A personal view of the shape of things to
come in Explosive Nuclear Astrophysics
PJ Woods
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University of Edinburgh
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Elemental abundances in novae ejecta
1.35 MSun ONe nova
J. José, M. Hernanz, C. Iliadis. Nucl Phys A, 777, (2006), 550-578
Presolar grains
o Grains of nova origin are
thought to have a large
30Si/28Si ratio.
o Abundance of 30Si is
determined by the
competition between the
30P β+ decay and the
30P(p,γ)31S reaction rate.
Andrew M Davis. University of Chicago
Novae Nucleosynthesis
(p,γ)
31Cl
32Cl
33Cl
34Cl
30S
31S
32S
33S
β+
(γ,p)
27P
28P
29P
30P
31P
26Si
27Si
28Si
29Si
30Si
30P(p,γ)31S
reaction rate using new resonance data
However, key resonance strengths, ωγ , based on
systematic values for proton spectroscopic factors
 
2J  1
1  2
( 2 J 1  1)( 2 J T  1)

use transfer reactions to estimate Гp for (p,γ) reactions
where resonance has Гp<< Гγ , ωγ is proportional to Гp.
Гp α Pl (barrier penetration factor) X S(spectroscopic factor)
σtransfer = σDWBA X S
New technique for (d,n) studies of (p,γ) resonance strengths
with GRETINA γ-array and S800 spectrometer
PJW, H Schatz et al., NSCL, April 2013
~106 30P 30 MeV/u ions on CD2 target
Measure σ(d,n)INT  Гp for
strong resonances
31S
gamma spectrum
CD2
CH2
5143 keV
6327 keV
Analysis - A Kankainen
Astrophysically relevant levels
31
in S
6833
T=0.6 GK
6636
6583
6542
6394
6393
6377
6357
6327
6283
6259
6159
6138
+
5/2
3/2
1+
30
P+p
T=0.4 GK
T=0.2 GK
T=0.1 GK
Sp=6130.9(4) keV
31
S
Reaction calculations of Γp from data being performed by F Nunes
Galactic abundance distribution of the cosmic
γ-ray emitter 26Al
INTEGRAL satellite telescope - 2.8(8) Msun of 26Al in our galaxy
[R. Diehl, Nature 439 45(2006)]
Mg-AlinCycle
Hydrogen burning
Mg – Al Cycle
26
25
Si
27
Al
26
Si
28
Si
Al
27
Al
6s
24
Mg
25
1Myr
Mg
26
Mg
MD1
ED1
Direct measurement of 26gAl(p,γ)27Si reaction on
188 keV resonance, PRL 96 252501(2006)
 lower energy resonances may play dominant
role for destruction of 26Al burning in W-R stars?
High resolution d(26gAl,p)27Al study of analog states of 27Si
resonances using Edinburgh TUDA Si array @ Triumf
proton
150 MeV 26gAl  (CD2)n target
Ibeam~ 5*108 pps
0  increasing excitation energy
Astrophysically
Important
Region
Exotic reaction since Jπ = 5+ for 26gAl!
8097 5/2+
9/2+
8043 9/2−
7948 11/2+
7806 9/2+
7664 9/2+
7444 13/2+
7402 11/2+
7292 13/2+
7175 9/2+
Key analog states
Future 26mAI(3He,d)27Si study on TSR storage ring@ISOLDE
In-ring target chamber & heavy-ion
recoil detection system in UHV
isomer can be excited in
core collapse supernovae
-influences ‘extinct’ 26Al
observed in meteorites as
excess 26Mg
In-ring DSSD System for ultra-high resolution (d,p), (p,d)
and (3He,d) transfer studies of astrophysical resonances
ISOL-SRS project
For ultra high resolution mode resolution should be entirely limited
by transverse beam emittance
 resolutions approaching 10 keV FWHM attainable
T Davinson
TSR@ISOLDE – Injection of RIBs into ring at MeV/u energies
Spokesperson K Blaum (MPIK)
entire issue of EPJ 207 1-117 (2012)
ISOLDE site (west) side
23.3m
24.6m
3m
Proposed layout to fit the TSR at the west side:
- Installation above the CERN infrastructure-tunnel
18
The 15O(,)19Ne reaction: the nuclear
trigger of X-ray bursts
Reaction regulates flow between the hot CNO cycles and rp process
 critical for explanation of amplitude and periodicity of bursts
The Hot CNO Cycles
Key unknown - α-decay probability from excited state at
-4
19
4.03 MeV in Ne compared to γ-decay, predicted to be ~ 10
8m
Study of the p(20Ne,2H)19Ne transfer reaction on the ESR@GSI
PJW, Y Litvinov et al.
