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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: [email protected]. Electromagnetic Transition Rates. EM transition rates ( = 1 / decay mean lifetime, t ) are related to the - PowerPoint PPT Presentation
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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: [email protected]
Electromagnetic Transition RatesEM transition rates ( = 1 / decay mean lifetime, ) are related to the multipole order of the transition by the expression
Tif (L) = 1 / = (ang.mom. fact) x (E)2L+1 x B(L:Ii->If)
Thus e.g, for E2 transitions, B(E2:Ii->If) = k. E-5 x Tif
Thus, if B(E2) is big (lots of overlap of wavefunctions), Tif is big and is small (i.e. fast = collective);
If B(E2) is small is big (i.e. slow = isomer)Also, slower for larger L values, (classically further away)
For lifetimes, , in units of seconds and and E in MeV,
T(E1) =1/= 1.59 x 1015 E3 B(E1)
T(E2) =1/ = 1.22 x 109 E5 B(E2)
T(E3) = 1/ = 5.70 x 102 E7 B(E3)
B(ML) in units of e2fm2L
i.e., transition rates get slower (i.e., longer lifetimes associated with) higher order multipole decays.
Annual Review of Nuclear Science (1968) 18 p265-290
In-beam, electronic technique (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
136Xe+198PtDobon et al.,
nano to microsecond isomer tagging ?
Identification of new ‘seniority’ isomer in 136Ba, N=80 isotone.
J.J. Valiente-Dobon, PHR, C.Wheldon et al., Phys. Rev. C69 (2004) 024316
T1/2=91(2) ns
Structure of 8+ final state changes from 134Xe -> 136Ba ?See Valiente-Dobon, PHR, Wheldon et al., PRC69 (2004) 024313
Isomer decayalso depends on structureof final state
N=80, (h11/2)-210+ isomers
Pair Truncated Shell Model
Calculations (by Yoshinaga,Higashiyama et al. Saitama)predict yrast 8+ in 136Ba no longer mostly (h11/2)-2
but rather, (d5/2)2(g7/2)2
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.,
100Pd
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.
100Pd • Z=46 4 proton holes in Z=50:
• N=54 4 neutron particles above N=50
24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c
75m
150m
200m
250m
500m
4+ →2+2+ →0+
6+ →4+
100Pd
24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c
75m
150m
200m
250m
500m
tof ~ 4ps
tof~ 9ps
tof~ 12ps
tof~ 15ps
tof~ 30ps
Es = Eo (1 +0.058cos(41.5o))Es = Eo * 1.0434
Es = Eo (1 +0.058cos(139.5o))Es = Eo * 0.9558
Eo Es (139.5o) Es (41.5o)
665 636 694
750 717 783
773 739 807
798 763 833
Time of flight = 16.8 m per ps
24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c
75m
150m
200m
250m
500m4+ →2+
24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c
75m
150m
200m
250m
500m4+ →2+
24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c
75m
150m
200m
250m
500m4+ →2+
24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c
75m
150m
200m
250m
500m4+ →2+
24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c
75m
150m
200m
250m
500m
4+ →2+2+ →0+
6+ →4+
24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c
75m
150m
200m
250m
500m
6+ →4+
24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c
75m
150m
200m
250m
500m
6+ →4+
24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c
75m
150m
200m
250m
500m
6+ →4+
24Mg (80Se , 4n) 100Pd EB=268 MeV, v/c ~5.8c
75m
150m
200m
250m
500m
6+ →4+
Some (cool) numbers?• Power: From 2 ps transition of E=800 keV
• P = E / t = (800 x 1.6 x 10-16 J) / (2 x 10 -12 s)→ 0.064 Watts per decay
Assume ~ 1000 per second measured = 64 W from per second…singles rate much larger (x 100 at least)
Beam Velocity: 280 MeV = ½ Mv2
v = sqrt ( 280 x 1.6 x 10-13 J x 2 / 80 x 1.66 x 10-27kg) v= 2.6x107 m/s = 8.6% speed of light.
Recoil velocity (measured from Es = Eo ( 1+ v/c COS ()) ~ 5.6% of c vrec ~ 1.7x 107ms-1 = 16.8 m per ps
• Now over to Vassia to get the final (accurate numbers)….does the structure change (from ~vibrator to ~rotor) with spin ?
• To be continued…
