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)