r-process: observations, theory, experiment

H. Schatz Michigan State University National Superconducting Cyclotron Laboratory Joint Institute for Nuclear Astrophysics

1. Observations: do we need s,r,p-process and LEPP? 2. r-process (and LEPP?) models 3. r-process experiments

SNR 0103-72.6 Credit: NASA/CXC/PSU/S.Park et al. Origin of the heavy elements in the solar system

s-process: secondary • nuclei can be studied Æ reliable calculations • site identified • understood? Not quite …

r-process: primary • most nuclei out of reach • site unknown

p-process: secondary (except for νp-process)

Æ Look for metal poor`stars

(Pagel, Fig 6.8) To learn about the r-process Heavy elements in Metal Poor Halo Stars

CS22892-052 (Sneden et al. 2003, Cowan)

2 1

+ solar r CS 22892-052

)

H /

X CS22892-052

( g

o red (K) giant

oldl stars - formed before

e located in halo

Galaxyc was mixed n distance: 4.7 kpc theya preserve local

d mass ~0.8 M_sol n

pollutionu from individual

b [Fe/H]= −3.0 nucleosynthesisa events [Dy/Fe]= +1.7

recall:

element number[X/Y]=log(X/Y)-log(X/Y)solar

What does it mean: for heavy r-process? For light r-process? • stellar abundances show r-process • process is not universal • process is universal • or second process exists (not visible in this star) Conclusions depend on s-process Look at residuals: Star – solar r Solar – s-process – p-process

s-processSimmerer from Simmerer (Cowan et etal.) al. /Lodders (Cowan et al.) s-processTravaglio/Lodders from Travaglio et al.

-0.50 -0.50

-1.00 -1.00

-1.50 -1.50 log e log e

-2.00 -2.00

-2.50 -2.50 30 40 50 60 70 80 90 30 40 50 60 70 80 90 Element number Element number

ÆÆNeedNeed reliable reliable s-process s-process (models (models and and nu nuclearclear data, data, incl. incl. weak weak s-process) s-process) ÆÆClearlyClearly something something is is going going on on for for Z Z < < ~50 ~50 (“light” (“light” p-process p-process elements) elements) Need to look at many stars … Look at many stars – consistent pattern?

CS22892-052

HD 115444 For highly r-process BD+1703248 enriched stars

CS 31082-001 Æ Very consistent pattern throughout except for U,Th HD221170 in CS 31082-001

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 What about less enriched stars?

Montes et al. to be published Light r / Heavy r (Eu) Heavy r / Heavy r (Eu) Slope indicates ratio of light/heavy changes for less enriched stars Solar r

Some stars have [La/Eu] light r-elements [Y/Eu] at solar level

Light r-elements at high enrichment fairly robust and Heay r-pattern [Ag/Eu] [Sm/Eu] subsolar – part of robust and main r-process(?) agrees with [Eu/Fe] [Eu/Fe] solar – main Enrichment with main r-process r-process ÆConsistent with second process producing also Sr-Ag LEPP, identified by Travaglio et al. 2004 Honda et al. 2006

Ivans et al. 2006 Why –1 slope ? recall:

[X/Y]=log(X/Y) - log(X/Y)solar [Y/Eu] = [Y/Fe] + [Fe/Eu] = [Y/Fe] – [Eu/Fe]

Const (e.g. as a function of [Fe/H]

ÆÆPrimaryPrimary process process makes makes Y Y ÆÆmademade with with Fe? Fe? The LEPP pattern? LEPP = HD122563 – (small) main r (black data points) LEPP = solar – s-process – main r (red data points)

ÆÆLEPPLEPP produces produces a a consistent consistent pattern pattern ÆÆItIt contributes contributes to to solar solar abundances abundances (Montes et al. 20007 to be published, see also Qian&Wasserburg 2007) The r-process

Temperature: ~1-2 GK Density: ~300 g/cm3 (~60% neutrons !) neutron capture timescale: ~ ms - μs

Rapid neutron capture β-decay

Seed

r

e b Equilibrium favors

m

u

n “waiting point” (γ,n) photodisintegration

n

o

t

o

r

P Neutron number Pt

Xe

Ni

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) r-process in Supernovae ?

