Directional Spherical Cherenkov Detector
- Thursday, 01 April 2010
Incident particles could be sorted by direction, speed, and electric charge.
A proposed radiation-detecting apparatus would provide information on the kinetic energies, directions, and electric charges of highly energetic incident subatomic particles. The apparatus was originally intended for use in measuring properties of cosmic rays in outer space, but could also be adapted to terrestrial uses — for example, radiation dosimetry aboard high-altitude aircraft and in proton radiation therapy for treatment of tumors.
The apparatus (see figure) would include a spherical Cherenkov detector surrounded by stacks of pairs of detectors. Each such pair and stack would be used in identifying incident particles and would respond to particles incident within a solid-angle range that, in conjunction with the number of such stacks, would define the angular resolution of the apparatus. The number of stacks and the number of pairs of detectors in each stack may be unlimited.
The detectors in each stack would typically have areas >1 cm2 and could be made, variously, from compensated silicon or from such wide-bandgap semiconductors as semi-insulating silicon carbide. Sheets of tungsten, lead, nickel, iron, and/or alloys thereof, serving as energy-moderating materials, could be inserted between detectors to enable discrimination of particles by energy. A scintillation counter could be used as a particle trigger with, or in place of, the detector stack.
The spherical Cherenkov detector would include a sphere of ultraviolet-transparent material (e.g., sapphire, quartz, or an acrylic polymer) having an ultraviolet index of refraction greater than 1. The sphere would be coated with an ultraviolet-reflecting material except at small ports. SiC photodiodes or optical fibers leading to photodiodes would be mounted facing into the sphere at the ports to enable detection of Cherenkov ultraviolet light emitted within the sphere.
The detectors in the stacks would serve as triggers for collection of light by the photodiodes of the spherical Cherenkov counter. The direction and length of the path of a triggering particle would be determined from the identities (and thus the positions) of the affected detectors and stacks. For incident ions having sufficiently high kinetic energies, the strengths of the signals from the SiC photodiodes or optical fibers would be proportional to the square of the electric charges of the ions multiplied by the path lengths. Hence, a velocity distribution for high-energy ions incident from multiple directions could be determined.
For less-energetic incident particles, further sorting could be accomplished through correlation of the Cherenkov signal from the sphere with differences among signals from stacked detectors that have different thicknesses and that may be interspersed with energy-moderating materials. Sensitivity of detection could be increased through substitution of low-noise SiC detectors for ordinary SiC detectors.
This work was done by John D. Wrbanek, Gustave C. Fralick, and Susan Y. Wrbanek of Glenn Research Center. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Physical Sciences category.
Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steve Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-18362-1.
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