The accuracy of density measurements and position resolution in flash (40 ns) radiography of thick objects with 24 Gev/c protons is investigated. A global model fit to step wedge data is shown to give a good description spanning the periodic table. The parameters obtained from the step wedge data are used to predict transmission through the French Test Object (FTO), a test object of nested spheres, to a precision better than 1%. Multiple trials have been used to show that the systematic errors are less than 2%. Absolute agreement between the average radiographic measurements of the density and the known density is 1%. Spatial resolution has been measured to be 200 μm at the center of the FTO. These data verify expectations of the benefits provided by high energy hadron radiography for thick objects.

We have measured the spectrum of UHE cosmic rays using the Flash ADC (FADC) detector (called HiRes-II) of the High Resolution Fly's Eye experiment running in monocular mode. We describe in detail the data analysis, development of the Monte Carlo simulation program, and results. We also describe the results of the HiRes-I detector. We present our measured spectra and compare them with a model incorporating galactic and extragalactic cosmic rays. Our combined spectra provide strong evidence for the existence of the spectral feature known as the "ankle."

Several proposed source models for Ultra-High Energy Cosmic Rays (UHECRs) consist of dipole distributions oriented towards major astrophysical landmarks such as the galactic center, M87, or Centaurus A. We use a comparison between real data and simulated data to show that the HiRes-I monocular data for energies above 10 eV is, in fact, consistent with an isotropic source model. We then explore methods to quantify our sensitivity to dipole source models oriented towards the Galactic Center, M87, and Centaurus A.

We have measured the cosmic ray spectrum above 10(17.2) eV using the two air-fluorescence detectors of the High Resolution Fly's Eye observatory operating in monocular mode. We describe the detector, phototube, and atmospheric calibrations, as well as the analysis techniques for the two detectors. We fit the spectrum to a model consisting of galactic and extragalactic sources.

Several proposed source models for ultra-high energy cosmic rays (UHECRs) consist of dipole distributions oriented towards major astrophysical landmarks such as the galactic center, M87, or Centaurus A. We use a comparison between real data and simulated data to show that the HiRes-I monocular data for energies above 1018.5 eV is, in fact, consistent with an isotropic source model. We then explore methods to quantify our sensitivity to dipole source models oriented towards the Galactic Center, M87, and Centaurus A.

Several proposed source models for Ultra-High Energy Cosmic Rays (UHECRs) consist of dipole distributions oriented towards major astrophysical landmarks such as the galactic center, M87, or Centaurus A. We use a comparison between real data and simulated data to show that the HiRes-I monocular data for energies above 10 eV is, in fact, consistent with an isotropic source model. We then explore methods to quantify our sensitivity to dipole source models oriented towards the Galactic Center, M87, and Centaurus A.

Proton radiography is a new tool for advanced hydrotesting. It is ideally suited for providing multiple detailed radiographs in rapid succession (~ 200 ns between frames), and for work on thick systems (100’s of g/cm thick) due to the long nuclear interaction lengths of protons. Since protons interact both via the Coulomb and nuclear forces, protons can simultaneously measure material amounts and provide material identification. By placing cuts on the scattering angle using a magnetic lens system, image contrast can be enhanced to give optimal images for thick or thin objects. Finally the design of a possible proton radiography facility is discussed.

The capability has successfully been developed at the Los Alamos Nuclear Science Center (LANSCE) to utilize a spatially and temporally prepared 800MeV proton beam to produce proton radiographs. A series of proton bursts are transmitted through a dynamic object and transported, via a unique magnetic lens system, to an image plane. The magnetic lens system permits correcting for the effects of multiple coulomb scattering which would otherwise completely blur the spatially transmitted information at the image plane. The proton radiographs are recorded either on a time integrating film plate or with a recently developed multi-frame electronic imaging camera system. The latter technique permits obtaining a time dependent series of proton radiographs with time intervals (modulo 358ns) up to many microseconds and variable time intervals between images. One electronically shuttered, intensified, CCD camera is required per image. These cameras can detect single protons interacting with a scintillating fiber optic array in the image plane but also have a dynamic range which permits recording radiographs with better than 5% statistics for observation of detailed density variations in the object. A number of tests have been carried out to characterize the quality of the proton radiography system for absolute mass determination, resolution, and dynamic range. Initial dynamic experiments characterized the temporal and spatial behavior of shock propagation in a high explosive sample with up to six images per experiment. Based on experience with the prototype system, a number of upgrades are being implemented including the anticipated capability for enhanced mass discrimination through differential multiple coulomb scattering radiographs and more images with improved imaging techniques.

