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Home , Electron capture, Neutron emission

The origin of heavy elements in the solar system

(Pagel, Fig 6.8)

each process contribution is a mix of many events ! 1 Abundance pattern: “Finger print ” of the r-process ? and Peak Peak

Solar abundance of the elements r-process only (subtract s,p processes) ) 6 Abundance (Si(Si ==AbundanceAbundance 10 10

Element number (Z) But: sun formed ~10 billion years after big bang: many contributed to elements ‰ This could be an accidental combination of many different “fingerprints ” ? ‰ Find a that is much older than the sun to find “fingerprint ” of single event 2 Heavy elements in Metal Poor Halo Stars

CS22892-052 red (K) giant located in halo distance: 4.7 kpc mass ~0.8 M_sol [Fe/H]= −−−3.0 recall: [Dy/Fe]= +1.7

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

old stars - formed before Galaxy was mixed they preserve local pollution from individual events 3 A single (or a few) r -process event(s)

CS22892-052 (Sneden et al. 2003) 1 solar r Cosmo Chronometer 0

-1 NEW: CS31082-001 with U (Cayrel et al. 2001) -2 40 50 60 70 80 90 Age: 16+ - 3 Gyr element number (Schatz et al. 2002 other, second ApJ 579, 626) r-process to fill main r-process this up ? matches exactly solar r-pattern (weak r-process) conclusions ? 4 More rII stars

Solar r-process elements from many events

J. Cowan

5 A surprise

J. Cowan

‰ A new process contributing to Y, Sr, Zr (early Galaxy only? Solar? In this case: some traditional “r-contributions” to solar are not (main) r-process) ‰ Call it LEPP (Light Element Primary Process) 6 Overview heavy element nucleosynthesis

process conditions timescale site s-process T~ 0.1 GK 10 2 yr Massive stars (weak) τ 7- 5-6 (n-capture, ...) n~ 1-1000 yr, n n~10 and 10 yrs Low mass AGB stars (main) 8/cm 3 r-process T~1-2 GK < 1s Core collapse supernovae ? τ µ 24 3 (n-capture, ...) n ~ s, n n~10 /cm Star Mergers ? p-process T~2 -3 GK ~1s Core collapse supernovae ? (( γ,n), ...) Type Ia supernovae?

Light Element ??? Primary Process (LEPP) ? Weak r-process? Failed r-process? νp-process? Primary s-process?

7 The r-process

Temperature: ~1-2 GK Density: 300 g/cm3 (~60% !) timescale: ~ 0.2 µs

Rapid neutron capture βββ-decay

Seed

Equilibrium favors (γγγ,n) “““waiting point ”””

Neutron number

8 Waiting point approximation

Definition: ASSUME (n, γ)-(γ,n) equilibrium within isotopic chain

How good is the approximation ? This is a valid assumption during most of the r-process BUT: freezeout is neglected Freiburghaus et al. ApJ 516 (2999) 381 showed agreement with dynamical models

Consequences During (n, γ)-(γ,n) equilibrium abundances within an isotopic chain are given by:

2/3 + +  + πh2  Y(Z, A 1) = G(Z, A 1) A 1 2 nn   exp( Sn / kT ) Y(Z, A) 2G(Z, A)  A mukT 

• time independent • can treat whole chain as a single nucleus in network • only slow beta decays need to be calculated dynamically • neutron capture rate independent (therefore: during most of the r-process n-capture rates do not matter !) 9 Waiting point approximation continued

In the approximation of continuous Sn and abundances Y the maximum abundance in an isotopic chain occurs for Y(Z, A +1) =1 Y(Z, A)

For a given temperature and neutron density one can solve for Sn (assuming A~A+1 and G=1)

 3/2  2 m kT  S = kT ln u   n   πh2    nn 2  T 3  S = 9  ln(T )− ln(n )+ 78.460 in MeV n 11.6042 9 n 

‰ r-process runs at fixed neutron (for given condition) 10 11 H. Schatz in the r-process

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

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

ννν-phyiscs ? Seed production rates ( ααα ,αααααα n, ααα2n, ..) Masses (Sn) (location of the path) 12 Sensitivity of r-process to astro and nuclear physics

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

Contains information about: But convoluted with nuclear physics: • n-density, T, time • masses (set path) (fission signatures) •T1/2 , Pn (Y ~ T 1/2(prog) , • freezeout key waiting points set timescale) • presence • n-capture rates • which model is correct • fission barriers and fragments 13 S2n (MeV) Mo Zr Shell quenching effectShellquenching masses/r-processon Ru r-process path r-process ETFSI-1 Pd Cd Neutron Neutron number 14 S2n (MeV) Mo Zr Shell quenching effectShellquenching masses/r-processon Ru ETFSI-1 Pd Cd Neutron Neutron number (N=82 quenched) ETFSI-Q distinguish 15 Endpoint of the r-process

r-process ended by n-induced fission

or

(different paths for different conditions)

