J.N. Wilson, EFNUDAT workshop, CERN, August 2010 Level Densities, Decay Probabilities and Cross sections in the Actinide Region J.N. Wilson Institut de Physique Nucléaire, Orsay

J.N. Wilson, EFNUDAT workshop, CERN, August 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 of low lying states Resonance spacings at the neutron binding energy 1. Fundamental Physics Oslo method Extrapolation

J.N. Wilson, EFNUDAT workshop, CERN, August Indirect Measurements

J.N. Wilson, EFNUDAT workshop, CERN, August 2010 S. Boyer et al. Nucl.Phys. A775, 175 (2006) Pa Capture Experiment Results

J.N. Wilson, EFNUDAT workshop, CERN, August x-section calculations

J.N. Wilson, EFNUDAT workshop, CERN, August 2010 Part I First Experimental Data

J.N. Wilson, EFNUDAT workshop, CERN, August 2010 Oslo Cyclotron Experiments Si RingCactus NaI array

J.N. Wilson, EFNUDAT workshop, CERN, August 2010 The 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 The Thorium Cycle 235 U 233 U 234 U 232 U 232 Pa 231 Th 233 Th 232 Th 230 Th 231 Pa  233 Pa  234 Pa 236 U (n,  ) (n, 2n) (n,  ) (n, 2n) (n,  ) -- -- -- -- -- FISSION

J.N. Wilson, EFNUDAT workshop, CERN, August MeV 232 Th( 3 24 MeV 351 M events135 M events Experiment 232 Th: 01/12/09 – 13/12/09 ReactionCompound Nucleus Ex-Eg counts 3He,p234Pa13 M 3He,d233Pa6.0 M 3He,t232Pa0.57 M 3He,a231Th0.79 M ReactionCompound Nucleus Ex-Eg counts d,p233Th23 M d,d’232Th0.24 M d,t231Th1.2 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

Part II Extracting the Level Density

J.N. Wilson, EFNUDAT workshop, CERN, August 2010 The Brink Axel hypothesis Assuming dominance of dipole radiation (E1 and M1) Level densityTransmission Coefficient Gamma strength function

J.N. Wilson, EFNUDAT workshop, CERN, August 2010

2.15 MeV ??? 3.1 MeV 3.9 MeV 3.6 MeV 0.87 MeV

J.N. Wilson, EFNUDAT workshop, CERN, August 2010

MCNP simulations of Cactus detector response

J.N. Wilson, EFNUDAT workshop, CERN, August 2010

Cactus Response Matrix

J.N. Wilson, EFNUDAT workshop, CERN, August 2010 Matrix *response; Spec *after=before->SubtractComptons(response );

J.N. Wilson, EFNUDAT workshop, CERN, August Th* - After Compton Subtraction

J.N. Wilson, EFNUDAT workshop, CERN, August Th* -Primary gamma rays

J.N. Wilson, EFNUDAT workshop, CERN, August 2010 Part III The surrogate method

J.N. Wilson, EFNUDAT workshop, CERN, August 2010 ε = k E γ Suppose detector has this property: Then effeciency of detecting a cascade becomes proportional to cascade energy and independent of cascade path!! Decay probability measurement Efficiency of detecting a cascade, Ec of m gammas is: 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 + cE 2 + d E 3 + eE 4 + f E 5 Minimisation with the Downhill simplex method

J.N. Wilson, EFNUDAT workshop, CERN, August 2010 Weighting Function Matrix

J.N. Wilson, EFNUDAT workshop, CERN, August 2010

17 O

J.N. Wilson, EFNUDAT workshop, CERN, August 2010

Primary gamma rays n,gamma spectral extrapolation below n,n’threshold (New Technique) n,n' correction to measured decay probability n,n' correction to measured decay probability

J.N. Wilson, EFNUDAT workshop, CERN, August 2010 Results

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. TALYS calculations TALYS calculations

J.N. Wilson, EFNUDAT workshop, CERN, August 2010 Level density measurements possible in: 233 Th - d,p (0- 5 MeV) 232 Th - d,d’ ( MeV) 231 Th - d,t (0 – 3 MeV) Surrogate reaction & decay probability measurements possible in: 233 Th* - d,p 230 Ac* - d,a 234 Pa* - 3 He,p 232 Pa* - 3 He,t 231 Th - 3 He, 4 He Conclusions

J.N. Wilson, EFNUDAT workshop, CERN, August 2010 Fission detectors 233 U, 231 Pa, 234 U targets The Future

J.N. Wilson, EFNUDAT workshop, CERN, August 2010 IPN Orsay J.N. Wilson B. Leniau Oslo Cyclotron S. Siem S. Rose A. Bürger M. Guttormsen A-C. Larsen T. Wiborg H. Toft CEA Saclay F. Gunsing A. Georgen Thankyou Takk Merci Lawrence Livermoore Lab M. Weideking L. Bernstein

J.N. Wilson, EFNUDAT workshop, CERN, August Sm 146 Sm

J.N. Wilson, EFNUDAT workshop, CERN, August 2010 Hauser-Feshbach Formalism Differential cross section depends on transmission coefficients, Γ and level densities of the residual nuclei, ρ a + AB + b

J.N. Wilson, EFNUDAT workshop, CERN, August 2010 Level 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 (n,  ) Nuclei where direct measurements are difficult 239 Pu 245 Cm 241 Am 242 Am 242 Pu 243 Am 238 U 240 Pu 241 Pu 246 Cm 247 Cm 242 Cm 243 Cm 244 Cm 244 Am 243 Pu 239 Np 239 U -- 236 U 237 U (n, 2n) (m) 238 Np 237 Np 238 Pu  234 U 235 U 233 U 233 Pa 232 U 231 Th 233 Th 232 Th 230 Th 231 Pa 229 Th     Target activity > 10 9 Bq/mg 69 y 88 y 163 d 26 h 22 m 6.8 d 5.0 h 26 h

J.N. Wilson, EFNUDAT workshop, CERN, August 2010