1 / 27

1 V. Alcayne , 2 A. Kimura, 1 E. Mendoza, 1 D. Cano Ott and the 3 n_TOF Collaboration

Study of photon strength functions of 241 Pu and 245 Cm from neutron capture measurements at n_TOF (CERN). 1 V. Alcayne , 2 A. Kimura, 1 E. Mendoza, 1 D. Cano Ott and the 3 n_TOF Collaboration 1 CIEMAT– Spain 2 JAEA – Japan 3 CERN-Switzerland. 1. Introduction.

elisabeth
Télécharger la présentation

1 V. Alcayne , 2 A. Kimura, 1 E. Mendoza, 1 D. Cano Ott and the 3 n_TOF Collaboration

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Study of photon strength functions of 241Pu and 245Cm from neutron capture measurements at n_TOF (CERN) • 1V. Alcayne, 2A. Kimura, 1E. Mendoza,1D. Cano Ottand the 3n_TOF Collaboration 1CIEMAT– Spain • 2JAEA – Japan • 3CERN-Switzerland 1

  2. Introduction 240Pu and 244Cm capture cross sections have been measured at n_TOF, with a BaF2 Total Absorption Calorimeter (EAR-1) and C6D6 liquid scintillators (EAR-2) (see talk last year at CPAN X). Very low mass samples but still high quality data due to the excellent performance of the CERN n_TOF facility

  3. The measured energy spectra can be used to determine the PSF of 241Pu and 245Cm at low excitation energies, below the neutron separation energy.

  4. Nuclear levels and their decay

  5. Nuclear levels and their decay Number of nuclear levels increases with the number of nucleons. (Actinides 106 -107 levels) At certain point: • Experiments can not resolve levels • Calculationsbecome extremely difficult But under some assumptions the decay can be described by statistical approach using: • Level Density • Photon/radiative/γ-ray Strength Function

  6. The CIEMAT nuclear de-excitation code: NuDEX The model operates in a similar way as DICEBOX(F.Bečvář, NIMA 417, 434 (1998)) or DECAYGEN (D. Jordán et al., NIMA 828,52 (2016)). It is written in C++ and can be fully integrated as an event generator in GEANT4 Known level scheme, levels, branching ratios and ICC factors from RIPL-3 Unknown level scheme, branching ratios and ICC factors from: • Level scheme: • The full level scheme of the compound nucleus is created (~106-107 levels in 241Pu and 245Cm below Sn). • Level density formulas: Back-Shifted-Fermi-Gas model, Constant Temperature, Back-shifted-Egidy. Parameters from RIPL-3. • Wigner law to sample distances between levels.

  7. The CIEMAT nuclear de-excitation code: NuDEX • Branching Ratios (BR): • Brink hypothesis: PSF do not depend on the excitation energy • PSF types: Standard Lorentzian model (SLO), Enhanced Generalized Lorentzian model (EGLO), Simplified Modified Lorentzian model (SMLO)  initially with the parameters from RIPL-3. • Internal Conversion Coefficients (ICC): • Taken from BrICC Huge amount of combinations = realizations of the EM de-excitation scheme References: • ENSAR2 workshop: GEANT4 in nuclear physics: A new Photon Evaporation model for Geant4, E. Mendoza et al. • ND China 2019: NuDEX: a new nuclear γ-ray cascades generator, E. Mendoza et al

  8. Procurement of the cascade • Very complex and ill-conditioned problem: • Construction of a de-excitation model of the nucleus: level scheme (level density formulas, spin, parity), branching ratios between levels • Good know response function of the detector: energy deposition spectra (sum and individual crystals vs multiplicity): Monte Carlo simulations. • Construction of the response (Monte Carlo) to a certain de-excitation pattern an comparison to the experimental data in the gamma-ray detector for a given resonance. Calculation of a user defined figure of merit (FOM), which could analogous to χ2 or more complex.. • Variation of the parameters (PSF + ???) until a good reproduction is achieved. Minimization of the FOM using a differential evolution algorithm (DEA).