(Goriely & Clerbaux A&A 348 (1999), 798

n-induced fission β-delayed fission spontaneous fission

n-capture (DC) β− (Z,A) (Z,A) fission fission fission (Z,A+1) (Z,A+1) (Z+1,A) 16 Consequences of fission

Fission produces A~A end /2 ~ 125 nuclei modification of abundances around A=130 peak

fission products can serve as seed for the r-process - are processed again into A~250 region via r-process - fission again fission cycling !

Note: the exact endpoint of the r-process and the degree and impact of fission are unknown because:

• Site conditions not known – is n/seed ratio large enough to reach fission ? (or even large enough for fission cycling ?) • Fission barriers highly uncertain • Fission fragment distributions not reliably calculated so far (for fission from excited states !) 17 Role of beta emission

β Neutron rich nuclei can emit one or more neutrons during -decay if Sn

(the more neutron rich, the lower S n and the higher Q β)

βββ−−− (Z,A) n

Sn (Z+1,A-1) γγγ

(Z+1,A)

If some fraction of decay goes above S n in daughter nucleus - ν)ν)ν) then some fraction Pn of the decays will emit a neutron (in addition to e and

(generally, competes favorably with γ-decay - strong interaction !) 18 Effects: during r-process : none as neutrons get recaptured quickly during freezeout • modification: of final abundance • late time neutron production (those get recaptured)

Calculated r-process production of elements (Kratz et al. ApJ 403 (1993) 216):

before β-decay after β-decay

smoothing effect from βββ-delayed n emission ! 19 Cs (55) Cs131 Cs132 Cs133 Cs134 Cs135 Cs136 Cs137 Cs138 Cs139 Cs140 Cs141 Cs142 Cs143 Cs144 Cs145 Cs146 Cs147 > 99 > 99 > 99 19.00 > 99 > 99 > 99 63.70 24.94 1.70 1.78 1.01 0.59 0.32 0.23 Xe130 Xe131 Xe132 Xe133 Xe134 Xe135 Xe136 Xe137 Xe138 Xe139 Xe140 Xe141 Xe142 Xe143 Xe144 Xe145 Xe146 Xe (54) r-process > 99 > 99 > 99 > 99Pn39.68=0% 13.60 1.73 1.24 0.30 1.15 0.90 I129 I130 I131 I132 I133 I134 I135 I136 I137 I138 I139 I140 I141 I142 I143 I144 I145 I (53) waiting point > 99 > 99 > 99 > 99 > 99 > 99 83.40 24.50 6.49 2.28 0.86 0.43 Te (52) Te128 Te129 Te130 Te131 Te132 Te133 Te134 Te135 Te136 Te137 Te138 Te139 Te140 Te141 Te142 Te143 Te144 > 99 > 99 > 99 > 99 > 99 19.00 17.50 2.49 1.40 P =99.9% Sb (51) Sb127 Sb128 Sb129 Sb130 Sb131 Sb132 Sb133n Sb134 Sb135 Sb136 Sb137 Sb138 Sb139 Sb140 Sb141 Sb142 Sb143 > 99 > 99 > 99 > 99 > 99 > 99 > 99 1.66 0.82 Sn (50) Sn126 Sn127 Sn128 Sn129 Sn130 Sn131 Sn132 Sn133 Sn134 Sn135 Sn136 Sn137 Sn138 Sn139 Sn140 Sn141 Sn142 > 99 > 99 > 99 > 99 > 99 56.00 39.70 1.20 1.12 In (49) In125 In126 In127 In128 In129 In130 In131 In132 In133 In134 In135 In136 In137 In138 In139 In140 In141 2.36 1.60 1.09 0.84 0.61 0.26 0.28 0.20 0.18 137 1 Example: impact of P n for Sb Cd (48) Cd124 Cd125 Cd126 Cd127 Cd128 Cd129 Cd130 Cd131 Cd13210 Cd133 Cd134 Cd135 Cd136 Cd138 Cd139 Cd140 1.24 0.65 0.51 0.43 0.34 0.27 0.20 A=136 A=137 Ag123 Ag124 Ag125 Ag126 Ag127 Ag128 Ag129 Ag130 Ag131 Ag132 Ag133 Ag135 Ag136 Ag137 Ag138 Ag139 Ag (47) ( 99%) ( 0%) 0.29 0.17 0.16 0.10 0.11 0.06 0.05 Si) 6 76 77 78 79 80 81 82 83 1084 0 85 86 87 88 89 90 91 92 r-process waiting point

