This report assesses the utility of lanthanum-halide detectors for isotope identification and total mass measurements for uranium and plutonium isotopes. Comparisons to similar measurements with NaI detectors are made.

We present results from Compton imaging of gamma-ray sources using an instrument constructed from thin silicon scattering detectors and CsI(Tl) absorbing detectors. We have successfully imaged single and double point sources for several common radioactive isotopes (137Cs, 60Co, 22Na, 54Mn). The measured angular resolution is 11.6∘ FWHM at 662 keV. In parallel with the hardware effort, a GEANT4-based simulation code was developed. Comparisons between real and simulated data are discussed.

Today we face serious threats from radiological dispersion devices, improvised nuclear devices, and unsecured nuclear materials. Detectors which are currently used to detect and characterize these radioactive materials (or the radioactive materials within larger assemblies) suffer from large background rates. In addition, these detectors have only minimal ability to localize the position of the source without the use of mechanical collimators which reduce efficiency. Imaging detectors using the Compton scattering process have the potential to provide greatly improved sensitivity through their ability to reject off-source background by localizing the source. We are developing a prototype device using readily available detector systems to explore Compton imaging technology. Our aim is to build a proof-of-concept device to study the Compton technology and to benchmark simulation efforts that will guide development of larger, more efficient devices that would be needed for deployment in the field. Here we discuss the concept of our detector design and results from Monte Carlo simulations of our prototype detector. We present an extension of an imaging technique used for gamma-ray astronomy to near-field sources.

Compton imaging, which reconstructs the direction of incident photons based on the kinematics of Compton scattering, is of interest in the fields of astrophysics, medical imaging, and homeland defense. We are attempting to build a device in which the Compton scatter takes place in one of several layers of thin Silicon detectors and the secondary photon is detected in an array of high resolution photon detectors. We have purchased prototypes for both detector systems. This paper presents performance results from simulations and tests of the detectors.

The most serious terrorist threat we face today may come from radiological dispersion devices and unsecured nuclear weapons. It is imperative for national security that we develop and implement radiation detection technology capable of locating and tracking nuclear material moving across and within our borders. Many radionuclides emit gamma rays in the 0.2 - 3 MeV range. Unfortunately, current gamma ray detection technology is inadequate for providing precise and efficient measurements of localized radioactive sources. Common detectors available today suffer from large background rates and have only minimal ability to localize the position of the source without the use of mechanical collimators, which reduces efficiency. Imaging detectors using the Compton scattering process have the potential to provide greatly improved sensitivity through their ability to reject off-source background. We are developing a prototype device to demonstrate the Compton imaging technology. The detector consists of several layers of pixelated silicon detectors followed by an array of CsI crystals coupled to photodiodes. Here we present the concept of our detector design and results from Monte Carlo simulations of our prototype detector.

Gamma imaging based on Compton scattering was first proposed approximately 25 years ago as a replacement for mechanically collimated imaging systems. The advantages of such instruments over mechanically collimated systems are a wider field of view, higher efficiency (more source photons are used in the image construction), source localization, use in high-background environments, and non-tomographic three-dimensional imaging of near-field sources. One can also image multi-energy photons by selecting events based on the summed energy deposited in multiple detectors. The traditional example of such imaging systems is a Compton camera. Until recently, limitations with associated hardware have resulted in Compton imaging seeing few applications. However, with advances in high spatial resolution detectors, and further developments in the physical principles there has been a renewed interest in gamma imaging based on Compton scattering in many areas including astronomy and nuclear medicine. In this paper we present an evaluation of a three plane Compton imaging concepts, the three plane Compton imaging technique. Such a technique, if valid, could lead to many useful applications.

It was recently shown that a logarithmic response-function technique based on the material basis set (MBS) formalism used in the tomographic gamma scanner (TGS) method allows gross spectra from NaI detectors to be used in both measuring MBS transmission corrections using external transmission sources and in applying the corrections to emission spectra to arrive at radionuclide mass estimates. In this work we have attempted to show that addition of the oblique scatter component can increase the accuracy of the GC-TGS measurements with both NaI and high-purity germanium detectors. This paper describes the formalism behind the GC-TGS method and the improvement achieved in the analysis by including the scatter component.

