Combining γ and particle spectroscopy The γ decay behaviour of the PDR in 92,94 Mo S.G. P ICKSTONE *, V. D ERYA , A. H ENNIG , M. S PIEKER *, M.W EINERT , J. W ILHELMY *, AND A. Z ILGES I NSTITUTE FOR N UCLEAR P HYSICS U NIVERSITY OF C OLOGNE supported by DFG ZI 510/7-1 and BMBF 06KY9136 * Bonn-Cologne Graduate School of Physics and Astronomy September 15 th , 2015 COMEX5 Kraków S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
Pygmy Dipole Resonance – decay properties Usually Γ 0 /Γ =1 assumed for B(E1) values from ( γ , γ ') – Possible explanation of B(E1)-value discrepancy Branching ratios probe wave functions Selective excitation needed to determine weak branchings − 1 PDR Bremsstrahlung Inelastic scattering + 2 1 + 0 gs D. Savran, T. Aumann, and A. Zilges, PPNP 70 (2013) 210 S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
Pygmy Dipole Resonance – decay properties Usually Γ 0 /Γ =1 assumed for B(E1) values from ( γ , γ ') – Possible explanation of B(E1)-value discrepancy Branching ratios probe wave functions Selective excitation needed to determine weak branchings − 1 PDR Monoenergetic photons 𝐹 𝑌 = 𝐹 𝛿 Particle- γ -coincidences 𝐹 𝑌 ≈ 𝐹 𝑞 − 𝐹 𝑞′ + 2 1 + 0 gs D. Savran, T. Aumann, and A. Zilges, PPNP 70 (2013) 210 S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
Setup for p- γ coincidence experiments SONIC HORUS 8 Δ E-E or single PIPS Detectors 14 HPGe θ = 60°, 90°, 120°, 130° θ = 35°, 45°, 90°, 135°, 145° Angles Efficiency 4% solid angle coverage ~ 2% @ 1.3 MeV Resolution typically 70 keV in-beam ~ 2 keV @ 1.3 MeV SONIC HORUS HORUS S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
p- γ coincidence matrix of 92 Mo 92 Mo(p,p' γ ) @ E p =10.5 MeV E γ [keV] E X [keV] Diagonal gates can be set to select decays to specific levels – Ground state decays S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
p- γ coincidence matrix of 92 Mo 92 Mo(p,p' γ ) @ E p =10.5 MeV E γ [keV] E X [keV] Diagonal gates can be set to select decays to specific levels – Ground state decays S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
Ground state decays – comparison to ( γ,γ ') Upper panel: 92 Mo(p,p' γ ) experimental results @10.5 MeV from (p,p' γ ) preliminary – Counts corrected by preliminary efficiency – Isotropic distribution assumed Lower panel: experimental results from ( γ,γ ') – ∝ B(E1) without 92 Mo( γ , γ ') branching G. Rusev, PhD Thesis, TU Dresden (2006) S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
Ground state decays – comparison to ( γ,γ ') Upper panel: 92 Mo(p,p' γ ) experimental results @10.5 MeV from (p,p' γ ) preliminary – Counts corrected by preliminary efficiency – Isotropic distribution assumed Lower panel: experimental results from ( γ,γ ') – ∝ B(E1) without 92 Mo( γ , γ ') branching G. Rusev, PhD Thesis, TU Dresden (2006) S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
p- γ coincidence matrix of 92 Mo 92 Mo(p,p' γ ) @ E p =10.5 MeV E γ [keV] E X [keV] Diagonal gates can be set to select decays to specific levels – Ground state decays – Decays to 2 1 + , to 4 1 + , … S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
p- γ coincidence matrix of 92 Mo 92 Mo(p,p' γ ) @ E p =10.5 MeV E γ [keV] E X [keV] Diagonal gates can be set to select decays to specific levels – Ground state decays – Decays to 2 1 + , to 4 1 + , … S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
Decay branching ratio vs. energy Γ 1 ≈ 92 Mo Branching to 2 1 + Γ 0 + Γ 1 • observed • not observed No trend with energy S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
Branching ratio: experiment vs. theory experiment 92 Mo Experiment and theory show similar picture theory QPM calculations by N. Tsoneva Smaller error bars needed for higher significance S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
Branching ratio: experiment vs. theory experiment 92 Mo No trend of branching ratio with strength observed Different theoretical theory QPM calculations by N. Tsoneva prediction Discrepancy for strong transitions S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
94 Mo( p,p'γ ) @ E p = 13.5 MeV transitions to 2 1 + Goals of experiment: – Study decay behaviour in 94 Mo( α , α ' γ ) non-magic nucleus transitions to g.s. – Individual and mean V. Derya et al. , NPA 906 (2013) 94 branching already observed in (α,α'γ) and (γ,γ ') – With our setup: • More states (if similar to 92 Mo) • Individual branching – Higher beam energy to excite states at higher energies Adopted from C. Romig et al. , PRC 88 (2013) 044331 S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
Excitation pattern vs. ( γ,γ') and (α,α'γ) 2 + ⨯3 - C. Romig et al. , V. Derya et al. , PRC 88 (2013) 044331 NPA 906 (2013) 94 Observed less states than in ( γ , γ '), but more states than in ( α , α ' γ ) S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
Decay branching ratios for 94 Mo 94 Mo Only statistical errors are shown No clear trend, again state to state difference preliminary 94 Mo Needs to be compared to theoretical predictions S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
Validation of setup and method 94 Mo preliminary V. Derya et al. , NPA 906 (2013) 94 C. Romig et al. , PRC 88 (2013) 044331 Very good agreement with b 1 values and upper limits from 94 Mo(α,α'γ) performed at KVI with E α =136MeV S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
Improvement of setup – solid angle coverage ʘ ʘ ʘ Beam E Old Current New 2.2% for E 3.9% for E 8.9% for E 1.6% for Δ E-E Up to 2.8% for Δ E-E 7.8% for Δ E-E S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
Summary & Outlook Many decays of PDR states to several final 92 Mo states observed in 92 Mo and 94 Mo + , 0 2 + , 2 2 + – 2 1 Preliminary branching ratios for PDR states could be determined for both nuclei 94 Mo – Thorough analysis ongoing Setup and method was validated by com- parison to 94 Mo( α , α ' γ ) experiment at KVI – Comparison to mean branching ratios Theoretical calculations needed for both cases! 119 Sn(d,p γ ) 120 Sn @E d =8.5MeV Future experiments for PDR – Inelastic scattering – Transfer reactions with p, d, α beams ≤ 30 MeV S.G. Pickstone, AG Zilges, University of Cologne The γ decay behaviour of the PDR in 92,94 Mo
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