b-delayed neutron emission and its role in the r-process

Transcription

1 Canada s national laboratory for particle and nuclear physics Laboratoire national canadien pour la recherche en physique nucléaire et en physique des particules b-delayed neutron emission and its role in the r-process Iris Dillmann Research Scientist TRIUMF Accelerating Science for Canada Un accélérateur de la démarche scientifique canadienne Owned and operated as a joint venture by a consortium of Canadian universities via a contribution through the National Research Council Canada Propriété d un consortium d universités canadiennes, géré en co-entreprise à partir d une contribution administrée par le Conseil national de recherches Canada

2 b-delayed neutron emission Catch me if you can! S n < Q b Delayed : emission with b-decay half-life of the precursor A Z Q b S n August 26th 2013 Iris Dillmann CGS15 Dresden 2

3 Discovery (1939) Irradiation of 100 g uranium nitrate with neutrons Maybe due to (g,n) reactions? R.B. Roberts, R.C. Meyer, P. Wang, Phys. Rev. 55, 510 (1939). August 26th 2013 Iris Dillmann CGS15 Dresden 3

4 Discovery (1939) R.B. Roberts, R.C. Meyer, P. Wang, Phys. Rev. 55, 664 (1939). Happy Birthday, beta-delayed neutron! August 26th 2013 Iris Dillmann CGS15 Dresden 4

5 Why do we need bn? Reactor kinetics: Important role in reactor control Reactor runs in prompt subcritical, delayed critical conditions Nuclear structure Dominant decay process for very n-rich nuclei Competition with other b-delayed emission processes Astrophysics (r process) Re-capture of neutrons in late-stage evolution Influence on solar r-abundance curve August 26th 2013 Iris Dillmann CGS15 Dresden 5

6 What can we learn from bn? S n Q b For new isotopes: fastest (easiest?) access to first nuclear properties Important nuclear structure information: Time-dependence of n-emission t 1/2 ( A Z) few ms 90 s ( 210 Tl) Emission probability P n and neutron spectrum: b-strength above S n August 26th 2013 Iris Dillmann CGS15 Dresden 6

7 Oldie but Goldie! Recent revival of bn-studies thanks to new RIB facilities Shorter-lived nuclei bn-emission will become dominant process b-delayed 2-/ 3-neutron emitters August 26th 2013 Iris Dillmann CGS15 Dresden 7

8 Some ongoing/ planned programs Choose your facility CERN GSI Darmstadt ILL Grenoble Orsay GANIL Jyväskylä FAIR Oak Ridge Argonne MSU ISAC + TRIUMF NSCL RIKEN Choose your bn-setup NERO TETRA 3Hen BELEN LOENIE BRIKEN VANDLE MONSTER DESCANT 3 He-filled counters Scintillators (liquid/ solid)...sorry if I missed one... August 26th 2013 Iris Dillmann CGS15 Dresden 8

9 Methods without neutron detection bgg-coincidences, e.g. 8p, EURICA, GRIFFIN,... Requires knowledge of absolute intensities, co-production of bn-daughter(s) and/or isomers, direct feeding into g.s., g- deexcitation from above S n Beta-decay Paul trap: Argonne b-/recoil ion coincidence; neutron energy spectrum and branching ratios; proof-of-principle: 137 I; new measurements: Sb, 138,140 I, 144,145 Cs R.M. Yee, N. Scielzo et al., Phys. Rev. Lett. 110, (2013) Particle detector and/ or Schottky-pickups in storage ring: GSI Darmstadt, CR@ FAIR Design study; detector ready but no beamtime available... A. Evdokimov, I. Dillmann, et al., Proc. Nuclei in the Cosmos XII, Cairns/ Australia, PoS (NIC XII)115 (2012) August 26th 2013 Iris Dillmann CGS15 Dresden 9

10 b-delayed neutrons in the r-process August 26th 2013 Iris Dillmann CGS15 Dresden 10

11 r-process residuals N r = N - N s - N p measured well-known negligible N=50 Rare Earth Peak How are these abundances created in stars? August 26th 2013 Iris Dillmann CGS15 Dresden 11

