Histologic effects of high energy electron and proton irradiation of rat brain detected with a silver-degeneration stain.

Application of the degeneration sensitive, cupric-silver staining method to brain sections of male Sprague-Dawley rats irradiated 4 days before sacrifice with 155 Mev protons, 2-8 Gy at 1 Gy/min (N=6) or 22-l0lGy at 20 Gy/min (N=16) or with 18.6 Mev electrons, 32-67 Gy at 20 Gy/min (N=20), doses which elicit behavioral changes (accelerod or conditioned taste aversion), resulted in a display of degeneration of astrocyte-like cell profiles which were not uniformly distributed. Plots of 'degeneration scores' (counts of profiles in 29 areas) vs. dose for the proton and electron irradiations displayed a linear dose response for protons in the range of 2-8 Gy. In the 20-100 Gy range, for both electrons and protons the points were distributed in a broad band suggesting a saturation curve. The dose range in which these astrocyte-like profiles becomes maximal corresponds well with the dose range for the X-ray eradication of a subtype of astrocytes, 'beta astrocytes'.     

Direct evidence for chromospheric evaporation in a well-observed compact flare

We have observed the flare of 1980 May 7 1456 UT with several Solar Maximum Mission instruments, in coordination with the Sacramento Peak Observatory Vacuum Tower Telescope. From the X-ray data we determine the total amount of plasma at T > 2 × 10⁶ K, commonly attributed to chromospheric evaporation. From Hα we have determined the amount of plasma that has been evaporated from the chromosphere. We find that enough material has been evaporated from the chromosphere to account for the X-ray plasma. Taken together, the Hα, soft and hard X-ray images suggest that chromospheric evaporation is driven both by flare accelerated electrons, during the impulsive phase, and conduction, during the thermal phase.     

Observational evidence for chromospheric footpoint penetration of nonthermal electrons during two well-observed flares

Recent advances have enabled simultaneous Hα and X-ray observations with substantially improved spatial, spectral, and temporal resolution. In this paper we study two events observed as part of a coordinated observing program between the Solar Maximum Mission and Sacramento Peak Observatory: the flares of 1456 UT, 7 May 1980 and 1522 UT, 24 June 1980. Using recently-developed physical models of static flare chromospheres, and corresponding theoretical Hα line profiles, we can distinguish effects of intense nonthermal electron heating from those of high conduction and pressure from the overlying flare corona. Both flares show the signature of intense chromospheric heating by fast electrons, temporally correlated with X-ray light curves at E > 27keV, and spatially associated with X-ray emission sites at E >62; 16 keV. Interpreting the Hα line profile observations using the theoretical Hα line profiles, we infer values of the thick-target input power contained in nonthermal electrons that are observationally indistinguishable (within a factor of 2–3) from those inferred from the X-ray data. Although these events are small, the energy flux values are large: of order 10¹¹ ergs cm^?2 s^?1 above 20 keV.