Scintillating Bolometer Crystal Growth and Purification for Neutrinoless Double Beta Decay Experiments

In the search to better understand the fundamental physics of our universe, a crucial goal is elucidating the nature of the neutrino. A key experiment to reaching this goal is searching for neutrinoless double-beta decay, which is a hypothesized process, where in some even-even nuclei it might be possible for two neutrons to simultaneously decay into two protons and two electrons without emitting neutrinos. This is possible only if neutrinos are Majorana particles, i.e. fermions that are their own antiparticles. Numerous experiments have searched for neutrinoless double beta decay but none has detected this reaction. To accomplish this, the next generation of detectors will need to be more sensitive. One approach for achieving this increased sensitivity is to use scintillating bolometers that can effectively reduce the background effects by simultaneously monitoring both the scintillation and bolometric responses. To achieve the needed sensitivity, the natural radioactive background of the detector materials must be extremely low. This requires the use of starting materials of exceptional radio-purity for the desired detector crystals. ZnMoO4 has been proposed as a promising scintillating bolometer material. The goal of this proposal is to develop ZnMoO4 detectors with extremely low intrinsic background radiation. This will be accomplished by intensive purification of raw materials used to synthesize it, followed by special processes for crystal growth and detector fabrication. In Phase I we will develop the processes to purify the material sand produce high quality single crystals. This effort will be carried out in collaboration with researchers at the Massachusetts Institute of Technology. The question of the Majorana nature of the neutrino is one of the most important questions being pursued in physics and has made searches for 0νββ the highest priority among proposed nuclear physics experiments. We are about to enter into an exciting era where experiments are probing new and interesting parameters space, however R&D is still needed for the next generation experiment. Scintillating bolometers are a promising technology, but the crystal growth has proven challenging. This is an area where the U.S. needs to build expertise. The proposed work would provide a new supply of radio-pure scintillating bolometer crystals that would enable new higher sensitivity double beta decay experiments to be constructed and deployed. Techniques developed for ultra-pure, low-radioactivity crystal manufacturing could also be applied to materials other than ZnMoO4 and help to further innovations for other rare event studies, and for other devices used in scientific research, non-destructive testing, and homeland security.The key to understanding the nature of our universe is to gain a better understanding of the fundamental particles that make up matter. This effort will develop the processes to produce the sensitive detectors that will enable the fabrication of the instruments needed to carry out this important physics research.