irfu CEASaclay SPh N GifsurYvette F Feb 18
irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 1 VERDI – a high resolution fission-fragment time-of-flight spectrometer S. Oberstedt IRMM - Institute for Reference Materials and Measurements Geel - Belgium http: //irmm. jrc. europa. eu/ http: //www. jrc. europa. eu/
irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 o Motivation o Concept of the particle spectrometer VERDI o Experiment set-up o Diamonds for fission-fragment timing o Scientific programme o Conclusion & Outlook 2
Motivation irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 3 GELINA neutron TOF spectrometer Mono-energetic neutron source • 7 MV Van-de-Graaff accelerator – – – 7 Li. F(p, n)7 Be, Ti. T(p, n)3 He, D 2(d, n)3 He, Ti. T(d, n)4 He DC (Ip, d < 50 A), pulsed beam available 4 + 1 non-T beam line • • • n < 109 /s/sr • • Bonner spheres NEPTUNE isomer spectrometer ionisation chambers, NE 213 neutron/gamma-ray detectors, BF 3 counters, HPGe detectors fast rabbit systems (T 1/2 > 1 s) for activation studies • • • 70 - 140 Me. V electron accelerator • • • ionisation chambers, C 6 D 6 detectors repetition frequency: 40 - 800 Hz neutron pulse: 2 s - 1 ns @ FWHM n = 3. 4 1013/s @ 800 Hz 12 different flight paths with a length between 8 and 400 m high-resolution -ray detectors fission chambers for flux monitoring
Motivation irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 o Neutron Data for Waste Transmutation and Safety of Different Reactor Systems (ADS, Generation IV, . . . ) o Basic Research in Nuclear Physics and Neutron Data Standards Ø 10 B(n, ) 7 Li, 16 O(n, ) 13 C Ø Neutron-induced fission cross-sections Ø Fission-fragment characteristics as Y(A, TKE), p, E ( ) Ø LCP emission, . . . ÞImprovement of nuclear cross-section data files ÞPrecise input data for improved modelling of neutroninduced reactions 4
Motivation irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 5 Nuclear Energy Agency IAEA - INDC Nucl. Sci. Committee NEA Databank WPEC: Working Party for Evaluation Co-operation JEFF: Joint European Fission + Fusion datafile BROND CENDL JEFF ENDF JENDL WPEC
Motivation irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 ü Reliable predictions on fission product yields 6 relevant in modern nuclear applications (GEN-IV, ADS…) Ø Radio-toxicity of the nuclear waste Ø Decay heat calculations Ø Delayed neutron yields relevant during reactor operation o Prediction of fission-fragment mass and kinetic energy distributions o Prompt -ray emission spectrum and multiplicity (as a function of fragment mass) o Delayed neutron emission / pre-cursor yields
Delayed neutron emission irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 v Resolution of discrepancies in existing delayed-neutron data pointed out in the JEFF/DOC-922 by A. D’Angelo and J. Rowlands, which may lead to an underestimation of the reactivity even for 235 U(fast) of about 16% (details and further examples in JEF/DOC-909) v Scarce experimental data about energy dependence of total delayed neutrons o Reduce the uncertainties in the delayed neutron data for the major actinides 235 U, 238 U (, and 241 Pu) o Improve the situation for the standard reaction 252 Cf (SF) 7
Delayed neutron emission irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 v neutron-rich nuclei v typical half lives between hundreds of microseconds and tens of seconds ü neutron-induced fission is the most efficient production mechanism for delayed neutron decay pre-cursors ü delayed neutron are released by delayed neutron pre-cursor nuclei, immediately after β- decay into a level above the neutron binding energy 8
Delayed neutron emission irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 v. Delayed neutron yield may show a variation of up to 3. 5% v. Need for measuring fission fragment emission yields with a high precision, i. e. high mass resolution 9
Fission-fragment characteristics irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 10
Fission-fragment characteristics irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 11 Are quantitative predictions of fission fragment yields possible ?
