Gamma spectroscopy in the fermium region at SHIP

Transcription

1 Nuclear Structure Physics with Advanced Gamma- Detector Arrays, Padova June 10-12, 2013 Gamma spectroscopy in the fermium region at SHIP Stanislav Antalic Comenius University, Bratislava

2 Collaboration GSI Darmstadt F. P. Heßberger D. Ackermann S. Hofmann S. Heinz B. Kindler I. Kojouharov B. Lommel R. Mann B. Sulignano (presently in Saclay) Comenius University (Bratislava) S. Antalic Š. Šáro Z. Kalaninová B. Streicher (presently in GSI Darmstadt) University of Jyväskylä M. Leino JAEA Tokai K. Nishio Helmholtz Institut Mainz L.-L. Andersson Padova, 9th - 13th of June

3 Transuranium nuclei Region accesible by present technique Production rate 1 event / week Desired region of double magic nuclei No chance to access it with present technique Region accessible for nuclear spectroscopy nuclei / hour Rich source for the nuclear structure data Padova, 9th - 13th of June

4 Efficiency ~30 % Flight time ~ 1-2 ms SHIP separator Detectors: S. Hofmann and G. Münzenberg, RMP 72, 733 (2000) Separator: G.,Munzenberg, et al., NIM 161, 65 (1979) + high intensity beam + reliable setup + low background - Low granularity - Lack of beamtime Recoils Esc. a, b CE, RTG 48 Ca ~ 1200 pna e ff a Bi 2 O 3, PbS target 400 mg/cm 2 Rotating wheel 31 cm diameter B. Kindler et al. NIM A561,107 (2006) Back detector PSSD Ge-Clover Padova, 9th - 13th of June

5 Fm Studies at SHIP since 2010 Topic for this talk 253 Fm single particle isomer 253 No K isomer Published data since 2010 Opened projects Bh Md Fm 0.18 s Md 0.35 s Fm 3 ms 0.9 ms Fm No Md 4.4 s 4.2 s 246 Md 1.0 s Rf Lr s e Fm s 247Md 0.2 s Db Sg No 248Md e e Fm 9.2 s s 247Fm 35 s ms 24 s 36 s Rf Lr No 2 µ s Md 7.87 e ms 0.36 s 52 s Db 253Rf 252Lr Db Sg 256Db 2.9 ms 258Sg Mt Hs 0.48 s Ds Bh 259Sg Db 258Db 11.8 ms 261Bh ms 8.0 ms ms Sg 0.23 s Db Hs Sg 260Db Ds 3µs Mt 1.7 ms Hs 0.26 ms 6.1 ms 0.8 ms 265Hs 1.7 ms 1.9 ms Ds 170 µs 269Ds 180 µs 270Ds 5.1 ms 1.1 ms ms Mt 70 ms Hs 59 ms Bh 262Sg ms s s Db 262Db 1.6 s 3.6 ms 0.76 s 1.5 s 4.4 s 0.5 s 1.5 s 1.8 s 34 s 27 s ? >90 > e 9.16? 8.97? e <10? 8.93 < s 250Md 23 ms m 254Rf Lr 0.57 s 1.64 s 255Rf ms 256Rf 3.9 s Lr 257Rf 4.0 s s e? 256Lr 13 ms 0.65 s 258Rf 3.1 s 259Rf Lr 258Lr 20 ms 0.36 s 260Rf Lr 78 s 3 m 261Rf e <1? 260Lr e ;209;305? e 252No 251 Md 7.82 e e e 248Fm 2.6 m 251No 249Fm 85 e 1.8 s I? Fm 30 m s 55 s 53 ms 2.3 s 1.7 m I? ? 886 I? m 5.30 h 254Lr 2.6 s 253No 0.26 s Md 254No <50 <50 e e 353? 251Fm e 7.00 I? m 25.9 s 55 s 25.4 h e ?;e 253Md 252Fm 3.1 m 255No 2.91 s 256No 3.9 s 26 s 257No e Md 255Md 256Md 1.2 ms 258No Md 58 m 259No e 258Md 10 m 28 m 27 m 1.30 h 5.52 h 57 m 51 d e e e e e 453;405? e ? e ? 3.0 d 253Fm 3.24 h 254Fm 20.1 h 255Fm 70 ns 256Fm 2.63 s 100 d 257Fm e I? 369? ?;e ? 99;44...?;e 81;58...?;e ;180...? 2.1 s 39 m Bh 1 s? 266Bh 17 s Sg 261Lr ms 95 m 0.38 ms 7.4 s 265Sg Md 258Fm 3.6 h 31.8 d 1.5 s 262 e No 21 s 5 ms 266? 262 Mt ms Hs 20.9 s Padova, 9th - 13th of June

