James D. Kellie

A tagged photon spectrometer for use with the mainz 180 MeV microtron

This paper describes a photon tagging system which has been installed on the 180 MeV electron microtron at the Institut fur Kernphysik in Mainz for use in experiments on photonuclear reactions at intermediate energies. The system enables bremsstrahlung produced photons in the energy range 80–174 MeV to be tagged at rates up to 5×107 s−1.

A large solid angle detector for medium energy charged particles

A charged particle detector with 0.7 sr solid angular acceptance has been built, principally to detect protons in the energy range 25–150 MeV in experiments with tagged photon beams. The detector consists of a three element ΔE1−ΔE2−E plastic scintillator telescope. Position information is obtained from the time difference between signals from the two ends of each scintillator. The design of the detector and tests of its performance are described. An energy resolution of 2.8 MeV fwhm at 60 MeV proton energy, and a two-dimensional position resolution of 24 mm × 41 mm fwhm has been obtained. Successful operation in the tagged photon environment is demonstrated.

A facility for fast neutron time of flight experiments

Abstract Nuclear reaction experiments involving neutrons as primary or secondary particles have been performed on a multi-angle time of flight spectrometer with an electron linear accelerator source. Essential features in the design of a flexible arrangement with good resolution are discussed, and examples are given to illustrate the quality of the experimental results.

Spin-isospin excitation in 12C(γ, π+)12B∗ using tagged photons

The energy spectra of positive pions from the reaction 12C(γ, π+)12B∗ were measured at five angles, using quasi-monochromatic, tagged photons in the energy range from 176 to 182 MeV. Strong transitions to the isovector nuclear states in 12B at 0–1, 4.5, and 7.5 MeV were observed. The differential cross sections to these states have been obtained for the momentum transfers 0.5 < q < 1.2 fm−1. DWIA calculations have been carried out in momentum space for each observed state or group of states. Comparisons are made between the present data, previous data from bremsstrahlung experiments, and various DWIA calculations.

Differential cross section for the reaction 2H(γ, p)n from 133 to 158 MeV

The cross section for the reaction 2H(γ, p)n has been measured at laboratory photon energies Eγ = 133−158 MeV and c.m. angles between 30° and 150°. The reaction was induced by a tagged bremsstrahlung photon beam incident on a liquid deuterium target. The uncertainty in the absolute cross sections is ⩽ 5%. There is now reasonable agreement between recent measurements in this energy region and the overall data set now defines the cross section sufficiently well to provide a test of current models of the reaction.

Electromagnetic form factors of the nucleon

Abstract The internal structure of proton and neutron is manifested in a variety of observables. The form factors for elastic electron scattering which describe the distribution of charge and magnetic moments provide information vital for our understanding of the confined quark system. The form factors of the proton could be measured over a wide range of momentum transfer through the conventional method of Rosenbluth separation. The determination of the neutron form factors is more demanding; it will now benefit from coincidence experiments at modern cw accelerators. For the neutron charge form factor a measurement of the asymmetry in the scattering of high energy polarised electrons from polarised targets or the spin transfer to the recoiling neutron from unpolarised targets promises a big improvement. Experiments of this type have already been started and deliver first results.

Search for the {theta}{sup +} Pentaquark in the Reaction {gamma}d{yields}pK{sup -}K{sup +}n

A search for the Theta+ in the reaction gammad --> pK-K+n was completed using the CLAS detector at Jefferson Lab. A study of the same reaction, published earlier, reported the observation of a narrow Theta+ resonance. The present experiment, with more than 30 times the integrated luminosity of our earlier measurement, does not show any evidence for a narrow pentaquark resonance. The angle-integrated upper limit on Theta+ production in the mass range of 1.52-1.56 GeV/c2 for the gammad --> pK-Theta+ reaction is 0.3 nb (95% C.L.). This upper limit depends on assumptions made for the mass and angular distribution of Theta+ production. Using Lambda(1520) production as an empirical measure of rescattering in the deuteron, the cross section upper limit for the elementary gamman --> K-Theta+ reaction is estimated to be a factor of 10 higher, i.e., approximately 3 nb (95% C.L.).

Experimental study of oscillations, using computers

We describe an experimental investigation of the waveforms of free and forced oscillations of electrical and mechanical systems. Computer control of data-taking facilitates accurate measurements and the study of transients when the sine wave is switched on.