2. Production of Exotic Nuclear Isomers in Fragmentation and Deep-Inelastic Reactions Paddy Regan Dept. of Physics, University of Surrey, Guildford, GU2 7XH, UK e-mail: p.regan@surrey.ac.uk

3. Outline of Talk Where do you find (long-lived) isomers ? Restrictions ? Isomer predictions. Towards the neutron rich…. Deep-inelastic reactions and results Projectile Fragmentation, effects of atomic stripping

4. What is an isomer ? Metastable (long-lived) nuclear excited state. ‘Long-lived’ could mean ~10 -19 seconds, shape isomers in alpha-clusters or ~10 15 years 180 Ta 9 - ->1 + decay. Why/when do you get isomers? If there is (i) large change in spin (‘spin-trap’) (ii) small energy change (iii) dramatic change in structure (shape, K-value) What do isomers tell you ? Isomers occur due to single particle structure.

5. Winnie the Pooh, (trapped by a potential barrier !) A.A. Milne (1927) Walker and Dracoulis, Physics World Feb. 1994

7. E0 (ec) decay 74 Kr, shape isomer High-spin, yrast-trap (E3) in 212 Fr K-isomer in 178 Hf  decay to states in 208 Pb. 212 Po, high-spin  - decaying yrast trap. (also proton decaying isomers, e.g, 53 Co PLB33 (1970) 281ff). T 1/2 =0.3  s

8. E x > 1 MeV, T 1/2 > 1 ms (red), T 1/2 > 1 hour (black) From Walker and Dracoulis, Nature 399, p35 (1999)

9. Bohr and Mottelson, Phys. Rev. 90, 717 (1953) NB. wrong spin for isomer !!! I  >11 shown later to be K  =8 -, Korner et al. Phys. Rev. Letts. 27, 1593 (1971) K-value and detailed spectroscopy very imporant in understanding isomers.

10. Search for long (>100ms) K-isomers in neutron-rich(ish) A~180 nuclei. low-K high-K mid-K j K Walker and Dracoulis Hyp. Int. 135 83 (2001) (Stable beam) fusion limit makes high-K in neutron rich hard to synthesise Alaga, Alder, Bohr and Mottelson, Mat. Fys. Medd. 29 no 9 (1955)

11. ‘Forbiddenness’ in K isomers Can use single particle (‘Weisskopf’) estimates for transitions rates for a given multipolarity. (E  (keV), T 1/2 (s), Firestone and Shirley, Table of Isotopes (1996). Hindrance (F) (removing dependence on multipolarity and E  is defined by Reduced Hindrance ( f  ) gives yardstick for ‘goodness’ of K- quantum number and validity of K-selection rule (possibly a measure of axial symmetry?) f   ~ 100 typical value for ‘good’ K isomer (see Lobner Phys. Lett. B26 (1968) p279)

12. Smith,Walker et al., in press Phys. Rev. C ‘Classic’ 31 yr 16 + isomer in 178 Hf, spin-trap + K-forbidden (NB. Idaho invention!)

13. Smith, Walker et al., in press Phys. Rev. C

14. 170 Dy, double mid-shell, best case yet for ‘pure’ K-isomer ? (see PHR, Oi et al. Phys. Rev. C65 (2002) 037302)

15. Ways to make 178 Hf 31 yr isomer ? Neutron capture 176 Yb( ,2n) 178 Hf 176 Yb( 9 Be,  3n) 178 Hf (see Dracoulis talk) Coulomb excitation (Hayes et al., PRL (2002)) Deep-inelastic heavy-ion binary reactions Projectile Fragmentation

16. Astrophysical Consequences of Isomers  Ta is ‘stable’ in its isomeric state, but its ground state decays in hours! Longstanding problem as to how the isomeric state is created in nature (via eg. S-process). Possible mechanism via heavier nuclei spallation or K- mixing of higher states in 180 Ta.

17. (from Wiescher, Regan and Aprahamian Physics World, Feb 2002). K=9 - isomer might be de-excited to 1 + ground state through intermediate path with states of K  =5 + (see Walker, Dracoulis and Carroll Phys. Rev. C64 061302(R) (2001))

18. Towards the Neutron-Rich ? Fusion-evap. great for high-spins, BUT….stable beams/targets create predominantly neutron-deficient nuclei. Z (protons) N (neutrons) A B C=A+BC=A+B Locus of  -stable nuclei

19. 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.

20. primary beam Pb @ 1GeV/u Production target Central focus, S2 Final focus, S4  E(Z 2 ) catcher degrader dipole, B  scint MW=x,y 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. Pfutzner et al. Phys. Lett. B444 (1998) p32 -> FRS Zs. Podolyak et al. Phys. Lett. B491 (2000) p225 -> FRS M. Pfutzner et al. Phys Rev. C65 (2002) 064604 -> FRS In-Flight Technique Using Projectile Fragmentation

21. C. Chandler et al. Phys. Rev. C61 (2000) 044309 67 Ge 69 Se 76 Rb 92 Mo fragmentation on nat Ni target

22. 74 Kr isomer from 92 Mo fragmentation at GANIL. 456 keV 2 + ->0 + transitions decays (a) too fast (500 ns flight time) & (b) too slow for measured value of 2 + state (~25 ps) ?

