Limits on radiative capture gamma-ray lines and implications for energy content in flare-accelerated protons

Measurements of radiative-capture gamma -ray lines can provide information on both the energy content of nonthermal protons below 1 MeV and the temper ature in the region where they interact. We have derived upper limits on th e fluences in three proton-capture lines of C-12 and C-13 in the flare-aver aged gamma-ray spectrum from 19 X-class flares observed with the Solar Maxi mum Mission (SMM). The most significant limit comes from the 2.37 MeV line that is excited by 0.46 MeV protons. We estimate an upper limit on the ener gy content in the accelerated protons by extrapolating the power-law spectr uzm derived at higher energies down to the resonant energy. The derived upp er limit on the temperature, similar to 5-10x10(7) K, is higher thazn measu red in the flaring region with other techniques, even for this optimistic e nergy content. It is possible that NASA's High Energy Solar Spectroscopic I mager (HESSI) will be sensitive enough to detect the 2.37 MeV line if tempe ratures exceed similar to 2x10(7) K.