The n_TOF project and its results
Paolo Maria MILAZZO
(on behalf of the n_TOF collaboration)
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
The n_TOF collaboration
CERN
Technische Universitat Wien
Austria
IRMM EC-Joint Research Center, Geel
Belgium
IN2P3 – IPN – Orsay, IN2P3 - IReS - Strasbourg,
CEA – Saclay
France
FZK – Karlsruhe
Germany
AstroParticle Consortium (Athens, Thessaloniki, Thrace …) Greece
INFN and Dipartimento Fisica – Bari, Bologna, LNL, Trieste
ENEA – Bologna, Università di Pavia
Italy
LIP - Universitade de Coimbra, ITN Lisbona
Portugal
INR – Dubna, IPPE – Obninsk
Russia
CIEMAT - Madrid, IFIC – Valencia, University of
Santiago de Compostela, University of Cataluna
Spain
University of Basel
Switzerland
University of Notre Dame, LNL, ORNL
USA
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
Objectives
Cross sections relevant for Nuclear Astrophysics
(but also)
Measurements of neutron cross sections for Nuclear
Waste Transmutation and related Nuclear Technology
purposes
(and)
Neutrons as probes for fundamental Nuclear Physics
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
To study Nuclear Astrophysics (@ n_TOF)
means to investigate:
Stellar nucleosynthesis
Stellar thermal conditions
Cosmochronology
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
Gap
B,Be,Li
a-nuclei
12C,16O,20Ne,24Mg, …. 40Ca
number fraction
0
10
-1
10
-2
10
-3
10
-4
10
-5
10
-6
10
-7
10
-8
10
-9
10
-10
10
-11
10
-12
10
-13
10
Elements heavier than Fe are the result
of neutron capture processes
NEUTRONS
r-process peaks (nuclear shell closures)
s-process peaks (nuclear shell closures)
Th, U
Fe peak
Au Pb
0
The n_TOF project and its results
50
100
150
mass number
Perugia, November 14th, 2012
200
paolo.milazzo@ts.infn.it
250
n_TOF is a CERN fecility
The n_TOF facility @ CERN
n_TOF is a spallation neutron source
based on 20 GeV/c protons from the CERN PS
hitting a Pb block (~360 neutrons per proton).
Experimental area at 200 m.
The n_TOF facility @ CERN
A 7x1012 protons/bunch beam @ 20
GeV/c from the PS accelerator,
with a short pulse width of 6 ns and a low duty cycle of 0.4 Hz
produces for spallation on a lead block a neutron beam, running on a base of
flight of ≈200
m
Very high instantaneous flux 105 n/cm2/pulse
Wide energy range
1 eV < En < 250 MeV
Good energy resolution
Low background
The n_TOF project and its results
Perugia, November 14th, 2012
DE/E ≈ 10-4 (fino a 100 keV)
10-5 (1 particle/cm2/pulse)
paolo.milazzo@ts.infn.it
n_TOF features
broad neutron energy
range
(1 eV < En < 250 MeV)
Effects on measurements
neutron capture cross sections in a
wide energy range (1 eV – 1 MeV)
small capture cross sections
high instantaneous flux
(105 n/cm2/bunch)
small sample quantities
(isotopically enriched samples)
radioactive samples
(low intrinsic background)
excellent energy resolution
(ΔE/E ≈ 10-4 up to 100 keV
resonance dominated cross sections
low neutron sensitivity
low backgrounds
(10-5 – 1
particle/cm2/bunch)
accurate cross section measurements
even for large σel/σcapture
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
N_TOF Vs Other facilities
Average flux
Instantaneous flux
n_TOF allows:
• The measurement of radioactive isotopes
