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Shirk, E. K.

Publications and source records attributed to Shirk, E. K..

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Research on CR-39 plastic detectors for cosmic ray astrophysics

The sensitivity of CR-39 is a strong function of catalyst concentration during its polymerization. Normal CR-39 will detect vertically incident particles with Z/beta as low as 10. An extrapolation suggests that CR-39 with a high catalyst concentration and sensitivity to within approximate 5% can be made by a suitable choice of cure cycle and mold material. CR-39 is less sensitive than Lexan to thermal annealing of tracks but cannot tolerate background radiation levels greater than a few Mrad.

Price, P. B.↗
NASA NTRS1980

High resolution image measurements of nuclear tracks

The striking clarity and high contrast of the mouths of tracks etched in CR-39 plastic detectors allow automatic measurement of track parameters to be made with simple image-recognition equipment. Using a commercially available Vidicon camera system with a microprocessor-controlled digitizer, resolution for normally incident C-12 and N-14 ions at 32 MeV/amu equivalent to a 14sigma separation of adjacent charges was demonstrated.

Shirk, E. K.↗
NASA NTRS1980

SPIRIT - A high resolution cosmic ray isotope spectrometer for Spacelab

An instrument to measure the isotopic abundances of cosmic ray nuclei with Z in the range 20-30 and A in the range 40-70 has been conceived. The instrument, named SPIRIT (Superconducting Passive Iron Isotope Telescope), will have the mass resolution (sigma less than 0.15 amu) and collecting power (151 sq m ster h for a 10 day flight) to detect and convincingly resolve isotopes as rare as 0.5% of the total abundance of each element. Both range and magnetic rigidity are measured by following tracks through an array of sheets of CR-39, a sensitive new track-recording plastic, which had been kept in fixed position at uniform temperature within the uniform field region of a large superconducting magnet.

Tarle, G.↗
NASA NTRS1978

Further measurements and reassessment of the magnetic-monopole candidate

The data on the 1975 Lexan event are reexamined in a framework that does not depend on the details of a particular track model. Instead, visual measurements of two quantities, photographic evidence, and silver-grain densities measured with an automated microscopic-image dissector are cited. It is shown that throughout the detector stack the particle had a roughly constant value of absolute Z/beta of about 109-114 based on energy deposition at radial distance less than about 0.01 micron. Its energy deposition at radial distance greater than about 20 microns was incompatible with that expected from any known cosmic ray nucleus with Z/beta in this range. A monopole is ruled out, and the three candidates compatible with the data are: (1) a slow, supermassive particle with beta about 0.4, charge about 45e, and mass above 1000-10,000 amu; (2) a fast antinucleus with Z/beta about -109 to -114 and absolute Z between 76 and 96; and (3) a very fast nucleus with Z about 110-114 and beta above about 0.99.

Price, P. B.↗
NASA NTRS1975

Evidence for detection of a moving magnetic monopole

A very heavy particle passed through a balloon-borne stack of Cherenkov film, emulsion, and Lexan sheets. In 33 Lexan sheets it produced tracks expected of either a nucleus with Z ranging between 125 and 137 and with beta less than about 0.92 or a magnetic monopole with g = 137e. Its track structure in emulsion indicated it was moving downward with beta equal to 0.5 (plus 0.1 or minus 0.05) and was either a nucleus with Z equal to 80 or a monopole with g = 137e. These facts strongly favor identification of the particle as a magnetic monopole of strength g = 137e and mass greater than 200 times proton mass.

Price, P. B.↗
NASA NTRS1975

The Skylab ultraheavy cosmic ray experiment

Cosmic-ray nuclides of charge Z from 65 to 110 were detected with a Lexan sheet array mounted on the spacecraft. The charge distribution showed 83 nuclei of Z not less than 65, 6 nuclei of charge not less than 90, one with Z not less than 93, and no superheavy nuclei (Z not less than 110). Measured Pb/Pt and U/Pt abundance ratios are examined for information on a possible r-process, on solar system abundances, and on the time and time scale of the related nucleosynthesis events. The resolution of the experiment is deemed adequate to rule out the presence of superheavy nuclei. Experimental procedures, statistical treatment, and correlation with balloon data are discussed.

Price, P. B.↗
NASA NTRS1974

Observation of transiron solar-flare nuclei in an Apollo 16 command-module window

The first measurements of the fluence of solar particles with nuclear charges not less than 32 and 44 are presented, along with the enhancement factors found. Using a track-etching technique, these transiron nuclei were detected in a window from the Apollo 16 command module which was exposed outside the magnetosphere during the solar-particle event of Apr. 18, 1972.

Shirk, E. K.↗
NASA NTRS1972

Charge and energy spectra of cosmic rays with Z equal to or greater than 30.

A 2 g/sq cm stack (22 sq m in area) containing 41 plastic sheets, one G-5 emulsion, and one high-speed Cerenkov film detector was launched by balloon from Minneapolis on Sept. 4, 1970. The stack received an effective exposure of 48 hr at 2.8 mbar and a cutoff rigidity of about 1.8 GV. The abundance ratios relative to Fe are reported for various charges and charge groups from Z = 29 to 105 on the basis of 70 presently measured events as well as previously obtained results. Between Fe and the Pt peak, the cosmic ray abundances appear to be similar to solar system abundances; the heavier nuclei are strongly overabundant and appear to have originated about 10 m.y. ago in a rapid neutron capture process.

Kobetich, E. J.↗