10 -1 Pn=0% solar

abundance (per 10 abundance (per Pn=99% 10 -2 125 130 135 140 145 mass number A 20 Summary: Nuclear physics in the r-process

Quantity Effect

Sn neutron separation path energy βββ T1/2 -decay half-lives • abundance pattern • timescale βββ Pn -delayed n-emission final abundance pattern branchings fission (branchings • endpoint and products) • abundance pattern? • degree of fission cycling G partition functions • path (very weakly) σσσ NA< v> neutron capture rates • final abundance pattern during freezeout ? • conditions for waiting point approximation

21 National Superconducting Cyclotron Laboratory at Michigan State University New Coupled Cyclotron Facility – experiments since mid 2001

Ion Source: 86 Kr beam

86 Kr beam 140 MeV/u

Tracking TOF start 86 Implant beam Kr hits Be (=Momentum) target and in detector and observe decay fragments Separated beam TOF stop of r-process dE detector nuclei

Fast beam fragmentation facility – allows event by event particle identification 22 Fragment yield after Br selection Fragment yield after Br selection First r-process experiments at new NSCL CCF facility (June 02)

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

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

neutron Fast Fragment Beam Si Stack (fragment. 140 MeV/u 86 Kr)

25 NSCL BCS – Beta Counting System

• 4 cm x 4 cm active area • 1 mm thick • 40-strip pitch in x and y dimensions ->1600 pixels

Si SiSi BCS βββ

26 NERO – Neutron Emission Ratio Observer

3He Proportional BF 3 Proportional Counters Counters

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

Polyethylene Carbide Moderator Shielding 27 NERO Assembly

28 Nero efficiency

NERO Efficiency vs. Neutron Energy

50 13C 40 %)

(( 11B 30 20 51V Efficiency 10 252Cf 0 0.001 0.01 0.1 1 10 Scaled MCNP Curve Neutron Energy (MeV)

29 Particle Identification

r-process nuclei

78 Ni Doubly

Energy loss in Si (Z) (Z) Si Si inin lossloss Energy Energy Magic ! 78Ni 77Ni

Fast RIB from fragmentation: • no decay losses 75Co 74Co 73Co • any beam can be produced • multiple measurements in one • high sensitivity Time of flight (m/q) 30 H. Schatz Decay data

time (ms) time (ms) time (ms) Fast radioactive beams: • No decay losses • Rates as low as 1/day useful ! • Mixed beam experiments easy 31 Results for the main goal: 78 Ni (14 neutrons added to stable Ni)

Decay of 78 Ni : major bottle-neck for synthesis of heavy elements in the r-process Managed to create 11 of the doubly magic 78 Ni nuclei in ~ 5 days

Time between arrival and decays: Result for half-life: +100 110 -60 ms Statistical Analysis Compare to theoretical estimate used:470 ms

time (ms)

‰ Acceleration of the entire r-process ‰ Models need to be adjusted to explain observed abundance distribution

32 Neutron Data

Nuclei with decay detected With neutron in addition

420 420

Nn 370 370

320 320 arb units) units) arb arb 76 76

( Ni

(arb units) units) (arb (arb Ni E 73 E 73

∆ Co ∆ Co 270 270

220 220 350 400 450 500 550 350 400 450 500 550 TOF (arb units) TOF (arb units)

N P = n neutron detection efficiency n ε Nβ n (neutrons seen/neutrons emitted) 33 Results ( Hosmer et al.)

DF+CQRPA Borzov et al. 2005, QRPA: Moller et al. 2003, Shell model: Lisetzky & Brown 2005

T1/2 (s)

A A Preliminary

Pn (%)

Preliminary

34 A A H. Schatz Impact of 78 Ni half-life on r-process models

Observed Solar Abundances 1.E+021.E+02 Model Calculation: Half-Lives from Moeller, et al. 97

Series4 1.E+011.E+01 Same but with present 78Ni Result

1.E+001.E+00 Abundance (A.U.) Abundance Abundance (A.U.) Abundance 11..EE--0011

1.E-021.E-02 7070 120 120 170 220 Mass (A) ‰need to readjust r-process model parameters ‰Can obtain Experimental constraints for r-process models from observations and solid nuclear physics ‰ remainig discrepancies – nuclear physics ? Environment ? ? Need more data 35 Recent r-process related experiments Mass measurements (need 1:10 6) N=126 Penning Traps TOF N=82 (spectrometers, storage rings) ANL Trap Neutron capture rates: Jyvaskyla use transfer such as (d,p) GSI Trap ESR Ring ORNL (d,p)

