Nuclear astrophysics: experiments

Transcription

1 Nuclear astrophysics: experiments Information needed for modeling: Masses (Q values) Half-lives Spins, parities, excitation energies Decay studies (branchings) Cross sections Theoretical estimates for the unmeasured cases Masses, Ex E.g. rates for resonant captures Cross section masses Spins, branchings 1

2 Example: Nuclear physics at JYFL JYFLTRAP at IGISOL Path of the process Decay spectroscopy at IGISOL Laser spectroscopy at IGISOL Nuclear spectroscopy at GAMMA/RITU/MARA Masses Half-lives Properties of the states: spin, energy, shape Observations: Light curves, spectral lines, meteorites, grains Energy release Time scale Abundance pattern: which elements are produced? 2

3 Mass measurements Thu Previously: beta-endpoint measurements or reaction Q-value measurements large errors Penning trap mass spectrometry: precisions of about 10 ppb achieved typically Several Penning traps located worldwide: JYFLTRAP (Jyväskylä), ISOLTRAP (CERN), SHIPTRAP (GSI, Germany), LEBIT (MSU, USA), CPT (ANL, USA), TITAN (TRIUMF, Canada) MLLTRAP (Germany), TRIGATRAP (Germany), trap at FSU(FSU, USA), SMILETRAP (Sweden) 3

4 Principle of a Penning trap Strong axial magnetic field B axial confinement RF electric field radial confinement Three eigenmotions: ωω cc = ωω + + ωω 4

5 JYFLTRAP Located inside a 7-T superconducting solenoid Compare: Earth s magnetic field µt 5

6 Double Penning trap JYFLTRAP Counts mass-selective buffer gas cooling A=91 91 Ru Purification trap 91 Tc 91 Mo Frequency (Hz) Routinely M/ M ~ 10 5 Space charge limit ~10 5 Good/Bad ~ SELECT 91 Tc + Precision trap TOF-ICR method Routinely few kev If required few tens of ev (δm/m < ) Basic equations for mass determination f c f f 1 = 2π c,ref c q m ref B m - me = m - m e

7 JYFLTRAP: measured nuclei Statistics: 267 ground states 25 isomers rp process νp process Neutron-rich 63.7% novae r process Neutron-deficient 33.6% 7

8 IGISOL: Ion guide Ion guide technique Target p U fission Heavy and light ion fusion Transfer reactions Laser ionization Extractor SextuPole Ion Guide (SPIG) Beam 8

9 New IGISOL layout K130 beam line Test ion sources MCC30 p/d cyclotron Dipole magnet RFQ Laser line IGISOL front-end JYFLTRAP

10 New IGISOL 10

11 Selected cases related to nuclear astrophysics 56 Ni waiting point nucleus νp process and the S p value of 93 Rh Endpoint of the rp process: SnSbTe cycle Some recent results on masses and rp process modeling 11

12 Waiting-point nucleus 56 Ni Earlier considered as the endpoint of the rp process (T 1/2 = d) Network of mass measurements around 56 Ni at JYFLTRAP S p of 57 Cu measured directly S pjyfltrap (kev) S pame03 (kev) 57 Cu 689.7(5) 695(19) A. Kankainen et al., Phys. Rev. C 82 (2010) rp-process path for steady-state burning 12

13 QEC values close to waiting-point nucleus 56 Ni 40 Q EC (AME2003) - Q EC (JYFLTRAP) (kev) Co JYFLTRAP AME Co m 55 Ni 56 Ni 57 Cu 58 Cu 59 Zn A. Kankainen et al., Phys. Rev. C 82 (2010) Nuclide 13

14 Calculated rate little higher than previously Removes large uncertainties below ~1 GK Supports the conclusion that the rp process can proceed beyond 56 Ni Reaction rate of 56 Ni(p,γ) 57 Cu δs p, δe x and δµ taken into account A. Kankainen et al., Phys. Rev. C 82 (2010)

15 νp process and the S p value of 93 Rh J. L. Fisker, R. D. Hoffman, J. Pruet, arxiv: v1 [astro-ph] 9 Nov 2007 The site for 92 Mo and 94 Mo unknown Solar ratio 1.57 S p =1.64(10) MeV 94 Pd 93 Rh 92 Ru 92 Ru(p,γ) 93 Rh depends on the S p ( 93 Rh) How much 92 Mo and 94 Mo produced? 92 Mo 94 Mo 15

16 Results JYFLTRAP+SHIPTRAP: S p ( 93 Rh) = 2001(5) kev C. Weber et al., Phys. Rev. C 78, (2008) CPT: S p ( 93 Rh) = 2007(9) kev J. Fallis et al., Phys. Rev. C 78, R (2008) A. Jokinen, ISOLDE Workshop, Dec-2007 JYFLTRAP+SHIPTRAP vs AME2003 (by C. Fröhlich et al.): Change in relative strength of 92 Rh(p,γ) 93 Pd(n,p) 93 Rh and 92 Rh(n,p) 92 Ru(p,γ) 93 Rh νp process cannot fully explain the observed solar 92 Mo/ 94 Mo abundance ratio Total flow very similar 16

