Twenty limb crossing light curves of solar active region emission in the 1-4 keV energy band have been constructed from data gathered by the Lockheed Mapping X-Ray Heliometer experiment on OSO-8. These light curves indicate that 50% of the observed counts arise from heights below 20 000 km and 90% from heights below 57 000 km. The best fit is obtained for a model in which the emission density increases steadily down to the lowest observable levels, but the possibility of a small emission free gap at the base cannot be ruled out. On the average, the temperature of the plasma appears to be slightly higher at the base of a region than in its upper levels.
The appearance of the Ha fibrils suggests the presence of magnetic fields inclined at noticeably non-radial angles in the Sun's chromosphere. We present evidence to suggest that these angles continue into the photosphere.The presence even of small non-radial inclinations can significantly affect the appearance of regions observed by a longitudinal magnetograph. In particular, a simple bipolar loop can appear unbalanced when viewed near the limb. We suggest that the observed polar signal may be nothing more than a geometric effect arising when a balanced but systematically aligned array of bipolar pairs is viewed at an angle.
127 hr of high-resolution Ha movies of young active regions have been compared with simultaneous 1.5-15 keV X-ray measurements from the Mapping X-Ray Heliometer experiment on OSO-8, with particular attention to preflare periods and to the possibility of X-ray emission associated with filament activity during that time. The period studied included 8 confirmed flares or subflares, 16 unreported events of comparable magnitude, and numerous examples of filament activity. We found no evidence for X-ray emission from areas of enhanced filament activity unless simultaneous brightenings were present in Ha. In addition, we detected no peculiar behavior of either filaments or X-rays during the period of approximately 20 min preceding these small flares which, even in retrospect, would have allowed them to be 'predicted'.
The purpose of this research is to investigate the temporal and spatial relationships of activated filaments, soft X-ray production, and Ha flares. The X-ray data are from the Lockheed Mapping X-Ray Heliometer (MXRH) on 0S0-8 (Wolfson et al., 1975, 1977). This instrument has been operating continuously since July 1975. It responds to radiation from solar plasma above about 2 × 106K, provides a time resolution of 20 sec, a spatial resolution of 2-3 arc min and has a basic sensitivity roughly equivalent to the 1-8 Å full disc monitors of, e.g., the SOLRAD and SMS/GOES satellites (threshold ≈ 2 × 10-9W/m2). However, because of its spatial resolution the MXRH permits study of small X-ray events in individual active regions even when the integrated solar X-ray emission is high.
The mass of C has been measured by counting delayed protons near the Be('He, n)'C threshold. The data are consistent with an s-wave threshold at E3H, =8980 +5 keV, giving a C mass excess of 28907+4 keV, and confirming the reported deviation of the A=9, lowest T = 2 quartet from the quadratic mass formula. The half-life of ' C. measured with a multiscaler, is 126.5~2 msec.The ground states of 'C and 'Li together with the T = & excited states at 14.392 MeV in 'Be and at 14.655 MeV in 'B have been the subjects of considerable investigation because they form one of the few presently accessible isospin quartets. This experiment was undertaken to attempt to verify and improve the measurement of the 'C mass.The experimental method of deducing that quantity from the threshold energy of the 'Be('He, n)'C reaction had been used previously by Barnes et al. 'A 'BeO target, prepared for an earlier experiment' by evaporating under vacuum a-', -in. -diam spot of 'BeF, onto a 1.2-mm-thick platinum bar and then oxidizing the layer in air, provided a surfa, ce density of 7x10" 'Be atoms per cm'. This number represents about half of the 'Be present when the target was first prepared, the other half having decayed to 'Li, which, along with the oxygen and other impurities, contributed to a measured target thickness of 10 keV for the 9-MeV 'He beam supplied by the Office of Naval Research-California Institute of Technology tandem Van de Graaff accelerator near the reaction threshold.The target was mounted in a chamber' equipped with a solenoid-operated arm capable of switching the target between a beam line and a counting position in an 873-msec cycle. For the first 290 msec of each cycle, the target spot was exposed to --, ' p. amp 'He. If 'C was formed, it would be expected to P' decay into the broad particle-unstable states of 'B, which almost immediately break up into a proton plus 'Be. Thus, in the second part of the cycle, after the beam had been deflected, the target was moved directly in front of a~+E telescope consisting of an 11and a 26p, m silicon detector, with a geometrical efficiency of -15%. This arrangement of counters was necessary in order to be able to sort out the protons accompanying 'C decays from the intense background of 478-keV y rays emitted by the 50 mCi of 'Be, as well as from the n particles and other activity induced by the 'He bombardment. When a pulse from the~counter consistent with a proton energy . loss of 0.27-0.55 MeV arrived in coincidence with a pulse from the E counter large enough to be distinguished from the yray background, the sum was recorded by a multichannel analyzer. The natural radioactivity of the target restricted both the choice of detector volume and the smallest (largest proton energy) that could be accepted. Two successive counting periods of 229 msec each were recorded separately to provide a check of the half-life. Figure 1 shows the sum of the spectra obtained during the 16 threshold runs. The broad group of protons with 0.75-3.0-MeV energy loss in the counters is clearly separ...
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