Calcium Molybdate for Low Background Beta Spectrometry
First Growth of the CaMoO4 Crystal with Mo-100 for Double Beta Decay Search in YangYang Underground Laboratory
Tech Area / Field
- PHY-PFA/Particles, Fields and Accelerator Physics/Physics
- INS-DET/Detection Devices/Instrumentation
- MAT-SYN/Materials Synthesis and Processing/Materials
8 Project completed
Senior Project Manager
Tyurin I A
ITEF (ITEP), Russia, Moscow
- MISIS (Steel and Alloys), Russia, Moscow\nJSC Fomos-Materials, Russia, Moscow
- Seoul National University / Department of Physics and Astronomy, Korea, Seoul\nKyungpook National University, Korea, Taegu
Project summaryThe most important event in elementary particle physics for last few years is a discovery of neurtrino mass. Next step should be determination of this mass value and nature, whether neutrino Dirac or Majorana particle. The only proof of Majorana nature (i.e. neutrino is equivalent to antineutrino) would be discovery of neutrinoless double beta decay of some even-even nuclei. Realization of experimental search of such a process requires big amount (tens and hundreds of kg) of expensive enriched isotopes, subject for double beta decay. It needs also low background setup situated deep underground. One of most effective ways to achieving high sensitivity in such experiments is usage of scintillation crystals containing enriched isotope (e.g. Mo-100).
Within the frame of this project the Ca100MoO4 scintillation crystals growth technology will be demonstrated providing good optical transparency and high light yield as well as low radioactive background. Single crystals based on Mo-100 isotope will be grown by Czochralsky method with platinum crucibles of SCM quality (sandwich-type composed material) in high-frequency induction ovens using stoichiometric high-purity raw materials
To demonstrate the technology CaMoO4 crystals of different volumes will be grown using both the raw material of optimized composition and a charge of the crucible. The methods of single crystals processing (main annealing conditions for the crystals, mechanical cutting, lapping and polishing of specimen) will be demonstrated.
The main goal of the project is demonstration of a possibility to grow the CaMoO4 crystals based on enriched Mo-100 isotope of specified dimensions and quality with taking into account the requirements on long-lived radioactive isotopes, which could create background in future experiment.
For the achievement of the desired level of “dangerous” radionuclides the raw material and blend with low content of such impurities will be used. Multiple recrystalization procedure of Ca100MoO4 will be also used. Certification of the crystals will be done at ITEP and MSAI independently. Content of radioactive elements will be measured by Inductively Coupled Plasma mass-spectrometry and gamma-spectrometry both during preparation of raw material and after production of the monocrystals.
Thus a possibility of isotopically enriched Ca100MoO4 crystals production at a big quantity (tens and hundreds kg) will be demonstrated to carry out full-scale experiment on double-beta decay search at Korean national laboratory YangYang.
The developed technology and methodological approaches will allow to prepare and conduct efficiently large scale double beta decay experiments with scintillation mono-crystals containing other isotopes of interest, for example 116Cd. Measurement of neutrinoless double beta decay time or setting of limits is extremely important because it helps to determine more accurately nuclear matrix elements.
The leading organization ITEP is one of world leaders in neutrino physics. Its staff has conducted the first experiment with enriched 76Ge, was main participants of international experiments IGEX and DBA and is participating in the NEMO experiment. Currently an experimental search of 150Nd double beta decay is being conducted at ITEP. The Institute is preparing also international experiments with 76Ge (MAJORANA and New Germanium Initiative). The staff, participating in this project, has good experience to participate in the high ranking conferences, exhibitions workshops and have a good experience in the creation of the detectors performance tests. ITEP participated in development of physical and chemical methods of purification of materials used for low background experiments, and certification of samples of these materials by different methods. ITEP was a leading institute in ISTC project 3293 devoted of technology development for growth of large volume Ca100MoO4 scintillation crystal.
Staff from MSAI participated in ISTC project 3293 and has longstanding experiences with growing of monocrystals based on oxides complexes, in particular molybdates and tungstates. Members of the team have experience on crystals growing, theirs treatment, investigation of their physical properties and analysis of defects into the monocrystals. This experience and knowledge in field of materials for crucible production for Chochralski method will help to resolve in undertime the problem of application of expensive material (Pt).
A staff from FOMOS Materials will complete a Ca100MoO4 crystals growing by Czochralsky method and preparation of the Ca100MoO4 samples for following analysis and certification. The part of the project to be carried out is manufacturing of the crystal specimens for further analysis, tests and demonstrations.
Collaborators of the project are Basic Science Research Institute of Seoul National University, Department of Physics and Astronomy and Kyungpook National University, Department of Physics. It was supposed that the experiment for neutrinoless double beta-decay search will be carried out at YangYang underground laboratory (Republic of Korea). Results of testing and certification of Ca100MoO4 monocrystals will be used for planning of future experiments at wide range of the temperature and two-modes signal read-out (scintillation and phonon signals) at YangYang underground laboratory