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Z A N  Z-1 A N+1 + e + +  for b +

Beta decay studies using total absorption gamma spectroscopy technique A. Algora , M. Csatlós, L. Csige, J. Gulyás, M. Hunyadi, A. Krasznahorkay Institute of Nuclear Research of the Hungarian Acad. of Sciences Debrecen, Hungary.

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Z A N  Z-1 A N+1 + e + +  for b +

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  1. Beta decay studies using total absorption gamma spectroscopy techniqueA. Algora, M. Csatlós, L. Csige, J. Gulyás, M. Hunyadi, A. KrasznahorkayInstitute of Nuclear Research of theHungarian Acad. of SciencesDebrecen, Hungary For the Valencia, Debrecen, GSI, Warsaw, St. Petersburg,Madrid, Strasbourg, Surrey, Jyväskylä collaboration

  2. b+ Basic relations ZAN ZAN Z+1AN-1 + e- +  for b- ZAN Z-1AN+1 + e+ +  for b+ Z-1AN+1 ZAN + e- Z-1AN+1 +  + xray EC In principle a good description of fiand ff good B(GT)

  3. How to measure the B(GT) Theoretical quantity Beta feeding Strength function Half life of parent Relationship Fermi function

  4. Z-1AN+1 Z-1AN+1 The problem of measuring the b- feeding b+ b+ ZAN ZAN Apparent situation g2 g1 Real situation g1 • We use Ge detectors to construct the level scheme populated in the decay • From the g intensity balance we deduce theb-feeding • What happens if we miss some gamma intensity???

  5. Experimental difficulties: Pandemonium Effect • Introduced by the work of Hardy et al (Phys. Lett 71B (1977) 307). Their study questions the possibility of building correctly a level scheme from a beta decay experiment using conventional techniques. • Several factors can contribute to this problem: • if the feeding occurs at a place where there is a high density of levels, there is a large fragmentation of the strength among different levels and there is a large number of decay paths, which makes the detection of the weak gamma rays difficult • we can have gamma rays of high energy, which are hard to detect

  6. Solution Since the gamma detection is the only reasonable way to solve the problem, we need a highly efficient device: A TOTAL ABSORTION SPECTROMETER g1 g2 NaI

  7. Analysis d = R(B)  f • Response (R): • It is calculated for -s and -s using Monte Carlo techniques (GEANT3,GEANT4) • Introduce branching ratios (guess, or from statistical nuclear theory) • Possible methods for the solution of the inverse problem: • Peel off • Regularization methods • Bayesian progresive learning • Maximum entropy method • See: Cano et al. NIM A 430 (1999) 333; 488,Cano PhD thesis, J. L. Tain et al. NIM A 571 (2007) 719, 728

  8. Example of the Pandemonium effect, measurements performed at GSI On-line Mass-separator Clustercube 6 cluster detectors in close geometry TAS

  9. The decay of 150Ho 2- isomer High resolution results (cluster cube) • No. total of : ~ 1064 • No. total of levels:~295 • Sharp resonance ~ 4.4 MeV • B(GT) is approx. 47 % of the TAS result. • Algora et al. PRC 68 (2003) 034301

  10. The decay of 150Ho 2- isomer: comparison with the TAS result

  11. Lucrecia, Total Absorption Gamma Spectrometer at ISOLDE (CERN) • A large NaI cylindrical crystal38 cm Ø, 38cm length • An X-ray detector (Ge) • A  detector • Collection point inside the crystal

  12. The NZ region around mass70 • Drastic shape changes depending on the occupancy of orbitals. •  Oblate to prolate transition and shape • coexistence are predicted. • [A. Petrovici et al. N P. A708 (2002) 190 and ref. therein]. Free neutron orbitals with same quantum numbers than the valence protons:  Gamow-Teller decay allowed.  Large part of the GT strength accesible inside the QEC window Theoretical calculations predict different B(GT) distributions on the daughter nucleus depending on the shape of the ground state of the parent (oblate, prolate or spherical). [I. Hamamoto et al., Z. Phys. A353 (1995) 145] [P. Sarriguren et al., Nuc. Phys. A635 (1999) 13]

  13. The 76Sr and 74Kr β-decays E. Poirier et al. PRC 69 (2004) 034307 E. Nácher et al. PRL 92 (2004) 232501 Ground state of 74Kr:(60±8)% oblate, in agreement with other exp results and with theoretical calculations (A. Petrovici et al.) Ground state of 76Sr prolate (β20.4) as indicated in Lister et al., PRC 42 (1990) R1191

  14. IGISOL proposals I77 and I116, study of the beta decay of nuclei that are important contributors to the reactor decay heatStudies of the heat (decay heat) in the cool (weather)

  15. Fission: the released energy • Kinetic energy of fission products (FP) and neutrons • Prompt  radiation from FP • and β decay energy through the natural decay of fission products

  16. Decay heat: definition Decay energy of the nucleus i (gamma, beta or both) Decay constant of the nucleus i Number of nuclei i at the cooling time t Requirements for the calculations: large databases that contain all the required information (nuclides, lifetimes, mean - and β-energy released in the decay, n-capture cross sections, fission yields, etc, etc …

  17. I77: measurement of the beta decay of 104,105Tc 239Pu example ( component of the decay heat ) The main motivation of this work was the study of Yoshida and co-workers (Journ. of Nucl. Sc. and Tech. 36 (1999) 135) See 239Pu example, similar situation for 235,238U

  18. Motivations, original plans In their work (detective work) Yoshida et al. identified some nuclei that may be responsible for the under-estimation of the E component. Possible nuclei that may be blamed for the anomaly were 102,104,105Tc Explanation: certainly suffer from the Pandemonium effect, their half lives are in the range needed, and their fission yields are also correlated in the way required to solve the discrepancy

  19. Results of the analysis for 104Tc (preliminary)

  20. Impact of the results on the decay heat summations (104,105Tc) ΔE()= 1373104+1068105= 2441 keV; ΔE(e-)= -680104-505105=-1185 keV

  21. Impact of the results for 239Pu

  22. Conclusions • Beta-decay still offers a very interesting field of research. The utilization of new devices and recently developed analysis techniques opens new possibilities for the understanding of nuclear structure. • We have discussed here a method to measure the B(GT) in beta decay, which can be considered more reliable. • The limitations on these kind of studies are determined by nature (we can only reach states inside the Q energy window) • The method is Total Absorption Spectroscopy • A very interesting physics programme running, mainly devoted to cases on the proton richside (ground state shape determination, conf. mixing, p-n pairing,..). We are also involved in studies of neutron rich side which are also important, but for other reasons (decay heat) and that will allow us to gain experience for the future FAIR

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