1 undressing (to fiddle the decay probability) 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).
2 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) ?
3 C. Chandler et al. Phys. Rev. C61 (2000) Ge 69 Se 76 Rb 92 Mo fragmentation on nat Ni target
4 Two level mixing The gamma-rays emitted from nuclear reactions exhibit angular distributions that can be expressed as follow: Q 2,Q 4 : Solid angle corrections, due to the finite size of the detectors
5 Backbending can be interpreted as the crossing of two bands The ‘G’ band (Ground state) is a fully paired configuration The ‘S’ band (Super or Stockholm) contains one broken pair Band Crossings
6 Backbending
7 Systematics of B(E2)s In near stable and proton rich nuclei there is a fixed relationship between B(E2) and E2 + “GRODZINS RULE” However, in neutron rich nuclei, this should break down, and the link between B(E2) and deformation WILL be more complicated.
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11 Can not use fusion-evaporation reactions to study high-spin states in beta-stable and neutron-rich systems. Z N E beam ~15-20% above Coulomb barrier beam target (i) (ii) (iii) Deep inelastic collisions
12 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.
13 Nuclear Reactions – very schematic! Gamma-ray induced no Coulomb barrier Neutron induced low-spin states no Coulomb barrier Light charged particles, e.g. p, d, t, Coulomb barrier low-spin states (“capture”) (“fast”) Near the line of stability
14 DCO Ratios is the angle between two planes opened by each detector and the beam axis probability (intensity) for this specific configuration, e.g. the intensity of transition , determined in detector 2, gated on the transition in detector 1
15 DCO Ratios is the angle between two planes opened by each detector and the beam axis probability (intensity) for this specific configuration, e.g. the intensity of transition , determined in detector 2, gated on the transition in detector 1
Hf 16 +, 4-qp Isomer
17 Courtesy to John Becker, LLNL MeV 31 y 28 g - boils 120 t of water 1 g - equivalent to 650 lbs. of TNT
18 Some Applications SPIEGEL ONLINE August 2003, 15:27 Pentagon-Pläne Handliches Höllenfeuer Das US-Militär entwickelt einen neuartigen Nuklearsprengstoff, der schon in kleinsten Mengen ungeheure Vernichtungskräfte entfesseln, zugleich aber auch in Kleinstwaffen eingesetzt werden kann. Experten warnen bereits vor einem neuen globalen Wettrüsten. Nuklearexplosion: Isomere können in großem und kleinem Maßstab eingesetzt werden New Scientist, 2003
19 Triggering of 178m Hf using X-rays Texas/AFRL/SNL Collaboration/Phys. Rev. Lett. 82 (1999) 695
20 Triggering of 178m Hf using X-rays – cont. ANL/LANL/LLNL /Phys. Rev. Lett. 87 (2001)
21 Can K-Mixing explain the results by Collins et al? Texas/AFRL/SNL Collaboration Phys. Rev. Lett. 82 (1999) 695 Before the mixing I ,K 1 I ,K 2 and K 2 >K 1 After the mixing |I ,K 1 > - |I ,K 2 > |I ,K 1 > + |I ,K 2 > two levels with the same I and <90 keV above the isomer must have I=15,16 or 17, e.g. high spin must have very different K V is very small (~eV!) V
Hf ANU Experiment Incomplete fusion n 9 Be 5 He 176 Yb 178 Hf
Hf ANU Experiment - cont.