23. undressing (to fiddle the decay probability) 0+0+ 2+2+ 0+0+ 456 keV gamma E0, 0 + ->0 + e - conversion decay E x =509 keV, T 1/2 ~20 ns Fully stripping the nucleus of its atomic electrons (in-flight) ‘switches off’ the electron conversion decay branches. Result is that the bare nuclear isomeric lifetime is increased compared to ‘atomic’ value. (important in explosive stellar scenarios).

24. from Bouchez et al., Phys. Rev. Lett. 90 082502 (2003)

25. 208 Pb beam at 1 GeV/u allows production of (a) neutron-rich heavy (A>160) and (b) high-spin isomers, Schlegel et al.Physica Scripta T88 (2000) p72 High spins (>35/2) populated

27. Gamma-gamma analysis on 200 Pt isomer (21 ns!), M. Caamano et al. Nucl. Phys. A682 (2001) p223c; Acta Phys. Pol. B32 (2001) p763 stripping effect again (a la 74 Kr).

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

29. Can not use fusion-evaporation reactions to study high-spin states in beta-stable and neutron-rich systems. Use deep-inelastic reactions. Z N E beam ~15-20% above Coulomb barrier beam target (i) (ii) (iii)

30. z x y    

31. Simon et al., Nucl. Inst. Meth. A452, 205 (2000) BLF TLF beam  tlf  tlf  blf  blf Ge TOF ~5-10 ns. ns-  s isomers can de-excite in be stopped by CHICO position detector. Delayed  s can still be viewed by GAMMASPHERE. Rochester Group

32. 198 Pt + 136 Xe @ 850 MeV, Dobon, Wheldon, PHR et al.,

33. 33 ns isomer in 195 Os (last stable 192 Os), useful test of structure in prolate/oblate shape coexistence region. 194 Os Wheldon et al. Phys. Rev. C63 (2001) 011304(R) First id of ‘doubly mid-shell’ nucleus, 170 Dy (N=104, Z=66). K=6 + isomers predicted for well deformed N=104 nuclei. TRS calcs (F.Xu) predict a very ‘stiff’, highly deformed prolate nucleus. Could be the best K-isomer? Data from M.Caamano et al.

34. Target-like fragment isomers from 136 Xe+ 198 Pt DIC, Valiente-Dobon et al., (Surrey/Rochester/Berkeley/Manchester/bPaisley/Daresbury collaboration)

35. Target-like fragment isomers from 136 Xe+ 198 Pt DIC, Valiente-Dobon et al., (Surrey/Rochester/Berkeley/Manchester/bPaisley/Daresbury collaboration)

38. Isomers in Nature, nuclear astrophysics aspects – 26 Al in r-p processed path, inversion of states – 180 Ta, nature’s only ‘stable’ isomer (nuclear battery ?) – 176 Lu, cosmic chronometer and thermometer –r-process path and structure of odd-odd nuclei Production and identification of isomers ? –Fusion-evap, projectile frag. Deep-inelastics, spallation, neutron capture… –electronic timing, proj. frag. –Mass separation for long-lived isomers Cheating with isomer half-lives….undressing! – 74 Kr (GANIL) bare, 201,200 Pt (GSI) H-like

39. Summary of some ‘special’, exotic cases! – 178 Hf K-isomer with many branches….e.g., E5 decays. – 176 Lu, cosmothermoter for two phases in s-process. – 26 Al decay seen from space as example of nucleosynthesis, rp-process ‘by-pass’. –Nuclear batteries/gamma-ray lasers, can we de-excite the isomers ? ( 180 Ta paper by PMW, GDD, JJC; 178 Hf 31 yrs state?). –Lengthing the half-life…stripping of 74 Kr, 201 Pt etc.

41. Thanks! Bertram Blank (Bordeaux) et al., GANIL Zsolt Podolyak (Surrey) et al. GSI Carl Wheldon (Surrey/GSI) Berkeley expts. Surrey PhD students, Katie Chandler, Jose Javier Valiente-Dobon, Monica Camaano, Arata Yamamoto, Sareh Al-Garni for hours and hours of analysis etc. Physics comments/help from Phil Walker, Bill Gelletly (Surrey), Dave Warner (Daresbury) + many others! Money from EPSRC (UK)

42. 100 Mo + 136 Xe @ 750 MeV GAMMASPHERE + CHICO, PHR et al. Submitted to Phys. Rev. C. (Surrey, Rochester, Berkeley, Manchester) TLFs BLFs elastics

