This award is for a collaborative research and development undertaking between the University of Stanford and the University of Alabama towards the feasibility of a high pressure gas phase detector using enriched Xenon for the detection of neutrino-less double beta decay. Research and Development is to proceed within the broader EXO collaboration to advance detection with liquid Xenon by the introduction of tagging and to a high pressure gas phase using Xe with low background. The proponents envision applying tagging with Barium for the liquid detector to drastically reduce the radioactive background and allow an unambiguous measurement of unprecedented sensitivity. This work will be mainly carried out by the University of Stanford group. The developments of the gaseous detector are not as advanced as the liquid case and the group from the University of Alabama will be exploring the characteristics of such a detector. It is expected that at completion of this project, there will be results to guide the detector development and technology selection for the ton-class of neutrino less double beta decay experiments for the Deep Underground Science & Engineering Laboratory.
Radiation detectors based on noble gases find wide application in basic and applied science. Such detectors offer good energy resolutions and, if equipped with the appropriate signals read-out, allow the reconstruction of event tracks for single particle interactions. Such devices, thus, act as a camera into the world of microscopic radiation interaction. The EXO collaboration has developed, built, and now operates a radiation detector using 200 kg of isotopically enriched liquefied Xe to search for the ultra-rare double beta decay of 136Xe. The experiment currently provides one of the most sensitive tests for the hypothetical identity of neutrinos and antineutrinos, a propety termed Majorana character. The research funded by the NSF led to the construction of a large prototype detector utilizing gaseous Xe. Compared to the successful liquid Xe detector this device offers potential improvements in the areas of energy resolution and track reconstruction. The detector has been set-up at Carleton University in Ottawa as a collaborative effort with Stanford University and the University of Alabama. The device is now operational. The scope of work of the Alabama group included Monte Carlo simulations of the detector background, construction of the handling system for the ultra clean xenon gas (delivered), and construction of an analysis system for electronegative impurities contained in the xenon that may adversely affect detector performance (being shipped to Carleton). The analysis system is based on a quadrupole mass spectrometer and utilizes a cold trap to boost sensitivity. Sensitivities for oxygen (the chief concern in terms of electron trapping and loss of energy resolution) has been shown to be 2 ppb (in units of gram oxygen per gram of xenon) using calibrated oxygen gas leaks. Part of the funding was used to pay two high school summer interns and allow them to work with us for one month during the summer. The detector is now ready for data taking and will be used to explore advantages and disadvantages of gaseous versus liquefied xenon used as radiation detection medium.
