Xenon Scintillation

Along with stopping power, position resolution and sensitivity, energy resolution is one of the key features of any x-ray detector. Energy resolution refers to a detector's ability to determine precisely the energy of any incident x-ray.  Improved energy resolution yields cleaner spectra of objects such as neutron stars. These cleaner spectra can then be used to build improved models of the interactions occurring in the magnetospheres of these highly magnetic stellar remnants.

Much of the work that I did as a graduate student and post-doc was aimed at improving the energy resolution of a xenon gas scintillation proportional counter designed for use in x-ray astronomy in the 20 to 300 keV energy band. Using plane parallel proportional counters with CsI photocathodes and low pressure methane gas,  we were able to achieve an ultimate energy resolution within a factor of two of the expected theoretical limit. The primary limiting factor in energy resolution should come from Fano fluctuations in the electron drift cloud resulting from the photoelectric absorption of the incident x-ray. You can find our results published in SPIE Conference Proceedings, 2806, pp. 361-371, 1996. A good deal of the work I have done with students has been in attempting to track down the cause of the factor of two worsening of the energy resolution.

Lately, this work has led us to search for infrared emission from xenon gas. Traditionally, vacuum ultraviolet scintillation emission has been used to form the basis xenon scintillation detectors. We decided that if infrared emission existed it might be a new channel we could use to get information on the incident x-ray’s energy.  We set about trying to determine if xenon did scintillate in the infrared and if that infrared emission could be used to form the basis of an x-ray or particle detector. We searched for emission around the known atomic xenon emission lines at 823 nm and 828nm. We found that infrared scintillation did, indeed, exist and its yield increased as the xenon pressure was decreased below one atmosphere. The xenon yield did not prove to be large enough to meet our needs for an astronomical x-ray detector but the yield was sufficient to perhaps be of interest to people working in other areas. The results can be found in the journal Nuclear Instruments and Methods.