Astrophysics with spallation sources

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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

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status of s-process (n,g) cross sections and
remaining quests

• current quests in s-process nucleosynthesis
• model tests 16 s-only isotopes
  1
• nn,T, r via
  branchings
• 20 unstable
  isotopes 5
• presolar grains anomalies in 20 elements
• with 75
  isotopes 1
• bottle neck 15 n-magic nuclei
  5
• reactions
• neutron poisons abundant light elements
• neutron sources (a,n) reactions on 13C
• and 22Ne
• thermally excited el. and inel. scattering
• states

even-even nuclei
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status and requests
needed cross sections with uncertainties
between 1 and 5 for complete
set of isotopes from 12C to 210Po,
including unstable samples
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s(En) measured by time of flight and folded
with stellar neutron spectrum
Maxwellian averaged cross sections
sv 2 ? s(En) En exp(-En/kT) dEn
s
vT
vp ? En exp(-En/kT) dEn

• MACS directly measured via activation

5
s(En) via TOF for 1 lt En lt 300 keV
s-process energies

• low mass stars kT 8 keV and 25 keV massive
  stars kT 25 and 90 keV

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En ½ m v2resolution DEn/En 2Dt/t 2Ds/s
pulsed neutron sources
g
low energy (VdG, FRANZ)
g
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LANSCE _at_ 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 lt En lt 300 keV, Dt 250 ns
WNR unmoderated tungsten spallation target
using the 800 MeV pulsed proton beam from the
LANSCE linac 0.5 lt En lt 750 MeV, Dt 150 ps
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DANCE _at_ 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
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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
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the 62Ni problem
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smallest sample ever used in TOF
237Np, 400 mg
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J-PARC in Japan
Japan Proton Accelerator Research Complex
Japan Spallation Neutron Source
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J-PARC beam parameters
LINAC
Ions Negative Hydrogen
Energy for RCS injection 400 MeV
Energy for ADS 600 MeV
Peak Current 50 mA
Beam Pulse Length 500 µs
Repetition Rate 50 Hz
3 GeV synchrotron
Extraction Beam Energy 3 GeV
Repetition 25 Hz
Average Beam Current 333 µA
Extraction Scheme Fast
50 n/p
Extraction Beam Energy 30 Gev (50 Gev)
Average Beam Current 25 µA (15 µA)
Repetition 0.2 Hz 0.7 Hz ( 0.3 Hz)
Extraction Scheme Slow, and Fast
50 GeV synchrotron
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ANNRI _at_ J-PARC
Accurate Neutron-Nucleus Reaction measurement
Instrument
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ANNRI inside/outside
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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 lt En lt 50 keV
• intensity at 1 MW at 21.5 m 4.3107 n/cm2/s
  (1.5 lt En lt 25 meV) 9.3105 n/cm2/s (0.9 lt En
  lt 1.1 eV) 6.0106 n/cm2/s (0.9 lt En lt 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_spe
c.html JKPS 59 1781, 2011
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ANNRI intensity and beam profile
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107Pd(n,g) with Ge spectrometer
sample mass 137 mg
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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

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J-PARC in Japan
Neutron detection
Neutron creation
1.4 GeV
50 MeV
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neutrons from spallation target
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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 lt En lt 1 GeV
• intensity at 185 m 0.2 2105 n/s/decade
• energy resolution 0.4 _at_ 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
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high resolution in neutron energy

• 186Os (2 g, 79 )
• 187Os (2 g, 70 )
• 188Os (2 g, 95 )
• Al can
• environmental background
• 197Au (1.2g)
• flux normalization
• (using Ratynski and Macklin
• high accuracy cross section data)
• natPb (2 g)
• in-beam gamma background
• natC (0.5 g)
• neutron scattering background

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n_TOF results for 62Ni
previous TOF measurements
(courtesy Iris Dillmann)
n_TOF campaign to determine (n, g) cross sections
of all stable Fe and Ni isotopes and of 63Ni
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2009 new target with separate moderator

• in-beam g rays from 1H(n,g) substantially
  reduced
• (borated water in saturated conditions, 1.28
  H3BO3)

gravitational cut-off at 0.02 eV
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borated water moderator
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63Ni(n,g) first results from n_TOF (2011)

courtesy by Claudia Lederer
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TAC with 40 BaF2 modules
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TAC data for 241Am(n,g)
Increase of the RRR limit above 150 eV
present URR limit about 320 keV
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astrophysics measurements at n_TOF
campaign 2002-4 (n,g) 151Sm 204,206,207,208Pb,
209Bi 24,25,26Mg 90,91,92,94,96Zr,
93Zr 186,187,188Os, 139La
19 isotopes (2 radioactive) 19 full publications
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n_TOF upgrade
NewExperimentalArea (EAR-2)
EAR-2
20 m
10 m
n_TOF target
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
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proposed EAR-2
n-flux x25, n-rate x10, lower background
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comparison of pulsed neutron sources
Facility Neutron flux at sample cm-2 s-1 dec-1 Repetition rate Hz Flight path m Pulse width ns Neutron energy range eV
Karlsruhe VdG 1104 250K 0.8 0.7 103-2105
LANSCE 5105 20 20 250 th -105
J-PARC 3106 25 21 2x100 th -105
n_TOF 5104 0.4 185 6 th -109
GELINA at Geel 5104 800 30 1 th -106