Measurement of the U-234(n,f)
cross section with PPAC detectors
at the n_TOF facility
Carlos Paradela Dobarro
Universidad de Santiago de Compostela
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
dissertation
1
Contents
• Motivation
• n_TOF facility and detection setup
description.
• Data reduction and efficiency estimation.
• 234U fission cross sections results.
• Conclusions.
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
dissertation
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Neutron-induced nuclear
reactions
Neutron scattering
AX
Z
nucleus
Cross
neutron
Target (AXZ nucleus)
+
Projectile (1n0)
Neutron capture
(n,)
Sections
f
Fission (n,f)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Why we measure these
cross sections?
Measurement of cross sections are relevant for:
1. Nuclear Technologies
•
•
Waste transmutation (ADS)
Thorium fuel reactors
2. Nuclear Astrophysics
– Heaviest element nucleosynthesis (“r” process)
3. Fundamental Nuclear Physics
– Nuclear structure
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Thorium-Uranium cycle
•
“La fisión del torio y la fusión de deuterio-tritio […] son nuevas energías nucleares
con residuos de corta duración y sin proliferación, capaces de proporcionar energía
durante los próximos milenios.” El mundo de mañana,hoy, Carlo Rubbia, El País,
233
233
233
2232
de Octubre.
Th + n 
Th 
Pa 
U (fissile)
“Thorium
and 234
deuterium-tritium
[…] are new non-proliferation nuclear
– 233fission
U+n 
U
energies producing short-term wastes, that can provide energy for the next
millenniums.”
– 233Pa+n 234Pa  234U
232U
233U
234U
235U
236U
231Pa
232Pa
233Pa
234Pa
235Pa
230Th
231Th
232Th
233Th
234Th
237U
238U
 decay
Neutron
Capture
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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The n_TOF collaboration
U.Abbondanno14, G.Aerts7, H.Álvarez24, F.Alvarez-Velarde20, S.Andriamonje7, J.Andrzejewski33, P.Assimakopoulos9, L.Audouin5,
G.Badurek1, P.Baumann6, F. Bečvář 31, J.Benlliure24, E.Berthoumieux7, F.Calviño25,D.Cano-Ott20,R.Capote23,A.Carrillo de
Albornoz30,P.Cennini4, V.Chepel17, E.Chiaveri4, N.Colonna13, G.Cortes25, D.Cortina24, A.Couture29, J.Cox29, S.David5, R.Dolfini15,
C.Domingo-Pardo21, W.Dridi7, I.Duran24, M.Embid-Segura20, L.Ferrant5, A.Ferrari4, R.Ferreira-Marques17, L.Fitzpatrick4, H.Frais-Koelbl3,
K.Fujii13, W.Furman18, C.Guerrero20, I.Goncalves30, R.Gallino36, E.Gonzalez-Romero20, A.Goverdovski19, F.Gramegna12, E.Griesmayer3,
F.Gunsing7, B.Haas32, R.Haight27, M.Heil8, A.Herrera-Martinez4, M.Igashira37, S.Isaev5, E.Jericha1, Y.Kadi4, F.Käppeler8, D.Karamanis9,
D.Karadimos9, M.Kerveno6, V.Ketlerov19, P.Koehler28, V.Konovalov18, E.Kossionides39, M.Krtička31, C.Lamboudis10, H.Leeb1, A.Lindote17,
I.Lopes17, M.Lozano23, S.Lukic6, J.Marganiec33, L.Marques30, S.Marrone13, P.Mastinu12, A.Mengoni4, P.M.Milazzo14, C.Moreau14,
M.Mosconi8, F.Neves17, H.Oberhummer1, S.O'Brien29, M.Oshima38, J.Pancin7, C.Papachristodoulou9, C.Papadopoulos40, C. Paradela24 ,
N.Patronis9, A.Pavlik2, P.Pavlopoulos34, L.Perrot7, R.Plag8, A.Plompen16, A.Plukis7, A.Poch25, C.Pretel25, J.Quesada23, T.Rauscher26,
R.Reifarth27, M.Rosetti11, C.Rubbia15, G.Rudolf6, P.Rullhusen16, J.Salgado30, L.Sarchiapone4, C.Stephan5, G.Tagliente13, J.L.Tain21,
L.Tassan-Got5, L.Tavora30, R.Terlizzi13, G.Vannini35, P.Vaz30, A.Ventura11, D.Villamarin20, M.C.Vincente20, V.Vlachoudis4, R.Vlastou40,
F.Voss8, H.Wendler4, M.Wiescher29, K.Wisshak8
1Atominstitut
der Österreichischen Universitäten,Technische Universität Wien, Austria, 2Institut für Isotopenforschung und ernphysik,
Universität Wien, Austria, 3Fachhochschule Wiener Neustadt, iener Neustadt, Austria, 4CERN, Geneva, Switzerland, 5Centre National de la
echerche Scientifique/IN2P3 - IPN, Orsay, France, 6Centre National de la echerche Scientifique/IN2P3 - IReS, Strasbourg, France,
7CEA/Saclay - DSM, Gif-sur-Yvette, France, 8Forschungszentrum Karlsruhe GmbH (FZK), Institut für Kernphysik, Germany, 9University of
