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	&lt;font face="TimesNewRomanPSMT"&gt;One of the major goals of high-energy solar physics, and therefore of the Solar and &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;Heliospheric Physics (SHP) Program, is a detailed understanding of the particle acceleration &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;processes taking place on the Sun during solar flares. Flares can accelerate electrons to tens of &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;MeV and ions to energies exceeding 1 GeV, as evidenced by the neutral radiation that can be &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;studied remotely. The intense scientific interest in understanding this process is evidenced by &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;the large number of wh ite papers dedicated to the topic that were submitted in response to the &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;current Heliophysics Decadal Survey. A recurring theme in many white papers is the central role &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;that new, sensitive observations of the &lt;/font&gt;&lt;b&gt;&lt;font face="TimesNewRomanPS-BoldMT"&gt;gamma-ray line emissions &lt;/font&gt;&lt;/b&gt;&lt;font face="TimesNewRomanPSMT"&gt;from flares must play in &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;disentangling the problem of acceleration and transport of energetic particles (Lin et al. 2010; &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;Shih et al. 2010; Desai et al. 2010). More specifically, to significantly advance the study of solar &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;flare particle acceleration, it will be necessary to&amp;nbsp; &lt;/font&gt;&lt;b&gt;&lt;font face="TimesNewRomanPS-BoldMT"&gt;compare in detail the spatial, spectral, and &lt;/font&gt;&lt;/b&gt;&lt;b&gt;&lt;font face="TimesNewRomanPS-BoldMT"&gt;temporal evolution of electron signatures&amp;nbsp; &lt;/font&gt;&lt;/b&gt;&lt;font face="TimesNewRomanPSMT"&gt;(hard X-ray and gamma-ray continuum emission &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;from bremsstrahlung) &lt;/font&gt;&lt;b&gt;&lt;font face="TimesNewRomanPS-BoldMT"&gt;and ion signatures &lt;/font&gt;&lt;/b&gt;&lt;font face="TimesNewRomanPSMT"&gt;(gamma-ray lines and pion-decay continuum from &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;accelerated ions colliding with the solar atmosphere) &lt;/font&gt;&lt;b&gt;&lt;font face="TimesNewRomanPS-BoldMT"&gt;over a wide dynamic range &lt;/font&gt;&lt;/b&gt;&lt;font face="TimesNewRomanPSMT"&gt;of flare sizes &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;and intensities.&lt;/font&gt;&lt;/p&gt;
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	&lt;font face="TimesNewRomanPSMT"&gt;&lt;font face="TimesNewRomanPSMT"&gt;For the gamma-ray lines, comprehensive measurements require angular resolution of ~10 &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;arcsec or better at energies up to ~10 MeV, energy resolution of a few percent or better, and &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;sensitivity at least 10 times better than that of previous instruments. Making such complex &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;measurements over a large dynamic range presents a serious challenge to gamma-ray &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;instrumentation, which must deal with large backgrounds for faint flares and high count rates for &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;bright flares. In addition, future missions to study flare particle acceleration, such as the Solar &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;Eruptive Events (SEE) 2020 concept presented by Lin et al. (2010), will contain entire suites of &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;instruments to ensure that complementary measurements are made in a coordinated manner. &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;Unprecedented gamma-ray measurements must therefore be made without consuming the &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;spacecraft&amp;rsquo;s mass, power, and telemetry budgets.&lt;/font&gt;&lt;/font&gt;&lt;/p&gt;
