Photomultiplier window materials under electron irradiation: fluorescence and phosphorescence

Abstract

The fluorescence and phosphorescence of photomultiplier window materials under electron irradiation have been investigated using a Sr(90)-Y(90) beta emitter as the electron source. Spectral emission curves of uv-grade, optical-grade, and electron-irradiated samples of MgF(2) and LiF, and of CaF(2), BaF(2), sapphire, fused silica, and uv-transmitting glasses were obtained over the 200-650-nm spectral range. Fluorescence yields, expressed as the number of counts in a solid angle of 2pi sr/MeV of incident electron energy deposited [MeV(-1) (2pi sr)(-1)], were determined on these materials utilizing photomultiplier tubes with cesium telluride, bialkali, and trialkali (S-20) photocathodes, respectively. Typical yields observed with a uv/visible sensitive bialkali cathode range from 10 MeV(-1) (2pi sr)(-1) for uv-grade MgF(2) to approximately 200 MeV(-1) (2pi sr)(-1) for CaF(2). For comparison, sodium-activated cesium iodide, one of the most efficient scintillator materials, yields about 700 MeV(-1) (2pi sr)(-1). High-purity fused silica has the lowest yield, approximately 6 MeVW(-1) (2pi sr)(-1). Optical-grade MgF(2)and LiF, as well as electron-irradiated uv-grade samples of these two materials, show enhanced fluorescence due to color-center formation and associated emission bands in the blue and red wavelength regions. Large variations in fluorescence intensities were found in uv-grade sapphire samples of different origins, particularly in the red end of the spectrum, presumably due to various amounts of chromium-ion content. Phosphorescence decay with time is best described by a sum of exponential terms, with time constants ranging from a few minutes to several days. Phosphorescence intensity expressed as a fraction of the steady-state fluorescence intensity is an extremely sensitive measure of crystalline perfection and purity. This fraction ranges from a high of approximately 10(-2) for some fluoride samples to a low of </=2 x 10(-6) for fused silica. Application of the parameters obtained in this work to the analysis of recent flight observations on low light-level experiments yields good quantitative agreement with flight data from OAO-3, OSO-7, and Apollo 17.

Parasitic Signals in the Method of Recoil Nuclei Applied to Direct Observation of the 229mTh Isomeric State

“…We start from fluorescence caused by β-particles. We know that it is selective by wavelength and in our case is significant at wavelength λ > 225 nm [18], consequently the excluding rule reliable for Cherenkov radiation give no information now. But the fluorescence at λ > 225 nm turns out to be on the same order as Cherenkov radiation, so they appear only together.…”

“…Analysing Ref. [18] we conclude that β-fluorescence efficiency may be roughly estimated by the value ε f = 2 photons 10 nm · MeV · 4π (11) physical sense of which is the number of photons irradiated per 10 nm of the spectrum into a unit solid angle for the loss of electron's energy at 1 MeV. As for Cherenkov radiation, we have already deduced the number of the photons irradiated in the range 115 -320 nm per an electron decelerating from initial kinetic energy to the threshold of Cherenkov effect equal to 170 keV in MgF 2 .…”

The Relativistic Proton Spectrometer (RPS) for the Radiation Belt Storm Probes Mission

“…These photons result from proton-induced scintillation in the MgF 2 radiator with an intensity of about 5 photons per MeV of energy deposit in our model. Viehmann et al (1975) The lower scintillation yield for RPS suggests that the RPS radiator has a higher purity than the material that Viehmann et al tested. We use the scintillation photon signal as an additional input to the algorithm that calculates the incident proton energy.…”

Far ultraviolet atomic and molecular nitrogen emissions in the dayglow

“…This rate increased during the upleg portion of the flight to approximately 4.5 counts s -• immediately prior to tip eject. This effect is attributed to phosphorescence induced by unscreened cosmic rays incident at the top of the earth's atmosphere [Viehmann et al, 1975].…”