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J.N. Wilson, EFNUDAT workshop, CERN, August 2010
Level Densities, Decay Probabilities and Cross sections in the Actinide Region
Level Densities, Decay Probabilities and Cross sections in the Actinide Region
J.N. WilsonInstitut de Physique Nucléaire, Orsay
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
1. Fundamental physics – NLD and GSF fine structure, statistical properties of the hot compound nucleus
2. Indirect cross section measurements via surrogate reactions
3. Level density knowledge helps cross section calculations where direct measurements are difficult or impossible
NLD Measurements in the Actinides: Goals & Motivations
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
Spectroscopy oflow lying states
Resonance spacingsat the neutron binding energy
1. Fundamental Physics1. Fundamental Physics
Oslo method
Extrapolation
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
S. Boyer et al. Nucl.Phys. A775, 175 (2006)
2. 233Pa Capture Experiment Results2. 233Pa Capture Experiment Results
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
Oslo Cyclotron Experiments Oslo Cyclotron Experiments
Si Ring Cactus NaI array
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
The Silicon RingThe Silicon Ring
• High efficiency/high angular resolution detection of the outgoing particles (<2°)
• E/ΔE collimators not necessary
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
2. The Thorium Cycle2. The Thorium Cycle
235U233U 234U232U
232Pa
231Th 233Th232Th230Th
231Pa
a
233Pa
a
234Pa
236U
(n, g)
(n, 2n)
(n, g)
(n, 2n)
(n, 2n) (n, g)
(n, g)
(n, g)
(n, g)
b-b-
b- b- b-
FISSION FISSION
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
232Th(d,x) @ 12 MeV 232Th(3He,x) @ 24 MeV
351 M events 135 M events
Experiment 232Th: 01/12/09 – 13/12/09 Experiment 232Th: 01/12/09 – 13/12/09
Reaction Compound Nucleus
Ex-Eg counts
3He,p 234Pa 13 M
3He,d 233Pa 6.0 M
3He,t 232Pa 0.57 M
3He,a 231Th 0.79 M
Reaction Compound Nucleus
Ex-Eg counts
d,p 233Th 23 M
d,d’ 232Th 0.24 M
d,t 231Th 1.2 M
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
Ring 0
16O (d,d’)
12C (d,d’)
12C(d,p) 13C
16O(d,p) 17O ex1
12C(d,p)13C ex1
12C(d,p)13C ex2
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
The Brink Axel hypothesis
)()(),( ETEEEP fi
Assuming dominance of dipoleradiation (E1 and M1)
Level density TransmissionCoefficient
Gamma strength function
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
Matrix *response;Spec *after=before->SubtractComptons(response);
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
ε = k EγSuppose detector has this property:
d
d kEEEREW ),()(
Then effeciency of detecting a cascade becomes proportional to cascade energy and independent of cascade path!!
Decay probability measurementDecay probability measurement
Efficiency of detecting a cascade, Ec of m gammas is:
)1(1..1
mj
jc
mj
jc..1
If ε is small, then:
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
« With four parameters, I could fit an elephant,
with five I could make him wiggle his trunk »
W(E) = a + bE + cE2 + d E3 + eE4 + f E5
d
d kEEEREW 0),()(
Minimisation with the Downhill simplex method
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
Primary gamma rays
n,gamma spectral extrapolation below n,n’threshold
(New Technique)
n,n' correctionto measureddecay probability
n,n' correctionto measureddecay probability
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
Compare results with TALYS calculations: Since 232Th(n,g) has been measured directly at nTOF we can perform a direct test of the optical model and the validity of the surrogate method.
TALYScalculationsTALYScalculations
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
Level density measurements possible in:
233Th - d,p (0- 5 MeV)232 Th - d,d’ (0- 3.5 MeV)231Th - d,t (0 – 3 MeV)
Surrogate reaction & decay probability measurements possible in:
233Th* - d,p230Ac* - d,a234Pa* - 3He,p232Pa* - 3He,t231Th - 3He,4He
ConclusionsConclusions
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
• Fission detectors
• 233U, 231Pa, 234U targets
The FutureThe Future
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
IPN OrsayJ.N. WilsonB. Leniau
Oslo CyclotronS. SiemS. RoseA. BürgerM. GuttormsenA-C. LarsenT. WiborgH. Toft
CEA SaclayF. GunsingA. Georgen
ThankyouTakkMerci
Lawrence Livermoore LabM. WeidekingL. Bernstein
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
Hauser-Feshbach FormalismHauser-Feshbach Formalism
Differential cross section depends on transmission coefficients, Γ and level densities of the residual nuclei, ρ
a + A B + b
J.N. Wilson, EFNUDAT workshop, CERN, August 2010
Level Densities Theory and ExperimentLevel Densities Theory and Experiment
- Level density changes due to collectivity, deformation etc.- Large effects can occur over a small number of nucleons
J.N. Wilson, EFNUDAT workshop, CERN, August 2010 44
(n, g)
Nuclei where direct measurements are difficultNuclei where direct measurements are difficult
239Pu
245Cm
241Am 242Am
242Pu
243Am
238U
240Pu 241Pu
246Cm 247Cm242Cm 243Cm 244Cm
244Am
243Pu
239Np
239U
b-
236U 237U
(n, 2n)
(m)
238Np237Np
238Pu
a
234U 235U233U
233Pa
232U
231Th 233Th232Th230Th
231Pa
229Th
a
a
a
a
Target activity > 109 Bq/mg
69 y
88 y
163 d
26 h22 m
6.8 d5.0 h
26 h