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	&lt;font face="TimesNewRomanPSMT"&gt;&lt;font face="TimesNewRomanPSMT"&gt;&lt;font face="TimesNewRomanPSMT"&gt;Three recent technological developments potentially allow us to combine the abilities of &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;these pioneering instruments: 1) Recently developed scintillator materials, in particular LaCl &lt;/font&gt;&lt;font face="TimesNewRomanPSMT" size="1"&gt;&lt;font face="TimesNewRomanPSMT" size="1"&gt;3&lt;/font&gt;&lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;:Ce &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;and LaBr &lt;/font&gt;&lt;font face="TimesNewRomanPSMT" size="1"&gt;&lt;font face="TimesNewRomanPSMT" size="1"&gt;3&lt;/font&gt;&lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;:Ce, offer a far more attractive mix of stopping power, energy resolution, and fast time &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;response than NaI and BGO scintillators. Energy resolution better than 3&#37; above 0.6 MeV and &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;timing resolution well below 500 ps are now well established. 2) Recently developed Silicon &lt;font face="TimesNewRomanPSMT"&gt;Photo-Multipliers (SiPMs) offer a compact, low-mass, and low-power alternative to PMTs. We &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;have already shown that detectors composed of LaBr &lt;/font&gt;&lt;font face="TimesNewRomanPSMT" size="1"&gt;&lt;font face="TimesNewRomanPSMT" size="1"&gt;3 &lt;/font&gt;&lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;scintillator coupled to SiPM readouts &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;perform well as gamma-ray spectrometers (Bloser et al. 2008, 2010a). 3) Newly available &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;compact arrays of SiPMs, with sensing elements typically 3 &amp;ndash; 4 mm in size, promise the &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;additional ability to achieve fine spatial resolution within scintillators in a compact Anger &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;camera configuration. Gamma-ray detectors of this nature are currently being developed by the &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;medical imaging community (e.g., Schaart et al. 2009), and position resolution of 1 mm or better &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;has been demonstrated&lt;/font&gt;&lt;/font&gt;&lt;/font&gt;&lt;/font&gt;&lt;/p&gt;
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	&lt;font face="TimesNewRomanPSMT"&gt;&lt;font face="TimesNewRomanPSMT"&gt;&lt;b&gt;&lt;font face="TimesNewRomanPS-BoldMT"&gt;We propose a program of instrument development and modeling to show that a fast &lt;/font&gt;&lt;/b&gt;&lt;b&gt;&lt;font face="TimesNewRomanPS-BoldMT"&gt;Compton telescope based on an innovative combination of new scintillator detectors and &lt;/font&gt;&lt;/b&gt;&lt;b&gt;&lt;font face="TimesNewRomanPS-BoldMT"&gt;light readout devices, combined with an imaging grid or mask, is a scientifically &lt;/font&gt;&lt;/b&gt;&lt;b&gt;&lt;font face="TimesNewRomanPS-BoldMT"&gt;competitive solution to this instrumentation challenge&amp;nbsp;&amp;nbsp;&lt;/font&gt;&lt;/b&gt;&lt;font face="TimesNewRomanPSMT"&gt;In effect, we will attempt to combine &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;the best features of past solar gamma-ray instruments into an efficient, low-background, imaging &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;gamma-ray spectrometer. The RHESSI mission (Lin et al. 2002) made the first high-angularresolution &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;images at gamma-ray energies, adapting Fourier-synthesis methods previously used at &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;hard X-ray energies (e.g., the Yohkoh Hard X-ray Telescope; Kosugi et al. 1991) to image the &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;2.2 MeV neutron-capture line with a resolution of about 35 arcsec (Hurford et al. 2006). Earlier &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;gamma-ray spectrometers based on efficient inorganic scintillators, including those on the Solar &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;Maximum Mission (SMM; Forrest et al. 1980), Yohkoh (Yoshimori et al. 1992), and the &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;Compton Gamma Ray Observatory (e.g., Murphy et al. 1993), made sensitive spectral &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;observations up to &amp;gt;10 MeV over a large range of flare intensities. The most sensitive gammaray &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;flare spectrometer of all was the COMPton TELescope (COMPTEL) on CGRO (Sch&amp;ouml;nfelder &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;et al. 1993; Ryan &amp;amp; McConnell 1996). As a scintillator-based Compton telescope, COMPTEL &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;was able to dramatically suppress background using a fast coincidence, time-of-flight (ToF) &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;measurements, and coarse imaging ability. COMPTEL was able to detect nuclear emission from &lt;/font&gt;&lt;font face="TimesNewRomanPSMT"&gt;a C4 flare, the faintest such detection to date (Young et al. 2001).&lt;/font&gt;&lt;/font&gt;&lt;/font&gt;&lt;/p&gt;
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