We describe an integrating cathode-pad read-out wire chamber for imaging high energy neutrons. This technology allows construction of a detector with a wide dynamic range, which is gatable, easily read out, and provides millimeter scale resolution. Results from a prototype 48 by 48 pixel array are presented.

High-energy spallation neutron sources are now being considered in the US and elsewhere as a replacement for neutron beams produced by reactors. High-energy and high intensity neutron beams, produced by unmoderated spallation sources, open potential new vistas of neutron radiography. We discuss the basic advantages and disadvantages of high-energy neutron radiography, and consider some experimental results obtained at the Weapons Neutron Research (WNR) facility at Los Alamos.

A variety of charge collection measurements by energetic protons and neutrons have been measured and compared. These include deposition in: small silicon junctions, large volume American and Russian silicon surface barrier detectors, and InGaAs photodiodes.

The Weapons Neutron Research Facility (WNR) is an intense, high energy spallation source, driven by the LAMPF 800 MeV proton linac. We describe below some of the basic and applied research projects which are currently being worked on at this facility

The RD-10/45 research and development effort on calorimeter/absorber optimization for a Relativistic Heavy Ion Collider dimuon experiment had an extended run in 1991 and 1992 at the BNL Alternating Gradient Synchrotron. Measurements were made of the leakage of 1–8 GeV/ c particles behind various model hadron calorimeters. Behavior of the calorimeter/absorber as a muon-identifier was studied. Comparisons of data from the RD-10/45 experiment to results calculated with the GEANT 3.15 simulation package using the GHEISHA and FLUKA hadron shower codes were made.

The statistical-model description of the neutron-induced fission of U isotopes has been developed using densities of intrinsic states and spin cutoff parameters obtained directly from appropriate Nilsson model single-particle levels. The first-chance fission cross sections are reproduced well when the rotational contributions to the nuclear level densities are taken into account. In order to fit the U(n,f) cross sections above the threshold of second-chance fission, we must: (1) assume that the triaxial level-density enhancement is washed out at an excitation energy of approximately 7 MeV above the triaxial barriers with a width of approximately 1 MeV, implying a gamma deformation for the first barriers where 10 < gamma < 20-degrees, and (2) include preequilibrium particle emission in the calculations. Above an incoming-neutron kinetic energy of approximately 17 MeV, our statistical model U(n,f) of cross sections increasingly overestimates the experimental data. This is not surprising since, at these high energies, little data exist on the scattering of neutrons to help guide the choice of optical-model parameters. A satisfactory reproduction of all of the available U(n,f) cross sections above 17 MeV is obtained by scaling our calculated compound-nucleus formation cross sections. This scaling factor falls from 1.0 at 17 MeV to 0.82 at 100 MeV.

Tritium ({sup 3}H, a heavy isotope of hydrogen) is produced by low energy neutron-induced reactions on various elements. One such reaction is n+{sup 3}He {yields}>{sup 3}H+{sup 1}H in which {sup 3}He is transmuted to tritium. Another reaction, which has been used in reactor production of tritium, is the n+{sup 6}Li {yields}> {sup 3}H+{sup 4}He reaction. Accelerator Production of Tritium relies on a high-energy proton beam to produce these neutrons using the spallation reaction, in which high-energy proton beam to produce these neutrons using the spallation reaction, in which high-energy protons reacting with a heavy nucleus produce a shower of low-energy neutrons and a lower-mass residual nucleus. It is important to quantify the residual radionuclides produced in the spallation target for two reasons. From an engineering point of view, one must understand short-lived isotopes that may contribute to decay heat. From a safety viewpoint, one must understand what nuclei and decay gammas are produced in order to design adequate shielding, to estimate ultimate waste disposal problems, and to predict possible effects due to accidental dispersion during operation. The authors have performed an experiment to measure the production of radioisotopes in stopping-length W and Pb targets irradiated by a 800 MeV proton beam, and are comparing the results to values obtained from calculations using LAHET and MCNP. The experiment was designed to pay particular attention to the short half-life radionuclides, which have not been previously measured. In the following, they present details of the experiment, explain how they analyzed the data and obtain the results, how they perform the calculations, and finally, how the experimental data agree with the calculations.

