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Selected in-beam fast timing experiments with ROSPHERE N. Marginean “Horia Hulubei” National Institute of Physics and Nuclear Engineering Bucharest – Magurele,

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Presentation on theme: "Selected in-beam fast timing experiments with ROSPHERE N. Marginean “Horia Hulubei” National Institute of Physics and Nuclear Engineering Bucharest – Magurele,"— Presentation transcript:

1 Selected in-beam fast timing experiments with ROSPHERE N. Marginean “Horia Hulubei” National Institute of Physics and Nuclear Engineering Bucharest – Magurele, Romania

2 ROmanian array for SPectroscopy in HEavy ion REactions Mixed array with 14 50% HPGe detectors with BGO shields (IFIN-HH) 11 LaBr 3 (Ce) scintillators: currently 7 of 2”x2” (IFIN-HH, INFN-LNL) and 4 of 1.5”x2” (UK) 25 positions, 5 symmetric rings of 5 detectors Absolute HPGe efficiency: ~ 1.2% LaBr 3 (Ce) efficiency ~ 3.5%

3 The 35 Ar – 35 Cl mirror pair J. Ekman et al. Phys. Rev. Letters 92(2004) 132502 The decay pattern of the yrast 7/2 - state is very different for the mirror partners If the B(M2) are equal almost exact cancellation of T=1/2 and T=3/2 E1 strength in 35 Cl isospin mixing larger than 5%

4 Electromagnetic transition matrix elements in |T z | = ½ mirror nuclei Isoscalar ∆T = 0 independent of T z Isovector ∆T = ±1 ~ ( T > 2 – T z 2 ) 1/2 Isovector ∆T = 0 ~ T z The matrix elements do not change sign by changing T z from -1/2 to 1/2 The matrix elements change sign by changing T z from -1/2 to 1/2

5 Lifetime of the first 7/2 - state in 35 Ar 12 C ( 28 Si,αn) 35 Ar @50MeV ROSPHERE: 14HPGe + 11 LaBr 3 :Ce Transition 35 Ar 35 Cl 7/2 - B(E1)[W.u]B(M2)[W.u.]B(E1)[W.u]B(M2)[W.u.] 7/2 + (1) 0.49(15)×10 -5 - 1.30(8)×10 -5 - 5/2 + (1) 2.1(5)×10 -6 - 1.8(4)×10 -8 0.008(4) 3/2 + (gs) -<0.021(7)-0.258(6)

6 Isospin mixing: E1 transitions Considering isospin mixing in both initial and final state (major component T=1/2, minor component T=3/2): Reduced matrix elements for pure transitions (ΔT=0 or ΔT=1) (no mixing): E1 transitionB(E1;1)[W.u.]B(E1;2)[W.u.] 7/2 - 7/2 + 8.5(10)×10 -6 4.8(25)×10 -7 7/2 - 5/2 + 6.3(14)×10 -7 4.3(11)×10 -7 We can assume B(E1; ΔT=1) ≈ 5-6×10 -7 W.u.

7 Isospin mixing: M2 transition Sign changing: ∆T=0 isovector (expected to be larger ) Sign invariant: ∆T=0 isoscalar and ∆T=1 isovector (expected to be smaller) M (M2;1) = ±0.326(12) sign changing M (M2;2) = ±0.182(12) sign invariant B (M2;∆T=0;IS) = 1.3(1) × 10 -3 W.u. B (M2;∆T=0;IV) = 0.107(8) W.u B (M2;∆T=1;IV) = 2.1(4) × 10 -2 W.u

8 Upper limits of the isospin mixing An upper limit of the integral isospin mixing of initial and final states can be obtained scaling the B(E1) and B(M2) values to the corresponding ones from the decay of the well-known 7/2 - analog state of 35 Cl F.W. Prosser, Jr., and Gale I. Harris, Phys. Rev. C4, 1611 (1971) Transition Type α 2 % 7/2 - 7/2 + E10.41(23) 7/2 - 5/2 + E11.9(6) or 1.3(4) 7/2 - 3/2 + M21.9(7)1.9(7)

9 Possible limit of the E1 symmetry rule Symmetry broken with a ΔT=1 matrix element B(E1) = 6.3×10 -7 W.u. Data taken from: 15 O - 15 N 19 Ne - 19 F 23 Mg - 23 Na 27 Si - 27 Al 31 S - 31 P 35 Ar - 35 Cl 39 Ca - 39 K 67 Se - 67 As All known B(E1) values from the decay of cross-conjugate bound states in |T z |=1/2 pairs