Most favored scenario for high entropy:

Neutrino heated wind evaporating from proto neutron star in core collapse

+ νe neutrino sphere (νe+p Æ n+e weak opacity because only few protons present)

- νe neutrino sphere (ve+n Æ p+e strong opacity because many neutrons present)

proto neutron star weak interactions regulate n/p ratio: + (n-rich) νe+p Æ n+e faster as νe come from deeper - and are therefore hotter ! νe+n Æ p+e therefore matter is driven neutron rich How does the r-process work ? Neutron capture ! Recent calculation

Martinez-Pinedo et al. 2006 (NIC proceedings)

MainMain problem: problem: conditions conditions needed needed for for full fullr-processr-process not not achieved achieved ••acousticacoustic mechanism? mechanism? (Arizona (Arizona group) group) •• reverse reverse shock shock (interaction (interaction of of fast fast wind wind with with slow slow main main ejecta)(Munich ejecta)(Munich group) group) •• OR OR don’t don’t need need ν ν-wind-wind for for full full r-process r-process – – look look for for other other scenarios? scenarios? What about LEPP? Trying to fit with n-capture flow

Low nn

High nn

Æ Low nn and high nn fit low Z but not high Z multi-component? A=130 overproduction!

Æ Low nn also fits small high Z abundances ??? Why nuclear physics I - Sensitivity of abundances

Sensitivity to astrophysics Sensitivity to nuclear physics 1 10 Hot bubble ETFSI-Q masses Classical model ETFSI-1 masses Same nuclear physics 0 10 Same r-process model

-1 10

-2 10 Abundance

-3 10

Freiburghaus et al. 1999 -4 10 100 120 140 160 180 200 220 Mass number Mass number

Contains information about: But convoluted with nuclear physics: • n-density, T, time • masses (set path) (fission signatures) •T1/2, Pn (Y ~ T1/2(prog), • freezeout key waiting points set timescale) • neutrino presence • n-capture rates • which model is correct • fission barriers and fragments Why nuclear physics II: disentangling LEPP and main-r

Remember before: r-process = solar – s-process needed accurate s-process

Isotopic: • s-process models (with solar s-only) • s-process data

LEPP = Solar – s-process – main-r (– p-process)

Elemental: Isotopic: • rII halo star abundances Reliable solar abundances Isotopic: • main r-process model • r-process data A=80-110

Becomes now possible ÆÆNowNow progress progress on on all all pieces pieces of of the the puzzle puzzle possible possible H. Schatz Nuclear physics in the r-process

Fission rates and distributions: • n-induced • spontaneous β-delayed n-emission • β-delayed branchings (final abundances)

β-decay half-lives (abundances and process speed) n-capture rates • in slow freezeout • maybe in a “weak” r-process ?

ν-physics ? Seed production rates (ααα,ααn, α2n, ..) Masses (Sn) (location of the path) H. Schatz Some recent r-process motivated experiments

ANL/CPT (Cf source) Remeasured masses with high precision

ORNL (ISOL) (d,p) and Coulex

GSI (in-flight fission) Masses (IMS) (Matos & Scheidenberger et al.)

GSI (in-flight fission) ISOLTRAP masses Half-lives, Pn values (Santi, Stolz et al., Kurtukian-Nieto et al.)

MSU/NSCL TOF masses ISOLDE (ISOL) (Matos, Estrade et al.) Decay spectroscopy (Dillmann et al. 2003)

MSU/NSCL (fragmentation) Half-lives, Pn values (Hosmer, Santi, Montes, Pereira Hennrich, Quinn, et al.)

GANIL (fragmentation) Decay spectroscopy, Sorlin et al. Coupled Cyclotron Facility since 2001 r-process beams at the NSCL Coupled Cyclotron Facility

86 136 86Kr,Kr, 136XeXe beam beam r-process ~140~140 MeV/u MeV/u beam

TOF dE Be target Tracking Be target (=rigidity Bρ)

AdvantagesAdvantages of of fast fast RIB RIB from from fragmentation: fragmentation: •• no no decay decay losses losses •• any any beam beam can can be be produced produced •• multiple multiple measurements measurements in in one one •• high high sensitivity sensitivity Particle Identification Z)

r-process nuclei

78 78NiNi DoublyDoubly

Energy loss in Si (Æ MagicMagic ! ! 78Ni 77Ni

75Co 74Co 73Co

Time of flight (Æ m/q – corrected for Bρ) Particle ID (Pereira, Hennrich, et al.)

