Breakout from the hot-CNO Cycle
via the 18Ne(α,p)21Na reaction
Lou Jisonna, Northwestern University
- Motivation: astrophysical and previous
experiments
- How we do it
- Preliminary results and what’s next
X-ray Burst Scenario Model
Neutron stars:
1.4 M‫סּ‬, 10 km radius
ρ ~ 1014 g/cm3
Donor Star
(MS or RG)
Neutron Star or White Dwarf
Accretion Disk
Typical systems:
accretion rate 10-8-10-10 M‫סּ‬/yr (0.5-50 kg/s/cm2)
orbital periods 0.01-100 days
orbital separations 0.001-1 AU
The CNO-cycles & Breakout reactions
Line of no return
to CNO-cycles
(α,p)
Current work
PRC 52, R460-R463 (1995)
PRC 67, 065809 (2003)
Z (proton #)
PRL 82, 3964 (1999)
N (neutron #)
Previous studies of 18Ne(α,p)21Na
W. Bradfield et al.(PRC,59,3402,1999)
D.Groombridge et al. (PRC 66,055802,2002)
•Two measurements
disagree
•The α-widths exhaust the
Wigner limit
•The levels are not in
the Gamow window
Lab Measurement via time inverse reaction
α(18Ne,21Na)p
p(21Na,18Ne)α
{9.5 - 10.5 MeV}
-Extended Gas target limits E – resolution
and requires tracking
- RIB
p(21Na,p) & p(21Na,p’)
8.14 MeV
18Ne
10 +
α
-Solid, thin target = better E resolution
-Energetically more favorable for particle ID
(kinematically forward focused)
-CH2 target contributes to background
(reactions on carbon)
-Start with the ground state of 21Na,
reaction may proceed to excited states
22Mg
12
5.50 MeV
21Na
11 +
p
First we need a beam! ATLAS
21Ne
primary beam ~5 × 1011 pps
Gas cell with H2 gas
p(21Ne,21Na)n
21Na
secondary beam
sent to target area
~ 5 × 105 pps
“Ludwig” Detectors
Ionization Chamber/PPAC (E, Z, R, t)
18Ne
CH2 target
4He
Si strip detectors (E, θ, φ, t)
detection efficiency > ~60%
21Na
beam
Kinematic calculations/data
Life is easy with calibration reaction: p(21Ne,18F)α
EludEic: 21Ne(p,a,)18F; T1=115.5
130
E(18F)
110
E(18F)
Recoil Z=18 Energy (MeV)
120
100
90
80
70
60
50
0
5
10
15
20
25
30
35
40
E(α)
Alpha Energy (MeV)
E(α)
Alpha Energy vs. Angle: 21Ne(p,a)18F; T1=115.5
20
18
θα (Ch#)
14
12
θα
Angle (degrees)
16
10
8
6
4
2
0
0
5
10
15
20
25
Alpha Energy (MeV)
E(α)
30
35
40
E(α)
Q-value spectrum: Not so easy with 21Na
18Ne(α,p)21Na
cross sections
*Lowest energy point was taken over a period of 3 days with a beam intensity of
~ 5 × 105 pps on target, with an upper limit for σ ~ few μb.
Stellar Reaction Rates: *Preliminary Results
1.E+02
NON-SMOKER
Görres, et al.
1.E+00
<σv> cm3 s-1 mol-1
Groombridge, et al.
1.E-02
Bradfield-Smith,
et al.
New ANL upper
and lower limits*
1.E-04
1.E-06
1.E-08
1.E-10
0.25
0.5
0.75
1
1.25
T9 (GK)
1.5
1.75
2
Summary/Outlook for 18Ne(α,p)21Na
•
•
Direct comparison at one energy, where only the ground state
contributes reveals a smaller cross-section than previous
measurements (by a factor of ~50)
Extended measurement to astrophysical energy regime,
preliminary results for reaction rate are in good agreement with
theoretical models from NON-SMOKER and Görres, et al.
Next: Determine contributions from elastic and inelastic scattering in both
21Ne and 21Na systems and extract Γ and Γ .
p
p’
Counts
θcm ~ 115.3°
Ground State
Excited State
331 keV
θcm ~ 115°
Ground State
Counts
Excited State
350 keV
y
r
a
in
21Ne
21Na
m
i
l
e
Pr
Ep
Ep
Thank You/Acknowledgements
Advisor: R.E. Segel1
Collaborators: K.E. Rehm2, C.L. Jiang2, A.H. Wuosmaa3,
R.V.F. Janssens2, J.P. Schiffer2, R.C. Pardo2, E.F. Moore2,
J. Greene2, D. Henderson2, M. Paul4, A. Chen5, S. Sinha2,
X.D. Tang2, others…
1Northwestern
University, 2Argonne National Laboratory, 3Western
Michigan University, 4Hebrew University, 5McMaster University
In-Flight Secondary Beam Production at ATLAS
20Ne(d,n)21Na
21Ne(p,n)21Na
21Na,
Q=11+
20,21Ne,
Q < 9+