DAPNIA Neutron capture cross section of 234 U

DAPNIA Neutron capture cross section of 234 U Walid DRIDI CEA/Saclay for the n_TOF Collaboration Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Outline DAPNIA üAnalysis procedure : Ø Subtraction of background Ø Dead time correction (MC simulation) Ø Detection efficiency (MC simulation) Ø Neutron flux ü SAMMY Analysis ü Results ü Conclusion Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

234 U(n, γ) cross sections availables DAPNIA Energy Uncertainty of σcapt(%) Pt therm - 0, 50 e. V 5 0, 50 – 450 e. V 10 After 2, 0 ke. V 20 Transmission measurement of James et al. (1) The alone capture measurement published : Experiment of Muradyan et al. (2) 2 sd capture measurement capture performed in 2004: Experiment in Los Alamos (1) Physical review C 15, p. 2023, 1977 Walid DRIDI, CEA/Saclay (2) Proceeding ISINN-7, JINR p. 292 (1999) n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Number of γ capture determination Subtraction background DAPNIA Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

MC simulation with GEANT 4 MC simulations include: DAPNIA • Very detailed TAC geometry (validated with multi-γ-rays sources) • Event reconstruction similar to experimental data, including : üEnergy resolution üThreshold effects üDead time effects Electronics • γ-rays cascade generator for (n, γ) processes using data for each nucleus (from J. L. Taín). Walid DRIDI, CEA/Saclay PM Ba. F 2 crystal n_TOF Collaboration Meeting, Paris December 4 -5, 2006

MC simulation: TAC response to 234 U The 5. 16 e. V of 234 U resonance is reproduced by MC simulation DAPNIA Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Dead time Correction v The simulation study of dead time effects is done by studying the efficiency loss due to missed events. Efficiency loss DAPNIA Dead time correction factor done on the experimental data Factor deduced from MC simulation Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

TAC detection efficiency The detection efficiency which should be included in the analysis, is the efficiency found by simulation for the chosen criterion (Ncluster > 1) and the counting rate equal to zero, corrected by a factor of correction : DAPNIA The correction factor equal to 0, 99, close to 1, presents another proof of validation of our simulations. The TAC efficiency for Ncluster>1: Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Neutrons flux DAPNIA Beam interception Fraction (CIEMAT) Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Capture Yield of 234 U DAPNIA Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

üAnalysis procedure : DAPNIA Ø Subtraction of background Ø Dead time correction (MC simulation) Ø Detection efficiency (MC simulation) Ø Neutron flux ü SAMMY Analysis ü Results ü Conclusion Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Normalization and sample thikness The capture yield was normalized in order to reproduce the ENDF/B-VI. 8 234 U(n, γ) cross section in thermal energy range lower than 0, 1 e. V and the first resonance. DAPNIA Procedure : v Normalization fitted Results : v Neutron and radiation width are fixed (ENDF) N 234 U = 0, 950 v Sample thikness composition fitted Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Low energy region DAPNIA First resonance n_TOF ENDF/B-VI. 8 JENDL 3. 3 Гγ (me. V) 38, 13 40 24, 6 Our best fit is not able to fairly reproduce the shape of the first resonance with very low residual : Why ? Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Sample of 234 U in SAMMY Real geometry sample Sample modeling in SAMMY Ø 10 DAPNIA Sample was inserted between two Al foils (0. 15 mm) and encapsulated into 0. 2 mm of Ti in order to fulfill the ISO 2919 certification (requested by the safety regulations at CERN) Walid DRIDI, CEA/Saclay Ti-Al-U 3 O 8 Sample is modeling as an homogenous mixture of all components n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Some fitted resonances DAPNIA 10 < En < 100 e. V 250 < En < 400 e. V 750 < En < 1000 e. V 1200 < En < 1500 e. V Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

DAPNIA üAnalysis procedure : Ø Subtraction of background Ø Dead time correction (MC simulation) Ø Detection efficiency (MC simulation) Ø Neutron flux ü SAMMY Analysis ü Results ü Conclusion Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Level statistics (1/3) Average radiation width < Гγ > DAPNIA i is the number of found resonance εi statistic uncertainty done by SAMMY n_TOF ENDF/B-VI. 8 JENDL-3. 3 36, 4 ± 1, 5 me. V 40 me. V 26 me. V Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Level statistics (2/3) Reduced neutron width distribution Porter et Thomas distribution DAPNIA Integral for distribution is : N 0 total number levels without threshold Results N 0= 136 ± 2 ( 123 observed levels), Average level spacing Walid DRIDI, CEA/Saclay 10. 92 ± 0. 2 e. V from Mughabgab n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Level statistics (3/3) S-wave strength fonction S 0 DAPNIA ΔE, the range of the energy study i, the resonance number S 0 is the slope the histogram presenting the cumulated value of according to energy S 0 = (0, 88 ± 0, 03). 10 -4 Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Capture cross section for 234 U DAPNIA Comparison between our results with ENDF/B-VI. 8 and JENDL 3. 3 Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Capture cross section for 234 U Average cross sections Comparison between our results with Muradyan DAPNIA Excellent agreement except on the first resonance Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Conclusions ü We have proceeded the analysis by bin time for subtraction of background ü Simulation of the TAC response to the 234 U capture cascade with G 4 197 234 DAPNIA ü TAC detection efficiency by simulation Au & U ü Dead time correction by simulation ü Absolute normalization (normalize to thermal cross section) using ENDF data ü Capture Yield has been extracted up to ~1. 5 ke. V Several problems : ØSome systematics errors may still remain in the data reduction procedure due to : Dead time, Pile-up, … Ø The Free Gas model is probably not well suited to describe the oxide target Ø Sample Modeling in SAMMY is inaccurate Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

DAPNIA Thank you for your attention Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Capture measurement principle To determine the neutron capture cross section of an isotope, is by the determination of experimental capture yield : Y(En) DAPNIA With : S–B : Number of capture counts without background Φn(En) : Number of neutron per bunch impinging on the sample εdétecteur : Detector efficiency f : Correction factor νγ : Events selection criteria Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Event selection criteria DAPNIA Ø Multiplicité γ : • Improve signal at low energy • Does not change scattering to capture ration Ø Clustering improves capture relatively to ambient background but also γ and neutron scattering Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Number of γ capture determination Raw Data : Ø Events selection criteria : Nclust > 1 Ø Energy spectra of three components : DAPNIA 1. ) Background due to the Ti canning 2. ) Activity 3. ) 32. 7 mg 234 U + 1. ) + 2. ) Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Number of γ capture determination Subtraction background DAPNIA Empty canning All signals Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

The negative resonance DAPNIA Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006

The 1 st resonance Thikness Effect Doppler broadening DAPNIA Гγ effect Walid DRIDI, CEA/Saclay Гn Effect n_TOF Collaboration Meeting, Paris December 4 -5, 2006

Dead time modeling v Dead time corresponds to events missed v The interval time spectra between two succesive events impinging a given detector : is supposing suited a Poissonian distribution DAPNIA v It could be seen by missing counts up to several µs. Walid DRIDI, CEA/Saclay n_TOF Collaboration Meeting, Paris December 4 -5, 2006