12 High neutron densities (n n >> cm -3 ) 1 ms per capture Moderate temperatures 56 Fe to Pu (Z=94, A 260) in few seconds The r-process End point: fission barriers (theory!) fission recycling (2x A 130) Freeze-out: decay back to stability Explosive scenario Fission recycling August January 26th Iris Dillmann The r-process CGS15 Dresden 12

13 Core collapse supernova? Open question: Where and how? T > 0.5 GK (n,g)-(g,n) equilibrium Hot r-process Credit: Hubble Space Telescope Neutron star mergers? Cold r-process Credit: Daniel Price (U/Exeter) and Stephan Rosswog (Int. U/Bremen). T< 0.5 GK little photodissociation equilibrium: b-decays and (n,g) August 26th 2013 Iris Dillmann CGS15 Dresden 13 R. Surman

14 Nuclear Physics Input Masses: define reaction path Half-lives & Fission parameters: define shape Shell structure far off stabilty: defines position of abundance peaks Neutrons recaptured from b- delayed neutron emission or (g,n): smoothing and shifting of abundance curve August 26th 2013 Iris Dillmann CGS15 Dresden 14

15 Influence of bn on r-process Production of additional neutrons: influence on n/seed ratio at later times A. Arcones and G. Martinez-Pinedo, PRC83, (2011) Abundance peaks shifted Smoothing of abundance curve Formation of Rare-Earth peak Shift of abundance peaks R. Surman, M. Mumpower, in preparation August 26th 2013 Iris Dillmann CGS15 Dresden 15

16 Status of bn-emitters August 26th 2013 Iris Dillmann CGS15 Dresden 16

17 Experimental status (I) August 26th 2013 Iris Dillmann CGS15 Dresden 17

18 Experimental status (II) August 26th 2013 Iris Dillmann CGS15 Dresden 18

19 Experimental status (III) GSI-FRS August 26th 2013 Iris Dillmann CGS15 Dresden 19

20 BEta delayed Neutron detector (BELEN) Universidad Politecnica de Cataluna, Barcelona IFIC Valencia CIEMAT Madrid GSI Helmholtz Center Darmstadt High-pressure 3 He long counters in polyethylene moderator: 3 He + n 3 H + p kev August 26th 2013 Iris Dillmann CGS15 Dresden 20

21 GSI Darmstadt (2011) 70 m 1 GeV/ u 238 U pps Be target Target Fragment Separator 1 m n n S4 focal area Implantation detector SIMBA Neutron-rich 238 U fragments n Shielding (PE + borated rubber) n Neutron detector BELEN-30 (e n 40%) August 26th 2013 Iris Dillmann CGS15 Dresden 21

22 Data Data analyzed by PhD students K. Smith (U Notre Dame/ GSI, now at UTK) R. Caballero Folch (UPC Barcelona, soon at TRIUMF) August 26th 2013 Iris Dillmann CGS15 Dresden 22

23 New half-lives "south-west" of 132 Sn to be published soon! Good agreement with literature values New t 1/2 : Pd K. Smith (APS Meeting, Savannah 2014) August 26th 2013 Iris Dillmann CGS15 Dresden 23

24 New P 1n values "south-west" of 132 Sn to be published soon! Experimental P n values higher than predictions K. Smith (APS Meeting, Savannah 2014) August 26th 2013 Iris Dillmann CGS15 Dresden 24

25 Ratio P 1n (exp)/ P 1n (theo) August 26th 2013 Iris Dillmann CGS15 Dresden 25

26 NO PREDICTIONS NO MEASUREMENTS P 1n Discrepancy August 26th 2013 Iris Dillmann CGS15 Dresden 26

27 "South-east" of 208 Pb R. Caballero, NIC-XII proceedings (2012), NIC XII_109 R. Caballero, 3rd North American Workshop on b-delayed neutron emission, July 2014 August 26th 2013 Iris Dillmann CGS15 Dresden 27

