Accurate Neutron-Induced Cross Section Measurements
at the CERN n_TOF facility
Paolo Maria MILAZZO
INFN - Trieste
CERN
The n_TOF collaboration
Technische Universitat Wien
Austria
IRMM EC-Joint Research Center, Geel
Belgium
Zagreb University
Croatia
Charles University, Prague
Czech Republic
IN2P3 – IPN – Orsay,
CEA – Saclay
France
Wolfgang Goethe Universität, Frankfurt
Karlsruhe Institute of Technology
Germany
National Technical University, Athens
University of Thessaloniki
Greece
Bhabha Atomic Centre, Mumbai
India
INFN Bari, Bologna, LNL, LNS, Trieste
Dipartimento di Fisica Università Bologna
Dipartimento di Fisica Università di Catania
ENEA – Bologna
Uniwersytet Lodz
Italy
Poland
Universidade de Lisboa
Portugal
Horia Hulubei Institute of Physics, Bucarest-Magurele
Romania
CIEMAT – Madrid
CSIC – Valencia
University of Santiago de Compostela
Universitat de Catalunya
Spain
Paul Scherrer Institute, Villigen
University of Basel
Switzerland
University of Manchester
University of York
United Kingdom
The problem:
World energy needs fastly increases
Burning fossil fuel till the end?
• Global warming? Atmospheric CO2 level higher than ever in the past 15 million years, increasing faster than ever
before (IPCC report, March 2014 > 2˚C more likely than ≤ 2˚C)
• Air pollution?
• Burning coal cost Europe alone 42.8 billion Euros in annual health care expenses
(2013 report by the Health and Environment Alliance)
• The ambient air pollution caused the premature deaths of > 400,000 Chinese in 2013
• WHO: in 2012 around 7 million people died - 1 in 8 of total global deaths – as a result of air pollution exposure
• Running out? The current tendency is to increase the use of fossil fuel
• Way out? Develop renewable energies, save, improve energy efficiency and innovate!
The nuclear option
Accidents
(Three Mile Island, Chernobyl, Fukushima)
Waste management (storage over ≤ one million years)
Proliferation
Sustainability
However
No CO2 and other air chemical polluants
Nuclear fission technology exists and is well understood
Breeding can make it essentially “sustainable” on the human time scale
Assuming by 2050
a substantial classic nuclear contribution
to heal the greenhouse effect
(≈ 30% of the projected,
increased world’ s power consumption of +2.3%/yr),
the yearly waste production would be of
100,000 ton/y
fill a Yucca Mountain type of repository every 8 months!
Nuclear waste
Yearly production
by a 1 GW LWR
244, 245Cm
Figura Nucleosintesi (frecce che si muovono)
1.5 Kg/yr
241Am:11.6
Foto FIC
243Am:
Kg/yr
4.8 Kg/yr
239Pu:
125 Kg/yr
237Np:
16 Kg/yr
LLFP
76.2 Kg/yr
LLFP
Options
Th/U fuel cycle
Thorium is:
Figura Nucleosintesi (frecce che si muovono)
3  4 times more abundant than U
 isotopically pure
Foto FIC
Th-U fuel cycle features:
 limited production of MA
 intrinsic proliferation resistance
LLFP
LLFP
Options
Recycling brings many advantages (IV Generation Reactors)
• Increase of fuel burn-up efficiency
• Strong reduction in the production of nuclear waste
• Improved security (e.g. ADS) and non-proliferation (Th/U cycle)
• Reduction of costs and delivery time
Nuclear waste Transmutation
•
Through neutron capture (n, γ)
for LLFF (79Se, 93Zr, 99Tc, 121I, 135Cs, 151Sm, …)
(e.g.) n+ 99Tc (2.1x105 y) →
•
100
Tc (16 s) →
100
Ru
Through neutron induced fission
for Pu and Minor Actinides (240Pu, 237Np, 241,243Am, 244,245Cm, …)
Summary Target Accuracies for Fast Reactors
(Aliberti, Palmiotti, Salvatores, NEMEA-4 workshop, Prague )
Energy Range
Current
Accuracy (%)
Target
Accuracy (%)
inel
0.5 ÷6.1 MeV
10 ÷ 20
2 ÷3
capt
2.04 ÷24.8 keV
3 ÷9
1.5 ÷ 2
Pu241
fiss
454. eV ÷1.35 MeV
8 ÷ 20
2÷5
Pu239
capt
2.04 ÷498 keV
7 ÷ 15
4÷7
Pu240
fiss
0.498 ÷1.35 MeV
6
1÷3
Pu242
fiss
0.498 ÷2.23 MeV
19 ÷ 21
3 ÷5
Pu238
fiss
0.183 ÷1.35 MeV
17
3 ÷5
Am242m
fiss
67.4 keV ÷1.35
MeV
17
3 ÷4
Am241
fiss
2.23 ÷6.07 MeV
9
2
Am243
fiss
0.498 ÷6.07 MeV
12
3
Cm244
fiss
0.498 ÷1.35 MeV
50
5
Cm245
fiss
67.4 ÷183 keV
47
7
Fe56
Inel
0.498 ÷2.23 MeV
16 ÷ 25
3÷6
Na23
inel
0.498 ÷1.35 MeV
28
4 ÷10
Pb206
inel
1.35 ÷2.23 MeV
14
3
Pb207
Inel
0.498 ÷1.35 MeV
11
3
inel
1.35 ÷6.07 MeV
14 ÷ 50
3÷6
capt
6.07 ÷19.6 MeV
53
6
U238
Si28
Necessary to reduce uncertainties to ≈ 3-7%
for most Pu isotopes and Minor Actinides,
in the energy range from few keV to several MeV
e.g.
neutron Time Of Flight @ CERN
n_TOF is a pulsed neutron source
designed to study neutron-nucleus interactions
for neutron kinetic energies ranging from a few meV to
several GeV
Neutrons are generated using a pulsed beam of protons
with a momentum of 20 GeV/c, hitting a lead spallation
target. The proton pulses are delivered by CERN's PS.
