150 Nd activities at TUM

1. 150Nd activities at TUM V. Lazarev1,E. Nolte1, L. Oberauer1, F. Pröbst2 1 - Technische Universität München, E15 2 - Max Planck-Institut für Physik, München with help of J. Doncev2, V. Kochurichin3, L. Nagorna4, D. Kovalev5, S. Schönert6, M. Stark1 3 - General Physics Institute, Coherent and Nonlinear Optics Department, Russia 4 - Institute for Single Crystals, Ukraine 5 - Technische Universität München, E16 6 - MPI, Heidelberg, Germany IDEA DBD Meeting, Heidelberg

2.  emitters • 150Nd: • the shortest half-time for neutrinoless 0 decay • the second largest Q-value • low 2 background A. Faessler A. Staudt IDEA DBD Meeting, Heidelberg

3. Tungstates and scintillation Almost all tungstates scintillate. The best known scintillators are: CdWO4, PbWO4, CaWO4 The reason is the structure of WO4 From: Williams R.T., Y.C. Zhang, Y. Abraham, and N.A.W. Holzwarth Electronic structure of pure and defective PbWO4, CaWO4, and CdWO4 Invited paper presented by R.T. Williams at the SCINT99 conference in Moscow, Aug. 1999 IDEA DBD Meeting, Heidelberg

4. Crystal scintillators • Tungstates are often scintillators: CaWO4, CdWO4, PbWO4 • Measurements with CdWO4 are done with low background: 0.03 counts/(keV kg a) (Danevich F.A. et al. Phys. Rev. C62:044501 (2000)) • Crystals of CaWO4 can have good resolution: 5% at 1332 keV (F. Pröbst) Crystal of Nd2(WO4)3 is probably a scintillator Detector resolution could be With |M0|2 from Staudt, IDEA DBD Meeting, Heidelberg

5. Current state of the investigation We need highly enriched neodymium (Russia!): • A process of Nd2(WO4)3 growing was investigated. • Sample crystals were grown using Czochralski method (V. Kochurichin, Moscow). IDEA DBD Meeting, Heidelberg

6. Crystals Successful crystals of CaWO4 IDEA DBD Meeting, Heidelberg

7. Current state of the investigation We need highly enriched neodymium (Russia!): • A process of Nd2(WO4)3 growing was investigated. • Sample crystals were grown using Czochralski method (V. Kochurichin, Moscow). • 3 small crystals (about 1 cm3 each) were delivered to Munich IDEA DBD Meeting, Heidelberg

8. Scintillation Jelena Doncev, MPI, München No clear result! IDEA DBD Meeting, Heidelberg

9. Spectral characteristics D. Kovalev, TU München, E16 IDEA DBD Meeting, Heidelberg

10. Current state of the investigation We need highly enriched neodymium (Russia!): • A process of Nd2(WO4)3 growing was investigated. • Sample crystals were grown using Czochralski method (V. Kochurichin, Moscow). • 3 small crystals (about 1 cm3 each) were delivered to Munich • The crystals showed no scintillation (J. Doncev, MPI, D. Kovalev, TUM, E16) • A powder of other compositions (e.g. LiNd WO4) showed no roentgen-luminescence • (L. Nagorna, Ukraine) IDEA DBD Meeting, Heidelberg

11. The choice of a detector Direct counting Other 150Nd is within detector 150Nd is outside detector Electron hole pairs (Semiconductors) Production of photons and photoelectrons (Scintillators) Production of phonons (Cryodetectors) Production of phonons (Cryodetectors) Crystal scintillators Liquid scintillators IDEA DBD Meeting, Heidelberg

12. Cryogenic detectors In case of thermalization Temperature increase Energy resolution Low heat capacity is necessary! Heat capacity of a ferromagnet If there is an energy splitting  Heat capacity of an insulator IDEA DBD Meeting, Heidelberg

