Transcript Stellar neutron capture rates and the s process

Astrophysics with spallation sources
Franz Käppeler
Karlsruhe Institute of Technology



(n,g) cross sections for the s process
operating spallation facilities: LANSCE, J-PARC, n_TOF
& examples for time-of-flight studies
comparison of spallation facilities and future options
1000
Xe
Te
Kr
Se
100
(mb)
MAXWELLIAN AVERAGED CROSS SECTION
status of s-process (n,g) cross sections
and remaining quests
Ge
Zn
Cr
Ni
Fe
Ru
Ba
Pd
Dy
Gd
Er
Hf
current quests in s-process
nucleosynthesis
Pt
Os
Hg
Ce
Sr
• model tests:
Sm
Cd
W
Mo
Yb
Nd
Pb
Zr
•
•
Sn
10
•
•
1
20
even-even nuclei
40
60
•
80
100
NEUTRON NUMBER
120
•
16 s-only isotopes
± 1%
nn,T, r via branchings
~20 unstable isotopes ± 5%
presolar grains: anomalies in ~20 elements
with 75 isotopes
± 1%
± 5%
bottle neck
reactions:
15 n-magic nuclei
neutron poisons:
abundant light elements
neutron sources: (a,n) reactions on 13C
and 22Ne
thermally excited el. and inel. scattering
states:
yields at A < 60:
(n,a) and (n,p) cross
sections
status and requests
needed: cross sections with uncertainties between 1 and 5%
for complete set of isotopes from 12C to 210Po,
including unstable samples
Maxwellian averaged cross sections
 s(En) measured by time of flight and folded with
stellar neutron spectrum
‹s› =
‹sv›
vT
2
=
∫ s(En) En exp(-En/kT) dEn
√π ∫ En exp(−En/kT) dEn
 MACS directly measured via activation
s-process energies
 low mass stars: kT = 8 keV and 25 keV
massive stars: kT = 25 and 90 keV
s(En) via TOF for 1 < En < 300 keV
pulsed neutron sources
low energy (VdG, FRANZ)
high energy with moderator
(spallation sources, e-linacs)
En = ½ m v2
resolution DEn/En = 2Dt/t + 2Ds/s
g
g
LANSCE @ Los Alamos
800 MeV proton linac plus PSR
17 n/p
Luhan Neutron Scattering Center:
pulsed, moderated spallation source
for time-of-flight studies
thermal < En < 300 keV, Dt = 250 ns
WNR:
unmoderated tungsten spallation target
using the 800 MeV pulsed proton beam
from the LANSCE linac
0.5 < En < 750 MeV, Dt ~150 ps
DANCE @ Luhan (FP 14)
„designed for neutron capture reactions on small quantities,
of order 1 mg, of radioactive or rare stable nuclei“
 pulse width:
250 ns
 rep rate:
20 Hz
 moderator:
water
 neutron energy:
th – 300 keV
 flight path:
20 m
 neutron beam diameter:
10 mm
 equipment:
BaF2 calorimeter,
160 modules
http://lansce.lanl.gov/about.shtml
Nucl. Sci. Eng. 106 (1990) 208
DANCE array: 160 BaF2 modules
(n,g) reactions →small samples,
small cross sections
the 62Ni problem:
integrated neutron flux in
massive stars too small,
reaction flow NOT in
equilibrium → strong impact
of single cross sections
abundance ratio
the 62Ni problem
62Ni(n,g)63Ni
35
22.6
12.5
mass number
 TOF
25.8 ± 3.7
37.0 ± 3.2
12.5 ± 4.0
26.8 ± 5.0
(2008)
(2005)
(1983)
(1975)
 activation
20.2 ± 2.1 (2009)
23.4 ± 4.6 (2008)
26.1 ± 2.6 (2005)
(courtesy I. Dillmann)
smallest sample ever used in TOF
237Np,
400 mg
J-PARC in Japan
Japan Proton Accelerator Research Complex
Japan Spallation Neutron Source
J-PARC beam parameters
LINAC
Ions
Negative
Hydrogen
3 GeV synchrotron
Energy for RCS injection
400 MeV
Extraction Beam Energy 3 GeV
600 MeV
Repetition
25 Hz
Average Beam Current
333 μA
Extraction Scheme
Fast
Energy for ADS
Peak Current
50 mA
Beam Pulse Length
500 μs
Repetition Rate
50 Hz
Extraction Beam Energy
50 GeV
synchrotron Average Beam Current
50 n/p
30 Gev (50 Gev)
25 μA (15 μA)
Repetition
0.2 Hz ~ 0.7 Hz ( 0.3 Hz)
Extraction Scheme
Slow, and Fast
ANNRI @ J-PARC
Accurate Neutron-Nucleus Reaction measurement Instrument
ANNRI – inside/outside
ANNRI specifications
 proton beam power:
17.5 kW → 120 kW (→ 1 MW)
 pulse width:
double pulse (100 ns separated by 600 ns)
