C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

The n_TOF Collaboration, www.cern.ch/nTOF

CERN-INTC-2011-045 / INTC-P-309

Measurements of neutron-induced capture and fission reactions on 235U: cross sections, a ratios, photon strength functions and

prompt g-ray from fission

C. Guerrero (CERN), E. Berthoumieux (CEA) and D. Cano-Ott (CIEMAT)on behalf of The n_TOF Collaboration

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

Figura Nucleosintesi (frecce che si muovono)

Foto FIC239Pu: 125 Kg/yr

237Np: 16 Kg/yr

241Am:11.6 Kg/yr 243Am: 4.8 Kg/yr

244, 245Cm 1.5 Kg/yr

FP

LLFP 76.2 Kg/yr

Quantities refer to yearly production in 1 GWe LW reactor

Neutrons and production of nuclear energy (& radioactive waste)

+Energy

Competition between fission and capture

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

Existing reactors have low burn-up efficiency and produce large amount of radioactive waste.

In all cases, a large reduction of actinide inventory is achieved by means of neutron-induced reactions (subsequent captures and fission).

Generation IV or ADS reactors based on recycling of the spent fuel (in particular actinides).

DIFF. FUEL COMPOSITION → DIFF. NEUTRON ENERGY RANGE → POORLY KNOWN s(n,x)

Neutrons and production of nuclear energy (& radioactive waste)

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

(FCA) Fast Critical Assembly (JAEA)

Soft Hard

Sensitive mainly to the 235U(n,g) below 2.25 keV (RRR)

Source: NEA-WPEC

The criticality of current and fast future reactors must be known within 0.3-0.5% for operation/safety.

Differences up to 2% in the measured and calculated criticality values for FCA (JAERI, Japan) assemblies with different hardness are due to 235U s(n,g) below 2.5 keV.

Effects of the uncertainties in the capture 235U cross section

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

Status of the235U capture cross section and a ratio

Isotope Field of interest Present Uncertainty* Target Accuracy*

235U U/Pu cycle100 eV - 2 keV 15-20%+ 5%

2 - 30 keV 12-15%+ 8%

30 keV – 1 MeV# 5-10%+ 3%+ From comparison between evaluations and data*From NEA-HPRL

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

The g−heating at the centre of a typical fast reactor core:20% from the γ produced in capture (fairly well known)40% from the prompt γ emitted by fission fragments, 30% from the delayed γ-rays produced by fission products, 10% from the inelastic scattering reactions (fairly well known)

Characteristics of γ-ray emission are MULTIPLICITY, TOTAL ENERGY and SPECTRUM SHAPE.

Present calculations based on data from the 70s, which are in 20-30% disagreement with each other and do not contain any information on possible correlations with the neutron energy.

Prompt g-ray emission from fission & capture

Characteristics 235U(n,f) prompt g-ray emission now in NEA High Priority Request List:New data for the 235U case will be of direct use in reactor calculations and will also help to test and fine-tune the physics models used for many other actinides for which no data are available yet.

The TAC response to capture reactions contains basic information on the properties of the compound nucleus (A+1Z*): - Level densities- Transition Probabilities (Photon Strength Functions)

Investigation on other actinides already carried out at n_TOF

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

Difficulty of measuring s(n,g) of fissile isotopes

Measurements of AZ s(n,g)

Detection of g-ray cascade from the compound nucleus A+1Z

If AZ fissile: g-rays also produced in fission reactions!

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

Experimental set-up: capture and fission detectors combined!

The n_TOF Total Absorption Calorimeter

-4p geometry (high tot. absorption effic.)-40 BaF2 crystals (segmentation)-Good energy resolution (back. discrimin.)- Used extensively for (n,g) on actinides

The n_TOF MicroMegas

-Two gas regions: conversion & amplification- High gain and low noise- Possibility for several samples in parallel. - Used extensively for (n,f) and (n,a)

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

CERN-INTC-2010-037 ; INTC-I-105Validation of simultaneous measurement of capture and fission reactions at n_TOF

Measurement performed in September 2010

Total – fissionBackgroundFission

Total - fission-backg.Fission

3 MGAS detectors each equipped with a 1 mg 235U sample

Signal+Mesh

HV (drift)

TAC

MGAS

neutrons

MGAS with 3 235U samplesMGAS signals

BaF2 module

Agreement with evaluations within 3-4% Goal: study the URR in 2012!!