An intensified/shuttered cooled PC-based CCD camera system was designed and successfully fielded on proton radiography experiments at the Los Alamos National Laboratory LANSCE facility using 800-MeV protons. The four camera detector system used front-illuminated full-Game CCD arrays (two 1024 x 1024 pixels and two 512 x 512 pixels) fiber optically coupled to either 25-mm diameter planar diode or microchannel plate image intensifiers which provided optical shuttering for time resolved imaging of shock propagation in high explosives. The intensifiers also provided wavelength shifting and optical gain. Typical sequences consisting of four images corresponding to consecutive exposures of about 500 ns duration for 40-ns proton burst images (from a fast scintillating fiber array) separated by approximately 1 microsecond were taken during the radiography experiments. Camera design goals and measured performance characteristics including resolution, dynamic range, responsivity, system detection quantum efficiency (DQE), and signal-to-noise will be discussed.

We report the results of an experimental study of the reaction ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}n{e}^{+}{e}^{\ensuremath{-}}$ at 300 MeV/c over the range of ${e}^{+}{e}^{\ensuremath{-}}$ effective mass from 140 to 160 MeV/${\mathit{c}}^{2}$. The observed number of events is only one quarter of that expected from a calculation of inverse pion electroproduction. We see no evidence for the production of light Higgs bosons or any other particle that decays into ${e}^{+}{e}^{\ensuremath{-}}$ in this mass region.

This paper reports the details of an experiment designed to detect the decay ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$ and to measure its branching ratio. The experiment used a beam of 300-MeV/c ${\ensuremath{\pi}}^{\ensuremath{-}}$ mesons incident on a liquid-hydrogen target to produce neutral pions in the reaction ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}n$. Electron-positron pairs were detected in a magnetic spectrometer by multiwire proportional chambers. A gas Cherenkov counter provided electron identification. The effective-mass distribution of ${e}^{+}{e}^{\ensuremath{-}}$ pairs was decomposed with the aid of a Monte Carlo simulation of the ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$ signal and background processes. The result is 59\ifmmode\pm\else\textpm\fi{}21 events, which corresponds to $\frac{\ensuremath{\Gamma}({\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}})}{\ensuremath{\Gamma}({\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma})}=(17\ifmmode\pm\else\textpm\fi{}6\ifmmode\pm\else\textpm\fi{}3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$, where the first error is due to statistics and the second is an estimate of systematic effects. The central value is almost four times the unitarity lower limit while existing calculations generally predict values no larger than twice the unitarity limit.

This paper describes a kinematically complete search for the muon decay ${\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\gamma}$. The experiment used a magnetic spectrometer outfitted with proportional chambers to measure the positron momentum vector and a large segmented NaI(T1) array to determine the $\ensuremath{\gamma}$-ray energy and impact point. The positrons were mostly from normal muon decay while the $\ensuremath{\gamma}$ rays were mostly from internal and external bremsstrahlung. Approximately 3\ifmmode\times\else\texttimes\fi{}${10}^{2}$ muons were stopped in a 50-mg/${\mathrm{cm}}^{2}$ polyethylene target. The relative timing between the positron and the $\ensuremath{\gamma}$ ray was measured with a resolution of 1.9 ns full width at half maximum (FWHM) by the use of a plastic-scintillator hodoscope for the positron and by NaI(T1) constant-fraction timing for the $\ensuremath{\gamma}$ ray. The positron energy resolution averaged over all data was 8.8% FWHM, and the $\ensuremath{\gamma}$-ray energy resolution was 8% FWHM, both at 52.8 MeV. When the $\ensuremath{\gamma}$ ray is assumed to originate at the same place in the target as the positron, the rms error in the measurement of the angle between the positron and $\ensuremath{\gamma}$-ray momentum vectors was 37 mrad. The acceptance of the apparatus for ${\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\gamma}$ events was (1.75\ifmmode\pm\else\textpm\fi{}0.04)%. A maximum-likelihood analysis established a 90%-confidence upper limit for the branching ratio $\frac{\ensuremath{\Gamma}({\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\gamma})}{\ensuremath{\Gamma}({\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\nu}\overline{\ensuremath{\nu}})}$ of 1.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$.

Evidence for the rare decay ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$ has been obtained in an experiment which measured the invariant mass spectrum of ${e}^{+}{e}^{\ensuremath{-}}$ pairs produced by 300-MeV/c ${\ensuremath{\pi}}^{\ensuremath{-}}$ mesons interacting in a liquid-hydrogen target. The branching ratio is (1.8\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$, about four times larger than the unitarity lower limit.

An examination of 3.6\ifmmode\times\else\texttimes\fi{}${10}^{10}$ ${\ensuremath{\mu}}^{+}$ decays yields an improved upper limit for the branching ratio $\frac{\ensuremath{\Gamma}({\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\gamma})}{\ensuremath{\Gamma}({\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}{\ensuremath{\nu}}_{e}{\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}})}<1.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ with 90% confidence.

An array of 45 NaI(Tl) crystals modules, each in 20 in. in length and hexagonal in cross section with six 3 in. sides, has been operated as a detector of 50 MeV γ-rays in a search for the decay μ+→e+γ. The calibration procedure used for this detector and the resolutions achieved in γ-ray energy, time of detection and point of impact on the detector face are described.