 rep rate:
25 Hz
 moderator:
coupled hydrogen moderator
 neutron energy:
0.0015 eV < En < 50 keV
 intensity at 1 MW at 21.5 m:
4.3×107 n/cm2/s (1.5 < En < 25 meV)
9.3×105 n/cm2/s (0.9 < En < 1.1 eV)
6.0×106 n/cm2/s (0.9 < En < 1.1 keV)
 beam diameter:
3, 7, 22 mm
 equipment:
Ge spectrometer at 21.5 m
NaI spectrometer at 27.9 m
http://j-parc.jp/MatLife/en/instrumentation/ns_spec.html
JKPS 59 1781, 2011
ANNRI: intensity and beam profile
107Pd(n,g)
with Ge spectrometer
sample mass 137 mg
n_TOF - the CERN spallation neutron
source
20 GeV protons on lead block
 300 neutrons per proton
 most luminous n-source worldwide
 high resolution TOF facility
J-PARC in Japan
Neutron detection
Neutron creation
1.4 GeV
50 MeV
1st collimator (Ø=11 cm)
halo cleaning and first
shaping
 + filter station
neutrons from
spallation target
2nd collimator (Ø=1.8/8 cm)
beam shaping
Experimental Area
185 m from the spallation target
 location of samples and detectors
n_TOF coordinates
 proton beam power:
20 GeV, 9 kW
 pulse width:
6 ns
 rep rate:
0.4 Hz
 moderator:
(borated) water
 neutron energy:
th < En < 1 GeV
 intensity at 185 m:
0.2 – 2·105 n/s/decade
 energy resolution:
0.4% @ 1 MeV
 neutron beam diameter:
30 (70) mm
 equipment:
TAC, C6D6 for (n,g)
FIC, PPAC for (n,f)
pCVD, Mgas for (n,cp)
https://twiki.cern.ch/twiki/bin/view/NTOF/
CERN / INTC-O-011
high resolution in neutron energy
g-ray detection: C6D6 scintillators
Sample
changer
C6D6
C6D6
•
•
•
186Os
•
Al can
environmental background
•
197Au
(2 g, 79 %)
187Os (2 g, 70 %)
188Os (2 g, 95 %)
(1.2g)
flux normalization
(using Ratynski and Macklin
high accuracy cross section data)
Neutron beam
•
natPb
•
natC
(2 g)
in-beam gamma background
(0.5 g)
neutron scattering background
n_TOF results for 62Ni
previous TOF measurements
(courtesy Iris Dillmann)
n_TOF
n_TOF
2009: new target with separate moderator
in-beam g rays from 1H(n,g) substantially
reduced
(borated water in saturated conditions, 1.28% H3BO3)
x13
x1.2
gravitational cut-off at 0.02 eV
borated water moderator
63Ni(n,g)
– first results from n_TOF (2011)
courtesy by Claudia Lederer
TAC with 40 BaF2 modules
TAC data for 241Am(n,g)
Increase of the RRR limit above 150 eV
present URR limit about 320 keV
astrophysics measurements at n_TOF
campaign 2002-4
(n,g)
151Sm
204,206,207,208Pb, 209Bi
campaign 2009-13
(n,g)
54,56,57Fe
58,60,62,63Ni
24,25,26Mg
90,91,92,94,96Zr, 93Zr
33S(n,a)
186,187,188Os, 139La
26Al(n,p)
59Ni(n,p)
19 isotopes (2 radioactive)
19 full publications
n_TOF upgrade
EAR-2
New
Experimental
Area (EAR-2)
~ 20 m
10
m
EAR-1
(at 185 m)
Flight-path length : ~20 m
at 90° respect to p-beam direction
expected neutron flux enhancement
drastic reduction of the t0 flash
n_TOF target
proposed EAR-2
Feb 2, 2012
n-flux x25, n-rate x10, lower background
Dear Colleagues,
EAR2 @20 m from pit, above ground
Kind regards
Enrico
n_TOF target pit
Existing hole
To be built
I'm very proud to announce that this morning the INTC committee
"strongly recommended " to the Research Board our proposal for
EAR-2.ISRSergio Bertolucci, Director for Research and Computing,
was present during the discussion
and gallery
gave (@10
a positive
Technical
m from reaction.
pit)
comparison of pulsed neutron sources
Facility
Neutron flux at Repetition Flight
sample
rate
path
[cm-2 s-1 dec-1]
[Hz]
[m]
Pulse
width
[ns]
Neutron
energy
range
[eV]
Karlsruhe VdG
1·104
250K
0.8
0.7
103-2·105
LANSCE
5·105
20
20
250
th -105
J-PARC
3·106
25
21
2x100
th -105
n_TOF
5·104
0.4
185
6
th -109
GELINA at Geel
5·104
800
30
1
th -106
Facility
Lansce
J-PARC
n_TOF
n/p
17
45
300
Upgrades
Neutron flux
at sample
FRANZ
1∙107
Lansce
5∙107
J-PARC
3·107
n_TOF
2·106