C. Guerrero et al., A new set-up for the simultaneous measurements of neutron-induced capture and fission reactions at n_TOF, Proc. Int. Conf. ANIMMA-2011 (Belgium, June 2011 )

C. Guerrero et al., Simultaneous measurement of neutron-induced capture and fission reactions at CERN, submitted to the n_TOF Ed. Board (to be submitted to NIM-A)

Capture dominated resonances

High fission contribution

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

Required accuracy of the capture cross section: 5% (RRR) and 8% (URR) BEAM TIME REQUEST so to reach statistical uncertainties lower than 3%

The constraints of the measurements are mainly:

Samples have to be thin (<300 mg/cm2) so that fission fragments can escape. There is no space in the TAC for more than 8-10 samples, yielding a total mass of ~40 mg. The counting statistics of the capture reactions is the liming factor, since the fission cross section and the efficiency of the MGAS detector are larger. At least 6000 bins per decade are needed in order to resolve the resonances in the keV region. The lowest counting rate per bin will correspond to the RRR in the keV region. A minimum of ~1000 counts integrated over each resonance are needed to reach the 3% stat. unc. The information from several resonances will be combined for the study of g-ray emission from capture and fission and therefore the statistics acquired will not be a limiting factor.

Objectives and Beam Time Request

IRMM (now a member of n_TOF) will manufacture the samples and deliver them by June 2012

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

Objectives and Beam Time Request

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

Sample Purpose # Protons 235U (x10) Cross section, prompt g-ray emission 3.0x1018

235U (x1 upstream/downstream) TAC sensitivity to sample position 0.2x1018

Sample-out Overall background 0.3x1018

197Au Check beam interception factor 0.2x1018

Graphite Background to scattered neutrons 0.3x1018

Beam-off Room background 0.0TOTAL 4.0x1018

Auxiliary measurements will help to identify and determine the different sources of background:

• Sample-out beam-On measurements: a similar set-up without 235U samples will provide data on the overall background of the measurement.•Beam-off: a measurement without beam will serve to identify and quantify the room background.•197Au: the measurement will be performed with a sample of 4.5 cm in diameter and serves for normalization purposes.•Single sample-upstream/sample-downstream: we plan to do two measurements leaving only one of the 235U samples in place: once the one upstream and another time only the one downstream. This will serve to quantify the dependence of the TAC response to the spatial origin of the g-ray emission.•Graphite: the measurement of a “pure-scatterer” sample will serve to determine the TAC response to scattered neutrons.

Objectives and Beam Time Request

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

Conclusions

Measurements of neutron-induced capture and fission reactions on 235U (FISSILE!!!): Capture cross section Fission cross section a Ratio Prompt g-ray from fission: g-ray heating in reactor cores. Prompt g-ray from capture: Photon Strength Functions

GOAL: MEASURE BOTH CROSS SECTIONS WITHIN 5%

The n_TOF TAC and MGAS detectors will be combined Individual detectors intensively used nowadays at n_TOF Combined detection system tested successfully in 2010 Samples will be produced at IRMM by June 2010 <3% statistical uncertainty required in the full energy range

BEAM REQUEST: 4x1018 protons (includes auxiliary backg. measurements)

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

Additional slides

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

Study of Photon Strength Functions on Actinides (TAC) Detection of the capture cascades from 234U, 237Np and 240Pu with the TAC provide information regarding the corresponding compound nuclei.

Known levels Capture level

Ground state

235U 28 (E<610 keV) 1/2+ 7/2-238Np 40 (E<460 keV) 2+,3+ 2+241Pu 9 (E<560 keV) 1/2+ 5/2+

mcr=1mcr=2 mcr=3

mcr=4 mcr=5

mcr=6

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

(n,g) TAC

?

Sn+En

A+1Z

J.L. Tain et al. NIM A 571 (2007) 719-727

Known level scheme

Statistical models(LD & PSF)

Study of Photon Strength Functions on Actinides (TAC) Characteristics of the cascade depend on:

levels (known+LD) & transition probabilities (PSF)

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

Study of Photon Strength Functions on Actinides (TAC)

DECAY GENerator (DECAYGEN)- Low energy level scheme (KNOWN!)- Level density (KNOWN!)- Photon Strength Functions (E1,M1,E2)

Geant4 MC simulation of the TAC- Detailed detector geometry- Geant4 Standard EM physics- Realistic event reconstruction

Capture Cascades: Egi=1,mg

Simulated TAC response(Esum, mcr)

Experimental TAC response (Esum, mcr)

Comparison

Assumption on PSF

C. Guerrero et al., “Measurements of neutron-induced capture and fission reactions on 235U” CERN-INTC-2011-045 / INTC-P-309 (November 2011)

Study of Photon Strength Functions on Actinides (TAC)

PSF from RIPL-2

PSF from RIPL-2

PSF from RIPL-2

PSF from RIPL-2PSF from RIPL-2

PSF from RIPL-2Tuned PSF

PSF from RIPL-2Tuned PSF

PSF from RIPL-2Tuned PSF

PSF from RIPL-2Tuned PSF

PSF from RIPL-2Tuned PSF

Pygmy (or spin-flip) mode associated to oscillations/vibrations neutron vs. protons241Pu