Measurement of the 240Pu(n,f) reaction cross-section at the CERN n_TOF facility EAR-2

47th Meeting of the INTCCERN, June 25, 2014

A. Tsinganis1, N. Colonna2, R. Vlastou1, P. Schillebeeckx3, A. Plompen3, J. Heyse3, M. Kokkoris1, M. Barbagallo2, E. Berthoumieux5, M. Calviani4, E. Chiaveri4, A. Stamatopoulos1

and the n_TOF Collaboration

1) National Technical University of Athens (NTUA), Greece2) Istituto Nazionale di Fisica Nucleare, Bari, Italy

3) European Commission JRC, Institute for Reference Materials and Measurements, Geel, Belgium4) European Organisation for Nuclear Research (CERN), Geneva, Switzerland

5) Commissariat a l‘ Energie Atomique (CEA) Saclay - Irfu, Gif-sur-Yvette, France

Spokespersons: A. Tsinganis, M. Kokkoris (NTUA)Technical Coordinator: O. Aberle (CERN)

Outline Introduction and motivation

The 2010 240,242Pu(n,f) proposal The 240Pu(n,f) measurement in EAR-1

Sample-induced damage to detectors Advantages of EAR-2

Neutron fluence gain Background suppression

Experimental Samples, detectors etc.

Analysis Software, simulations etc.

Beam request Summary

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014

The measurement in EAR-1: motivation Proposal CERN-INTC-2010-042 / INTC-P-280 (21/05/2010) An (n,f) measurement on 240,242Pu

Both included in the NEA Nuclear Data High Priority Request List Pu isotopes and minor actinides represent the main long-term contribution to waste

radiotoxicity, persisting for ~105 y 240Pu is produced in significant quantities in conventional reactors Fission cross-sections of these isotopes are of great significance in the context of nuclear waste

management and advanced nuclear systems, especially fast reactors (Generation IV, ADS) Discrepancies ~10% exist above the fission threshold in 240Pu data Physics motivation has already been endorsed by the INTC In addition, recent attempts at n_TOF and elsewhere within the ANDES project were not

successful for different reasons

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014

1. ANDES: Accurate Nuclear Data for Nuclear Energy Sustainability, www.andes-nd.eu2. Fission cross section measurements for 240Pu, 242Pu. Deliverable 1.5 of the ANDES project, DOI:

10.2787/810043. A. Plompen, “Minor Actinides, Major Challenges, the Needs for and Benefits of International

Collaboration”, Nucl. Data Sheets (2014), Under publication

The measurement in EAR-1: detector degradation An unexpected alteration of some detectors was observed after removal from the

chamber A distinct discoloration of the micromesh is visible in the 4 detectors used with the 240Pu samples Physical damage to the micromesh is visible under inspection with a microscope A unique – if inadvertent – ageing test

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014

3cm

Courtesy A. Teixeira (CERN)

The measurement in EAR-1: detector degradation This leads to a deterioration of the electrical field Separation of α-particles and fission fragments becomes impossible A significant part of the data had to be discarded Even under normal operation, the analysis would be challenging due to the long α-pile-up tail

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014

The measurement in EAR-1: detector degradation This leads to a deterioration of the electrical field Separation of α-particles and fission fragments becomes impossible A significant part of the data had to be discarded Even under normal operation, the analysis would be challenging due to the long α-pile-up tail

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014

By comparison, 242Pu…

Two experimental issues identified

Gradual deterioration of detector performance due to high current / high α-activity Shorter measurement due to higher flux

High α-activity of the 240Pu samples (>6MBq/sample) Improved signal-to-background due to shorter acquisition window

Both issues can be addressed in EAR-2

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014

Neutron fluence gain

Comparing EAR-2 (3cm diameter) with conditions of previous measurement in EAR-1

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014

x10-15

x40-55

x30-45

x7-10x100-

1000

Samples Four 240Pu samples manufactured at IRMM

3 cm diameter PuO2 deposit 0.25 mm aluminium backing (5cm diameter) The same samples used in the previous measurement

238Pu 0.0733%239Pu 0.0144%240Pu 99.8915%241Pu 0.00041%242Pu 0.02027%244Pu 0.000046%

Mass 3.1mg

Activity 25.7MBq

Surface density 110 μg/cm2/sample

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014

Reference samples (to be manufactured) 235U (≈ 70 μg/cm2) 238U (≈ 340 μg/cm2) Preferably of 3cm diameter to match the Pu samples Could add 237Np (≈ 60 μg/cm2) as additional reference

Sample impurities

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014

NEA request range

Measurement unaffected by impurities above ~1keV and at selected resonances

Sample holders Samples adapted to internal frame of the chamber

Samples kept in place by mechanical pressure only, “sandwiched” between to thin aluminium rings kept together by two-sided adhesive tape and two thick aluminium rings compatible with the chamber support frame.

Already designed & sample safety file in place

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014

Experimental setup

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014

Detector chamber

Preamplifier module

Micromegas detectors

FINAL SETUP (picture from EAR-1)

Chamber support for EAR-2

Analysis software, simulations Already developed for previous measurement

Peak-search routine, routine for high-energy data analysis etc....

Simulations of detector response:

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014

Simulated amplitude spectrum compared with experimental spectrum

Beam request 2x1018 protons on target 3-5 weeks, depending on beam delivery rate 240Pu (435 μg/cm2, 4 samples)

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014

Statistical uncertainty <3% above 10keV <1% above 300keV

Expected systematic uncertainties ~3-4% Detector efficiency Amplitude threshold

correction Selected resonances will also

be studied with good statistics

Summary An important measurement

…especially in the light of recent not-so-successful attempts within ANDES 2x1018 protons requested Statistical uncertainty < 3% above 10keV, <1% above 300 keV Improved conditions in EAR-2: Shorter experiment (3-5 weeks) due to higher flux

Avoiding detector degradation Shorter acquisition window

Stronger background suppression Cross-check with different reference reactions

235U(n,f), 238U(n,f), 237Np(n,f) A useful study also for future measurements

Hardware already available Procedures for Pu samples already in place Analysis software already developed

Improvements, adjustments… Could be ready to go on day 1

Only foreseeable delay could be sample manufacturing and transport One PhD student (NTU Athens) starting in September

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014

Thank you for your attention…

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014

Extra slides

Beam request 2x1018 protons on target Reference sample masses chosen to keep countrate <1 count/μs 235U (70 μg/cm2) 238U (340 μg/cm2)

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014

237Np (60 μg/cm2)

Beam request 2x1018 protons on target 237Np (60 μg/cm2)

240Pu(n,f) measurement @ n_TOF EAR-247th INTC Meeting, CERN, June 25, 2014