• The extension of the resolved resonance region to higher energies
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
neutron magic nuclei
A<120
unstable branching isotopes
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
The Experimental Area
Setup for capture
Flux monitor
The n_TOF project and its results
Perugia, November 14th, 2012
Setup for fission
paolo.milazzo@ts.infn.it
The neutron capture reactions
g
fn
Detector
Capture reactions are measured by detecting γ-rays emitted in the de-excitation process.
At n_TOF, built two different detection systems.
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
Capture experimental set-up (1):
Liquid scintillators
C6D6 detector
neutrons
C6D6 (deuterated liquid scintillators)
Samples
The n_TOF project and its results
Perugia, November 14th, 2012
Specifically designed low neutron sensitivity device
paolo.milazzo@ts.infn.it
Capture experimental set-up (2):
Total Absorption Calorimeter
•
•
•
•
10B
loaded
42 BaF2 crystals, 15 cm in length
High efficiency to γ-rays from capture events
Good discrimination from the background
Discrimination between γ-rays cascades from capture
and => ideal for capture measurements on fissile
samples and/or samples available in small quantities
Carbon Fibre Capsules
sample
C12H20O4(6Li)2
Neutron Absorber
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
The s-process branching at A=151
(n,γ) x-sections of 151Sm
152Gd
154Gd
151Sm
151Eu
152Eu
153Eu
154Eu
150Sm
151Sm
152Sm
153Sm
used as stellar thermometer
s-Process
laboratory half-life of 93 yr
reduced to t1/2 = 3 yr
at s-process site
a probe for the temperature at s-process site
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
The s-process branching at A=151
(n,γ) x-sections of 151Sm
Measured for the first time at a time-of-flight facility
Resonance analysis with SAMMY code
(≈ 500 resonances, mostly new)
Maxwellian averaged cross-section
experimentally determined for the first time
s-process in AGB stars
produces 77% of 152Gd,
23% from p process
Maxwellian averaged (n,γ) cross section of the
151Sm and previous calculation (symbol)
NO PREVIOUS MEASUREMENTS!
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
Bottlenecks in the s-process at N=50,82
(n,γ) x-sections of 90Zr, 139La
Zr
La
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
The border between main and weak component
(n,γ) x-sections of 90Zr, 91Zr, 92Zr, 93Zr, 94Zr, 96Zr
The branching point at 95Zr depends on
• Thermodinamic stellar conditions
• Zr(n,γ) cross sections
Mo
93
95
97
Nb
90 91 92 93 94 95 96 97 Zr
95
Probing the neutron
exposure and neutron flux
in Red Giant Stars
S process
T½ = 35 d
T½ = 1.5 Myr
97
T½ = 72 m
T½ = 16 h
T½ = 64 d
R process
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
The border between main and weak component
(n,γ) x-sections of 90Zr, 91Zr, 92Zr, 93Zr, 94Zr, 96Zr
Sntof
14% lower than previous data
Weaker kernels
reflects in
lower MACS
The n_TOF project and its results
Perugia, November 14th, 2012
90Zr
paolo.milazzo@ts.infn.it
Cosmocronology
(n,γ) x-sections of 186Os, 187Os, 188Os
BANG!
Tnucleosynthesis
4.5 Gyr
nuclear clocks
The n_TOF project and its results
Perugia, November 14th, 2012