  9. TAC Setup EAR1 (~180m) • TAC( Total Absorption Calorimeter). • Sphere of 40 BaF2crystals, 95% solid angle • Detecting all the gammas in the cascade • Experiment • 2 weeks • 5·1017 protons of 20 GeV/c • Analysis • Coincidence between • the 40 detectors. Reject Background • Montecarlo Simulations with Geant4

  10. Monte Carlo simulations of 88Y with the TAC • Obtain the PSF of 245Cm and 241Pu • Using the cascade generator developed at CIEMAT

  11. Monte Carlo simulations of 88Y with the TAC • Obtain the PSF of 245Cm and 241Pu • Using the cascade generator developed at CIEMAT

  12. Measurement with the TAC in EAR1 Resonance 240Pu Resonance 244Cm

  13. Cascade for 244Cm with TAC using RIPL-3 data FOM 𝞪 χ2R,1+ χ2R,2

  14. Cascade for 245Cm with TAC Model used

  15. Cascade for 244Cm with TAC Model used

  16. Cascade for 244Cm with TAC Model used

  17. Cascade for 244Cm with TAC Model used

  18. C6D6 Setup EAR2 (~20 m) Sample • Three BICRON C6D6 detectors • Experiment • 3 months • 8·1018 protons of 20 GeV/c to target • Analysis • Precise background subtraction. • Monte Carlo Simulations with Geant4 Neutron Beam

  19. Monte Carlo simulation of the C6D6 88Y calibration source

  20. Measurement with C6D6 liquid scintillators Resonance 240Pu Resonance 244Cm

  21. Cascade for C6D6 in EAR2 MC-RIPL MC-DEA 244Cm

  22. MC-RIPL MC-DEA 240Pu

  23. Dependency with the realization Different realizations of a nucleus: same LD and PSF parameters, different levels and BR generated with a different random number sequence. In the figures, the solid lines correspond to the average between 200 realizations of the same 241Pu nucleus, and the shadowed area to the standard deviation (1σ).

  24. Summary and conclusions • Capture cross section data from n_TOF  information about the nuclear EM de-excitation  PSF of different nuclei below Sn. • We have measured 240Pu and 244Cm with both the TAC and C6D6 detectors. • We have developed very accurate Monte Carlo simulation tools of our detectors: TAC and C6D6. We reproduce the cascades with high accuracy in both setups. • We have developed a realistic nuclear EM de-excitation code (NuDEX), fully integrated in GEANT4 and very fast. • We have started to perform some PSF analysis and investigated important aspects/problems of the very “ill-conditioned” inverse problem of finding which PSF reproduces best the data in a statistical sense: multi-spectrum and multi-detector fit, parameter correlation analysis, effect of realizations.

  25. Holaquetal BACKUP SLIDES

  26. Methodology: total Monte Carlo • Objective: • Which PSF are reproducing out experimental results? • Are they unique? • How sensitive is our data to the PSF? • … • General idea: • Define a FOM to be minimized (FOM 𝞪 χ2R,1+ χ2R,2) • Find the parameters which minimize the FOM • Perform a sensitivity/correlation analysis of the parameters • First variations of RIPL-3 data performed: • Tail of the E1 PSF at low energies • Structures in the M1 PSF at 2-3 MeV (Ullman et al, PRC 96, 024627 (2017))

  27. Nuclear de-excitation model with NuDEX (C++) • Two modes of operation: • Input mode (to study cascades in detail) • Data are obtained from databases (RIPL-3 + ENSDF + BrICC)  large amount (200-300) of nuclei. • Can be integrated into Geant4  capture cascades are obtained from NuDEX References: • ENSAR2 workshop: GEANT4 in nuclear physics: A new Photon Evaporation model for Geant4, E. Mendoza et al. • ND China 2019: NuDEX: a new nuclear γ -ray cascades generator, E. Mendoza et al. • ND China 2019: Study of photon strength functions of measurements 241Pu and 245Cm from neutron capture, E. Mendoza et al.

More Related