This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Anderson, B.D.

Baldwin, A.R.

Foster, C.C.

Lamm, D.

Madey, R.

Manley, D.M.

Wang, Y.

Watson, J.W.

Wetmore, B.

Zhang, W.M.

English

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SEARCH FOR A STATE AT E, = 2.6 MeV 
IN 20Na VIA THE 2 0 ~ e ( p , n ) 2 0 ~ a  REACTION 
AND POSSIBLE BREAKOUT FROM THE HOT CNO CYCLE 
B.D. Anderson, B. Wetmore, A.R. Baldwin, D. Lamm, R. