X-ray precipitation in the auroral zone



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An instrumented payload has been developed to investigate the auroral X-ray flux at altitudes below 55-60 km. The payload is boosted to the high-altitude region on an Areas rocket. From apogee, the instruments descend slowly by parachute, enabling observation of the temporal features of auroral X-rays. This represents a new concept for auroral investigations; the initial flights are described herein. The measurements are made with a scintillation counter and the payload also contains a small Geiger counter and a magnetometer for determining the orientation of the detectors. Three packages were flown during 1970 from the Churchill Research Range, Manitoba, Canada. Two payloads were flown under active auroras simultaneously with other rockets with payloads for measurement of the auroral electron flux; the trajectories of these rockets carried them above the auroral form directly into the region of precipitating electrons. The other flight consisted of a daylight, quiet-time background X-ray measurement. The X-ray differential spectra measured on these three flights were found generally to agree with previous observations. Using available techniques, the auroral component of the X-ray spectrum observed on the February 24, 1970 flight was corrected for atmospheric absorption and was then used to determine a parent electron spectrum which had the differential form nlowered e = (7.2 x 10[raised 8]) E[raised -4.0] electrons/cm[squared] • sec • keV where E is energy in keV. This result agreed with the observed electron spectrum within an order of magnitude. The probable sources of discrepancy are a loss of calibration settings during flight, requiring an empirical adjustment, and the large separation distance between the positions of the electron and X-ray measurements, possibly with a change in precipitation intensity between observations. The present results give an indication of the potential of the technique used here to determine the auroral electron flux and spectrum from that of the resultant X-rays. However, experimental verification of the technique is needed; the present result is a first step in this regard. The flight program will continue with more closely controlled trajectories to insure electron and X-ray measurements within closer horizontal proximity. Compton scattering effects and a finite X-ray production layer may be considered in future correlation calculations where measurements at depths more than 3 g/cm[squared] are being used.