Particle physics experiments at International Neutrino Experiment Xenon TPC advances with new ultra-high vacuum vessel

07/25/2016 - 22:59

Ben Bowers

In 1976, Dr. David R. Nygren developed the first time projection chamber (TPC) at Lawrence Berkeley National Laboratory to study 29 GeV electron-positron collisions at SLAC’s PEP storage ring. A TPC is a gas chamber that is instrumented to detect and image electrons resulting from ionization of gas molecules caused by high energy particles traversing the chamber. As a result, particle trajectories and interactions could be resolved in three dimensions yielding what is considered to be one of the greatest contributions to particle physics of the 20th century. Since then, TPCs have been developed all over the world to detect and study various types of subatomic particle interactions. One of the most notable TPC’s was built to study heavy ion collisions (ALICE experiment) at CERN’s Large Hadron Collider.

Recently, Dr. Nygren joined the faculty at the University of Texas at Arlington to “establish a new unit to foster research at the forefront of particle detector technologies and train the next generation of detector experts”. In particular, Dr. Nygren will maintain a lead role in the international Neutrino Experiment Xenon TPC (NEXT)Collaboration to search for an extremely rare nuclear decay (neutrino less double beta decay) that could teach us whether or not the neutrino is its own anti-particle.

If the experiment ultimately shows that the decay occurs, at any non-zero rate, then the neutrino is its own anti-particle. In turn, the result would support theoretical concepts that explain the matter-antimatter asymmetry of the universe through the fleeting existence of massive neutrinos. Only certain isotopes of a few elements exhibit this decay mode, one of which is Xenon 136, which decays to Barium 136; this element also makes a good TPC gas. We measure total released energy (in the form of gas ionization) and compare with the mass difference between Xe 136 and Ba 136 to determine whether or not neutrinos were emitted, however this type of measurement is not conclusive, and a real “smoking gun” proof would be, additionally, detecting the single Barium ion left from the decay.


New technology must be developed for this task; Anderson Dahlen, Inc. is manufacturing a dual-certified UHV/ASME pressure vessel just for this purpose. The chamber provides gas containment as well as the housing and support for a Bariumion source and various detector prototypes. The chamber will contain gaseous xenon (primary), or argon,up to 15 bar pressure, and have voltages up to 20 kV inside. The chamber will be designed, fabricated, and tested according to ASME Boiler and Pressure Vessel Code section VIII, division 1 (ASME BPVC-VIII-1) as well as being certified for UHV.

Once the detection technology is proven, a large scale experiment having several tons of Xenon 136 under high pressure in similar UHV/vessels will be pursued. Even with such large quantities of Xenon 136, only a few decays per year are expected to occur.