The Long and the Short of it: Measuring picosecond half-lives…

1. The Long and the Short of it:Measuring picosecond half-lives… Paddy Regan Dept. of Physics, University of Surrey, Guildford, GU2 7XH, UK e-mail: p.regan@surrey.ac.uk

2. Electromagnetic Transition Rates EM transition rates ( = 1 / decay mean lifetime, t) are related to the multipole order of the transition by the expression Tif (lL) = 1 / t = (ang.mom. fact) x (Eg )2L+1 x B(lL:Ii->If) Thus e.g, for E2 transitions, B(E2:Ii->If) = k. Eg-5 x Tif Thus, if B(E2) is big (lots of overlap of wavefunctions), Tifis big and t is small (i.e. fast = collective); If B(E2) is small tis big (i.e. slow = isomer) Also, slower for larger L values, (classically further away)

3. For lifetimes, t, in units of seconds and and Eg in MeV, T(E1) =1/t = 1.59 x 1015 Eg3 B(E1) T(E2) =1/t = 1.22 x 109 Eg5 B(E2) T(E3) = 1/t = 5.70 x 102 Eg7 B(E3) B(ML) in units of e2fm2L i.e., transition rates get slower (i.e., longer lifetimes associated with) higher order multipole decays.

4. Annual Review of Nuclear Science (1968) 18 p265-290

7. In-beam, electronic technique (g-g-t) eg, PHR 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

8. nano to microsecond isomer tagging ? 136Xe+198Pt Dobon et al.,

9. 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

10. 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

11. 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

12. 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.

13. From Henryk Mach et al., 96Pd.

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

18. 100Pd

22. Fusion evaporation…good way to populate nuclei for study…put into (high spin) excited states. Fuse beam and target nucleus and boil off excess energy via neutron evaporation. e.g. 80Se beam (Z=34; N=46) + 24Mg target (Z=12; N=12) to make 104Pd* (Z=46; N=58). Boil off 4 neutrons to leave 100Pd which decays by gamma to ground state. Whole process from creation to gs takes < 1ns.

30. 100Pd • Z=46 4 proton holes in Z=50: • N=54 4 neutron particles above N=50

39. 100Pd 2+→0+ 4+→2+ 6+→4+ 500mm 250mm 200mm 150mm 75mm 24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c

40. 500mm tof~ 30ps 250mm tof~ 15ps 200mm tof~ 12ps 150mm tof~ 9ps 75mm tof ~ 4ps 24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c

41. Es = Eo (1 +0.058cos(139.5o)) Es = Eo * 0.9558 Es = Eo (1 +0.058cos(41.5o)) Es = Eo * 1.0434 Time of flight = 16.8 mm per ps

42. 4+→2+ 500mm 250mm 200mm 150mm 75mm 24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c

43. 4+→2+ 500mm 250mm 200mm 150mm 75mm 24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c

44. 4+→2+ 500mm 250mm 200mm 150mm 75mm 24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c

45. 4+→2+ 500mm 250mm 200mm 150mm 75mm 24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c

46. 2+→0+ 4+→2+ 6+→4+ 500mm 250mm 200mm 150mm 75mm 24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c

47. 6+→4+ 500mm 250mm 200mm 150mm 75mm 24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c

48. 6+→4+ 500mm 250mm 200mm 150mm 75mm 24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c

49. 6+→4+ 500mm 250mm 200mm 150mm 75mm 24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c

50. 6+→4+ 500mm 250mm 200mm 150mm 75mm 24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c