r-process: observations, theory, experiment · Temperature: ~1-2 GK Density: ~300 g/cm3 (~60%...
Transcript of r-process: observations, theory, experiment · Temperature: ~1-2 GK Density: ~300 g/cm3 (~60%...
r-process: observations, theory, experimentH. Schatz
Michigan State UniversityNational Superconducting Cyclotron Laboratory
Joint Institute for Nuclear Astrophysics
SNR 0103-72.6Credit: NASA/CXC/PSU/S.Park et al.
1. Observations: do we need s,r,p-process and LEPP?
2. r-process (and LEPP?) models3. r-process experiments
(Pagel, Fig 6.8)
s-process: secondary• nuclei can be studied
reliable calculations• site identified• understood? Not quite …
r-process: primary• most nuclei out of reach• site unknown
p-process: secondary(except for νp-process)
Origin of the heavy elements in the solar system
Look for metal poor`starsTo learn about the r-process
Heavy elements in Metal Poor Halo Stars
old stars - formed beforeGalaxy was mixedthey preserve localpollution from individualnucleosynthesis events
recall:[X/Y]=log(X/Y)-log(X/Y)solar
CS22892-052red (K) giantlocated in halodistance: 4.7 kpcmass ~0.8 M_sol[Fe/H]= −3.0[Dy/Fe]= +1.7
element number
abun
danc
e lo
g(X
/H)+
12CS22892-052 (Sneden et al. 2003, Cowan)
solar r CS 22892-052
• stellar abundances show r-process• process is universal
What does it mean: for heavy r-process? For light r-process?
• process is not universal• or second process exists(not visible in this star)
Simmerer (Cowan et al.) /Lodders
-2.50
-2.00
-1.50
-1.00
-0.50
30 40 50 60 70 80 90
Element number
log
e
Travaglio/Lodders
-2.50
-2.00
-1.50
-1.00
-0.50
30 40 50 60 70 80 90
Element numberlo
g e
Conclusions depend on s-process
s-process from Simmerer et al. (Cowan et al.) s-process from Travaglio et al.
Need reliable s-process (models and nuclear data, incl. weak s-process)Clearly something is going on for Z < ~50 (“light” p-process elements)
Need reliable s-process (models and nuclear data, incl. weak s-process)Clearly something is going on for Z < ~50 (“light” p-process elements)
Need to look at many stars …
Star – solar r Solar – s-process – p-process
Look at residuals:
Look at many stars – consistent pattern?
CS22892-052
HD 115444
BD+1703248
CS 31082-001
HD221170
Cowan et al. NIC9 proceedings
Find more such stars ?• Only 1:1.2 Mio halo stars r-process element enhanced • Ongoing Surveys (e.g. SEGUE at Apache Point)might find 1000s of stars in relevant metallicity range
For highly r-processenriched stars
Very consistentpattern throughoutexcept for U,Thin CS 31082-001
Enrichment with main r-process
Light r / Heavy r (Eu) Heavy r / Heavy r (Eu)
What about less enriched stars?
Consistent with second process producing also Sr-AgLEPP, identified by Travaglio et al. 2004
Montes et al. to be published
Solar r
Slope indicatesratio of light/heavychanges for lessenriched stars
Heay r-patternrobust andagrees with solar – mainr-process
Some stars havelight r-elementsat solar level
Light r-elementsat high enrichmentfairly robust andsubsolar – part of main r-process(?)
[Y/Eu] [La/Eu]
[Ag/Eu] [Sm/Eu]
[Eu/Fe] [Eu/Fe]
Ivans et al. 2006
Honda et al. 2006
Why –1 slope ?
[Y/Eu] = [Y/Fe] + [Fe/Eu] = [Y/Fe] – [Eu/Fe]
recall:[X/Y]=log(X/Y) - log(X/Y)solar
Const (e.g. as a function of [Fe/H]
Primary process makes Ymade with Fe?
Primary process makes Ymade with Fe?
The LEPP pattern?
LEPP produces a consistent patternIt contributes to solar abundances
LEPP produces a consistent patternIt contributes to solar abundances
LEPP = HD122563 – (small) main r (black data points)LEPP = solar – s-process – main r (red data points)
(Montes et al. 20007 to be published, see also Qian&Wasserburg 2007)
(γ,n) photodisintegrationEquilibrium favors“waiting point”
β-decay
Temperature: ~1-2 GKDensity: ~300 g/cm3 (~60% neutrons !)