17 End-point of the rp-process: SnSbTe cycle V.-V. Elomaa, G.K. Vorobjev, A. Kankainen et al., PRL 102, (2009) 3% 13% 17

18 SnSbTe cycle Branching into the cycle reduced from 50% to 3% at 105 Sn C. Mazzocchi et al., PRL 98, (2007) Reduces late-time He production Slightly longer, less luminous burst tail Final composition: broader distribution of 68 Zn, 72 Ge, 104 Pd, 105 Pd and residual He S p =930(210) kev A. Plochocki et al., Phys. Lett. B 106, 285 (1981) JYFLTRAP: S p = 424(8) kev 18

19 rp process path Varied all proton-capture Q-values by +3σ or -3σ high/low Q value datasets large changes in the reaction paths low Q path 1-2 mass units closer to stability high Q SnSbTe cycle at 103 Sn? A. Kankainen, H. Schatz et al., EPJA 48, 50 (2012) IGISOL seminar for summer students

20 JYFLTRAP and the rp process Penning trap measurements A=68 uncertainties of important most abundant isotopes at A = 68, 91, 92, 105, 106 drastically reduced A. Kankainen, H. Schatz et al., EPJA 48, 50 (2012) A=91,92 A=105,106 20

21 Effect on light curves Very high Q-values (+3σ): waiting points bypassed efficiently processing accelerated increase in energy generation a fast exhaustion of fuel a shoulder and a second peak Very low Q-values (-3σ): increase photodisintegration slower, closer to stability energy generated at a reduced rate, but for a longer time X-ray burst light curve shoulder 2nd peak long burst tail A. Kankainen, H. Schatz et al., EPJA 48, 50 (2012) 21

22 Mass uncertainties - isomers Nuclide Isomer: E x (kev) protons and neutrons filling the g 9/2 shell region A= rich of isomers identification of the measured states ground or isomeric? production ratios? 83 Y m 61.98(11) 84 Y m Nb m > Nb m 250(160)# 87 Nb m 3.84(14) 88 Nb m 40(140) 88 Tc m 300, unknown level scheme 92 Rh 50, unknown level scheme 100 Ag m 15.52(16) 104 In m 93.48(10) Post-trap spectroscopy! 22

23 Mass measurements and the r-process Penning traps: typical precision < 10 kev/c 2 Accurate mass values needed (note: isomers!) Mass models Nuclear structure Pairing effects A. Kankainen, J. Äystö and A. Jokinen, J. Phys. G 39 (2012)

24 Region close to 132 Sn J. Hakala et al., Phys. Rev. Lett. 109 (2012) Ground states: Large deviations to AME03, e.g.: 131 In : 112(28) kev 134 Sn: 360(100) kev 140 Te: 600(300) # kev 25 MeV p beam on nat U or 232 Th at IGISOL First measurements! Odd-even staggering A. Kankainen et al., arxiv: v1 [nucl-ex] Isomers Large deviations to literature Single-particle energies 24

25 Future of mass measurements New IGISOL facility More beam time More measurements Plenty of interesting nuclei to be measured 25

26 Decay studies at IGISOL Decay studies provide information on Half-lives Branching ratios (decay channels) Spins, parities and excitation energies of the states Studies of triple-alpha decay Beta decay of 31 Cl 26

27 Examples: 12 C Triple-alpha reaction studied with inverse processes: β-delayed α s from 12 B and 12 N ISOLDE CERN IGISOL JYFL H.O.U. Fynbo et al., Nature 433 (2005)

28 12 C CNO cycle ignited in half the time in primordial stars old rate with an uncertainty band (NACRE compilation) New rate incl. only Hoyle state New rate incl. broad 0 + resonance + Hoyle size of the Fe core in supernovae reduction of 56 Ni and heavier in νp process H.O.U. Fynbo et al., Nature 433 (2005) 136 Proposal I161 for IGISOL4: C.Aa. Diget et al., Search for the second excited 12 C 2 + state using 12 N and 12 B decay beta-triple-alpha coincidence measurements at IGISOL 28

29 Future plans New proposal Search for the second excited 12 C 2 + state using 12 N and 12 B decay beta-triple-alpha coincidence measurements at IGISOL To be measured in June 2014 at IGISOL Silicon Cube setup 29

