34th Solar Physics Division Meeting, June 2003
Session 22 RHESSI Results III
Oral, Thursday, June 19, 2003, 9:00-10:30am, Auditorium

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[22.07] Physical Implications of {\it{RHESSI}} Neutron Capture-Line Measurements

R. J. Murphy, G. H. Share (Naval Research Laboratory), X.-M. Hua (L3 Communications, EER Systems, Inc.), R. P. Lin, D. M. Smith (Space Science Lab., UC Berkeley), R. A. Schwartz (NASA/GSFC)

We report high spectral-resolution measurements of the 2.223 MeV neutron capture-line obtained with the Reuven Ramaty High Energy Spectroscopic Imager from the 2002 July 23 solar flare. The time history of this line is affected by both the photospheric 3He abundance and the angular distribution of the interacting flare-accelerated particles producing the neutrons. The measured time history is compared with predicted time histories calculated using a magnetic loop model with a magnetic field perpendicular to the solar surface at the footpoints. The model includes energy losses due to Coulomb collisions, removal by nuclear reactions, magnetic mirroring in the convergent flux tube, and MHD pitch-angle scattering in the corona. This is the first analysis of the neutron-capture line using such a physically-based model. The derived constraints on the interacting angular distribution require that the accelerated particles had to suffer pitch-angle scattering during their transport through the coronal portion of the loop. The derived photospheric 3He/H ratio was not well-constrained, primarily due to uncertainties associated with the measured nuclear deexcitation-line flux used to represent the neutron-production time profile.

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