measurement of prompt fission g -rays with lanthanum halide scintillation detectors a. oberstedt
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Measurement of prompt fission g -rays with lanthanum halide scintillation detectors A. Oberstedt. This work was supported by the EFNUDAT programme of the European Commission (agreement number 31027). Measurement of prompt fission g -rays …. Outline. - PowerPoint PPT PresentationTRANSCRIPT
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Measurement of prompt fissionMeasurement of prompt fission-rays with lanthanum halide-rays with lanthanum halide
scintillation detectorsscintillation detectors
A. OberstedtA. Oberstedt
This work was supported by the EFNUDAT programme of the European Commission (agreement number 31027)
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
• Motivation• Characterization of LaCl3(Ce) detectors
- intrinsic activity- energy resolution- intrinsic efficiency- timing resolution
• Experiment at IKI Budapest (cold neutrons)• Results• Summary and conclusions• Outlook
Measurement of prompt fission -rays …
Outline
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Assessment of -heating for design of Gen-IV reactors• about 10 % of total energy released in the core of a standard nuclear reactor by fission -rays• about 40 % of those due to prompt -decay of fission productsModelling requires uncertainty not larger than 7.5 % (1) • but: present -ray emission data determined in early 1970’s, underestimating -heating with 10 - 28 % for 235U and 239Pu
->NEA Nuclear Data High Priority List:• measurement of prompt -ray emission from 235U(n,f) and 239Pu(n,f)!
Motivation
Measurement of prompt fission -rays …
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Time-of-flight method to distinguish between -rays and neutrons (i.e. neutron-induced -rays) ->requires good timing resolution
Back then:• NaI detectors and ionization chambers• ≈ 3 - 5 ns and 1 ns Today & tomorrow: new detectors offer new possibilities• lanthanum halide crystals and pcCVD diamond detectors
->intended fission -ray measurements - a prerequisite to the assessment of -heating!
Experimental task
Assessment of -heating
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Energy resolution
Characterization of LaCl3(Ce) detectors
• expected E-1/2 behaviour• E/E = 3.8 - 4.2 % (FWHM) at 662 keV (137Cs)
19F(n,)16O*
232Th
In comparison:NaI(Tl)
1,5”x 1,5”
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Intrinsic efficiency
Characterization of LaCl3(Ce) detectors
• in agreement with other LaCl3 detectors (interpolated)
• 53 % better than NaI(Tl) detectors of same size
232Th
1,5”x 1,5”
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Timing - coincidence measurement
Characterization of LaCl3(Ce) detectors
60Co (1173 keV; 1332 keV)
22Na (511 keV; 1273 keV; 1786 keV)
• two LaCl3 detectors with multiple source (22Na and 60Co)
thresholdsaround1.1 MeV
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Timing - TAC spectrum
Characterization of LaCl3(Ce) detectors
1,5”x 1,5”
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Timing - TAC spectrum
Characterization of LaCl3(Ce) detectors
1,5”x 1,5”
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Fission-fragment and -spectrometry
Experiment at IKI Budapest
Simultaneous measurement of:
• post-neutron fission fragment distributions of 235U + nth
– time-of-flight and kinetic energy– fission-fragment spectrometer VERDI (-> talk S. Oberstedt)– pcCVD diamond detectors as fission trigger
• prompt fission -rays – two LaCl3(Ce) scintillation detectors (1,5”x 1,5”, coaxial)
– one LaCl3(Ce) scintillation detector (3”x 3”, coaxial)
– one LaBr3(Ce) scintillation detector (2”x 2”, coaxial)
– 6Li shielding against thermal neutrons– coincidence with fission trigger (stop: fission - start: -ray)
Location:• 10 MW research reactor at IKI Budapest
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Experimental details
Experiment at IKI Budapest
Sample: 235U (113 g)Thermal neutron flux: 7 · 107 cm-2 s-1
Fission rate: 1.18 · 104 s-1
Fission fragment count rate: 12 s-1
Fission count rate: 10 s-1
Beam time: 2 weeks (10 days)Expected number of counts
– fission fragments: 8.5 · 106
-rays: ~ 3 · 107
Performed in February/March 2010
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Experimental setup
Experiment at IKI Budapest
fission fragment spectrometer VERDI
-detectors: LaBr3 (2”x 2”), 2 x LaCl3 (1,5”x 1,5”), LaCl3 (3”x 3”)
cold neutron beam
sampleholder
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Experiment at IKI Budapest
Pulse height (channels)
Tim
e o
f flig
ht
(channels
)
Prompt fission peak
“shadows”fromother
detectors
TAC signal vs. PH signal
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Experiment at IKI Budapest
Prompt -peak + inelastic neutron scattering + neutron capture
TAC spectrum (zoomed)
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Pulse height (channels)
Tim
e o
f flig
ht
(channels
)
Experiment at IKI Budapest
Characteristic spectra vs. TAC signature
Prompt fission -rays(n,n’) -rays
activation -rays
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Experiment at IKI Budapest
Energy calibration
after irradiation!
