Carol Jo Crannell

Characteristics of cesium iodide for use as a particle discriminator for high-energy cosmic rays

Abstract The possible use of CsI to discriminate between high-energy cosmic-ray electrons and interacting protons has been investigated. T The pulse-shape properties as a function of ionization density, temperature, and spectral response are presented for thallium-activated CsI and as a function of ionization density for sodium-activated CsI. The results are based on previously published data and on corroborative measurements from the present work. Experimental results on the response of CsI to electron-induced electromagnetic cascades and to interacting hadrons are described. Bibliographies of publications dealing with the properties of CsI and with pulse-shape discrimination techniques are presented.

Energy calibration of a cosmic ray ionization spectrometer

Abstract The NASA/GSFC High Energy Cosmic Ray Experiment was calibrated at the AGS at Brookhaven National Laboratory during the summer of 1970 using protons and pions with energies from 9.3 GeV to 17.6 GeV. The best measure found for the energy E of an incoming primary particle is ΣI , the total number of ionizing particles observed in the instrument, summed over the various iron modules. The resolution in the calibration energy range is about ±30% (s.d.) over a wide range of incident angles and positions. The calibration function may be parameterized as E = ∑ I / K , where K is predominantly a function of the location of the first interaction and the trajectory of the incoming particle. To a fair approximation the geometrical dependence of K can be encompassed by writing K as a function of d , the distance from the first interaction along the primary ray to the edge of the instrument. Empirically, K =5.83 [1−exp(− d / λ )] cos θ , where λ is a characteristic length which is a slowly varying function of energy. The value of K , and thus the average energy values calculated from the experimental data are accurate to about ±10% under calibration conditions.

Electron calibration of a high energy cosmic ray detector

Abstract The response of the GSFC High Energy Cosmic Ray Detector has been studied using electrons in the energy range 5.4 to 18 GeV. A semi-empirical analytic form has been developed to determine the starting points and the energies of electron-induced cascade showers. The energy resolution thus obtained has a fwhm of 17%, and the starting point can be determined to within 0.1–0.2 radiation length. The results of this response calibration provide a basis on which cosmic ray electrons can be reliably identified and analyzed in the presence of a large proton background.

Particle Track Enhancement in Cellulose Nitrate by Application of an Electric Field

The number and length of etchable tracks, created by alpha particles in a cellulose nitrate sheet, are significantly enhanced by the application of an electric field across the cellulose nitrate.

Geometrical - factor determination using a monte carlo approach

Abstract A Monte Carlo technique is employed to compute the geometrical factor, path-length spectra, and zenith angle distribution for a variety of detector configurations. An incident flux is simulated by choosing four initial parameters for each of a large number of events according to the appropriate probability distributions. The resultant paths are individually tested to determine the exit plane from the detector and the path lenght within the detector. The desired data are tabulated by summing over numerous simulated events. The flexibility, speed, and accuracy achieved with this technique make it extremely useful for evaluating detector designs with simple or relatively complicated geometry.

Cerenkov Light Collection in the High Energy Astronomical Observatory a Cosmic Ray Experiment

An improved Cerenkov counter for the High Energy Cosmic Ray Experiment on the first High Energy Astronomy Observatory will make the resolution between different nuclei much better. A more UV reflecting paint and improved radiator and PMT positioning should give us hoped for results.

Development of Spark Chambers for Use in Measurements of the Charge Spectrum of High Energy Cosmic Rays

The High Energy Cosmic Ray Experiment, flown on balloons by a group at Goddard Space Flight Center, is designed to measure the charge, the energy, and the arrival direction of high-energy cosmic rays. A wiregrid spark chamber is employed to determine the trajectory of each incident primary particle which satisfies the experiment trigger criteria. Optimum trajectory-determination efficiency depends on parameters, the values of which vary with the charge of the incident particle. The functional dependence on the voltage applied to the wire grids and on the delay in application of the high voltage trigger for several different values of the DC clearing field was measured for fully ionized nitrogen nuclei and for singly charged particles. The voltage was found to be the most suitable parameter to vary in order to maximize the spark formation efficiencies and to minimize spurious spark formation. Because of the low fluxes of high-Z, high-energy cosmic rays, long experiment exposure times such as those obtained in satellites are desirable. To adapt the spark chambers for use with experiments with a duration of more than one year and total accumulated events in excess of 3 × 108, the useful life times of both the high-voltage triggering circuit and the spark-chamber gas needed to be improved. Krytron high-voltage triggering devices have been developed which will perform satisfactorily for more than 3 × 108 simulated events at a rate of 10 events/ sec, an improvement of approximately a factor of 10.

Response of TlCl(I,Be) Crystals to Energetic Ionizing Radiation

Studies of scintillation TlCl(I,Be) crystals have been conducted using 8-GeV negative pions and 50- to 130-MeV positrons. Pulse shapes and resolutions of these crystals have been measured. Pulses from TlCl(I,Be) are observed to have a fast rise time (?2 nsec) and a complicated decay scheme consisting of at least three separate components. Attempts were also made to observe the Cerenkov radiation from these crystals due to highly relativistic particles. The resolution of the pulse height spectrum for a 2.9-cm diameter by 3.8-cm length TlCl(I,Be) scintillator was measured for 8-GeV negative pions. For comparison, the resolution of the same size CsI(Tl) scintillator was measured using the same experimental configuration. The resolution of CsI(Tl) is only slightly greater than theoretical prediction. The resolution of TlCl(I,Be) is greater, being limited by photon statistics even for 35 MeV of deposited energy. The resolution of a 7.6-cm diameter by 7.6-cm length TlCl(I,Be) crystal used as a Total Absorption Shower Counter for 50-130 MeV positrons has also been measured. This resolution is in reasonable agreement with previously reported data.

Enhancement of Alpha Particle Tracks in Cellulose Nitrate Using Electric Fields

We have observed that the application of an electric field across samples of cellulose nitrate during irradiation by alpha particles enhances the formation of etchable tracks. The track formation efficiency has been studied as a function of the strength of the electric field for alpha particles energies from 2.75 to 5.0 MeV. Both the number of etchable tracks and the amount of damage along individual tracks have been found to be enhanced by the application of an electric field. Approximately the same enhancement is observed either if the field is applied during irradiation by alpha particles or if the field is applied, then turned off before the irradiation is initiated. It is hypothesized that phenomena, associated with corona discharge in the air near the surface of the dielectric sample, is responsible for the observed enhancement. The present results are dominated by chemical effects which eclipse any indication of enhancement due directly to the application of an electric field.