undressing (to fiddle the decay probability )
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1 undressing (to fiddle the decay probability) 0 + 2 + 0 + 456 keV gamma e E E E tot , 2 , 2 0 E0, 0 + ->0 + e - conversion decay E x =509 keV, T 1/2 ~20 ns ping the nucleus of its atomic electrons (in-flight ff’ the electron conversion decay branches. hat the bare nuclear isomeric lifetime is increased ‘atomic’ value. (important in explosive stellar sc
description
E x =509 keV, T 1/2 ~20 ns. 0 +. 2 +. 456 keV gamma. E0, 0 + ->0 + e - conversion decay. 0 +. undressing (to fiddle the decay probability ). Fully stripping the nucleus of its atomic electrons (in-flight) ‘switches off’ the electron conversion decay branches. - PowerPoint PPT Presentation
Transcript of undressing (to fiddle the decay probability )
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undressing (to fiddle the decay probability)
0+
2+
0+
456 keV gamma
eEEEtot ,2,20
E0, 0+->0+
e- conversiondecay
Ex=509 keV, T1/2~20 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).
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74Kr isomer from 92Mo fragmentationat 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) ?
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C. Chandler et al. Phys. Rev. C61 (2000) 044309
67Ge
69Se
76Rb
92Mo fragmentation on natNi target
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Two level mixingThe gamma-rays emitted from nuclear reactions exhibit angular distributions that can be expressed as follow:
)(cos)(cos1)( 44442222 PAQPAQW
max4444
max2222 ; AAAA
Q2,Q4: Solid angle corrections, due to the finite size of the detectors
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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
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Backbending
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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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Can not use fusion-evaporation reactions to study high-spin states in beta-stable and neutron-rich systems.
Z
N
Ebeam ~15-20% above Coulomb barrier
beam
target
(i) (ii) (iii)
Deep inelastic collisions
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Projectile Fragmentation Reactions
hotspot
Excited pre-fragment
Finalfragment
projectile
target
Energy (velocity) of beam > Fermi velocity inside nucleus ~30 MeV/uCan ‘shear off’ different combinations of protons and neutrons.Large variety of exotic nuclear species created, all at forward angleswith ~beam velocity.
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Nuclear Reactions – very schematic!
1*
*
gsJJ
EE
][][
44.1 MeVfmR
ZZVc tb
2/1*
*
gs
nn
JJ
SEE
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”)
QEE CM *
ngs EJJ * (“fast”)
)(* cpgs VEJJ
Near the line of stability
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DCO Ratios
is the angle between two planes opened by each detector and the beam axis
),,( 21 W
probability (intensity) for this specific configuration, e.g. the intensity of transition , determined in detector 2, gated on the transition in detector 1
)(/)(),,(/),,( 1
1
2
2
1
2
2
12112
GateIGateIWWRDCO
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DCO Ratios
is the angle between two planes opened by each detector and the beam axis
),,( 21 W
probability (intensity) for this specific configuration, e.g. the intensity of transition , determined in detector 2, gated on the transition in detector 1
)(/)(),,(/),,( 1
1
2
2
1
2
2
12112
GateIGateIWWRDCO
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178Hf 16+, 4-qp Isomer
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Courtesy to John Becker, LLNL
0+
16+
2.4 MeV
31 y
28 g - boils 120 t of water
1 g - equivalent to 650 lbs. of TNT
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Some ApplicationsSPIEGEL ONLINE - 14. 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
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Triggering of 178mHf using X-raysTexas/AFRL/SNL Collaboration/Phys. Rev. Lett. 82 (1999) 695
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Triggering of 178mHf using X-rays – cont.
ANL/LANL/LLNL /Phys. Rev. Lett. 87 (2001) 072503
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Can K-Mixing explain the results by Collins et al?
Texas/AFRL/SNL CollaborationPhys. Rev. Lett. 82 (1999) 695
Before the mixing
I,K1 I,K2 and K2>K1
After the mixing
|I,K1> - |I,K2>|I,K1> +|I,K2>
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
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178Hf ANU Experiment Incomplete
fusion
n
9Be5He
176Yb178Hf
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178Hf ANU Experiment - cont.