Fission-fragment characteristics irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 12 235 U(n, En= 0. 01 Me. V En= 0. 25 Me. V 237 Np(n, f) f) @ 10 e. V 237 Np(n, f)
Fission-fragment characteristics irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 13 238 U(n, f)
Fission-fragment characteristics irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 14 o 238 U (n, f) @ En = 0. 9 – 2 Me. V E* 5. 8 Me. V E* 6. 1 Me. V E. Birgersson et al. , Nucl. Phys. A 817 (2009) 1 -34
Fission-fragment characteristics irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 Ø Why does this concept fail? Ø Is prompt neutron emission well under control? v microscopic neutron emission data do not fit to results from integral experiments (even for 235 U !!!) ü although average emission energy ( ) differs by only 50 ke. V v Is the dependence on excitation energy incorrectly treated? v Extra/interpolation of prompt neutron data from neighbouring nuclei not correct? v Uncertainty due to iterative neutron correction in a 2 E-experiment. . . v. . . Ø Is the multi-modal fission model not correct? 15
irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 VElocity fo. R Direct particle Identification 16
VERDI – the concept irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 ü Double time-of-flight spectrometer to measure the velocity of each 17 individual fission fragment (FF) pre neutron-emission masses ü Subsequent measurement of the FF kinetic energy post neutronemission masses E ~ A v 2 A ~ E t 2/L 2 unambiguous identification of the particle mass precise fission-fragment decay studies
VERDI – the concept irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 ü Simultaneous measurement of kinetic energy and velocity of both fission fragments § 2 v pre-neutron masses, Ai* (i = l, h), TKE § v, E post-neutron masses, Ai, Ek, i (i = l, h) Ø i(Ai*) from the difference Ai* - Ai TXE(Ai) Ø delayed decay modes of fission fragments 18
VERDI – the requirements irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 fragment mass (arbit. units) 19 fragment mass (amu) ü Set-up of the time-of-flight tube with an energy-sensitive detector device energy resolution : timing resolution : flight path length : E/E = 0. 005 for fission fragment kinetic energies t = 50 ps L = 40 cm fragment mass resolution : A/ A > 130
VERDI – basic ingredients irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 Ø High resolution energy detector Ø High precision (transmission) time pick-up Ø radiation hard Ø spectrometer efficiency 0. 005 – 0. 01 Ø for a mass resolution of A/ A 100 20
VERDI – the energy side irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 o Axial ionisation chamber: ü ü ü Simple to construct and to use Splitted electrodes allow element identification (cf. LOHENGRIN) No radiation damage Very good intrinsic energy resolution Timing characteristics? ? ? v Difficult to get a large area detector v Energy loss in the entrance window o Large area silicon detectors: ü Relatively cheap ü Easy to use ü Excellent pulse height stability ü Excellent energy resolution ü Promising timing characteristics v Subject to radiation damage 21
VERDI – the energy side irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 22 PIPS (area: 900 mm 2) 239 Pu, 241 Am, 244 Cm ü Energy resolution for αparticle kinetic energy: E = 0. 006 → close to our design specifications for fission-fragments
VERDI – the timing side irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 23 o -channel plate detectors: ü Very good intrinsic timing characteristics v Difficult to handle v Requires excellent vacuum p < 10 -6 mbar v Subject to radiation damage (especially in an intense neutron field)? ? ? v Difficult to build o Diamond detectors: ý New detector material ý Relatively few experimental results v Difficult to produce single-crystal diamonds v Pulse height stability difficult to predict ü Promising timing characteristics (with Ni-ion @ 30 Me. V/u t 30 ps) v Never tested with fission fragments (0. 5 Me. V/u < v. FF < 2 Me. V/u) ü Radiation hard
VERDI - the design irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 24 ü 2 x 19 PIPS detectors ü CVD (or MCP) ultra-fast time pick-up detectors ü Can be handled with NIM electronics L = 50 cm
CVDD - material properties irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 25 Physical properties @ 300 K CVD Si Atomic charge Mass density [g/cm 3] 6 3. 5 14 2. 33 Band gap [e. V] Energy to create e h pair [e. V] Energy to create lattice defect [e. V] 5. 45 13 80 1. 12 3. 6 28 Thermal conductivity [W/cm/K] Thermal expansion coefficient [/K] 20 8 10 -7 1. 27 2. 6 10 -6 Resistivity [ cm] Breakdown field [V/cm] Electron mobility [cm 2/Vs] Hole mobility [cm 2/Vs] > 1011 107 2200 1600 2. 3 105 1500 600 CVD synthesis is based on the decomposition of gaseous hydrocarbon molecules, usually CH 4 neutron-dose meter (ITER) first applied to beam diagnostic applications, e. g. intensity and profile start detectors for fixed-target heavy -ion experiments
CVD diamonds irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 o chemical vapour deposited (CVD) diamond o poly-crystalline (pc) and as single crystals (sc) available o ultra-fast timing characteristics o No pulse-height resolution for pc. CVDDs o sc. CVDD provide excellent energy resolution comparable with PIPS detectors (tested @ GSI) o limited in size and expensive 26
