Future Challenges Using Decay Spectroscopy with Projectile Fragmentation and In-Beam Deep Inelastic Reactions Paddy Regan Dept. of Physics University of.

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Presentation transcript:

Future Challenges Using Decay Spectroscopy with Projectile Fragmentation and In-Beam Deep Inelastic Reactions Paddy Regan Dept. of Physics University of Surrey,UK E-mail: p.regan@surrey.ac.uk

Outline of Talk (Some) Physics questions in heavy neutron-rich nuclei. Thin target multinucleon transfer reactions: 100Mo+136Xe : reaction mechanism info. 198Pt+136Xe: 136Ba Ip=10+seniority isomers, effective charges. Projectile-fragmentation isomer spectroscopy. The Stopped Beam RISING Campaign, some physics aims. g-factors and BaF2 timing below isomers.

Main physics interest in neutron-rich nuclei is based on the EVOLUTION OF SHELL STRUCTURE and the appearance of ‘large gaps in the nuclear single-particle spectrum’. Reasons to study neutron-rich nuclei Evolution of collective modes (vibrations, rotations, superdef ?) from spherical states by altering (N,Z,Ip, Ex). 2) Identification of specific nucleonic orbitals, e.g. via isomeric decays, g-factors, B(E2:I->I-2), effective charges, shell model descriptions, seniority schemes, deformed (Nilsson) schemes etc. 3) Identifying new nuclear ‘exotica’, e.g., the unexpected, beta-decaying high-spin states, new symmetries (e.g., a32), neutron ‘skins’, new shell closures, shape changes etc.

How do we study the heavy neutron-rich ? Multi-nucleon transfer reactions: Backed/thick target technique (made famous by Broda, Fornal, Krolas (Crakow group) + Daly, Janssens, Khoo, Lunardi et al.,) Projectile-fragmentation reactions: Isomer spectroscopy (made famous by Pfützner, Rykaczewski, Grzywacz, Janas, Lewitowicz et al., & the Warsaw Group). In both cases, the reaction mechanism is not fully studied and experiments are needed in order to set the limits of both of these techniques.

Aim? To perform high-spin physics in stable and neutron rich nuclei. Problem: Fusion makes proton-rich nuclei. Solutions? (a)fragmentation (b) binary collisions/multi-nucleon transfer Modified from Introductory Nuclear Physics, Hodgson, Gadioli and Gadioli Erba, Oxford Press (2000) p509 See eg. Broda et al. Phys. Rev Lett. 74 (1995) p868 Juutinen et al. Phys. Lett. 386B (1996) p80 Wheldon et al. Phys. Lett. 425B (1998) p239 Cocks et al. J. Phys. G26 (2000) p23 Krolas et al. Acta. Phys. Pol. B27 (1996) p493 Asztalos et al. Phys. Rev. C60 (1999) 044307

z x q2 q1 f1 f2 y

BLF TLF beam qtlf,ftlf qblf,fblf Ge Simon et al., Nucl. Inst. Meth. A452, 205 (2000) Rochester Group TOF ~5-10 ns. ns-ms isomers can de-excite in be stopped by CHICO position detector. Delayed gs can still be viewed by GAMMASPHERE.

100Mo + 136Xe @ 700 MeV GAMMASPHERE + CHICO PHR, A.D. Yamamoto et al., AIP Conf. Proc. 701 (2004) p329

Can we use the data from the CHICO+Gammasphere expt. to understand the ‘DIC’ reaction mechanism ? A wide range of spins & nuclei are observed.

R.Broda et al., Phys. Rev. C49 (1994)

Wilczynski (‘Q-value loss) Plot A.D.Yamamoto, Surrey PhD thesis (2004) Wilczynski (‘Q-value loss) Plot

Gating on angle gives a dramatic channel selection in terms of population. Relative Intensities of 6+->4+ yrast transitions in TLFs (relative to 100Mo) for 136Xe beam on 100Mo target at GAMMASPHERE + CHICO.

Fold distributions highlight different reaction mechanisms +2p -2n +2n PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313

Emission angle of TLFs can give information/selection on reaction mechanism (and maybe spins input ?)

