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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
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