A statistical model is used with parameters obtained by fitting 232U(n,f) through U-236(n,f) and U-238(n,f) cross-section data to determine the U-237(n,f) fission cross section in the neutron energy range of 0.5 to 20 MeV. Below an incoming neutron energy of 0.5 MeV, the cross section is extrapolated using the neutron energy dependence of the U-235(n,f) reaction. The calculated values to experimental U-237(n,f) cross-section data are compared, and some adjustments are made to the calculated values to obtain a better fit to the existing data.

Measurements of the response of the participant calorimeter to 250–400 MeV/c π+, μ−, and e+ are described. The participant calorimeter is a Pb/Fe/scintillator sampling calorimeter with a novel wavelength shifting fiber optic readout which is used in experiment 814 at Brookhaven National Laboratory. The e+/π+ response ratio at 250–400 MeV/c is larger than it is at higher momenta. Previous measurements of the e/π response ratio with sampling calorimeters found that the value decreased as the particle energies were reduced below about 1 GeV. This difference is attributed to the different absorption probabilities for π+ and π− at low momentum.

Multiple Coulomb scattering is incorporated into numerous particle transport codes using various approximation techniques. We present a new technique that incorporates the Rutherford scattering process directly into the transport code as an additional interaction process. We avoid divergent values of the cross section by introducing a cutoff angle, and examine the effect of its value on the results we obtain.

We have incorporated some additions and modifications to LAHET (the Los-Alamos High-Energy Transport code) which enable it to be used for hydrocarbon scintillator pulse-height and efficiency calculations.

We consider interactions between 0.2–2.6 GeV protons on Au as a benchmark. We examine whether the utilization of improved intra-nuclear cascade and evaporation models improve the agreement between the codes and experimental data.

Neutron-induced fission cross section ratios from 0.5 to 400 MeV for samples of 233,234,236U relative to 235U have been measured at the WNR neutron Source at Los Alamos. The fission reaction rate was determined using a fast parallel plate ionization chamber at a 20-m flight path. Cross sections over most of the energy range were also extracted using the neutron fluence determined with three different proton telescope arrangements. Those data provided the shape of the 235U(n,f) cross section relative to the hydrogen scattering cross section. That shape was then normalized to the very accurately known value for 235U(n,f) at 14.1 MeV which will allow us to obtain cross section section values from the ratio data and our values for 235U(n,f).

By adapting routines from existing simulation programs for the interaction of neutrons and gammas with organic scintillators, a code has been produced to calculate the response of multi-element detectors to neutrons below 200 MeV and gammas below 10 MeV. The approach for the gamma calculations is similar to the macroscopic model used for neutron interactions. To test the approximations concerning gamma multiple-scattering and electron range-energy relations, measurements were made for the response of plastic scintillators to gammas at energies up to 1.3 MeV. The measurements focus on count rates and light-output distributions, and their analysis includes discussions of energy-to-light conversion and detector resolution. All measurements and calculations are in good agreement. The conclusions are discussed in terms of calculations of detection efficiencies for neutrons at energies of 1–200 MeV.

The Participant Calorimeter for Experiment 814 at BNL is a lead-scintillator sampling calorimeter. The response of the calorimeter to beams of e, μ, π and p from 1.56 to 6.8 GeV/c is presented. The design and performance of two gain monitoring systems are described, one system measures the response of single scintillator plates in the calorimeter. The calorimeter electromagnetic energy resolution varies from 24 to 32%√E for different towers. For hadron energies over 5 GeV the σh/E = 43±3%/√E, and e/h = 1.02±0.07.

A detector design that is capable of finding the image of neutron sources within a nuclear missile is discussed. The method involves the double scatter of a neutron in an array of organic scintillator elements and the partial reconstruction of the incident neutron direction vector from the information the array provides. The Monte Carlo simulation results for a basic design and several modifications are presented. The results of an experimental demonstration of the technique using a crude prototype detector are given. Problems expected in a real application are discussed.