Neutron number
Prot
on n
umbe
r
Seed
Rapid neutroncapture
neutron capture timescale: ~ ms - μs
The r-process
Pt
Xe
78Ni, 79Cu first bottle necks in n-capture flow (80Zn later)79Cu: half-life measured 188 ms (Kratz et al, 1991)78Ni : half-life predicted 130 – 480 ms
2 events @ GSI (Bernas et al. 1997)
Ni
r-process in Supernovae ? Most favored scenario for high entropy:
Neutrino heated wind evaporating from proto neutron star in core collapse
protoneutron star(n-rich)
νe neutrino sphere (ve+n p+e- strong opacitybecause many neutrons present)
νe neutrino sphere (νe+p n+e+ weak opacitybecause only few protons present)
weak interactions regulate n/p ratio:
νe+p n+e+
νe+n p+e-
faster as νe come from deeperand are therefore hotter !
therefore matter is drivenneutron rich
How does the r-process work ? Neutron capture !
Main problem: conditions needed for full r-process not achieved• acoustic mechanism? (Arizona group)• reverse shock (interaction of fast wind with slow main ejecta)(Munich group)• OR don’t need ν-wind for full r-process – look for other scenarios?
Main problem: conditions needed for full r-process not achieved• acoustic mechanism? (Arizona group)• reverse shock (interaction of fast wind with slow main ejecta)(Munich group)• OR don’t need ν-wind for full r-process – look for other scenarios?
Recent calculation
Martinez-Pinedo et al. 2006 (NIC proceedings)
What about LEPP? Trying to fit with n-capture flow
Low nn and high nn fit low Z but not high Zmulti-component? A=130 overproduction!
Low nn also fits small high Z abundances???
Low nn
High nn
100 120 140 160 180 200 22010-4
10-3
10-2
10-1
100
101
Contains information about:• n-density, T, time(fission signatures)
• freezeout • neutrino presence• which model is correct
But convoluted with nuclear physics:• masses (set path)• T1/2, Pn (Y ~ T1/2(prog),
key waiting points set timescale)• n-capture rates• fission barriers and fragments
Sensitivity to astrophysics Sensitivity to nuclear physics
Why nuclear physics I - Sensitivity of abundances
Hot bubbleClassical model
Same nuclear physics
ETFSI-Q massesETFSI-1 masses
Same r-process model
Abu
ndan
ce
Mass number
Freiburghaus et al. 1999
Mass number
LEPP = Solar – s-process – main-r (– p-process)
Isotopic: • s-process models(with solar s-only)
• s-process data
Elemental:• rII halo star abundancesIsotopic:• main r-process model• r-process data A=80-110
Isotopic:Reliable solar abundances
Becomes now possible
Now progress on all pieces of the puzzle possibleNow progress on all pieces of the puzzle possible
Why nuclear physics II: disentangling LEPP and main-r
Remember before: r-process = solar – s-process needed accurate s-process
H. Schatz
Nuclear physics in the r-process
Masses (Sn)(location of the path)
β-decay half-lives(abundances andprocess speed)
Fission rates and distributions:• n-induced• spontaneous• β-delayed β-delayed n-emission
branchings(final abundances)
n-capture rates• in slow freezeout• maybe in a “weak” r-process ?
Seed productionrates (ααα,ααn, α2n, ..)
ν-physics ?
H. Schatz
Some recent r-process motivated experiments
GSI (in-flight fission)Half-lives, Pn values(Santi, Stolz et al., Kurtukian-Nieto et al.)
ISOLDE (ISOL)Decay spectroscopy(Dillmann et al. 2003)
GSI (in-flight fission) Masses (IMS)(Matos & Scheidenberger et al.)
GANIL (fragmentation)Decay spectroscopy, Sorlin et al.
ANL/CPT (Cf source)Remeasured masses with high precision
ORNL (ISOL)(d,p) and Coulex
MSU/NSCL (fragmentation)Half-lives, Pn values(Hosmer, Santi, Montes, PereiraHennrich, Quinn, et al.)
ISOLTRAP masses
MSU/NSCL TOF masses(Matos, Estrade et al.)
Coupled Cyclotron Facility since 2001
86Kr, 136Xe beam~140 MeV/u
86Kr, 136Xe beam~140 MeV/u
Be targetBe target
r-processbeam
Tracking(=rigidity Bρ)
TOF
r-process beams at the NSCL Coupled Cyclotron Facility
Advantages of fast RIB from fragmentation:• no decay losses• any beam can be produced• multiple measurements in one• high sensitivity
Advantages of fast RIB from fragmentation:• no decay losses• any beam can be produced• multiple measurements in one• high sensitivity
dE
r-process nuclei
Time of flight ( m/q – corrected for Bρ)
Ener
gy lo
ss in
Si(
Z)
77Ni78Ni
75Co 74Co 73Co
78NiDoublyMagic !
78NiDoublyMagic !