198Pt +136Xe, 850 MeV J.J. Valiente-Dobon, PHR, C.Wheldon et al., Phys. Rev. C69 (2004) 024316

nano and microsecond isomers on gated 198Pt+136Xe with J.J. Valiente-Dobon, PHR, C.Wheldon et al., Phys. Rev. C69 (2004) 024316 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 nano and microsecond isomers on gated 198Pt+136Xe with GAMMASPHERE+CHICO DIC 84 83 82 81 80 79 78 77 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 76 75 74 73 59 58 57 56 55 54 53 52 51 50 N/Z compound

J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313 136Xe+198Pt reaction beam-like fragment isomers. 131I 133I 128Te 130Te 136Xe 132Xe 138Ba 137La

J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313 136Xe+198Pt Target-like fragment isomers 184W 195Os 192Pt 185Re 191Os 198Pt 193Au 192Os

Identification of new ‘seniority’ isomer in 136Ba, N=80 isotone. T1/2=91(2) ns J.J. Valiente-Dobon, PHR, C.Wheldon et al., Phys. Rev. C69 (2004) 024316

N=80 isotonic chain, 10+ isomers, (nh11/2)-2I=10+ Q. Why does Ex(10+) increase while E(2+) decreases ? 91(2) ns

Structure of 8+ final state changes from 134Xe -> 136Ba ? See Valiente-Dobon, PHR, Wheldon et al., PRC69 (2004) 024313 Isomer decay also depends on structure of final state N=80, (nh11/2)-210+ isomers

Energy of N=80 Ip=10+ isomers correlates with energy increase of 11/2- single neutron in N=81 isotones. Increase in 10+ energy, plus expansion of proton valence space means 8+ yrast state now (mostly) NOT (nh11/2)-2 for Z>54 Ex, Ip=11/2 - N=81 Ex, Ip=10 N=80

Pair Truncated Shell Model Calculations (by Yoshinaga, Higashiyama et al. Saitama) predict yrast 8+ in 136Ba no longer mostly (nh11/2)-2 but rather, (pd5/2)2(pg7/2)2

Expect neutron ‘seniority scheme’ for (nh11/2)-2 ‘j2’ mutliplet configuration at N=80 (e.g. 130Sn). 132Te, 134Xe have proton excitations due to g7/2, d5/2 at 0+,2+,4+,6+ but not competing 8ħ and 10ħ states. Extra collectivity for higher-Z pushes down 0+ and 2+. Proton s.p. energies used in 136Ba SM calcs h11/2 2.760 Protons, max. seniority 2 spin = 6 ħ (from (pg7/2)2. Seniority 4 states though can have up to 7/2 + 5/2 + 5/2 +3/2 = 10 ħ d5/2 0.963 g7/2 0.000

Use FRS@GSI or LISE3@GANIL to ID nuclei. In-Flight Technique Using Projectile Fragmentation Production target Central focus, S2 Final focus, S4 primary beam Pb @ 1GeV/u dipole, Br degrader degrader MW=x,y scint scint catcher DE(Z2) scint (veto) Use FRS@GSI or LISE3@GANIL to ID nuclei. Transport some in isomeric states (TOF~ x00ns). Stop and correlate isomeric decays with nuclei id. eg. R. Grzywacz et al. Phys. Rev. C55 (1997) p1126 -> LISE C.Chandler et al. Phys. Rev. C61 (2000) 044309 -> LISE M. Pfützner et al. Phys. Lett. B444 (1998) p32 -> FRS Zs. Podolyak et al. Phys. Lett. B491 (2000) p225 -> FRS M. Pfützner et al. Phys Rev. C65 (2002) 064604 -> FRS

8+ isomer in 78Zn, real evidence of 78Ni shell closure. J.M.Daugas et al. Phys. Lett. B476 (2000) p213

Heaviest odd-odd,N=Z gammas, isobaric analog states. 86Tc, C Heaviest odd-odd,N=Z gammas, isobaric analog states ? 86Tc, C. Chandler et al. Phys. Rev. C61 (2000) 044309 Can perform spectroscopy at rates of few ions per hour.

M. Mineva et al. Eur. Phys. J. A11 (2001) 9 Use FRS to select projectile fission products (forward boosted ones). Note transmission a few %. T1/2=565(50) ns state in 136Sb (Z=51, N=85) 135Te 136Sb

Prompt ‘flash’ is a limiting problem for isomer Fragmentation. Reduces effective Ge efficiency by factor of 3-4 ! (Partial) Solution ? Use a low-Z (e.g., plastic stopper)

Simulated by P. Detistov Surrey/Sofia

M.Pfutzner,M.Hellstrom et al.