235U

232Th
/ 238U

187Re
/ 187Os
/ 238U
paolo.milazzo@ts.infn.it
Now
The Re/Os cosmochronometer
(n,γ) x-sections of 186Os, 187Os, 188Os
σNs(186Os) = σNs(187Os)
s-only
Os 184 Os 185 Os 186 Os 187 Os 188 Os 189 Os 190 Os 191 Os 192
0.02
94 d
1.58
1.6
13.3
16.1
26.4
15.4 d
41.0
Re 183 Re 184 Re 185 Re 186 Re 187 Re 188 Re 189 Re 190
71 d
38 d
37.4
90.64 h
62.6
16.98 h
24.3 h
3.1 m
42.3x109 a
W 182
W 183
W 184
W 185
W 186
W 187
26.3
14.3
30.67
75.1 d
28.6
23.8 h
W 188
69 d
s-process
r-only
the β-decay half-life of
187Re
(42.3 Gyr)
contributes to the abundance of the daughter
The n_TOF project and its results
r-process
187Os
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
The Re/Os cosmochronometer
(n,γ) x-sections of 186Os, 187Os
187
 (186)
Os c  Os 
 (187)
187
186
Os
 (186)
 0.42  0.02
 (187)
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
The Re/Os cosmochronometer
(n,γ) x-sections of 186Os, 187Os
The use of Re/Os abundance pair as a clock address few complications:
The β-decay half-life of
187Re
is strongly dependent on temperature
The stellar (n, γ) cross section of 187Os is influenced by low-lying excited levels (strong
population of 1st state at 9.8 keV, competition by inelastic channels)
Branching(s) at
Destruction of
185W
187Re
and/or at
186Re
in later stars (Astration)
The chemical evolution of the galaxy was not uniform Re and Os abundance uncertainties
Ages
• Cosmological way
13.7 ± 0.2 Gyr
based on the Hubble time definition (“expansion age”)
• Astronomical way
14.
± 2. Gyr
based on observations of globular clusters
• Nuclear way
15.3 ± 2.(*) Gyr
based on abundances & decay properties of long-lived radioactive species
(*) 0.4 Gyr uncertainty due to x-sections
http://physics.aps.org/synopsis-for/10.1103/PhysRevC.82.015802
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
The end of the s-process
(n,γ) x-sections of 204Pb, 206Pb, 207Pb, 208Pb, 209Bi
a-recycling
Normalization of s-process abundances
Discrimination between stellar models (accuracies of 3-5% are needed)
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
The end of the s-process
(n,γ) x-sections of 204Pb, 206Pb, 207Pb, 208Pb, 209Bi
207Pb
206Pb
209Bi
209Bi
The n_TOF project and its results
Perugia, November 14th, 2012
Reduction of neutron
background
sel>>sg
paolo.milazzo@ts.infn.it
neutron poison in the s process,
constraints for the 22Ne(a,n)25Mg reaction
(n,γ) x-sections of 24Mg, 25Mg, 26Mg
Main component
Weak component
22Ne(a,n)25Mg
22Ne(a,n)25Mg
is a neutron source in AGB stars:
1Msun < M < 3Msun
kT=8 keV and kT=25 keV
The n_TOF project and its results
is the main neutron source in massive stars:
M > 10 – 12Msun
kT=25 keV and kT=90 keV
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
neutron poison in the s process,
constraints for the 22Ne(a,n)25Mg reaction
(n,γ) x-sections of 24Mg, 25Mg, 26Mg
Resonance
shape analysis:
Capture
&Transmission
ORELA
Result: reduced poisoning effect
Lower MACS of 25Mg higher neutron density
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
Seeds of the s-process
(n,γ) x-sections of 54Fe, 56Fe, 57Fe, 58Fe, 58Ni, 60Ni, 61Ni, 62Ni, 63Ni
63Cu
64Cu
69.17
12.7 h
61Ni
62Ni
63Ni
64Ni
1.140
3.634
100 a
0.926
59Co
60Co
61Co
100
5.272 a
1.65 h
59Fe
60Fe
44.503 d
1.5 106 a
60Ni
26.223
s-process
The n_TOF project and its results
56Fe
57Fe
58Fe
91.72
2.2
0.28
Perugia, November 14th, 2012
61Fe
6m
paolo.milazzo@ts.infn.it
Seeds of the s-process - (n,γ) x-sections of 62Ni
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
First branching point along the s-process path
(n,γ) x-sections of 63Ni
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
First branching point along the s-process path
(n,γ) x-sections of 63Ni
Sample prepared at Paul Scherrer Institute

NiO powder

Total mass: 1156 mg

Diameter: 20 mm

Enrichment in 63Ni: ~ 11 % (= 108.4 mg)

63Ni

encapsulated in a cylinder made of PEEK
(Polyetheretherketone)

