John F. Arens

Highly Reflecting Stable White Paint for the Detection of Ultraviolet and Visible Radiations

The use of polyvinyl alcohol polymer as a binder for barium sulfate does not allow the intrinsically high reflectance of barium sulfate in the 200-300-nm range to be optimally employed. In an effort to better utilize this property, totally inorganic coating systems are described. Potassium sulfate turns out to be the preferred binder for reflectance enhancement. Compositions, formulating procedures, and application techniques are included. For completeness, absolute and relative reflectance data are included for intrasystem and intersystem comparisons.

Optical transmission measurements on monocrystalline and polycrystalline cesium iodide

Abstract Optical transmission measurements in the visible wavelength region have been made on commercial monocrystalline and poly crystalline cesium iodide in order to characterize quantitatively the optical quality of presently available state-of-the-art material and to define and measure parameters which determine its performance in large-area scintillation counters for which the light-collection efficiency depends primarily on multiple internal reflections within the scintillator crystal. Losses associated with surface scattering, volume scattering and scattering under total internal reflection were determined on CsI crystals whose surface had degraded as a result of prolonged storage in ambient atmosphere, on newly polished material and on highly polished samples encapsulated with lucite and silicon oil. For blue ( λ = 425 nm), normally incident light, scattering losses per surface are typically of the order of 30% to 40% for degraded material, 20% to 25% for newly polished material and 5% to 10% for well-polished, encapsulated crystals. Volume losses are mainly due to scattering, although absorption bands indicative of color centers were observed in some samples. Considerable variations in volume absorption length were observed from sample to sample as well as within individual samples, with absorption lengths ranging from 500 cm to 20 cm at λ = 633 nm. Scattering losses per reflection in the total internal reflection mode are generally higher by a factor of 1.5–2 than those measured under normal incidence. Scattering coefficients decrease with increasing wavelength, approximately proportional to λ −1 . Presently available polycrystalline CsI is substantially inferior in surface quality to single-crystal material, particularly in samples of large dimensions. For large-area CsI modules utilizing total internal reflection for light collection and requiring a high degree of spatial uniformity of response, carefully selected single-crystal material of good optical quality is essential.

Position-determining scintillator

Abstract Pulse-height measurements of the signals of two or more photomultiplier tubes looking at a thin scintillator system can be used to determine the position of the light-producing region. Calculations for a system of photomultiplier tubes directly coupled to a scintillator are presented. Locations of tracks of heavily ionizing particles are calculated to be accurate to within ⪅ 1 cm over an area of ≈ 1 m 2 for reasonably shaped systems.

Position-sensitive scintillation detectors

Abstract The variation of detected light with the position of the light-emitting source has been measured for a number of configurations of plastic scintillator, light pipes, and phototubes. The light source intensity and position can be determined if four phototubes view the scintillators. Strong gradients in detected light as a function of source location were observed which yield a position accuracy adequate for some experiments.

Infrared Camera For Ten Micrometer Astronomy

We describe an infrared imaging photometer employing a monolithic 32 X 32 pixel bismuth doped silicon charge injection device array. The device is primarily useful in the 8 to 13 karl atmospheric window. The detector is sufficiently sensitive to provide good performance on ground-based telescopes and promises to be very good for low background space flight operation.

Multielement detector data analysis

Abstract A geometric method of analyzing multidetector data by using a multidimensional space is presented. The χ2 is minimized for each event and the resulting χ2 curve provides the selection criterion for separating good events from background.

Cosmic ray studies with a gas Cherenkov counter in association with an ionization spectrometer

The results from a ballon-borne gas Cherenkov counter (threshold 16.5 GeV nuc−1) and an ionization spectrometer are presented. The gas Cherenkov counter provides an absolute energy calibration for the response of the calorimeter for 5⩽Z⩽26 nuclei of cosmic rays. The contribution of scintillation to the gas Cherenkov pulse height has been obtained by independently selecting particles below the gas Cherenkov threshold using the ionization spectrometer. Energy spectra were derived by minimizing the χ2 between a Monte Carlo simulated data and flight data. Best fit power laws (dN/dE=AE−γ) were determined for C, N, O, Ne, Mg, and Si. The power laws, all consistent withE−2.7, are not good fits to the data. A better fit is obtained using the spectrum derived from the spectrometer. The data from the ionization calorimeter (Simonet al., 1979) and the gas Cherenkov are thus completely self-consistent.

Cerenkov Light Collection in the High Energy Astronomical Observatory a Cosmic Ray Experiment

An improved Cerenkov counter for the High Energy Cosmic Ray Experiment on the first High Energy Astronomy Observatory will make the resolution between different nuclei much better. A more UV reflecting paint and improved radiator and PMT positioning should give us hoped for results.

Infrared array detectors

Abstract Arrays of detectors sensitive to infrared radiation will enable astronomical observations to be made with shorter observing times than with discrete detectors and with good relative spatial accuracy. Systems using such arrays are being developed for astronomy in several regions of the electromagnetic spectrum. An example of an infrared system is given here consisting of a 32×32 element bismuth doped silicon charge injection device array that has been used in an astronomical camera.

Infrared Camera For 10 μm Astronomy

We describe an infrared imaging photometer employing a monolithic 32x32 pixel bismuth doped silicon charge injection device array. The device is primarily useful in the 8-13 pm atmospheric window. The detector is sufficiently sensitive to provide good performance on ground-based telescopes and promises to be very good for low background space flight operation.