208Pb region 217Ac, 29/2+, 1μs 215Ra, 43/2-, 800ns 212Po, 18+, 65s many μs isomers expected N=126, holes in 208Pb

(pg9/2)-2 ‘2j’ multiplet (and isomer) in 130Cd (Z=48, N=82) should look like 98Cd (Z=48, N=50) A real test of valence anaolgue scheme. Do with fission fragments. (pg9/2)-2

Doubly-mid-shell nucleus, 170Dy N=104, Z=66 (Np.Nn=352=Maximum!). Best K-isomer? Doubly-mid-shell nucleus, 170Dy N=104, Z=66 (Np.Nn=352=Maximum!). Appears to be a correlation between fn values and NpNn for K=6+ isomers in A~180 region. (see PHR, Oi, Walker, Stevenson & Rath, Phys. Rev. C65 (2002) 037302) Extrapolation suggests isomer in 170Dy lives for hours….could be beta-decay candidate. 170Dy ? N=104 isotones, K=6+ energy 172Hf, 174Yb, 174Hf, 176Hf, 178Hf, 178W K=6+ isomers Xu, Regan, Walker et al

First id of ‘doubly mid-shell’ nucleus, 170Dy (N=104, Z=66). Data from M.Caamano et al. 33 ns isomer in 195Os (last stable 192Os), useful test of structure in prolate/oblate shape coexistence region. 194Os Wheldon et al. Phys. Rev. C63 (2001) 011304(R)

BaF2 ‘fast timing’ data from H. Mach et al. Contribution to ENAM 2001 Allows an ordering of the gammas under isomer from their (~ps) lifetimes.

From Henryk Mach et al., 96Pd.

Use (BaF2,BaF2) coincidences below isomers to get B(E2) values ( & order gamma-transitions) 96Pd H. Mach et al.,

g-factors from fragmentation isomers Basic idea, put isomer in B-field. Perturbation of gamma-ray angular distribution depends on induced Torque. Rate of precession gives Larmor frequency, which gives g-factor. ‘Wiggles’ in count ratio between different angles from 13/2+ isomer, T1/2= 354(2)ns in 69Cu. G.Georgiev EPJA20 (2004) p93; J. Phys. G28 (2003) p2993 See poster by Steve Mallion

50 delegates, ~ 20 presentations, 4 working groups….. Stopped Beam Physics Workshop, Guildford 29-30th March 2004

Major campaign using ‘retired euroball’ detectors for fragmentation-based nuclear spectroscopy. Stopped-Beam Campaign to study decays from isomers and following beta-decay. First call for proposals (deadline was last week), three proposals initially submitted for ‘isomer only’ study 1) A~110 neutron-rich Zr,Mo,Ru,Pd (Alison Bruce) 2) A~140 proton drip-line, proton decay daughters (Dave Cullen) 3) N=126, ‘south’ of 208Pb (Zsolt Podolyak) + g-factor letter of intent (Gerda Neyens) ‘Active stopper’ experiment planned for next EA (170Dy, 130Cd, etc.)

International Conference On NUclear STructure, Astrophysics & Reactions University of Surrey, Guildford, UK 5-8 January 2005 http://www.ph.surrey.ac.uk/cnrp/nustar05

Happy Birthday Rafal !!

PHR, Valiente-Dobon, Wheldon et al., Laser Phys Letts. 1 (2004) 317

Crossing and alignments well reproduced by CSM, although AHVs

Smith, Walker et al., Phys. Rev. C68 (2003) 031302

Kinematics and angular mom Kinematics and angular mom. input calcs (assumes ‘rolling mode’) for 136Xe beam on 100Mo target. Estimate ~ 25hbar in TLF for ~25% above Coul. barrier. For Eb(136Xe)~750 MeV, in lab qblf~30o and qtlf~50o. 100Mo +136Xe (beam) DIC calcs.

Gamma-gamma analysis on 200Pt isomer (21 ns. ), M. Caamano et al. Nucl Gamma-gamma analysis on 200Pt isomer (21 ns!), M. Caamano et al. Nucl. Phys. A682 (2001) p223c; Acta Phys. Pol. B32 (2001) p763 stripping effect to extend lifetime

“Power” of fragmentation Z. Podolyak et al., “Power” of fragmentation Low spin ~1 ms PROTON RICH I=43/2

76Rb 69Se 67Ge Chandler et al. Phys. Rev. C61 (2000) 044309

(Stable beam) fusion limit makes high-K in neutron Search for long (>100ms) K-isomers in neutron-rich(ish) A~180 nuclei. low-K high-K mid-K j K Walker and Dracoulis Nature 399 (1999) p35 (Stable beam) fusion limit makes high-K in neutron rich hard to synthesise N=104 also a good number for K-isomers.

