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