Three-step gamma cascades following the neutron capture in 161 Dy

Transcription

1 Three-step gamma cascades following the neutron capture in 161 Dy F. Beèváø, T. Belgya, G. de France, M. Jentschel, U. Koester, J. Kroll, M. Krtièka, P. Mutti, R. Schwengner, G. Simpson, I. Tomandl, W. Urban, S. Valenta Faculty of Mathematics and Physics, Charles University in Prague Institute of Isotopes, Hungarian Academy of Sciences, Budapest Grand Accélérateur National d'ions Lourds (GANIL) Institut Laue-Langevin, Grenoble Helmholtz-Zentrum Dresden-Rossendorf Université Joseph Fourier in Grenoble Nuclear Physics Institute of the Academy of Science of Czech republic

2 Motivation Results of TSC experiment in 24 with reaction 162 Dy(n th, γ) 163 Dy showed necesity of postulating the scissors mode (SM) with these properties: E SM 3 MeV, Γ SM.6 MeV, B(M1) = 6.2µ 2 N above all states up to 4MeV of excitation energy follows Brink hypothesis

3 Motivation

4 Motivation What happens with SM at higher excitation energies? How is the SM fragmented? Can we get this information from TSC-like experiment? The answer is (hopefully) YES, but one needs: suitable pair of nuclei 161 Dy(n th, γ) 162 Dy suitable aparatus ILL beam time

5 { capturing { low Why 161 Dy(n th, γ) 162 Dy? stable target with reasonable σ and stable well-deformed product S n = MeV - not that lower than 3 E SM suitable spins and parities of levels involved in decay: state J π = 3 lying states of both parities and spins from to 6 available target enriched to > 9% possible three step cascades M1-M1-M1 (and other combinations) possible two step cascades of all combinations

6 ILL = EXILL Campaign EXOGAM was borrowed to ILL for 2 reactor cycles during Our experiment was granted 2.5 days of data taking (list mode, several TB) in the end of rst cycle in December 212.

7 What has been measured and it's use 6 Co - channel to energy, total & peak eciency, data reduction checks 152 Eu - channel to energy, peak eciency, checks of event builder for higher multiplicities (n,γ) 36 Cl - channel to energy, peak eciency, data reduction checks, time aligment (n,γ) 162 Dy

8 6 Co decay scheme

9 6 Co energy spectrum for multiplicity m = 1 events Intensity (arb. units) E γ

10 6 Co energy sum spectrum for multiplicity m = 2 events Intensity (arb. units) k=1 k E γ

11 6 Co TSC spectrum for \ground state" TSC intensity (arb. units) i E γ

12 6 Co energy sum spectrum for multiplicity m = 2 events Intensity (arb. units) k E γ k=1

13 6 Co \TSC" spectrum from central (\") part of energy sum spectrum TSC intensity (arb. units) i E γ

14 6 Co TSC spectrum after background subtraction TSC intensity (arb. units) i E γ

15 162 Dy energy sum spectrum for multiplicity m = 2 events Intensity (arb.units) SEP 4 1 SEP k k=1 E γ

16 162 Dy energy sum spectrum for multiplicity m = 3 events Intensity (arb.units) SEP 4 1 SEP k k=1 E γ

17 162 Dy energy sum spectrum for multiplicity m = 4 events Intensity (arb.units) k k=1 E γ

18 162 Dy TSC spectrum for 2 1 state intensity (arb.units) i 8 E γ

19 162 Dy binned TSC spectra intensity (arb.units) intensity (arb.units) intensity (arb.units) i E γ intensity (arb.units) i E γ i E γ i E γ

20 162 Dy 3SC spectrum for 2 1 state intensity (arb.units) i 8 E γ

21 162 Dy binned 3SC spectra intensity (arb.units) intensity (arb.units) i E γ i E γ intensity (arb.units) intensity (arb.units) i E γ i E γ

22 Intermediate states matrix Imagine you get a cascade of 3 photons of 5MeV, 2.9MeV and 185 kev from simulations. You directly know the energies of intermediate states. You might see same cascade in the experimental data but generally You cannot be sure about the order. Why not plot all 6 combinations? E γ j i k=1 E γ k - E γ i

23 Intermediate states matrix above ground state of 36 Cl j i 8 E γ 7 6 Intensity (arb.units) k i E γ - E γ k=1 1

24 Intermediate states matrix above ground state of 36 Cl j i E γ Intensity (arb.units) k i E γ - E γ k=1 1

25 st Intermediate states matrix above 1 exited state of 162 Dy Intensity (arb.units) 3 8 j i Eγ transition (Eγ = kev) k=1 7 8 Ekγ - Eiγ 1

26 st Intermediate states matrix above 1 exited state of 162 Dy j E γ 8 i transition (E γ = kev) Intensity (arb.units) k i E γ - E γ k=1 1

27 What input to DICEBOX simulation will translate to that? no SM at all? st 162 Intermediate states matrix above 1 exited state of Dy st 162 Simulated intermediate states matrix above 1 exited state of Dy 8 j i E γ 7 6 Intensity (arb.units) 3 8 j i E γ 7 6 Intensity (arb.units) k i E γ - E γ k= k i E γ - E γ k=1 1

28 What input to DICEBOX simulation will translate to that? no SM above 3 MeV of excitation energy? st 162 Intermediate states matrix above 1 exited state of Dy st 162 Simulated intermediate states matrix above 1 exited state of Dy 8 j i E γ 7 6 Intensity (arb.units) 3 8 j i E γ 7 6 Intensity (arb.units) k i E γ - E γ k= k i E γ - E γ k=1 1

29 What input to DICEBOX simulation will translate to that? SM built on all states? st 162 Intermediate states matrix above 1 exited state of Dy st 162 Simulated intermediate states matrix above 1 exited state of Dy 8 j i E γ 7 6 Intensity (arb.units) 3 8 j i E γ 7 6 Intensity (arb.units) k i E γ - E γ k= k i E γ - E γ k=1 1

30 { total { parasitic TODO list: GEANT simulations of detectors: eciency for higher E γ efects = crosstalk simulations under various assumptions compare the experimental spectra with simulations comparison with other results talk at 5 th Workshop on NLD and GS in Oslo 215

31 Comparison with other data Total dipole PSF in (,B n ) region 15 SLO KMF EGLO Oslo f [ -9 MeV -3 ] E γ [MeV]