TRIUMF Trap

CERN/ISOLDE Seed producing reaction rates: Trap 9Be( γ,n) with HIgS Neutrino physics CERN/ISOLDE

NSCL T1/2 Pn TOF

GSI/Mainz T1/2 Pn N=50 Future facility reach RIKEN T1/2 β-decay studies: (FRIB)

T1/2 , Pn ORNL T1/2 Pn NSCL T1/2 Pn Penning Trap Mass Meausrements (stopped beams)

Example: TRIGA Penning Trap (Mainz) Rare Production Techniques: Uniqueness of FRIB

• Target and fragmentation by light (ISOLDE/HRIBF/TRIUMF ) Target/ Source Post beam Accelerator Acceleration • Neutron induced fission (2-step target) ( SPIRAL2/TRIUMF ) Neutrons/Photons target Post Accelerator Acceleration • In-flight Separation following projectile fragmentation/fission ( RIKEN,FAIR,FRIB ) beam Accelerator Beam Beams used without stopping target Fragment Separator Post Acceleration Gas cell catcher/ion source

Hendrik Schatz NNPSS 2012, Slide 40 Slid 40 Fission yields

SPIRAL2 projected production

Hendrik Schatz, NNPSS 2012 Slide 41 NSCL and FRIB Laboratory 506 employees, incl. 36 faculty, 59 graduate and 71 undergraduate students (as of August 6, 2012) NSCL user group is part of the FRIB User Organization (over 1,250 members) ° FRIB will be the world ’s premier rare isotope user facility, a national user facility for the U.S. Department of Energy Office of Science

2011 2009 2003

Enabling over 1250 users to do world-leading rare-isotope science

42 FRIB Layout example: experiment

Fast beams: Gas stopped beams: Fast Beam Area Gas Stopping Stopped Beam Area Reaccelerated Beam Area • Charge exchange Gas • Mass measurements • Drip line • Laser spectroscopy • Knockout, Coulex Stopping • TOF masses • Decay studies Isotope harvesting ReA3 ReA6,9,12 Fragment Reaccelerator Reaccelerator separatorFragment Reaccelerator Separator ReA3 reaccelerated beams: ReA6-12 reaccelerated beams: • Astrophysical rates • High spin • Lighter nuclei transfer • Transfer reactions • Coulex • γγγ-spectroscopy

Target

Front End Folding Segment 2 Beam Delivery System Linac Segment 1 LINAC

Folding Segment 1

Linac Segment 2 Linac Segment 3

, Slide 43 Overview of the FRIB Facility

Existing NSCL

Target

Accelerator Systems

Linac Support Front End

Cryogenic Facility

Sherrill NN2012 , Slide 44 Rendered Perspective Southeast View

Sherrill NN2012 , Slide Driver Linear Accelerator

Front End

Linac Segment 1

Linac Segment 3

Beam Delivery System

Folding Segment 2

Linac Segment 2

° Tunnel is • 550 ft long • 70 ft wide Folding Segment 1 • 25 ft underground

Sherrill NN2012 , Slide Overview FRIB Reaccelerators, and Experimental Stations ReA3 Exp All buildings exist Completed Summer 2013

ReA12 Completed not yet Fall 2012 funded Existing

ReA6 MSU will move forward

Rare from FRIB LINAC 30 meters

Hendrik Schatz NNPSS 2012, Slide 47 Slid 47 FRIB On Track, Moving Toward Construction

° Project Start 6/2009 ° Conceptual design completed 9/2010 (CD-1) ° Preliminary design 2010-2012 • CD-2/3A (civil) review in April 2012 ° Site prep 2012 • DOE approves pilings for earth ret. ~140M committed ° Civil construction begins 2012 • Pending DOE approval ° Final design 2012-2013 • CD-3B (technical) review in 2013 ° Technical construction begins 2013 ° Early project completion 2019 (completion 2021) ° Total project cost $680M ($585 Federal)

, Slide 48 NSCL/FRIB current view

Major investments have been made – construction underway

49 Why is it called FRIB ???

1. frib 17 up, 6 down birf spelled backwards

2. frib 4 up, 12 down

A word that can be used to describe happiness, joy etc. Commonly replaces 'wow', 'cool' or 'great'. FRIB: a key instrument for nuclear astrophysics

rp-process in X-ray bursts/Novae/Supernovae s-process in AGB stars • Direct reaction rates (SECAR) • Harvesting of targets for n-capture on branchpoints • Indirect reaction rate studies • Masses and p-drip line