Ioannina, Greece, 10Aristotle University of Thessaloniki, Greece, 11ENEA, Bologna, Italy, 12Laboratori Nazionali di Legnaro, Italy, 13Istituto
Nazionale di Fisica Nucleare, Bari, Italy, 1Istituto Nazionale di Fisica Nucleare, Trieste, Italy, 15Università degli Studi Pavia, Pavia, Italy,
16CEC-JRC-IRMM, Geel, Belgium, 17LIP - Coimbra & Departamento de Fisica da Universidade de Coimbra, Portugal, 18Joint Institute for
Nuclear Research, Frank Laboratory of Neutron Physics, Dubna, Russia, 19Institute of Physics and Power Engineering, Kaluga region,
Obninsk, Russia, 20Centro de Investigaciones Energeticas Medioambientales y Technologicas, Madrid, Spain, 21Consejo Superior de
Investigaciones Cientificas - University of Valencia, Spain, 22Universidad Politecnica de Madrid, Spain, 23Universidad de Sevilla, Spain,,
24Universidade de Santiago de Compostela, Spain, 25Universitat Politecnica de Catalunya, Barcelona, Spain, 26Department of Physics and
Astronomy - University of Basel, Basel, Switzerland, 27Los Alamos National Laboratory, New Mexico, USA, 28Oak Ridge National
Laboratory, Physics Division, Oak Ridge, USA, 29University of Notre Dame, Notre Dame, USA, 30Instituto Tecnológico e Nuclear, Lisbon,
Portugal, 31Charles University, Prague, Czech Republic, 32Centre National de la Recherche Scientifique/IN2P3 - CENBG, Bordeaux, France,
33University of Lodz, Lodz, Poland, 34Pôle Universitaire Léonard de Vinci, Paris La Défense, France, 35Dipartimento di Fisica, Università di
Bologna, and Sezione INFN di Bologna, Italy, 36Dipartimento di Fisica Generale, Università di Torino and Sezione INFN di Torino, I-10125
Torino, Italy, 37Tokyo Institute of Technology, Tokyo, Japan, 38Japan Atomic Energy Research Institute, Tokai-mura, Japan, 39NCSR, Athens,
Greece, 40National Technical University of Athens, Greece
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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n_TOF facility (I)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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n_TOF facility (II)
4 - 7 x 1012 protons per pulse
FTN transfer line
7ns
Lead target
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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n_TOF facility (III)
Second Collimator
TOF TUBE
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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n_TOF facility (IV)
Neutron beam monitors
Micromegas
SiMon
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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n_TOF facility (V)
PPAC gas regulation
Escape Line
DAQ
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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n_TOF
beam characteristics
• Neutron spectrum
DEn/En < 10-3
@ En < 104 eV
• Beam profile
Y (mm)
• Energy resolution
X (mm)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Fission detection setup
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Fission Detection Setup (I)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Fission Detection Setup (II)
•
•
Fissile target in a thin backing sandwiched by two
detectors  Detection of both fission fragments in
coincidence.
Fission event reconstruction: target position and
emission angle. Efficiency limited by the cut at large
angles.
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Targets (I)
Epoxy frame
Uranium target
80 mm Ø
300 µg/cm2
2 µm Al backing
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Targets (II)
• Measurement of thickness and homogeneity by alpha counting.
Y (mm)
• High purity samples (> 99 % for U-234).
234U
X (mm)
 activity
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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PPAC (I)
Parallel Plate Avalanche Counter
•
•
•
•
Very thin detectors.
High FF efficiency
Fast timing (0.5 ns de
resolution using anode
signal).
FF position by using
cathode signals.
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Discrimination
with coincidences
U-234: singles
U-234: coincidences
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Det0 Amplitud (a.u.)
