A discussion of the limits imposed by thermodynamics on the collection of light from scintillation counters by photocathodes is given, and a method for concentrating the light energy to any degree is pointed out. The method employs a fluorescent material to slightly reduce the photon energy and thus to emit fluorescence. A light pipe-fluorescent converter-light pipe arrangement for increasing light intensity is discussed. (D.L.C.)

The Collection of Light from Scintillation Counters

Various embodiments described herein comprise mixers comprising a light pipe having input and output ends and a central region therebetween. An optical path extends in a longitudinal direction from the input end through the central region to the output end. The central region of the light pipe comprises one or more rippled reflective sidewalls having a plurality of elongate ridges and valleys and sloping surfaces therebetween. Light from the input end propagating along the optical path reflects from the sloping surfaces and is redirected at a different azimuthal direction toward the output end thereby mixing the light at the output end. Illuminance and/or color mixing can therefore be provided.

Rippled mixers for uniformity and color mixing

Design principles of fluorescence radiation converters

Electromagnetic calorimeter modules based on a uniform array of plastic scintillating fibers embedded in a lead alloy have been built and tested. Techniques have been developed to assemble large volumes of this composite material and to machine it into the tapered trapezoidal modules appropriate for modern, hermetically-sealed calorimeters with pointing geometry. Using this technique, a 300-element array of such modules has been built and instrumented. Prototypes and subsets of the larger array have been tested in electron and photon beams ranging in energy from 0.035 to 5.0 GeV. Improvements in fiber characteristics, assembly procedures, and geometrical optimization have led to substantial performance gains over previous similar detectors. The average resolution of these detectors is determined to be σ/E ≈ 6.3%/√E (GeV). The techniques of fabrication and the detector tests are described.

A high-resolution lead /scintillating fiber electromagnetic calorimeter

If light comes from a fixed direction and is to be collected onto an absorbing body which is approximately a point or a straight line, it is well known that a mirror of parabolic profile serves the purpose efficiently. If the light is diffuse, or its direction of incidence variable, or if the absorber is not approximately a point or a straight line, the parabola is less useful. This paper describes various particular collecting problems of this more general sort, together with efficient solutions for them, mainly by means of mirrors. The subject represents a corner of geometric optics little explored until recently, in which the notion of image formation scarcely appears. A unifying principle is the invariance of the ‘Lagrange-Helmholtz’ invariant, which is related to Liouville's theorem of Hamiltonian mechanics, and there is a unifying method of construction of the mirror profiles by means of string.

R. L. Garwin

Papers

The Design of Liquid Scintillation Cells