Every proton yields about 300 neutrons.
The initially fast neutron spectrum is slowed down, first by
the lead target, and then by a water slab in front of the
lead target.
Neutrons are collimated and guided through an evacuated
beam pipe to two experimental areas at a distance of 19
and 185 m from the spallation target.
The innovative feature of the n_TOF neutron facility, i.e.
the high instantaneous flux, the high energy resolution
and low background, allow for an accurate determination
of neutron induced cross sections.
neutron Time Of Flight @ CERN
Features of n_TOF:
• wide energy spectrum
(check normalization and extend data to high energy)
• high instantaneous flux
(useful for measurements of radioactive isotopes)
• low repetition rate
(no wrap-around problem)
• good energy resolution
Two experimental areas working in parallel
EAR-1: flight path of 185 m
EAR-2: (shorter) flight path of 19 m
(n, γ) set-up
2. Total Absorption Calorimeter
1. Liquid scintillators
- 4π geometry
- 40 BaF2 crystals
- Good energy resolution
- Discrimination of spurious events and background
- low neutron sensitivity measurements
C6D6 detectors
neutrons
Sample changer
NIM A496 (2003) 425
CERN Public Note n_TOF-PUB-2013-002 (2013)
10B
loaded
Carbon Fibre Capsules
(n, p), (n, α) set-up
MicroMegas
Silicon detectors
- High gain, low noise
- Several samples can be measured in parallel
- (n,f) measurements
- Diamond detectors
- ΔE-E telescope
- Sandwich of detectors in beam
Silicon 1
neutrons
sample
Silicon 2
(n, f) set-up
Multi-sample Fission Ionization
Chamber
Parallel Plate Avalanche Counters
- Fission fragments detected in coincidence
- α (from sample decay) discrimination
- low sensibility to γ-rays
The 233U(n,f) reaction: the Resolved Resonance Region - RRR
n_TOF results agree with ORELA measurement
(Guber et al. Nucl. Sci. Eng. 135 (2000) 141)
which has a smaller energy range
(from 0.4 eV to 700 keV)
NOTE: ORELA’s data are normalized to Deruytter and Wagemans (1974)
between 8.1 and 17.6 eV.
Physical Review C 80 (2009) 044604
Both data (Guber 2000 and n_TOF) show resonance structures
well above current limit in ENDF/B-VII.0 (600 eV) and JEFF 3.1
(150 eV).
Important for self-shielding calculations in reactors based on
U/Th fuel cycle
The 243Am(n,f) reaction: the high energy regime
Solved a long-standing discrepancy of more than 15%
n_TOF data confirm current evaluations, against previous results
(even recent ones, 2004).
F.Belloni et al., European Journal of Physics A 47:160 (2011)
Performed measurements
Isotope
Purpose
90,91,92,94Zr(n,
93Zr(n,
Structural material
γ)
Transmutation
γ)
232Th(n,
Th/U cycle
γ)
233,234U(n,
Th/U cycle
γ)
237Np(n,
γ)
ADS, nuclear waste
240Pu(n,
γ)
ADS, nuclear waste
241,243Am(n,
209Bi(n,
ADS, nuclear waste
γ)
Structural material
f)
233,234,235,236,238U(n,
f)
Th/U cycle
232Th(n,
f)
Th/U cycle
237Np(n,
f)
ADS, Gen IV, nuclear waste
241,243Am(n,
245Cm(n,
γ)
γ)
ADS, Gen IV, nuclear waste
ADS, nuclear waste
Summary
• There is strong need of accurate new data on neutron-induced crosssection of many isotopes involved in advanced nuclear reactors
• At n_TOF several data taken on fission cross sections of interest for
Th/U cycle and for Gen IV and ADS programs
• Large effort, but necessary
Response (counts / ns)
10
2014-201X
n_TOF Phase 3
2
10
1
10
0
2013-2014
EAR-2 construction
n-TOF
232
Th (0.0041 at/b)
208
Pb
GELINA
232
Th (0.0016 at/b)
208
Pb
10
-1
10
100
1000 10000 100000
Neutron Energy / eV
2001-2004
n_TOF Phase 1
2000
Commissioning
1998
Preliminary studies
CERN/LHC/98-02+Add
2009
Re-Commissioning
1999
Construction
2011
EAR-2 project
2010
Upgrades:
Borated-H2O
Second Line
Class-A
2004
Spallation target
seriously damaged
2009-2012
n_TOF Phase 2
2008
New target
1997
Idea from C.Rubbia
CERN/ET/Int. Note 97-19
>60 isotopes investigated
>300 publications