Studies of r-process nuclei with fast radioactive beamsStudies of r-process nuclei with fast radioactive beams

Fernando MontesNational Science Superconducting Cyclotron

Joint Institute for Nuclear Astrophysics

Supernova 2002bo in NGC 3190

• Motivation: Origin of the elements heavier than iron• Signatures of different nucleosynthesis processes in the solar system and in the abundances of metal-poor stars

• Nuclear properties required for an understanding of the r-process• R-process experiments at the NSCL• Conclusions

Supernova 1997bs in M66

OutlineOutline

Nucleosynthesis is a gradual, still ongoing process:

Life of a star

Death of a star(Supernova, planetary nebula)

Interstellarmedium

Remnants(White dwarf,

neutron star, black hole)

Nucleosynthesis:Stable burning

Nucleosynthesis:Stable burning

Nucleosynthesis:Explosive burning

Nucleosynthesis:Explosive burning

H, He

continuousenrichment,increasingmetallicity

Condensation

M~104..6 Mo

108 y

106..10 y

M > 0.7MoStar formation

Dust mixing

NucleosynthesisNucleosynthesis

Dense cloudsBig Bang

Creation of the elements

pro

ton

s

neutrons

Mass knownHalf-life knownnothing known

Big Bang

Cosmic Rays

stellar burning

rp process

p process

s process

r process

Most of the heavy elements (Z>30) are formed in neutron capture processes, either the slow (s) or rapid (r) process

p processLight element primary process

LEPP

Creation of the elements: nucleosynthesis

Contribution of different processes

Ba: s-processEu: r-process

Ba

Eu

Contribution of the diff. processes to the solar abundances

s-process: Astrophysical model

p-process: Astrophysical model

r-process:Abundance of

enriched-r-process star

LEPP = solar-s-p-r

F. Montes Nuclear Astrophysics

Metal-poor star abundances

“Solar r”

agreement stars and solarunderabundantMetallicity (amount of iron) ~ time

Very metal-poor stars are enriched by just a few nucleosynthesis

events

R-process + LEPP

F. Montes Nuclear Astrophysics

Element formation beyond iron involving rapid neutron capture and radioactive decay

Waiting point(n,)-(-n) equilibrium

-decay

Seed

igh neutron density

G(Z,A)~ nnT-3/2 G(Z,A+1)

eSn(Z,A+1)/kT

Y(Z,A)

Y(Z,A+1)

Waiting point approximation

R-process basics

Masses: • Sn location of the path• Q, Sn theoretical -decay properties, n-capture rates

-decay half-lives(progenitor abundances, process speed)

Fission rates and distributions:• n-induced• spontaneous• -delayed -delayed n-emission

branchings(final abundances)

n-capture ratesSmoothing progenitor abundances during freezeout

Seed productionrates

-physics ?

Nuclear physics in the r-process

F. Montes Nuclear Astrophysics

Future: low energy beams1-2 MeV/u

Fast beams fromfragmentation with Coupled Cyclotrons

r-process beams at the NSCL Coupled Cyclotron Facility

Primary beam100-140 MeV/u

Primary beam100-140 MeV/u Be targetBe target

Tracking(=Momentum)

TOF

Delta E

r-processbeam

Experimental station

F. Montes Nuclear Astrophysics

Silicon PIN Stack

4 x Si PIN DSSD (

•Implantation DSSD: x-y position (pixel), time•Decay DSSD: x-y position (pixel), time

6 x SSSD (16) Ge

Implantation station: The Beta Counting System (BCS)

Veto light particles from A1900

Beta calorimetry

105Zr

Fit (mother, daughter, granddaughter, background)

T1/2

F. Montes Nuclear Astrophysics

Implantation station: The Neutron Emission Ratio Observer (NERO)

Boron Carbide Shielding

Polyethylene Moderator

BF3 Proportional Counters

3He ProportionalCounters

G. Lorusso, J.Pereira et al., PoS NIC-IX (2007)

F. Montes Nuclear Astrophysics

Implantation station: The Neutron Emission Ratio Observer (NERO)

Nuclei with -decay Nuclei with -decay AND neutron(s)

Pn-values

Measurement of neutron in “delayed” coincidence with -decay

F. Montes Nuclear Astrophysics

Implantation station: The Segmented Germanium Array (SeGA)

16 SeGA detectors around the BCS Efficiency ~7.5% at 1 MeV

W.Mueller et al., NIMA 466, 492 (2001)

F. Montes Nuclear Astrophysics

Implantation station: The Segmented Germanium Array (SeGA)

-delayed gamma spectroscopy of daughter

F. Montes Nuclear Astrophysics

Known before

NSCL Experiments done

• P. Hosmer, P. Santi, H. Schatz et al. • F. Montes, H. Schatz et al.• B. Tomlin, P.Mantica, B.Walters et al.• J. Pereira, K.-L.Kratz, A. Woehr et al.• M. Matos, A. Estrade et al.