28 New t 1/2 and P 1n -values 9 first t 1/2 measurements 10 first P 1n -value measurements August 26th 2013 Iris Dillmann CGS15 Dresden 28

29 Systematic trends in t 1/2? Half-lives in comparison to QRPA calc. (e.g. Möller 2003) Overestimation for N 126 Underestimation for N>126 Ratio theo/exp ( ) Element Z / N -> At 85 Po 84 Bi 83 long t 1/2 Pb 82 Tl Hg Au Pt Ir Os Half-life (s) Ratio theo/exp Element Bi Pb Tl Hg Au Hg 213,214 Tl August 26th 2013 Iris Dillmann CGS15 Dresden 29

30 Outlook The BRIKEN project (2015/16) August 26th 2013 Iris Dillmann CGS15 Dresden 30

31 BRIKEN project (2015/16) "Beta delayed neutron emission measurements at RIKEN" Implantation >82 people setup: from AIDA (Advanced Implantation Detector Array): Liverpool, 25 institutes Edinburgh, Daresbury/ UK 3 He neutron detectors: GSI Darmstadt + JINR Dubna + Oak Ridge + RIKEN + UPC Barcelona = 182 neutron counters! Spokespersons: Cesar Domingo-Pardo (IFIC Valencia) Giuseppe Lorusso (RIKEN) August 26th 2013 Iris Dillmann CGS15 Dresden 31

32 BRIKEN neutron detectors 2 configurations planned: High-efficiency setup (BRIKEN-1) e bn ~80% (E n = ev- 5 MeV) e b2n ~40% (E n = ev- 5 MeV) Hybrid setup (BRIKEN-2) incl. 2 HPGe clovers e n =76-66% (E n = MeV) August 26th 2013 Iris Dillmann CGS15 Dresden 32

33 Proposed program 2015 Early 2015: Setup phase 2 proposals submitted, got 6.5 days beamtime (from 30 days total) Measurements of new beta-delayed neutron emission properties around doubly-magic 78 Ni Spokespersons: Rykaczewski, Tain, Grzywacz, Dillmann Request: 7 days beamtime 76 Co- 92 Se (ca. 30 isotopes) Measurement of beta-delayed neutron emission probabilities relevant to the A = 130 r-process abundance peak Spokespersons: Estrade, Lorusso, Montes Request: 10 days beamtime 121 Rh- 152 Ba (33 isotopes) August 26th 2013 Iris Dillmann CGS15 Dresden 33

34 Summary Renewed strong interest in bn-programs at all RIB facilities Going more neutron-rich: bxn-emission will be the dominant process BELEN GSI Darmstadt: - t 1/2 for 13 isotopes measured for the first time - P 1n for 20 isotopes measured for the first time Heaviest bn-emitters detectec so far! BRIKEN neutron RIKEN: one proposal accepted, setup will start early 2015; high impact of research expected! August 26th 2013 Iris Dillmann CGS15 Dresden 34

35 Canada s national laboratory for particle and nuclear physics Laboratoire national canadien pour la recherche en physique nucléaire et en physique des particules Thank you! TRIUMF: Alberta British Columbia Calgary Carleton Guelph Manitoba McMaster Montréal Northern British Columbia Queen s Regina Saint Mary s Simon Fraser Toronto Victoria Winnipeg York Merci! Owned and operated as a joint venture by a consortium of Canadian universities via a contribution through the National Research Council Canada Propriété d un consortium d universités canadiennes, géré en co-entreprise à partir d une contribution administrée par le Conseil national de recherches Canada

36 Astrophysical influence During Freeze-out : detour of b-decay chains r-abundance changes FRDM(GT+ff) predictions: b-decay: 6.9% P(1n): 6.5 % P(2n): 86.7% P. Möller et al., Phys. Rev. C 67, (2003) In ms bn, b2n August 26th 2013 Iris Dillmann CGS15 Dresden 36

37 New P 1n standards Should be measured with independent methods and agree Standard for every mass region: Missing: A>150 and A~60 www-nds.iaea.org/publications/indc/indc-nds-0599.pdf August 26th 2013 Iris Dillmann CGS15 Dresden 37