Supernova cores p-process in supernovae • capture rates with • Direct reaction rates charge exchange reactions r-process β Explosive Si burning in • decay properties supernovae ( 44 Ti, ..) • Masses • Indirect neutron capture rate studies • Reaction rates (SECAR) • Fission barriers • Indirect reaction rate studies

Neutron star crusts • Fusion reactions of n-rich isotopes • rates with charge exchange • Masses • Complete mapping of n-drip line

H. Schatz, September 2012 51 Rare isotopes are common in many astrophysical scenarios FRIB is critical to address a broad range of astrophysics questions Overview of common r process models

• Site independent models:

• [nn, T, t parametrization (neutron density, temperature, irradiation time)]

• S, Y e, t parametrization (Entropy, electron fraction, expansion timescale) • Core collapse supernovae • Neutrino wind • Jets • Explosive burning • mergers

52 A star ready to die

Neutron star forms Matter evaporated off the hot neutron star (size ~ 10 km radius) r-process site ? 53 Cooling Shock

54 How does the r-process work ? Neutron capture !

55 τ S, Y e, parametrization

1. Consider a blob of matter with entropy S, electron abundance Y e in NSE 2. Expand adiabatically with expansion timescale τ 3. Calculate abundances - what will happen: 1. NSE 2. QSE (2 clusters: p,n, α and heavy nuclei) 3.3.3.ααα -rich freezeout (for higher S) (3a and aan reactions slowly move matter from p,n, α cluster to heavier nuclei – once a heavy nucleus is created it rapidly captures a-particles

as a result large amounts of A~90-100 nuclei are produce which serve as seed for the r-process 4. r-process phase initially: n, γ – γ,n equilibrium later: freezeout

56 Evolution of equilibria: cross : most abundant nucleus colors: degree of equilibrium with that nucleus (difference in chemical potential)

from Brad Meyers website 57 Results for neutron to seed ratios: (Meyer & Brown ApJS112(1997)199)

n/seed is higher for

• lower Y e (more neutrons)

• higher entropy (more light particles, less heavy nuclei – less seeds) (or: low density – low 3a rate – slow seed assembly)

• faster expansion (less time to assemble seeds)

2 possible scenarios:

1) high S, moderate Y e 2) low S, low Y e 58 r-process in Supernovae ?

High entropy neutrino driven wind:

Neutrino heated wind evaporating from proto neutron star in core collapse

ννν ν + e neutrino sphere ( e+p ‰ n+e weak opacity because only few present)

ννν - e neutrino sphere (v e+n ‰ p+e strong opacity because many neutrons present)

proto neutron star weak interactions regulate n/p ratio: ν + ννν (n-rich) e+p ‰ n+e faster as e come from deeper ν - and are therefore hotter ! e+n ‰ p+e therefore matter is driven neutron rich

59 Results for r-process

Takahashi, Witti, & Janka A&A 286(1994)857 (for latest treatment of this scenario see Thompson, Burrows, Meyer ApJ 562 (2001) 887)

A~90 overproduction can ’’’t produce A~195 anymore

density artificially reduced by density artificially reduced by factor 5.5 factor 5

artificial parameter to get A~195 peak (need S increase) 60 other problem: the ααα effect Breakthrough in Theoretical Astrophysics Neutrino driven wind

Hoffman et al. 2008

Winteler et al. 2012

Overproduction Mass Number Korobkin et al. 2012 Neutron star mergers MHD Supernova Jets Abundance

° We now have several robust, rather self-consistent r-process models ° To test them against observations ‰ Need nuclear data now! ° Goal: reveal model deficiencies and site physics signaturesH. Schatz, September 2012 61 r-process in neutron star mergers ?

62 Ejection of matter in NS-mergers Rosswog et al. A&A 341 (1999) 499

Destiny of Matter: red: ejected blue: tails green: disk black: black hole

(here, neutron stars are co-rotating – tidally locked)

63 r-process in NS-mergers

large neutron/seed ratios, fission cycling !

But: Y e free parameter …

64 Summary theoretical scenarios

NS-mergers Supernovae Frequency 1e-5 - 1e-4 2.2e-2 (per yr and Galaxy) Ejected r-process mass 4e-3 – 4e-2 1e-6 – 1e-5 (solar masses) Summary less frequent but more frequent and more ejection less ejection

65 What does galactic chemical evolution observations tell us ?

Argast et al. A&A 416 (2004) 997

Supernovae NS mergers Model star average with error observations

Average ISM

Dots: model stars

‰ Neutron Star Mergers ruled out as major contributor 66