Activity: 470 GBq
/ 62Ni content ~ 12 %
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
First branching point along the s-process path
(n,γ) x-sections of 63Ni
63Ni:
First (n,γ) measurement in the resonance region
63Ni-sample
62Ni-sample
Preliminary results
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
First branching point along the s-process path
(n,γ) x-sections of 63Ni
Maxwellian Averaged Cross Sections
[combination of RRR (<10 keV, n_TOF) and URR (> 10 keV, JENDL)]
Submitted to PRL
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
Now opening !
(n,α) x-sections of 33S, 59Ni
First (n,α) measurement at n_TOF !
with a Chemical Vapor Deposition (CVD) diamond
or MicroMegas detectors
CVD diamond
detector
n
a
Isotope of interest
etc.
59Ni, 10B, 33S, 149Sm,
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
Now opening !
(n,α) x-sections of 33S, 59Ni
Last week a measurement of the 59Ni(n, α) reaction has been
completed with a mosaic-detector.
Sample: 516 kBq (174 mg 59Ni), 1.5 cm diameter
59Ni
The n_TOF project and its results
sample
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
Future EAR-2
flight-path ≈19 m at 90⁰ with respect to the proton beam
New
experimental
area at 19 m (EAR-2)
n_TOF target
Experimental
area at 185 m
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
Future EAR-2
The main advantages of EAR-2 will be:
 Neutrons fluxes on average increased by a factor 25
(with respect to EAR-1)
 Very small mass samples (< 1 mg)
 Very small cross-sections
 Much shorter time scales measurement
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
Future EAR-2
 very small samples
important candidates :
79Se, 90Sr, 93Zr, 107Pd, 135Cs, 147Pm, 163Ho,171Tm, 182Hf, 204Tl
 very small cross sections
important candidates
86Kr, 88Sr, 138Ba, 140Ce, 208Pb;
isotopes of C, O, Ne, Mg
 short measuring times
important candidates
64Zn, 70Ge, 76Ge, 80,82Kr, 86,87Sr, 95,96Mo, 104Pd, 164,166Er, 198Hg
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
EAR-2, when?
n_TOF EAR1 will restart after LS1
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
EAR-2, experiments “in preparation”
1. Measurement of the 25Mg(n,α)22Ne cross section
2. Neutron capture measurement of the s-process branching point 79Se
3. Destruction of the cosmic γ-ray emitter 26Al by neutron induced
reactions
4. Measurement of 7Be(n,p)7Li and 7Be(n,α)4He cross sections, for the
cosmological Li problem
5. ...
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
Summary
Neutron cross sections are key quantities for studying stellar
evolution and nucleosynthesis.
n_TOF offers the best conditions to obtain these nuclear physics
quantities with the required accuracy.
The n_TOF Collaboration is carrying on an extensive plan to
measure cross sections relevant for nuclear astrophysics, in
particular for s-process nucleosynthesis studies.
Opportunities for obtaining new data for presently inaccessible
nuclei (using extremely low quantities of material) will be soon
open.
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it
Publications
Isotope
Reference
24,25,26Mg
PRC 85 (2012) 044615
62Ni
Submitted to PRC
63Ni
Submitted to PRL
90Zr
PRC 77 (2008) 035802
91Zr
PRC 78 (2008) 045804
92Zr
PRC 81 (2010) 055801
93Zr
Submitted to PRC
94Zr
PRC 84 (2011) 015801
96Zr
PRC 84 (2011) 055802
139La
PRC 75 (2007) 035807
151Sm
PRL 93 (2004) 161103 – PRC 73 (2006) 034604
186,187,188Os
PRC 82 (2010) 015802 – PRC 82 (2010) 015804
204Pb
PRC 75 (2007) 015806
206Pb
PRC 76 (2007) 045805
207Pb
PRC 74 (2006) 055802
209Bi
PRC 74 (2006) 025807
The n_TOF project and its results
Perugia, November 14th, 2012
paolo.milazzo@ts.infn.it