THE SIZE DISTRIBUTION AND MINERAL COMPOSITION OF INTERSTELLAR DUST AFFECTS GAS COOLING AND THE EFFICIENCY OF RADIATION PRESSURE DRIVEN WINDS. IDENTIFYING THE DUST GRAIN MINERALS IS ALSO IMPORTANT FOR UNDERSTANDING THE LIFE CYCLE OF DUST -- FROM DESTRUCTION IN THE DIFFUSE INTERSTELLAR MEDIUM (ISM) TO GRAIN GROWTH IN COLD MOLECULAR CLOUDS. USING X-RAY BRIGHT SOURCES ONE CAN MEASURE ABSOLUTE INTERSTELLAR METAL ABUNDANCES FROM PHOTOELECTRIC ABSORPTION AND INVESTIGATE INTERSTELLAR DUST MINERALOGY THROUGH X-RAY ABSORPTION AND SCATTERING. THE SPECTROSCOPIC IMAGING CAPABILITIES OF THE XARM-SXS OFFER UNIQUE OPPORTUNITIES TO STUDY THE SPECTRUM OF DUST SCATTERING HALOS NOT JUST THEIR EFFECT ON PHOTOELECTRIC ABSORPTION. THESE SCATTERING HALOS ARE LARGER THAN OR COMPARABLE TO THE FIELD OF VIEW FOR THE XARMSXS. THE 1.3 ARCMIN HPD EXPECTED FOR XARM WILL ALSO CAUSE POINT SOURCE LIGHT TO MIX WITH DUST SCATTERED LIGHT AND VICE VERSA. AS AN XARM PARTICIPATING SCIENTIST I WILL RUN RAY-TRACE SIMULATIONS OF DUST SCATTERING HALOS TO EVALUATE: (I) THE OBSERVATIONAL APPROACH FOR XARM TO OBTAIN A HIGH RESOLUTION SPECTRUM OF A DUST SCATTERING HALO. THIS WOULD PROVIDE A DIRECT EXPERIMENTAL MEASUREMENT OF THE INTERSTELLAR DUST SCATTERING CROSS-SECTION IN HIGH RESOLUTION WHICH WILL EXHIBIT RESONANT FEATURES AROUND THE K AND L SHELL EDGE ENERGIES THAT WILL DIRECTLY IDENTIFY THE SOLID-PHASE CONSTITUENTS OF THE SCATTERING MATERIAL; AND (II) IDEAL TARGETS AND EXPOSURE TIME NEEDED TO BE ABLE TO RESOLVE X-RAY ABSORPTION FINE STRUCTURE (XAFS) FROM SOLID-PHASE INTERSTELLAR METALS WHICH CAN BE USED TO IDENTIFY THE MINERAL STRUCTURE OF INTERSTELLAR DUST GRAINS. HIGH RESOLUTION MEASUREMENT OF THE DUST SCATTERING CROSS-SECTION: TO MEASURE THE DUST SCATTERING CROSS-SECTION ONE NEEDS TO NORMALIZE THE SCATTERING HALO SPECTRUM BY THE POINT SOURCE SPECTRUM. I AM AN EXPERT ON MODELING THE SURFACE BRIGHTNESS PROFILES OF DUST SCATTERING HALOS. I WILL USE MIE SCATTERING THEORY TO CALCULATE DUST SCATTERING HALOS AROUND THE ABSORPTION EDGE FEATURES EXPECTED FOR TYPICAL DUST MATERIALS. I WILL SIMULATE THE SCATTERING HALOS UNDER THE EFFECTS OF BACKGROUND SOURCE SPECTRA WITH VARYING DEGREES OF SPECTRAL SMOOTHNESS (E.G. A FEATURELESS POWER LAW VERSUS A SPECTRUM WITH AN EMISSION LINE OVERLAPPING THE ABSORPTION EDGE POSITION). I WILL RUN MY SIMULATIONS THROUGH RAY-TRACING SOFTWARE IN ORDER TO EVALUATE THE EFFECTS OF THE XARM PSF MIXING WITH THE DUST SCATTERING HALO. THE RESULTS WILL DETERMINE WHETHER MEASUREMENTS OF THE DUST SCATTERING CROSS-SECTION CAN BE DONE WITH XARM ALONE OR IF COORDINATED OBSERVATIONS WITH CHANDRA OR XMM-NEWTON ARE NEEDED. XAFS WITH XARM: MY WORK HAS SHOWN THAT DUST SCATTERING HALOS CAN ALTER THE APPARENT SHAPE AND DEPTH OF THE PHOTOELECTRIC ABSORPTION EDGE -- DEPENDING ON GRAIN SIZES LOCATION AND IMAGING RESOLUTION OF THE X-RAY TELESCOPE OF INTEREST. I WILL USE THE RAY-TRACING SIMULATIONS DESCRIBED ABOVE TO EVALUATE HOW THE DUST SCATTERING HALO WILL AFFECT XARM SPECTRA. I WILL DETERMINE IDEAL TARGETS EXPOSURE TIME AND SIGNAL-TO-NOISE NECESSARY TO CHOOSE BETWEEN XAFS TEMPLATES FOR DIFFERENT MINERALS. MY MAIN SCIENCE FOCUS WILL BE ON THE FOLLOWING QUESTIONS: - WHERE IS THE X-RAY SIGNATURE OF SOLID O? RECENT WORK UTILIZING THE MOST UP-TO-DATE THEORETICAL O CROSS-SECTIONS SHOW THAT THE O K EDGE CAN BE DESCRIBED BY GAS-ONLY MODELS. YET OXYGEN IS A CRUCIAL INGREDIENT FOR SILICATE MINERALS. IDENTIFYING A 0.5 KEV FEATURE IN THE DUST SCATTERING CROSS-SECTION WILL UNAMBIGUOUSLY RESOLVE THIS ISSUE. - IS THERE ANY GAS PHASE NEUTRAL FE AND IF SO WHAT IS THE ABSORPTION CROSS SECTION? WE CAN SEARCH FOR RESIDUALS IN THE FE L SHELL EDGE TO DIRECTLY MEASURE THE CROSS-SECTION OF NEUTRAL FE. - CAN WE EXAMINE PAHS WITH X-RAYS? DUE TO INCREASED ABSORPTION C K EDGE FEATURES HAVE BEEN IDENTIFIED IN ONLY A FEW SOURCES WITH LOW ISM COLUMN. I WILL EVALUATE THE ABILITY OF XARM TO RESOLVE FEATURES FROM C K (0.3 KEV) NEAR THE LIMIT OF THE SXS BANDPASS.