13. Cryodetectors at TUM • Particle or light interaction with absorber • High frequency phonons are produced • Phonons become ballistic and fill the crystal homogeneously • In the Al-phonon collector those phonons break up quasiparticles • Quasi particles diffuse to the Ir/Au- superconducting thermometer and heat it up • Resistance of the film changes and the resistance of the thermometer Ir/Au- thermometer Al-phonon-collector IDEA DBD Meeting, Heidelberg

14. Cryodetectors at TUM • Particle or light interaction with absorber • High frequency phonons are produced • Phonons become ballistic and fill the crystal homogeneously • In the Al-phonon collector those phonons break up quasiparticles • Quasi particles diffuse to the Ir/Au- superconducting thermometer and heat it up • Resistance of the film changes and the resistance of the thermometer Ir/Au- thermometer Al-phonon-collector IDEA DBD Meeting, Heidelberg

15. Cryodetectors at TUM • Particle or light interaction with absorber • High frequency phonons are produced • Phonons become ballistic and fill the crystal homogeneously • In the Al-phonon collector those phonons break up quasiparticles • Quasi particles diffuse to the Ir/Au- superconducting thermometer and heat it up • Resistance of the film changes and the resistance of the thermometer Ir/Au- thermometer Al-phonon-collector IDEA DBD Meeting, Heidelberg

16. Cryodetectors at TUM quasi particles cooper- pairs E Eprox aluminum Ir/Au • Particle or light interaction with absorber • High frequency phonons are produced • Phonons become ballistic and fill the crystal homogeneously • In the Al-phonon collector those phonons break up quasiparticles • Quasi particles diffuse to the Ir/Au- superconducting thermometer and heat it up • Resistance of the film changes and the resistance of the thermometer phonon IDEA DBD Meeting, Heidelberg

17. Cryodetectors at TUM quasi particles cooper- pairs E Eprox aluminum Ir/Au • Particle or light interaction with absorber • High frequency phonons are produced • Phonons become ballistic and fill the crystal homogeneously • In the Al-phonon collector those phonons break up quasiparticles • Quasi particles diffuse to the Ir/Au- superconducting thermometer and heat it up • Resistance of the film changes and the resistance of the thermometer IDEA DBD Meeting, Heidelberg

18. Cryodetectors at TUM R T • Particle or light interaction with absorber • High frequency phonons are produced • Phonons become ballistic and fill the crystal homogeneously • In the Al-phonon collector those phonons break up quasiparticles • Quasi particles diffuse to the Ir/Au- superconducting thermometer and heat it up • Resistance of the film changes -> this is the signal IDEA DBD Meeting, Heidelberg

19. NdGaO3 Thermostat Neodymium cooling M. Stark, E15, TUM • Ir/Au thermometer was glued on the NdGaO3 crystal • Only signals from the thermo- meter were detected • Ir/Au thermometer was sputtered on the NdGaO3 crystal • The results are not available yet IDEA DBD Meeting, Heidelberg

20. Liquid scintillators A scintillator like CTF could be used PMTs cover about 20% of the solid angle The energy resolution for CTF where npe – number of photoelectrons Photoelectron yield of the CTF with100 PMT IDEA DBD Meeting, Heidelberg

21. Liquid scintillators With 400 PMT the energy resolution Background at 3.3 MeV Now it is possible to solve about 1 %0 of Nd (S. Schönert, MPI, Heidelberg) IDEA DBD Meeting, Heidelberg

22. Local tasks If we assume that everything is perfect and not additional problem arises 1. Preliminary investigation with natural Nd This is sufficient to prove the results of Klapdor-Kleingrothaus, m=400 meV 2. The second step with enriched Nd This is sufficient to prove the inverse hierarchy IDEA DBD Meeting, Heidelberg

23. Summary • 150Nd is one of the most interesting candidates to detect a neutrinoless double beta decay • There is no established method to measure this decay • Estimations show that it could be possible to build a • scintillation detector. However, till now no scintillator with • Nd was found. (Maybe because of the properties of Nd). • It is possible to cool Nd-crystal at least down to 60 mK. However, no phonon signal could be measured • A liquid scnitillator with dissolved 150Nd is the most promising idea at the moment IDEA DBD Meeting, Heidelberg