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Experiment at IKI Budapest
Preliminary results I
TAC regime of thermal neutron induced -rays: energy spectrum
Activation of iron (VERDI): 56Fe(n, p) -> 56Mn (T1/2 = 2.58 h)!
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Experiment at IKI Budapest
Preliminary results II
TAC regime of fast neutron induced -rays and isomers
Observe: more peaks have still to be identified!
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Experiment at IKI Budapest
Preliminary results III
All TAC regimes: energy spectra - normalized & calibrated
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Experiment at IKI Budapest
Preliminary results IV
To guide the eye: simulation according to Verbeke et al., LLNL (2009)
Prompt fission -spectrum - background subtracted
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Experiment at IKI Budapest
Background on simulation
Prompt fission -energy distribution
Obtained from measurements by Maienschein et al., Neutron Phys. Ann. Prog. Rep., ORNL (1958)
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Characterization of LaCl3:Ce detectors (1,5”x 1,5”):
• Energy resolution E/E 4 % at 662 keV– 40 % better than NaI (Tl) up to E ≈ 7 MeV
• Intrinsic peak efficiency determined– 50 % better than NaI (Tl) of same size up to E ≈ 2.6 MeV
• Timing resolution intr ≈ 630 ps (FWHM) for entire energy range (441 ps for 60Co) intr ≈ 3 - 5 ns for NaI(Tl)
– previously published intr ≈ 300 ps, but smaller detectors and higher Ce-concentration
• Considerable intrinsic activity, but controlled by coincidence• Good linearity (residuals < 0.3 % above 100 keV)• Dynamical range up to ~ 17 MeV -rays
Summary and conclusions I
Fission -ray measurements …
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
LaCl3 scintillation detectors do indeed fulfill requirements for the measurement of prompt fission -rays, in particular in conjunction with pcCVD diamond detectors ( ≈ 300 ps)
– excellent timing resolution– improved n/-discrimination (time-of-flight method)
– neutron sensitive, but no activation of LaCl3 by fast neutrons
Summary and conclusions II
Prompt fission -rays from 235U(nth, f) measured: -rays distinguished with respect to their origin (fission,
neutron-induced, -delayed …)– preliminary prompt fission -spectrum presented– interactions between thermalized neutrons and detector
material extremely rare, i.e. (nth) < 0,2 s-1 cm-2
Fission -ray measurements …
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Outlook
To come:• data analysis to be completed (3 more detectors)• response functions have to be determined and applied
• LaBr3:Ce (2”x 2”) detectors to be characterized
• new LaCl3:Ce (1.5”x 2”) detectors to be characterized
• effect of BGO anti-Compton shield to be investigated• new experiment contemplated: detection of fission -rays
during measurement of 252Cf(sf) at IRMM with VERDI• …
Fission -ray measurements …
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Collaborators
Örebro University R. Billnert, A. Göök, J. Karlsson, A. Oberstedt
JRC - IRMM Geel R. Borcea, F.-J. Hambsch, S. Oberstedt
IKI Budapest T. Belgya, Z. Kis, L. Szentmiklosi, K. Takács
CIEMAT Madrid D. Cano-Ott, T. Martinez-Perez
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt
Thank you!
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Final Scientific EFNUDAT Workshop, CERN, Aug 30 - Sep 2, 2010 Andreas Oberstedt