Time & Amplitude selection
• Selection of fission
events from 234U
(target 0)
Time coincidence window
Time difference (1/10 ns)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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PPACs @ n_TOF
10 detectors  9 targets
• U-234(2) and Th-232(5)
• Two reference targets:
U-235 y U-238
• Less than 1 % of flux
attenuation in the full
setup.
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Three detectors in coincidence
Detector 0
Detector 1
Detector 2
LEFT TARGET
n
FF1
FF2
Detector 0
Detector 1
Detector 2
RIGHT TARGET
FF1
n
FF2
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Three detectors in coincidence
Fissions from target on the left
Fission from target on the right
Correlation between time differences
of detectors 0,1 and 2
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Cathode Positioning (I)
• Positioning by
using stripped
cathodes and
delay line readout.
• The cathode signal
is split in the delay
line and
transmitted to both
ends
Stripped Cathode
Delay Line
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Cathode positioning (II)
Diagonal condition:
(Tch1-Tanode)+(Tch2-Tanode)=DLT
DLT: Total delay line length (~320 ns)
The time difference
between both cathode
ends provides
the position of the signal.
Tc1-Tc2
Tc1
Tc2
cathode active surface 200 mm
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Cross section analysis
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Cross Section Analysis
•
•
•
•
 (E): fission cross section
n (x,y,E): fission rate obtained from raw data
 (x,y): surface density of the target
 (E): detection setup efficiency
a (x,y,E)/ b (x,y,E) ≈ 1 ± 0.01 (1%)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Efficiency estimation
Factors determining the efficiency:
1. Setup angular acceptance.
2. Hardware threshold cut.
3. Fission fragment angular distribution
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Expected angular
acceptance
100% efficiency
70º
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Angular acceptance
Simulations
70º
Measurements
58º
50º
50º
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Hardware threshold cut
Cathode signals for En < 100 keV
Cathode signals for En > 1 MeV
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Hardware threshold cut (II)
HFF
HFF
LFF
LFF
Target 0
Energy < 10 MeV (Assymetric fission)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Hardware threshold cut (IV)
E ~ 5 MeV
Fit to a double Gaussian with the areas
below the peaks: AHFF and ALFF
Efficiency estimation obtained
from the ratio:
Detected events/Expected events
where the expected events are
assumed to be 2 x ALFF.
AHFF ALFF
E < 200 keV
AHFF ALFF
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Hardware threshold cut (V)
Detected/Expected
U-234 (Target 0)
High Energies
Low Energies
High Energies
Low Energies
U-234 (Target 1)
High Energies
U-235
Low Energies
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Fission Fragment
Angular Distribution
Log E =6.0
Cos ()
Log E =5.6
Log E =5.9
Cos ()
Log E =5.5
Log E =5.8
Cos ()
Log E =5.4
U-234 FFAD for neutron energies near the fission threshold
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Fission Fragment
Angular Distribution (II)
W()1+Bcos2 ,
B  Anisotropy parameter
W()= C(P0+P1cos  )(1+Bcos2),
P0 and P1 intrinsic parameters
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Fission Fragment
Angular Distribution (III)
B
U-238 this work
Leachman +Tutin
U-238 anisotropy
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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B
Fission Fragment
Angular Distribution (III)
U-234 anisotropy
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Efficiency estimation
IN THE LOW ENERGY RANGE
 B supposed as 0
U-235
U-234 (target 1)
W()= CE (P0+P1cos )
U-234 (target 0)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Efficiency estimation (II)
IN THE HIGH ENERGY RANGE
U-234 target (0)
0.75
U-234 target(1)
E = 800 keV
0.75
0.7
0.7
Calculated efficiency
Calculated efficiency
0.65
0.6
0.55
0.65
0.6
0.55
0.5
0.5
0.45
0.4
5
5.5
6
6.5
7
7.5
8
8.5
9
9.5
0.45
5
5.5
6
6.5
7
7.5
8
8.5
9
9.5
log E (eV)
log E (eV)
Efficiencies for both U-234 targets
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Efficiency estimation (III)
U-235 target
0.75
0.7
Calculated efficiency
0.65
0.6
0.55
0.5
0.45
0.4
-1
0
1
2
3
4
5
6
7
8
9
log E (eV)
U-235 efficiencies in the full energy range
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Efficiency estimation (IV)
• The cosine distribution at very high energies is
disturbed because of wrong trajectory
reconstruction.
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Cross section results
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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U-234(n,f) cross section
Present work
ENDF/B-VI
Normalised to ENDF/B-VI in the 1-4 MeV interval
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Resolved Resonance
Region
•
234U(n,f)
cross section presents important
subthreshold resonances.