(corrected for momentum Preliminary dependence)

r-process

111 Energy loss Mo

107Zr 105Y

velocity Setup

Measure:Measure: ••ββ-decay-decay half-lives half-lives •• Branchings Branchings for for β β-delayed-delayed n-emission n-emission

Detect:Detect: • Particle type (TOF, dE, p) New NSCL Neutron detector • Particle type (TOF, dE, p) NERO •• Implantation Implantation time time and and location location ••ββ-emission-emission time time and and location location 3He + n -> t + p •neutron-•neutron-ββcoincidencescoincidences

neutron Fast Fragment Beam Si Stack (fragment. 140 MeV/u 86Kr) NERO – Neutron Emission Ratio Observer

3He Proportional BF3 Proportional Counters Counters

Specifications: • 60 counters total 3 (16 He , 44 BF3) • 60 cm x 60 cm x 80 cm polyethylene block • Extensive exterior shielding • 43% total neutron efficiency (MCNP)

Polyethylene Boron Carbide Moderator Shielding NERO Assembly Nero efficiency

NERO Efficiency vs. Neutron Energy

50 13C 40 11B 30 20 51V

Efficiency (%) 10 252Cf 0 Scaled MCNP 0.001 0.01 0.1 1 10 Curve Neutron Energy (MeV) Decay curves

Decay-curves fits (mother, daughter, granddaughter)

106 107 105Zr Zr Zr

Branchings for neutron emission (Pn) from counting β-n coincidences

β− Pn probes strength near gs and near Sn (Z,A) Æ First constraint on strength distribution n

Sn (Z+1,A-1) γ (Z+1,A) Results from earlier experiment in Ni-Cu region H. Schatz Impact of 78Ni half-life on r-process models

Observed Solar Abundances 1.E+021.E+02 Model Calculation: Half-Lives from Moeller, et al. 97 1.E+011.E+01 SameSeries4 but with present 78Ni Result

1.E+001.E+00 Abundance (A.U.) Abundance Abundance (A.U.) Abundance 1.E-011.E-01

1.E-021.E-02 7070 120120 170 220 Mass (A) Æneed to readjust r-process model parameters ÆCan obtain Experimental constraints for r-process models from observations and solid nuclear physics Æ remainig discrepancies – nuclear physics ? Environment ? Neutrinos ? Need more data NSCL r-process campaign – MSU/Mainz/Notre Dame/Maryland

Known before

NSCL reach

Future Facility Reach (here ISF – RIKEN,FAIR

NSCL Experiments done Towards an experimental nuclear physics basis for the r-process

Final isotopes, for which >90% of progenitors in the r-process path can be reached experimentally for at least a half-life measurement today Existing facilities Future facility

ÆÆTheseThese abundances abundances can can be be compared compared with with observations observations toto test test r-process r-process models models 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

Nuclear Physics Experiments Astronomical Observations

Astrophysical Models Associated: Nuclear Theory • ANL Core institutions: • LANL • Notre Dame • U of Arizona • MSU • UC Santa Barbara • U. of Chicago • UC Santa Cruz • VISTARS (Mainz,GSI) Some conclusions

Interesting times for nuclear astrophysics and for our attempts to understand the origin of the elements

• Astrophysics and nuclear physics are growing closer together (JINA, Exzellenzcluster “Origin and Structure of the Universe”, …

• Major advances in astronomy will provide detailed information on how the r-process has enriched the early Galaxy

• With next generation nuclear physics rare isotope accelerator facilities we are at the verge of entering broad stretches of the r-process path experimentally ÆCan start to compare abundance patterns between models and observations ÆCan start to disentangle multiple processes isotopically

• With advances in astro- and nuclear theory there is hope to solve the problem of the r-process r-process experiments LEPP collaboration

Mainz: MSU: F. Montes (MSU) S. Hennrich J. Pereira T.C. Beers (MSU) O. Arndt P. Hosmer J.J. Cowan (Oklahoma) K.-L. Kratz F. Montes T. Elliot (MSU) B. Pfeiffer R.R.C. Clement K. Farouqi (Mainz, Chicago) A. Estrade R. Gallino (Torino) S. Liddick M. Heil (GSI) PNNL P.F. Mantica K.-L. Kratz (Mainz) P. Reeder C. Morton B. Pfeiffer (Mainz) W.F. Mueller M. Pignatari (Torino) M. Ouellette Notre Dame: H. Schatz (MSU) E. Pellegrini M. Quinn P. Santi A. Aprahamian H. Schatz A. Woehr M. Steiner A. Stolz Maryland: B.E. Tomlin W.B. Walters