Prompt flash knocks out a large portion of the detectors… Prompt flash knocks out a large portion of the detectors….effectively reduces the gamma efficiency by upto 80%! Need digital electronics and time stamping

M. de Jong et al. Nucl. Phys. A613 (1997) p435 M. Pfutzner et al. Phys Rev. C65, 064604 (2002)

Isomeric Ratio Calculations M. Pfutzner et al. Phys Rev. C65, 064604 (2002)

Pfutzner, Hellstrom, Mineva et al.

PHR, Beausang, Zamfir, Casten, Zhang et al. , Phys. Rev. Lett

BUT….what is the microscopic basis ? E-GOS plot appears to indicate that Vibrator-Rotator phase change is a feature of near stable (green) A~100 nuclei. BUT….what is the microscopic basis ? ‘Rotational alignment’ can be a crossing between quasi-vibrational GSB & deformed rotational sequence. (stiffening of potential by population of high-j, equatorial (h11/2) orbitals). PHR, Beausang, Zamfir, Casten, Zhang et al., Phys. Rev. Lett. 90 (2003) 152502

50 82 [550]1/2- 1h11/2 1g9/2 [541]3/2-

See PHR, Yamamoto, Beausang, Zamfir, Casten, Zhang et al., AIP Conf. Proc. 656 (2002) p422 ‘Weak Coupling’ Eg/(I-j) E-GOS extension for odd-A Suggests 11/2- band is anharmonic, g-soft rotor? BUT seems to work ok for +ve parity bands vib ->rotor following (nh11/2)2 crossing.

What about odd-A nuclei….are the nh11/2 bands ‘rotational’ ?

Carl Wheldon (HMI-Berlin) has suggested extension of E-GOS by ‘renormalising’ the rotational energies at the bandhead. If the band-head spin of a sequence is given by j then substituting I-j in place of I, one obtains,

PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313 Can see clearly to spins of 20ħ using thin-target technique.

Even-Even yrast sequences and odd-A +ve parity only show rotational behaviour after (nh11/2 )2 crossing…. seems to work ok, nh11/2 bands now look like rotors,

215Ra τ = 800 ns, 43/2-, 3.8 MeV 407 keV γ-ray from 206Pb(13C,4n) Stuchbery et al. Nucl. Phys. A641 (1998) 401

215Ra γ-ray spectrum from 238U fragmentation Z. Podolyak, private communication from 238U fragmentation

Abrasion-ablation model (1-2/3) k = 2 A>10 De Jong, Ignatyuk, Schmidt, NP A613 (1997) 435. “sharp cut-off” approximation:

179W populated in: fragmentation of 208Pb at 1 GeV/u fusion evaporation: 170Er(13C,4n) at 67 MeV

Higher spins for greater DA. M. Pfutzner, PHR et al. Phys Rev. C65, 064604 (2002) Higher spins for greater DA.

High spins (>35/2) populated 208Pb beam at 1 GeV/u allows production of ( high-spin isomers, M. Pfützner et al. Phys Rev. C65 (2002) 064604 High spins (>35/2) populated

Projectile Fragmentation Reactions hotspot Excited pre-fragment Final fragment projectile target Energy (velocity) of beam > Fermi velocity inside nucleus ~30 MeV/u Can ‘shear off’ different combinations of protons and neutrons. Large variety of exotic nuclear species created, all at forward angles with ~beam velocity. Some of these final fragments can get trapped in isomeric states. Problem 1: Isotopic identification. Problem 2: Isomeric identification.

PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313 TLFs BLFs elastics

Can see 184-194Os in binary partner channels. i.e.in 2p transfer, up to 14 neutrons evaporated. ( 4n -> 194Os is heaviest known).

J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313 198Pt, 2+ 136Xe, 2+

J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313 138Ce 125Sb

Super-FRS yields 215Ra

170Dy, double mid-shell, ‘purest’ K-isomer ? (see PHR, Oi, Walker, Stevenson and Rath, Phys. Rev. C65 (2002) 037302) Kp=6+state favoured Max at 170Dy