• Resolved Resonance Region extends to
1.5 keV.
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Resolved Resonance
Region (II)
Previous data
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Resolved Resonance
Region (III)
f (b)
------ ORNL 1977
------ n_TOF PPAC 2003
E (eV)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Resolved Resonance
Region (IV)
ENDF/B-VI
n_TOF PPAC 2003
JEFF-3.1
n_TOF PPAC 2003
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Resolved Resonance
Region (V)
------ ORNL 1977
f (b)
------ n_TOF PPAC 2003
Narrow intermediate structure shown by James and Rae1
1. G. D James and E. R. Rae,, Nucl. Phys. A118, 313 (1968)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Region up to 20 MeV
N_TOF PPAC 2003
ENDF/B-VI
f (b)
JEFF-3.1
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Region up to 20 MeV
n_TOF PPAC 2003
ENDF/B-VI
f (b)
JEFF-3.1
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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f (b)
Fission threshold
310 keV
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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f (b)
f (b)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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f (b)
Fission threshold (I)
450 keV
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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f (b)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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f (b)
Fission threshold (II)
550 keV
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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f (b)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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f (b)
Fission threshold (III)
780 keV
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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f (b)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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f (b)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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f (b)
Region up to 20 MeV
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Region above 20 MeV
n_TOF PPAC 2003
ENDF/B-VI
f (b)
Prokofiev*
* A.V.Prokofiev, Nucl. Instr. Meth. A 463 (2001) 557
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Conclusions
• A new neutron facility (n_TOF) where a detection setup
based on PPACs have been used for measuring fission cross
sections by using coincidence technique and trajectory
reconstruction.
• An original data reduction has been developed including
specific features of the DAQ, detection setup and method.
• Efficiencies for each target have been studied in detail
including its dependency of the fission fragment angular
distribution.
• New U-234(n,f) cross section experimental data in an
extended energy range that benefit from the good resolution
of n_TOF and detector.
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Cross Section
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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The n_TOF Data Acquisition System (I)
•The n_TOF DAQ consists of 54 flash ADC
channels with 8 bit amplitude resolution and
sampling of 500 MSample/s.
•The full history of EVERY detector (BaF2
crystals and monitors) is digitised during a
period of 16 ms (0.7 eV < En < 20 GeV) and
recorded permanently on tape. Very useful feature
since the raw data can be always re-investigated.
•The system has nearly zero dead time.
•7.5 TB disk space for temporary storage.
•Typical data rate of 2-3 TB/day on tape after
compression.
•Pulse shape analysis is performed on the fly at
the LXBATCH Linux Batch Farm at CERN (30
CPUs exclusively dedicated) and stored in highly
compressed Data Summary Tapes.
•Quasi on-line analysis of the data with full
statistics.
One of the big successes of n_TOF. Many TOF facilities are following the n_TOF
example and moving to digital electronics!
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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The n_TOF facility
The n_TOF facility is a spallation source built in 1999 – 2000, driven by the CERN PS and
coupled to a Time Of Flight (TOF) beam line of 200 m. Typical pulses of 7·1012 protons at 20
GeV/c and a time width of 6 ns are used for producing a spallation neutron beam with a spot
of 4 cm diameter and 6·105 n/cm2/pulse at a 200 m flight path.
Unique features worldwide for measuring
highly radioactive samples!
•High instantaneous neutron
fluence with low repetition
rate at a VERY long flight
path of 200 m and VERY
favourable duty cycle (key
point
for
measuring
radioactive samples).
•Excellent energy resolution
DEn/En < 10-4 for En < 105 eV
•Highly advanced detection
systems (TAC) and monitors.
•Innovative and pioneering
Data Acquisition System
based on flash ADCs.
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Resolved Resonance Region (IV)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Hardware threshold cut (II)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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n_TOF
beam characteristics
• Neutron spectrum
• Energy resolution
• Beam profile
• Background (-Flash)
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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f (b)
Resolved Resonance
Region (V)
Narrow intermediate structure shown by James
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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n_TOF
James
Lestone
ENDF-B/VI
f, barns
10
1
0.3
0.2
0.1
0.0
1
10
100
1000
10000
100000
1000000
1E7
1E8
En, eV
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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f (b)
f (b)
Cross Sections
Capture (n,)
Elastic scattering
En (log scale)
En (log scale)
Total cross section
f (b)
f (b)
Fission
Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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Measurement of 234U(n,f) cross section. Carlos Paradela. PhD
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