pc. CVDD - material properties irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 triple -source irradiated with a 90 Sr/90 Y -source (3 MBq, 72 h) 27
Experimental set-up irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 28 252 Cf pc. CVD, 100 m PIPS, 300 m 225 mm pc. CVDD material ü size: 1 1 cm 2 ü thickness: 100 m
Pulse-height “analysis” irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 CVD pulse height spectrum no coincidence with 7 PIPS 29 PIPS pulse height spectrum no coincidence with 7 PIPS
pc. CVDDD - Intrinsic timing resolution irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 252 Cf pc. CVD, 100 m 30 pc. CVD, 100 m 95 mm pc. CVDD material ü size: 1 1 cm 2 ü thickness: 100 m
Determination of the timing resolution irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 31 o By means of a Monte-Carlo simulation o Experimental fission-fragment distribution o Post-neutron fragment yield o Post-neutron fragment kinetic energy o Geometry of the detector set-up o Variation of the time-resolution parameter until reproduction of the measured time distribution
pc. CVDDD - Intrinsic timing resolution irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 32
pc. CVDDD – pulse-height stability irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 33
VERDI - the timing resolution irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 34 252 Cf pc. CVD, 100 m pc. CVDD material ü size: 1 1 cm 2 ü thickness: 100 m PIPS, 300 m 330 mm Up to 7 PIPS detectors ü ORTEC 900 mm 2 ü CANBERRA (same specs. ) ü CANBERRA 450 mm 2) ü Eurysis (40 mm 2)
VERDI - the timing resolution irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 35 Ortec PIPS 900 mm 2 Eurysis 40 mm 2 t 1. 0 ns t 0. 6 ns
VERDI – data analysis irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 36 ü Energy calibration from reference distributions published in “The Nuclear Fission Process” ü Channel-to-time conversion using a systematic trend obtained from 233, 235 U and 239 Pu v. No pulse-height defect correction applied
VERDI – FF distributions irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 Ortec 900 mm 2 37 Eurisys 40 mm 2
VERDI – challenges irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 L Timing properties of the PIPS detectors v CANBERRA offers “specially treated” detectors v Standard detectors useless v… K CVDD detectors not yet at their intrinsic limit: v Present limits due to the high capacitance ? v Signal rise time ? v Limited by the available pre-amplifier modules ? 38
Scientific programme irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 39 o single (v, E) measurements: Ø thermal-neutron induced fission (233, 235 U, 239(, 241)Pu) and Ø KFKI, SCK CEN, ILL, . . . 252 Cf(SF) Ø with a 1 1 cm 2 CVDD and n, th > 107/s/cm 2: cth > 2. 5 /s or 106 /(120 h) Ø thermal flux (10 - 100) Ø sample or CVDD size 4 o double (v, E) measurements: Ø same as for the single (v, E) set-up Ø ternary particle emission
Scientific programme irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 o single (v, E) measurements: Ø post-neutron mass and kinetic energy distributions Ø delayed-neutron pre-cursor yields Ø investigation of sub-sequent decay processes o double (v, E) measurements: Ø post-neutron mass- and energy-distributions Y(A, Ek) Ø pre-neutron mass- and energy-distributions Y(A*, Ek*) Ø p as a function of fragment mass Ø total kinetic energy distribution TKE Ø p as a function of the total excitation energy TXE 40
Scientific programme irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 o Measurements at accelerator-driven neutron sources: Ø fission cross-sections are about 200 – 500 smaller Ø neutron fluxes in general not much higher than 107/s/cm 2 Ø charged-particle induced (fission) reactions possible Ø Central VERDI flange can be easily adapted 41
Fundamental aspects irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 o Spectroscopy of neutron-rich isotopes: ü relevant for the nucleosynthesis ü astrophysical r-process) 42
Summary irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 43 ü Fission fragment timing resolution < 250 ps possible ü Optimization of detectors possible to reduce timing resolution ü VERDI with mass resolution A/ A 100 possible v To reach at < 100 ps seems to be very challenging ü radiation hardness of the CVDD start trigger proven ü spectrometer efficiency 0. 5% ü Next improvement: ü single crystal diamond as event tirgger ü energy resolution (v, 2 E) ü 100% trigger efficiency
Outlook irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 ü First experiment @ KFKI beginning 2010 § EFNUDAT programme § Proposal submission ü CVDD transmission detector ü under investigation ü thickness around 5 m ü first -particle signals extracted § Test with fission fragments soon o Construction of a -channel plate detector… 44
Nothing without a good team! irfu CEA-Saclay SPh. N, Gif-sur-Yvette (F), Feb. 18, 2009 45 R. Borcea F. -J. Hambsch Van de Graaff technical team A. Oberstedt Örebro University
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