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

44. Identification of new isomeric state in 136 Ba, N=80 isotone.

45. N=80 isotonic chain, 10 + isomers ( h 11/2 ) -2 I=10 +

46. Structure of 8 + final state changes from 134 Xe -> 136 Ba ? Isomer decay also depends on structure of final state N=80, ( h 11/2 ) -2 10+ isomers

47. 136 Sb 135 Te Use FRS to select projectile fission products (forward boosted ones). Note transmission a few %. T 1/2 =565(50) ns state in 136 Sb (Z=51, N=85) M. Mineva et al. Eur. Phys. J. A11 (2001) p9-13

48. Online-Mass Separation Technique Select by mass Select by decay times Lifetimes from grow-in curve Surrey/GSI/Liverpool, 136 Xe+Ta nat

49. A=184 A=185 A=186 A=183 A=182 136 Xe @11.4 MeV/u on to 186 W target in thermal ion source (TIS), tape speed 160 s. Mass selection achieved using dipole magnet in GSI Online mass separator (ASEP). Z selection by tape speed to remove activity. See Bruske et al. NIM 186 (1981) p61 S. Al Garni, PhD thesis, Surrey (2002) Surrey/GSI/Liv./Goettingen/Milano

50. Gate on electron (  or ec) at implantation point of tape drive, gives ‘clean’ trigger. Use add-back Use grow-in curve technique R=A o (1-exp(t/  Select cycle length for specific , add together multiple tape cycles.

52. Basic Technical Requirements for Studies with Isomers Beam pulsing, good t=0 reference for short (ns) lifetimes. In-flight separator (eg. FMA, LISE, FRS...) for ~microsecond-ms decays. Tape drive/helium jet system for 10ms->hours lifetimes Traps, cyclotrons etc. for longer lived species

53. Full-sky Comptel map of 1.8 MeV gammas in 26 Mg following 26 Al GS  -decay. (a) Spin traps, eg. 26 Al, (N=Z=13) 0 + state  -decaying spin-trap. 5 +, T=0 0 keV, T 1/2 =7.4x10 5 yrs 0 +, T=1 228.3 keV, T 1/2 =6.3 secs (decays direct to 26 Mg GS via superallowed Fermi  + …forking in rp-process (decays to 2 + states in 26 Mg via forbidden,  l=3 decays). e.g., Diehl et al., Atron. Astrophys 97, 181 (1993); Publications of the Astr. Society of the Pacific 110:637 (1999)

54. 26 Al isomer and the rp-process 5+5+ 0+0+ 3+3+ 1+1+ 0 228 417 1058 20702+2+ t 1/2 =6s t 1/2 =0.7My Thermal photons equilibrate isomer and ground state populations for T>5x10 9 K. see Runkle et al., Astr.J. 556, 970 (2001) T<4x10 8 K not in equilibrium, must be modelled as separate isotopes in rp-process path. Jose et al., Astr. J. 520, 347(1999) rp-process can bypass 26 Al ground state, decays via isomer Yield of 1.8 MeV  s from 26 Al gs decay (e.g., relative to 22 Na decay) gives insight into T and  where rp-process forming 26 Al occurs.

55. How do you produce and measure (high-energy) isomers ? Produce via nuclear reaction e.g., fusion-evaporation, deep-inelastic, projectile fragmentation….. Isomeric targets ? (see A.Tonchev NIM paper). Isomeric ‘beams’ –Measure, depending on lifetime using ns : Use in-beam electronic techniques (eg. start-stop) ns -> ms: In-flight technique, projectile fragmentation. 100 ms -> hours: On-line mass-separator (eg. GSI set-up). > hours: Measure mass differences from ground state using e.g. ion traps, coupled cyclotrons etc.

56. In-beam, electronic technique (  t) eg, PHR, G.D. Dracoulis et al. Nucl. Phys. A586 (1995) p351 Fusion-evaporation reaction with pulsed beam (~1ns), separated by fixed period (~500ns). Using coincidence gamma-rays to see across isomer 94 Zr+ 16 O-> 110 Cd * -> 103 Pd+  3n

57. Proton drip line isomer physics from 208 Pb fragmentation. N=74 chain of K  =8 - isomers. Next in chain would be 140 Dy, proton decay daughter of (deformed) 141 Tb. (See Filip Kondev’s talk) 136 Sm, 138 Gd Isomers orginally seen in fusion-evap (ANU data) A.M.Bruce et al. Phys. Rev. C50 (1994) p480 and C55 (1997) p620

59. Heaviest odd-odd,N=Z gammas, isobaric analog states ? N=Z=43; 86 Tc, C. Chandler et al. Phys. Rev. C61 (2000) 044309 ~500 86 Tc in ~ 1 week

60. 8 + isomer in 78 Zn, real evidence of 78 Ni shell closure. J.M.Daugas et al. Phys. Lett. B476 (2000) p213

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

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

63. Bock et al., Nukleonika 22 (1977) 529