Abstract : Astronomy has always depended heavily on spectroscopy to become "astrophysics", and X-ray astronomy is no exception. Astronomical X-ray sources turn out to be interesting things like neutron stars, black holes, and concentrations of million to hundred-million-degree gas that are otherwise unobservable but contain most of the normal matter in the Universe. Since we can't usually have these goodies in the lab, we need to learn all we can from the astrophysical examples. Unfortunately, dispersive X-ray spectrometers are too inefficient for extensive application to astronomy, and ionization statistics fundamentally limit the energy resolution of solid state detectors to a level inadequate for most spectroscopic investigations. Our solution to this dilemma has been to attach a thermometer to the detector and do thermal calorimetry on individual photons. This idea turns out to be not quite as dumb as it sounds (even remembering that a 6 keV photon is one femtojoule): the best energy resolution results are currently almost two orders of magnitude better than a theoretically perfect silicon solid state detector. These detectors also offer greatly increased flexibility in choice of materials. Without the stringent requirement for good charge transport properties, they can be made out of almost anything and in addition to X-rays have been used for measuring electrons, alphas, excitons, infrared, and even for neutrino spectroscopy. Getting back to X-rays, it turns out there actually are a lot of constraints on the ideal detector material, and I will discuss why we're now using HgTe and HgCdTe.

The seminar will be held at 3.30 pm in 238 . UIC Physics Dept/SES. is located at 845 W Taylor St., Chicago, IL, 60607