angular distribution for the 13 c ( π + , π °) 13 N (IAS) reaction for angles from 0° to 45° at a bombarding energy of 150 MeV is presented. The partial angle integrated cross section ( θ

Chaos in a Gravo-Magneto Neutron Trap

Performance of a neutron trap for cleaning quasi-trapped neutrons depends on what fraction of the neutron orbits are chaotic. In this paper we argue that the Lyapunov characteristic exponent is a good measure the chaos because regular orbits have Lyapunov exponent zero and chaotic orbits of a given energy have a common non-zero Lyapunov exponent. The Lyapunov exponent describes the rate of exponential divergence for infinitesimally perturbed initial conditions [1,2]. We show how to calculate the fraction of chaotic trajectories using Benettins algorithm [1]. We evaluate the fraction of non-chaotic orbits for a trap that consists of a vertical multipole, gravity, and a current loop at the bottom of the trap.

Test of time reversal symmetry with resonance neutron scattering

Discussions for using thermal neutron scattering from nuclei for symmetry measurements stem from past experiments which have observed large parity violating effects in neutron scattering. The proposed LAMPF II proton storage ring spallation neutron source is a vast improvement over the neutron source used in the parity measurements. A proposal for a time reversal symmetry measurement at the LAMPF II facility is presented. (AIP)

Tests of time reversal in neutron-nucleus scattering

Experiments to test time‐reversal invariance are discussed. The experiments are based on observables constructed from the momentum and spin vectors of epithermal neutrons and from the spin of an aligned or polarized target. It is shown that the proposed tests are detailed balance tests of time‐reversal invariance. The status of the experiments is briefly reviewed.

Study of parity nonconversation with epithermal neutrons

I describe a new generation of experiments studying the weak interaction between nucleons. Measurements of the effect of this interaction are few in number and the significance of the observed effects are generally small. It is well known that the weak interaction violates parity. This was first experimentally established by C. S. Wu through measurement of an asymmetry of electrons emitted in the beta-decay of polarized 60Co. The measured asymmetry was large because beta decay is a weak interaction process. For a process in which the strong interaction can contribute, we expect much smaller asymmetries, or order 10-7.

ISOVECTOR RESONANCES IN PION CHARGE EXCHANGE

The (..pi../sup + -/, ..pi../sup 0/) reactions as probes of isovector resonances are discussed. Experimental observation of the isovector monopole resonance is reported. Experimental results are presented for L = 0, 1, and 2 isovector resonances and are compared to random-phase approximation calculations.