Intermediate-energy Experiments Research Articles

A liquid hydrogen/deuterium target with very thin windows

Liquid hydrogen/deuterium targets with a typical size of a few millimeters have been constructed for use in intermediate energy experiments with phase space cooled particle beams. With a purely mechanical pressure stabilization system very thin target windows of 1.5 μm Mylar have been obtained. The main advantage of reduced window thickness is a diminution of background events from the window material. The working pressure of 0.2 bar allows the use of oxygen, nitrogen, and helium without modification of the setup. The design and operational characteristics of the target are described.

Spectral function of p-n pairs in 6Li, from the 6Li(p,p alpha )pn reaction at 200 MeV.

The spectral function for {ital p}-{ital n} pairs in the {sup 6}Li ground state (i.e., the distribution in {ital p}-{ital n} relative momentum {h bar}{ital k} for pairs whose c.m. is at rest in the laboratory) was measured for {ital k} ranging from 0.6 to 1.5 fm{sup {minus}1}, using the {sup 6}Li({ital p},{ital p}{alpha}){ital pn} reaction at 200 MeV. These and earlier 120 MeV {sup 6}Li({alpha},2{alpha}){ital pn} measurements show that, when {ital k} increases from 0.1 to 1.5 fm{sup {minus}1}, this function decreases by 4 orders of magnitude and is predicted within a factor of 2 by the plane-wave impulse approximation. The asymmetry for the {sup 6}Li({ital p},{ital p}{alpha}){ital pn} reaction induced with polarized protons was measured at 56{degree} c.m. and found to have the same bombarding-energy dependence as that for {ital p}-{alpha} elastic scattering. The {ital d}-{alpha} cluster probability of {sup 6}Li, determined by the {sup 6}Li({ital p},{ital p}{alpha}){ital d} reaction, was consistent with that found in other intermediate-energy experiments.

Electroweak interactions with the nucleon and tests of the standard model

Electroweak single-nucleon elastic scattering processes at all energies are calculated, motivated in part by possible future low and intermediate energy experiments with intense neutrino beams. We discuss means to extract nucleon form factors from a complete set of experiments. The goal is to provide model-independent tests of the standard model in the confinement regime of hadronic structure. This includes tests of the conserved vector current theorem, the presence of second-class currents, and the form of the weak neutral current. As a guide for future experiments, numerical calculations for charge-changing neutrino processes are presented using empirical form factors. Interesting low-energy (≈500 MeV) structure is found in cross sections and final lepton polarizations.

Experiments with Sub-Nanosecond Tandem Beam Pulses

The beam pulsing system, which was installed on the Florida State University FN tandem accelerator to prepare the beam for injection into the superconducting linac booster, has been used for a variety of experiments. The beam pulsing system consists of a 48 MHz buncher at the low-energy end and a 24 MHz parallel-plate chopper at the high-energy end, followed by a spiral-loaded cavity phase detector of F.S.U. design. Use of this detector in a phase-locked-loop circuit significantly improves the stability and resolution of the beam pulses. A second high-energy chopper operating at 9.7 MHz was installed to increase the time between pulses from 20 to 100 nsec for experiments. The system has been used to study the 11B(d,n)12C reaction at 12 MeV. Neutrons were detected in a plastic scintillator viewed by two photomultiplier tubes connected to a mean timer circuit. The overall timing resolution of about 500 psec provides adequate time-of-flight resolution at a distance of 2 m. Of particular interest in this reaction are a triplet of states in 12C between 18 and 21 MeV which have recently been studied in several intermediate-energy experiments. Angular distributions have been measured and coincidence experiments are underway to investigate the decay properties of these states. Another experiment has used the pulsed beam in conjunction with the mid-column stripper to search for nanosecond isomers and yrast traps with the 28Si + 56Fe reaction at 103 MeV.