Studies of r-process nuclei with fast radioactive beams
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Studies of r-process nuclei with fast radioactive beams
Fernando MontesNational Science Superconducting Cyclotron
Joint Institute for Nuclear Astrophysics
Supernova 2002bo in NGC 3190
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• 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
Outline
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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:Explosive burning
H, He
continuousenrichment,increasingmetallicity
Condensation
M~104..6 Mo108 y
106..10 y
M > 0.7MoStar formation
Dust mixing
Nucleosynthesis
Dense cloudsBig Bang
Creation of the elements
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prot
ons
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 process Light element primary processLEPP
Creation of the elements: nucleosynthesis
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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
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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
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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
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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
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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
Be target
Tracking(=Momentum)
TOF
Delta E
r-processbeam
Experimental station
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F. Montes Nuclear Astrophysics
Silicon PIN Stack4 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
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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)
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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
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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)
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F. Montes Nuclear Astrophysics
Implantation station: The Segmented Germanium Array (SeGA)
-delayed gamma spectroscopy of daughter
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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
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1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
70 120 170 220
Mass (A)
Abu
ndan
ce (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)
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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
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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
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10
100
1000
10000
62 63 64 65 66 67 68
N
Hal
f-life
(ms) Zr literature
Zr preliminaryQRPA 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
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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).
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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
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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
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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
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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)
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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 fragmentation
Fast beams from fragmentation complement other techniques and they have these particular features :
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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 -1310 -1210 -1110 -10
10 -910 -810 -710 -610 -510 -410 -310 -210 -1100
num
ber fr
actio
n
Mass number