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Scintillators for beta-spectroscopy

#3293


Technology Development for Growth of Large Volume СаМоО4 Scintillation Сrystal for Double Beta-Decay Experiment in Yang-Yang Korean National Laboratory

Tech Area / Field

  • PHY-PFA/Particles, Fields and Accelerator Physics/Physics
  • INS-DET/Detection Devices/Instrumentation
  • MAT-SYN/Materials Synthesis and Processing/Materials

Status
8 Project completed

Registration date
06.06.2005

Completion date
06.11.2007

Senior Project Manager
Tyurin I A

Leading Institute
ITEF (ITEP), Russia, Moscow

Supporting institutes

  • MISIS (Steel and Alloys), Russia, Moscow\nInstitute for Nuclear Problems, Belarus, Minsk

Collaborators

  • Seoul National University / Basic Science Research Institute, Korea, Seoul

Project summary

The most important event in elementary particle physics for last few years is a discovery of neutrino mass. Next step should be determination of this mass value and nature, whether neutrino Dirac or Majorana particle. [2] 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 the most effective ways of achieving high sensitivity in such experiments is usage of scintillation crystals containing enriched isotope (e.g. Mo-100) [3]

Within the frame of this project the large (not less than 45х45х200 mm3) СаМоО4 scintillation crystals growth technology will be developed providing good optical transparency and high light yield (2500 photelectrons/MeV) as well as low radioactive background. Single crystals will be grown by Czochralski method with platinum crucibles in high-frequency induction ovens using stoichiometric high-purity raw material

The set aims require improving both CaMoO4 crystal growth technique (initial charge composition, feed material synthesis depth, crucible capacity for growing crystals with certain sizes, seed pulling and rotation rates, gas ambient composition in the crystallization chamber) and further crystal processing (main annealing conditions for the crystals, mechanical cutting, lapping and polishing of specimen).

Fulfillment of the formulated tasks will allow to develop stable СаМоО4 crystal production technology of the specified size and quality with minimal expenses, taking into account radioactive isotopic purity requirements.

During crystal certification procedure the temperature dependence of light yield and scintillation kinetics will be studied in 78K to room temperature range as well as the influence of chemical impurities and crystal growth process parameters.

For the achievement of the desired level of radionuclide impurities (U, Th) effective methods [4,5] of purification will be applied to row material and blend (including multiple recrystalization of СаМоО4. Certification of the crystals will be done independently at ITEP, INP and YangYang laboratory (Korea). Contents of radioactive elements will be controlled by various methods both at raw material preparation stage, and after crystal growth.

Upon fulfillment of the project, it will be possible to grow big volume Са100МоО4 single crystals for full scale double beta decay experiment in Korean laboratory YangYang, using developed technology, growth setup and selected low background materials.

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. 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 double beta decay study. It’s staff have conducted the first experiment with enriched Ge-76, were main participants of international experiments IGEX and DBA and are participating in the NEMO experiment. Currently an experimental search of Nd-150 double beta decay is being conducted at ITEP. The Institute is preparing also international experiments with Ge-76 (MAJORANA and New Germanium Initiative).

The staff, participating in this project, has good experience in development of purification and screening methods for low background materials, and development of new scintillators for neutrino physics Yb:YAG and Yb:YAP working at low temperature.

MSAI is one of the world major research centers possessing modern equipment that has been working in the field of metals and inorganic compounds for over 40 years. The part of the project to be carried out is growing CaMoO4 crystals by the Czochralski method and preparing the specimens for further analysis and tests. The work will be executed by the Crystal Physics Department staff that has been working long with single-crystal oxide compounds, molybdates and tungstates in particular.

INP. Scientists of the institute took part in preparation and implementation of high-energy physics experiments at CERN in 1992-2002. The main activity was development of a new scintillation material to meet the unprecedented goals of new experiments. Lead tungstate scintillation crystal (PbWO4, PWO) was developed within the frames of ISTC projects ##354, 1718. INP played a key role in development of mass production technology, quality assurance means and certification of PWO. All principal characteristics of PWO scintillators were radically improved up to the level of CERN experiments requirements

Collaborator of the project is the Dark Matter Research Center of Seoul National University. Experimental search of double beta decay is supposed to be done at Korean national underground laboratory YangYang. The samples being obtained during the project fulfillment will be controlled independently by the collaborators (light yield, transparency, decay time, radiopurity). The blend monitoring on the contents of radioisotopes 214Bi and 208Tl will be performed at YangYang laboratory.

  1. M. Baldo-Сeolin, Neutrino oscillations (Topical review) J. Phys. G: Nucl. Part. Phys. 29 (2003) R133–R156.
  2. S.M.Bilenky et. al. The Majorana neutrino masses, neutrinoless double beta decay and nuclear matrix elements. hep-ph/04022250.
  3. Yu.Zdesenko, ‘Colloquium: The future of double beta decay researchRev. Modern Physics, vol.74 (2002) 663.
  4. R.Arnold, C. Augier,… V.N.Kornoukhov et al., Chemical purification of molybdenum samples for the NEMO 3 experiment, Nucl. Instrum. Meth. A474 (2001) 93-100.
  5. A.S. Barabash, I.R. Barabanov, V.N.Kornoukhov, I.V. Orekhov, Ra-226 Measurement in Mo, Cd and Nd2O3 Samples with the Emanation Method, Nucl. Instrum. Meth. A469 (2001) 159-163.


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