Critical region78Ni

107Zr

NSCL reach

120Rh

Astrophysics motivated experiments

69Fe

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

70 120 170 220

Mass (A)

Ab

un

da

nc

e (

A.U

.)Observed Solar Abundances

Model Calculation: Half-Lives fromMoeller, et al. 97

Same but with present 78Ni Result

Predicted 78Ni T1/2: 460 ms

P. Hosmer et al. PRL 94, 112501 (2005)

Exp. 78Ni T1/2 = 110 ms +100

-60

I)-decay half-live of 78Ni50 waiting point

Half-live of ONE single waiting-point nucleus: Speeding up the r-process clock Increase matter flow through 78Ni bottle-neck Excess of heavy nuclei (cosmochronometry)

F. Montes Nuclear Astrophysics

II) “Gross” nuclear structure around 120Rh45 from -decay properties

F. Montes et al., PRC73, 35801 (2006)

Inferring (tentative) nuclear deformations with QRPA model calculations

•120Rh Pn value direct input in r-process calculations •Half-lives and Pn-values sensitive to nuclear structure• Over-predictions for Ru and Pd isotopes: larger Q-values or problems in the GT strength• Need microscopic calculations beyond QRPA

F. Montes Nuclear Astrophysics

II)Probing the strength of N=82 shell-closure from -delayed -spectroscopy

B.Walters, B.Tomlin et al., PRC70 034414 (2004)

• No evidence of shell-quenching when approaching shell closure in Pd isotopes up to N=74• Need more E(2+) data at 74<N<82• R-process abundances at A~115 are directly affected by the strength of shell closure• Experimental evidence is mixed: 130Cd E(2+) does not show evidence of quenching

10

100

1000

10000

62 63 64 65 66 67 68

N

Hal

f-life

(ms) Zr literature

Zr preliminary

QRPA Def.

QRPA Spher.

J.Pereira et al., in preparation

•Possible double-magic Z=40, N=70: Effects from spherical shape of 110Zr70 observable at 66<N<70?•Shorter half-life of (potential) waiting-point 107Zr affect predicted r-process abundances at A~110•Mean-field model calculations predict N=82 shell-quenching accompanied by a new harmonic oscillator shell at N=70

III) -decay properties of Zr isotopes beyond mid-shell N=66

F. Montes Nuclear Astrophysics

Nuclear Physics

• Theoretical models are in the majority of cases within a factor of 3 from observed abundance• Models agree within a factor of 3-4 except for In (Z=49) and Lu (Z=71)

Same “astrophysical model”, different nuclear physics …

This “agreement” however is not good enough to calculate LEPP isotopic abundances

Montes et al. AIP Conf. Proc., 947, 364 (2007).

F. Montes Nuclear Astrophysics

Light element primary process (LEPP)

If it involves high neutron densities peak should be here

If it involves low neutron densities peak should be here instead

LEPP = solar-s-p-r

Reach for future r-process experiments with new facilities (ISF, FAIR, RIBF…)

Future Facility Reach(here ISF)

Known before

NSCL Experiments done

NSCL reach

78Ni

107Zr

Almost all -decay half-lives of r-process nuclei at N=82 and N=126 will be reachable with ISF

F. Montes Nuclear Astrophysics

•Despite many years of intensive effort, the r-process site and the astrophysical conditions continues to be an open question. New LEPP process complicates the situation

•Besides being direct r-process inputs, beta-decay properties of exotic nuclei turned out to be an effective probe for nuclear structure studies of exotic nuclei

•R-process experimental campaigns at NSCL provide beta-decay properties of r-process nuclei and comparisons with theoretical calculations will improve astrophysical r-process calculations

•New facilities will largely extend the r-process regions accessible (FAIR, ISF). Meanwhile, new observations (SEGUE) and new measurements of exotic n-rich nuclei are highly necessary

Conclusions

F. Montes Nuclear Astrophysics

Multiple nucleosynthesis processes in the early universe

More metal-poor stars

Solar r

Slope indicatesratio of light/heavy

Some stars havelight elementsat solar level

Heavy r-patternrobust andagrees with solar

Light elementsat high enrich-ment fairly robust and subsolar

[Y/E

u][A

g/E

u]

[Eu/Fe] [Eu/Fe]

Z=62

Z=57

Z=47

Z=39

Metal poor star =r-process

+Light element primary process

[La/

Eu]

[Sm

/Eu]

Qian & Wasserburg Phys. Rep 442, 237 (2007); Montes et al. ApJ 671 (2007)

F. Montes Nuclear Astrophysics

• High selectivity even with mixed (“cocktail”) beams because due to its high energy, relevant particle properties can be detected (TOF, energy losses …)

• Fast beam – negligible decay losses (~100 nanoseconds..)

• Production of broad range of rare isotope beams with a single primary beam

Typical beam energies: 50-1000 MeV/nucleonTypical new rare isotope beams can be produced within ~ 1h

Summary features of fast beams from fragmentationSummary features of fast beams from fragmentation

Fast beams from fragmentation complement other techniques and they have these particular features :

F. Montes Nuclear Astrophysics

GapB,Be,Li

-nuclei12C,16O,20Ne,24Mg, …. 40Ca,44Ti

Fe peak(width !)

s-process peaks (nuclear shell closures)

r-process peaks (nuclear shell closures)

Au Pb

U,Th

Nuclear physics behind everything…

0 50 100 150 200 250m a ss num b e r

10-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

num

be

r fra

ctio

n

Mass number