Particle Identification
107Zr105Y
111Mo
Particle ID (Pereira, Hennrich, et al.)
r-process
Ene
rgy
loss
velocity
(corrected for momentumdependence)Preliminary
New NSCL Neutron detectorNERO
Fast Fragment Beam Si Stack
neutron
3He + n -> t + p
Measure:• β-decay half-lives• Branchings for β-delayed n-emission
Measure:• β-decay half-lives• Branchings for β-delayed n-emission
Detect:• Particle type (TOF, dE, p)• Implantation time and location• β-emission time and location• neutron-β coincidences
Detect:• Particle type (TOF, dE, p)• Implantation time and location• β-emission time and location• neutron-β coincidences
(fragment. 140 MeV/u 86Kr)
Setup
NERO – Neutron Emission Ratio Observer
Boron CarbideShielding
PolyethyleneModerator
BF3 ProportionalCounters
3He ProportionalCounters
Specifications:• 60 counters total
(16 3He , 44 BF3)• 60 cm x 60 cm x 80 cm
polyethylene block• Extensive exterior
shielding• 43% total neutron
efficiency (MCNP)
NERO Assembly
NERO Efficiency vs. Neutron Energy
0
10
20
30
40
50
0.001 0.01 0.1 1 10Neutron Energy (MeV)
Effic
ienc
y (%
)
13C
11B
51V
252Cf
Scaled MCNPCurve
Nero efficiency
Decay-curves fits (mother, daughter, granddaughter)
105Zr107Zr106Zr
Decay curves
Branchings for neutron emission (Pn) from counting β-n coincidences
(Z,A)
(Z+1,A)
(Z+1,A-1)Sn
γ
n
β− Pn probes strength near gs and near SnFirst constraint on strength distribution
Results from earlier experiment in Ni-Cu region
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
70 120 170 220Mass (A)
Abu
ndan
ce (A
.U.)
Observed Solar Abundances
Model Calculation: Half-Lives fromMoeller, et al. 97
Series4
H. Schatz
Impact of 78Ni half-life on r-process models
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
70 120 170 220Mass (A)
Abu
ndan
ce (A
.U.)
Observed Solar Abundances
Model Calculation: Half-Lives fromMoeller, et al. 97
Same but with present 78Ni Result
need to readjust r-process model parametersCan obtain Experimental constraints for r-process modelsfrom observations and solid nuclear physicsremainig discrepancies – nuclear physics ? Environment ? Neutrinos ?Need more data
Future Facility Reach(here ISF – RIKEN,FAIR
NSCL r-process campaign – MSU/Mainz/Notre Dame/Maryland
Known before
NSCL reach
NSCL Experiments done
Final isotopes, for which >90% of progenitors in the r-process path can be reachedexperimentally for at least a half-life measurement
These abundances can be compared with observationsto test r-process models
These abundances can be compared with observationsto test r-process models
Future facilityExisting facilitiestoday
Towards an experimental nuclear physics basis for the r-process
Astrophysical Models
Nuclear Physics Experiments Astronomical Observations
Associated: • ANL• LANL• U of Arizona• UC Santa Barbara• UC Santa Cruz• VISTARS (Mainz,GSI)
Nuclear Theory
Core institutions:• Notre Dame• MSU• U. of Chicago
Joint Institute for Nuclear Astrophysics (JINA)a NSF Physics Frontiers Center – www.jinaweb.org
• Identify and address the critical open questions and needs of the field • Form an intellectual center for the field• Overcome boundaries between astrophysics and nuclear physics
and between theory and experiment• Attract and educate young scientists – undergraduate/graduate research
Some conclusions
Interesting times for nuclear astrophysics and for our attempts to understand the origin of the elements
• Major advances in astronomy will provide detailed informationon how the r-process has enriched the early Galaxy
• With next generation nuclear physics rare isotope accelerator facilitieswe are at the verge of entering broad stretches of the r-processpath experimentally
Can start to compare abundance patterns between models and observationsCan start to disentangle multiple processes isotopically
• With advances in astro- and nuclear theory there is hope tosolve the problem of the r-process
• Astrophysics and nuclear physics are growing closer together(JINA, Exzellenzcluster “Origin and Structure of the Universe”, …
MSU:J. PereiraP. HosmerF. MontesR.R.C. ClementA. EstradeS. LiddickP.F. ManticaC. MortonW.F. MuellerM. OuelletteE. PellegriniP. SantiH. SchatzM. SteinerA. StolzB.E. Tomlin
Mainz:S. HennrichO. ArndtK.-L. KratzB. Pfeiffer
Notre Dame:M. QuinnA. AprahamianA. Woehr
Maryland:W.B. Walters
PNNLP. Reeder
r-process experiments LEPP collaboration
F. Montes (MSU)T.C. Beers (MSU)J.J. Cowan (Oklahoma)T. Elliot (MSU)K. Farouqi (Mainz, Chicago)R. Gallino (Torino) M. Heil (GSI)K.-L. Kratz (Mainz)B. Pfeiffer (Mainz)M. Pignatari (Torino)H. Schatz (MSU)