30 Examples:Beta-decay of 31 Cl At T > K: 30 P(p,γ) 31 S controls the synthesis of heavier elements via two paths: 33 Ar.. a) 30 P(p,γ) 31 S(p,γ) 32 Cl(β + ) 32 S 31 Cl 32 Cl 33 Cl b) 30 P(p,γ) 31 S(β + ) 31 P(p,γ) 32 S Beta decay of 31 Cl gives information on the excited states of 31 S relevant for this synthesis Reactions: (p,γ) 30 S 29 P 31 S 32 S 30 P 31 P... (p,α) A X β + 28 Si 29 Si 30 Si (γ,p) J. José et al., Astr. Phys. J. 560, 897 (2001) 30

31 Setup for 31 Cl 32 S(p,2n) MeV β-particles: ISOLDE Silicon Ball + E1,E2,E3 protons: Double-Sided Silicon Strip Detectors gammas: HPGe (Euroball) 31

32 Levels from literature: Beta-delayed gamma rays 3/2 + IAS (3/2,5/2) (10) 5781(8) E(IAS)= 6282(3) kev? 3545(8) 4032(10) 5/ (4) 3/ (2) 1/ S 0 A. Kankainen et al., EPJA 27, 67 (2006) 32

33 Beta-delayed protons well-known observed previously J. Äystö et al. Phys. Rev. C 32, 1700 (1985) but controversial T.J. Ognibene et al. Phys. Rev. C 54, 1098 (1996) A. Kankainen et al., EPJA 27, 67 (2006) 33

34 Decay scheme A. Kankainen et al., EPJA 27, 67 (2006) Note! After this experiment studied at MARS (Momentum Achromat Recoil Spectrometer) at Texas A&M A. Saastamoinen PhD Thesis, JyU (2011) 34

35 Another experiment on 31 Cl Beta-delayed protons at TAMU. A. Saastamoinen PhD, University of Jyväskylä (2011) 35

36 Updated level scheme A. Saastamoinen PhD, University of Jyväskylä (2011) 36

37 Gamma-decay spectroscopy In-beam technique Prompt gamma-rays detected with a sphere of Ge detectors Recoils separated with a separator At JYFL: RITU gas-filled separator (QDQQ magnets) Recoils implanted at the focal plane detect decays, connection to the prompt gamma rays 37

38 MARA vacuum mode separator Under construction Better efficiency for lower mass nuclei Better mass resolution, beta-tagging N=Z nuclei relevant for nuclear astrophysics 38

39 Cross section/reaction rate measurements For example reaction: 16 O(α,γ) 20 Ne Normal kinematics 4 He beam 16 O 20 Ne γ 16 O target Inverse kinematics 16 O beam 4 He 20 Ne γ 4 He target Select laboratory energy of the beam to obtain a proper CM energy Sometimes normal kinematics impossible since the target is radioactive must use inverse kinematics: radioactive beam + hydrogen/helium target 39

40 Example: 16 O(α,γ) 20 Ne at TRIUMF Direct capture dominant at astrophysically relevant temperatures Unnatural parity (2 - ) state More information needed for more precise direct capture rate calculation U. Hager et al., PRC 86 (2012)

41 DRAGON recoil separator at TRIUMF BGO gamma-ray detector array time-of-flight through the separator connect gammas and recoils Ionization chamber to detect 20 Ne U. Hager et al., PRC 86 (2012)

42 S factor U. Hager et al., PRC 86 (2012) First direct measurement at E cm =1.694 MeV 42

43 Radioactive beam experiments Such as 26 Al(p,γ) 27 Si 21 Na(p,γ) 22 Mg Require primary production of the radioactive beam (such as 70 microa 500 MeV protons of a SiC target to produce 26 Al) 43

44 Alternative method for radioactive beam Exotic Radionuclides from Accelerator Waste (ERAWAST) project Cu beam dump from the 590 MeV ring cyclotron at PSI (Villigen, Switzerland) an average exposure of 1.5 ma protons over 12 years chemical extraction of 44 Ti deposit 44 Ti on a surface of a tantalum foil place the foil in an Mk-5 Febiad ion source CF 4 leak a molecular beam of 44 TiF + 44

45 44 Ti(α,p) 47 V at ISOLDE 44 Ti + 45

46 REX-ISOLDE (The Radioactive beam EXperiment at ISOLDE ) REXTRAP: Penning trap for bunching REX-EBIS: Electron beam ion source for charge breeding 44 Ti 13+ Mass separator 10-m long linear acccelerator Final energy: 0.8 and 3.0 MeV/u 46

47 Measurement setup: 44 Ti(α,p) 47 V Inverse kinematics! Helium gas cell 47

48 The measurement setup 48

49 Results Sonzogni et al.,prl 84 (2000) 49

50 Many more interesting experiments coming with the advent of new facilities: - HIE-ISOLDE, FAIR at GSI, SPIRAL-2 at GANIL, - JYFL: IGISOL-4, MARA Good opportunities for MSc and PhD studies! + many other facilities worldwide! 50