A method is described for the extraction of isotopic information from attenuated gamma ray spectra using the gross-count material basis set (GC-MBS) model. This method solves for the isotopic composition of an unknown mixture of isotopes attenuated through an absorber of unknown material. For binary isotopic combinations the problem is nonlinear in only one variable and is easily solved using standard line optimization techniques. Results are presented for NaI spectrum analyses of various binary combinations of enriched uranium, depleted uranium, low burnup Pu, {sup 137}Cs, and {sup 133}Ba attenuated through a suite of absorbers ranging in Z from polyethylene through lead. The GC-MBS method results are compared to those computed using ordinary response function fitting and with a simple net peak area method. The GC-MBS method was found to be significantly more accurate than the other methods over the range of absorbers and isotopic blends studied.

Differential cross sections for ${\ensuremath{\pi}}^{+}{+}^{12}\mathrm{C}$ elastic scattering in the energy range of 18--44 MeV for six scattering angles have been measured with an increment in the incident energy of 2 MeV. The measured cross sections are compared to calculations within the framework of a unitary scattering theory of the pion-nucleus interaction. It is shown that the excitation function at angles around $90\ifmmode^\circ\else\textdegree\fi{}$ is dominated by the $D$ wave of the pion-nucleus interaction.

A study of the reaction pi(+) + d --> p + p has been performed in the energy range of 18-44 MeV. Total cross sections and differential cross sections at six angles have been measured at 15 energies with an energy increment of 1-2 MeV. This is the most systematic data set in this energy range. No structure in the energy dependence of the cross section has been observed within the accuracy of this experiment.

Angular distributions for pi(+) and pi(-) elastic and inelastic scattering from the Z=28 closed-proton-shell nuclei Ni-58,Ni-60,Ni-62,Ni-64 have been measured at an incident pion kinetic energy of 180 MeV. Values for the neutron and proton matrix elements for the transition to the J(pi)=2(1)(+) state have been extracted using the distorted wave impulse approximation in which the pi(+) and a data were fitted simultaneously and the neutron and proton vibrational transition strengths were treated as free parameters. While all transitions are predominantly collective, extracted values of M(n)/M(p) indicate increasing collectivity as a function of neutron number and are consistent with the collective limit of N/Z for Ni-64.

Experimental differential cross sections for pi+ and pi- elastic scattering on Si-28 at an incident pion energy of 400 MeV are reported. The data fall above the predictions of a calculation using a momentum-space first-order optical potential. The behavior is similar to earlier results for pion scattering at T(pi) = 672 MeV and to K+ nucleus scattering in this energy range, suggesting that there may be a common origin for the observed discrepancy that is not yet understood.

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.

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 multiplexing scheme for cathode strip chamber readouts which is cost-effective and efficient is described. This scheme provides an inexpensive alternative to individual-wire readout schemes, while not compromising the attractive qualities of cathode-strip chambers. A chamber with an area of 72×36 cm was built and tested. A position resolution of 130±50 μm (FWHM) was obtained with the multiplexing scheme. Details of the construction and operation of the cathode-strip chamber and its response to cosmic rays are presented here.

A Pb/scintillator sampling calorimeter covering the pseudorapidity interval of η = 0.83 to 4.20 has been designed and constructed for Experiment 814 of Brookhaven National Laboratory. The calorimeter uses wavelength shifting optical fibers for readout. Such fibers allow the construction of a highly granular and longitudinally compact device. A novel scheme for coupling a fiber to a scintillator plate has been designed that yields a high photoelectron response. Longitudinally, the calorimeter has a depth of four interaction lengths divided into two electromagnetic sections and two hadronic sections of 0.4, 0.4, 1.6, and 1.6 interaction lengths, respectively.