6 253 Fm single particle isomer Applied reaction 48 Ca+ 207 Pb 253 No + 2n (1.8 x 10 6 nuclei) 253 Fm Produced via 45% beta decay of 253 No and beta decay of 253 Md Electron - coincidences γ delayed after CEs CE-γ coincidences γ before CEs S. Antalic et al. EPJ A47, 62 (2011) First beta decay data in region Z> Padova, 9th - 13th of June

7 a vs. b decay production of 253 Fm 253 Fm produced via a decay of 257 No at JAERI M. Asai et al. PRL 95, (2005) S. Antalic et al. EPJ A47, 62 (2011) How is isomer connected to g.s.? Opened problem: How to connect upper part populated by beta decay of 253 Md, with the lower part populated by 257 No alpha decay [M. Asai et al., PRL 95, (2005)]? Padova, 9th - 13th of June

8 253 Fm and N=153 isotones S. Antalic et al. EPJ A47, 62 (2011) How is isomer connected to g.s.? Opened problem: How to connect upper part populated by beta decay of 253 Md, with the lower part populated by 257 No alpha decay [M. Asai et al., PRL 95, (2005)]? Padova, 9th - 13th of June

9 K isomers Multi-quasiparticle states are located typically above 1 MeV. Very complex decay schemes Rich source of data on the structure (chance to populate many low lying levels) K-isomers might have additional hindrance against radioactive decay and might play a important role for enhanced stability of superheavy nuclei. In some cases lifetime of the isomer exceeds the g.s. lifetime. (see e.g. 270 Ds or 250 No.) [experiment: S. Hofmann et al., Eur. Phys. J. A 10, 5 (2001) and D. Peterson et al., (2006). Phys. Rev. C ] J Padova, 9th - 13th of June K

10 254 No complex decay scheme 48 Ca+ 208 Pb 254 No+2n ~ nuclei ~ 6300 in K=16 isomer Known isomer since 1973 A. Ghiorso et al. PRC 7, 2032 (1973) JYFL: R.D. Herzberg et al. Nature 442, 896 (2006) E / Argonne: S.K. Tandel et al_prl97, (2006) Padova, 9th - 13th of June 2013 /18 Ereignisse Ereignisse Ereignisse F.P. Hessberger et al., EPJ A43, 55 (2010) No254m2_clo_einzel_r229_r

11 E electron / 253 No K isomer Back to the 48 Ca+ 207 Pb 253 No + 2n Decay spectroscopy E / S. Antalic et al. EPJ A47, 62 (2011) F.P. Hessberger, Phys. At. Nucl. 70, 1445 (2007) Crucial requirement: We need low background to see low-energy electron- coincidences! Padova, 9th - 13th of June

12 253 No Produced in rection 48 Ca+ 207 Pb 253 No + 2n (1.8 x 10 6 nuclei) Delayed e - - coincidences showed the presence of second isomer with many lines Decay spectroscopy In-beam spectroscopy S. Antalic et al. EPJ A47, 62 (2011) F.P. Hessberger, Phys. At. Nucl. 70, 1445 (2007) 9/2-[734]: R.D. Herzberg et al., EPJ A42, 333 (2009) 7/2+[624]: P. Reiter. et al, PRL 95, (2005) Isomer helped to detect rotational band and provide independent information about its assignment Padova, 9th - 13th of June

13 Possible decay scheme Suggested decay scheme from Dubna Multi-quasi particle isomer Opened problem: Despite of high statistics (1.8 x 10 6 nuclei) very weak - coincidences. A. Lopez-Martens et al. NPA (2011) Single-particle isomer To confirm the decay scheme, more detailed spectroscopy data are necessary Padova, 9th - 13th of June

14 Geant simulations for present setup How important is the detector granularity? % 27 % Germanium clover: 60 x 60 x 140 mm Encapsulated in 1 mm Al % 209 9% % Al Ge Padova, 9th - 13th of June

15 GEANT simulation ( events) 4 crystals 20 crystals single spectrum single spectrum single spectrum 3 counts 30 counts coinc. to counts 140 counts coinc. to counts coinc. to counts coinc. to 714 Increase from one to 5 clovers brought significant increase for Ga-Ga coincidences (factor of 5-6) Padova, 9th - 13th of June

16 Conclusion Interesting new data are on the way (see examples 253 No and 253 Fm) Present limit for spectroscopy is Sg (Z = 106), however already for Rf (Z = 104) its challenging. Requirements for these measurements: High intense beam (1 pma and more) low background (low energy electrons and gammas delayed after ER implantation) high-sensitivity detectors (granularity is critical) Still lot of work is waiting for us and we need to do many small steps to understand superheavy elements! Thank you Padova, 9th - 13th of June