108 20Ne ions
@ 50 MeV/u
ESR
1013 H2/cm2
gas target
Electron
cooler
A few hours of data
from test run on ESR
DT Doherty, PhD Thesis (2014)
Nucleosynthesis above Fe
Se
Ge
~1%
Zn
Ni
Fe
s-process: tb<tn
~50%
tb>tn
~ 50%
Puzzle of the origin of heavy ‘p-nuclei’ – abundant
proton-rich isotopes eg
92
Mo and
96
Ru
Supernova shock
passing through
O-Ne layers of
progenitor star
Predicted p-process abundances compared to
observed abundances
Arnould & Goriely Phys. Rep. 384,1 (2003)
Study of
96
97
Ru(p,γ) Rh reaction with decelerated beams
using the ESR storage ring at GSI
Fully stripped
ions
96 44+
Ru
Gas Stripper
Carbon Foil
Stripper
ions injected
@ 100 MeV/u
Reduced to
Pioneering new technique on ESR (Heil, Reifarth) – heavy recoils
detected with double-sided silicon strip detector (Edinburgh)
Particle detectors
Position distribution of recoiling
ions measured by DSSD
Gas jet
σ(p,γ)= 3.6(5) mb ~10 MeV/u
New DSSD system being developed (Edinburgh/GSI/Frankfurt)
for use in UHV on ESR to measure p-process capture reactions
in Gamow burning energy region – test run Autumn 2014.
Observations of Elemental Abundances in old metal poor stars:
 Evidence for robust r-process mechanisms
(C. Sneden, J.J. Cowan, et al.)
However, for elements below Z ~50 eg Yttrium evidence of
need for a second astrophysical mechanism/site
Sites of the r-process
r-process related to environments with high-neutron
density and high temperature.
Type II supernovae prime suspects…
Neutron star mergers and accretion disks in
-ray bursts promising alternatives.
Not enough is known at
present about the physics
to create realistic models
First direct evidence for neutron star merger - kilonova
Hubble space telescope images of afterglow of a
gamma-ray burst, Berger et al. arXiv:1306
Accessing the r-process path @ RIKEN and FAIR
b-delayed n-emission
branchings
(final abundances)
b-decay half-lives
(progenitor abundances,
process speed)
Masses (Sn)
(location of the path)
Advanced Implantation Detector Array (AIDA) will be used
for decay studies of r-process nuclei at RIBF and FAIR
Compact high density ASIC electronics instrumentation for multi-channel
Double-sided Silicon Strip Detectors (DSSD)
238
U fission fragments from
BIG RIPs @ RIKEN
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AIDA Test at
RIKEN May 1st
for 10 days
First full use of AIDA system will be in conjunction with
EURICA gamma-ray array on BIG RIPs separator@RIKEN
 Accepted proposal, PI Alfredo Estrade
to measure simultaneously masses, half-lives and
spectroscopy of nuclei in N~56 region of r-process
Are nuclear shell effects responsible for anomalous
abundances of light r-process elements in metal poor stars?
Double shell closure at 90Se56 ?
BRIKEN collaboration formed for proposed campaign of
β-n measurements on Big RIPS separator@RIKEN
Also plans to couple to Total Absorption Spectroscopy system
 GT – strength function measurements
Direct and indirect neutron induced reaction studies
• Direct studies with small radioactive target samples will
benefit from the new EAR-2 n_ToF facility @ CERN and
the high intensity FRANZ facility@Frankfurt
• New ideas should be explored for ‘neutron targets’ for
RIBs eg Reifarth/Litvinov storage ring/reactor idea PR
ST- accelerators and beams 17, 014701 (2014).
• Indirect/surrogate methods eg Coulex ( eg R3B@FAIR),
transfer reactions (eg TSR@ISOLDE) need to be
explored in much greater depth for reproducing (n,γ)
reactions with radioactive species.
Summary
• variety of techniques and facilities needed to address
key reactions and properties of unstable nuclei for
explosive nuclear astrophysics
• need world class ISOL and fragmentation facilities in
Europe to lead this burgeoning area of science