10 Measurement of E1 transition strengths in the N=Z nucleus 50 Mn 50 Mn f 7/2 x d 3/2 f 7/2 x g 9/2 47 V: B(E1;5/2 +  3/2 - ) ~10 -4 W.u. - + + A. Schmidt et al., PRC 62, 044319 (2000)

11 50 Mn : in-beam fast timing experiment 50 Cr(p,nγ) 50 Mn E p =15 MeV d= 150 mg/cm 2 Symm matrix Gate: 927 keV R. Lica et al., to be published

12 Results of the experiment T 1/2 = 51 (5) ps B(E1;1 -  2 + ) = 4.0 (4) 10 -6 W.u. B(E1;1 -  0 + ) = 1.2 (1) 10 -6 W.u R. Lica et al., to be published

13 B(E1) estimations from the Nilsson model

14 B(E1;1 -  0 + ) ~ 10 -4 W.u. B(E1) estimations from the Nilsson model 93.5% d 3/2 6.5 % d 5/2

15 More realistic estimations of the E1 strength N. Pietralla et al., PRC 65, 024317 (2002) B(E1;1 -  0 + ) = 0.9 10 -6 W.u. B(E1;1 -  2 + ) = 1.4 10 -6 W.u... B(E1;1 -  0 + ) ~ 10 -4 W.u. D. Delion, private communication (D. Delion, private communication)

16 166 Er(α,2nγ) 168 Yb E α = 24 MeV d = 2 mg/cm 2 8 HPGe and 11 LaBr 3 Lifetime measurements in 168 Yb Sorin Pascu, accepted in Phys. Rev. C

17 Results of the experiment Very short lifetime for the fast-timing method

18 Comparison with the neighboring isotopes 2+2+ 4+4+ 6+6+

19 2 neutrons more than heaviest stable Tungsten (Z=74) isotope ( 186 W). Populate 188 W using 186 W( 7 Li,ap) 188 W ‘incomplete fusion’reaction. (Not really a fusion-evap reaction, but populates medium spin states). See e.g., Dracoulis et al., J. Phys. G23 (1997) 1191-1202 Lifetime of the first 2 + state in 188 W P.J.R. Mason, Zs. Podolyak (University of Surrey, UK)

20 Why the yrast 2 + state in 188 W Neutron-rich A ~ 190 region predicted prolate – oblate shape transition. (e.g. Bengtsson et al. PLB190 (1987) 1) Strange (energy) deviation at 190 W compared to trend of other nuclides. Measurement of B(E2;2 + ->0 + ) gives best measure of (evolution of) collectivity The production cross section is small, thus one have to separate an 10 -3 good signal from a huge background Time response and walk correction are difficult to handle for low-energy gamma rays

21 Lifetime of first excited 2 + in 188 W 186 W( 7 Li,  p) 188 W, 31 MeV Reaction mechanism is a mix of incomplete fusion and low-energy transfer 8 HPGe 11 LaBr 3 (Ce) Bucharest/Surrey T. Shizuma et al. Eur. Phys. J. A30, 391 (2006)

22 Lifetime of first-excited 2 + in 188 W T 1/2 = 0.89(13) ns B(E2) = 83(12) W.u. Sum of time differences between 143-keV transition and any higher lying feeding transition (assumes negligible half-life for intermediate states. Rapid drop in collectivity for W isotopes compared to Os and Pt chains. Overall relatively linear decrease in B(E2) with increasing N. P.J.R Mason et al. Phys. Rev. C 88 044301(2013)

23 Octupole correlations and the 3 - state of 44 Ti ROSPHERE plunger + fast-timing experiment September 2013 Spokesperson: C.A. Ur (INFN Padova and ELI-NP Bucharest) K  = 1/2 + 45 Ti, 49 Cr If  (3 - )= 10 ps  B(E3) = 20 W.u. Isoscalar M1 reduced hindrance ?? Forbidden E1

24 44 Ti – Combined plunger-fast timing experiment C.A. Ur, preliminary analysis

25 Conclusions The mixed HPGe-LaBr 3 (Ce) array ROSPHERE Fully functional, running with open access and establishing an international user community Fills a gap on the lifetime measurements techniques using large gamma spectroscopy arrays Suitable for approaching many nuclear structure problems Provides know-how for the building of new arrays at large nuclear physics facilities which are now under construction (e.g. FAIR, ELI-NP)

26 Acknowledgements D. Bucurescu Gh. Cata-Danil C. Costache N. Florea D.G. Ghita T. Glodariu R. Lica R. Marginean R. Mihai C. Mihai Al. Negret C. Nita A. Olacel S. Pascu L. Stroe G. Suliman R. Suvaila N.V. Zamfir To the ROSPHERE team in Bucharest and to all international collaborators

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