Peter B. Lyons

Interlaboratory comparison of radiation-induced attenuation in optical fibers. II. steady-state exposures

For pt.I see ibid., vol.6, no.2, p.165-71 (1988). For pt.III see ibid., vol.8, no.6, p.977-89 (1990). The results of steady-state /sup 60/Co irradiations of silica core multimode fiber and silica core single-mode and Ge-doped graded index fibers are reported. These data were acquired over the interval of 1987-9. Several significant differences from the results and measurement procedures presented in pt.I must be accounted for in drawing comparisons between the two sets of reported data. Fiber wrap diameter and launched power level were observed to significantly influence the radiation-induced attenuation measured in silica core multimode and single-mode fibers, while the effect was less in Ge-doped silica core multimode fibers. >

Time response of plastic scintillators

Abstract Time-response characteristics of eight commercial plastic scintillators have been studied. Samples were excited by 50 ps electron or bremsstrahlung pulses. Sampling techniques were used to record the signal from a fast vacuum photodiode. Effects of surface preparation on time response were studied. The observed fwhm (in ns) for the three fastest plastics was 1.5, 2.0, and 2.3 for NE111, Pilot U, and KL236 respectively. The effect of various optical filters was studied for NE111. With suitable filtration, a minimum fwhm of 1.15 ns was observed for NE111. Time response of NE102 samples was studied as a function of thickness. For thin samples, improvement in time response was observed.

X-ray calibration of RAR 2490 film for application to laser plasma experiments

An x-ray sensitometric calibration of Kodak RAR 2490 film has been performed over the 0.28-8.04-keV range of photon energies. The characteristic curves (optical density D vs exposure H) are fit well over the entire range by a two-parameter, analytic function, loglo(1O(D) - 1) = A log(10)H + B. Solarization is found to occur at an exposure of 2 x 10(3) photons/(microm)(2) for 1.49-keV photons. Comparison with other films is made.

Enhanced radiation resistance of high-OH silica optical fibers

High purity, high-OH, silica optical fibers were irradiated in a hydrogen atmosphere to explore hydrogen binding into defects created by the ionizing radiation. Significant improvements in subsequent measurements of steady state radiation-induced attenuation were observed. Transient and steady state radiation-induced attenuations and long term stability of the phenomena were evaluated.

A total absorption ionization chamber for 1.5–10 keV X rays☆

Abstract This report presents the design of a xenon gas ionization chamber. Corrections to energy fluence measurements were considered. The correction for escape of xenon fluorescent L X rays was measured with a xenon-methane proportional counter. The chamber was compared to a Si(Li) detector and an argon-methane proportional counter over the energy range from 1.7–10.5 keV. The chamber was shown to be accurate to ±2%, independent of uncertainties in entrance window transmissivity. Overall chamber accuracy is ±3%. The useful energy fluence rate range for the chamber was shown to be from below 10−11 to 5 × 10−5 W/cm2. A value of 21.5±0.4 eV for the mean energy per ion pair in xenon was obtained from the measurements. A chamber useful up to 35 keV could be constructed without accuracy degradation by an increase in chamber size.

The use of optical time domain reflectometers to measure radiation-induced losses in optical fibers

Fiber-optics exposed to ionising radiation suffer from induced transmission loss from which recovery can take place over periods up to years after exposure. Measurement of this behavior presents difficulties over the longer times, but is necessary to permit predictions of fiber behavior in applications where long-term exposure to ionising radiation is involved, as in reactor environments, medical applications, space or accelerator instrumentation. This paper presents a summary of a study by a number of laboratories of the NATO Panel IV, Research Study Group 12 Nuclear Effects Task Group into the suitability of the use of optical time domain reflectometry for these measurements. Results are shown which validate this approach when used according to recommended guidelines. >

Fiber Optics In Transient Radiation Fields

Fiber optics have been utilized in a variety of sensor and data transmission roles, some of which are complicated by the presence of ionizing radiation. In this paper, transient radiation effects in fibers are reviewed. The paper by E. J. Friebelel (in this same Conference) concentrates on longer term radiation effects, but includes selected transient effects data as well. Several literature reviews and conferences have covered related topics.2-5

Influence Of Preform Variations And Drawing Conditions On Transient Radiation Effects In Pure Silica Fibers

Radiation resistance for several fiber samples is explored, with emphasis on variations in draw temperatures for both low- and high-OH content preforms. For a given prqorm type, draw temperature had minimal effect on radiation resistance for transient conditions below 10-7s. Dosimetry techniques were inter compared for pulsed electron accelerators. A high purity, high-RH content, fiber was tested for radiation response to determine transient attenuation from 4 ns to 104s.

Ultra-fast detectors for laser fusion diagnostics

Abstract An ultra-high speed detector with sub-nanosecond time resolution was developed to diagnose many short-time-interval phenomena, particularly those occuring in laser-matter interaction. The detector consists of a quenched plastic scintillator that is coupled to a microchannel plate photomultiplier. Full characterization of the detector components and sample data from measurements are described.

Sub-nanosecond plastic scintillators

Quenched plastic scintillators have been developed that yield much faster short decay components and greatly reduced long decay components compared to conventional plastic scintillators. The plastics are produced through the addition of selected quench agents to NE111 plastic scintillator that result in reduced total light output. Eight different agents have been studied. Benzophenone and piperidine are two of the most effective quench agents. Data are presented both for short and long decay components. The plastics are expected to make significant contributions in areas of plasma diagnostics.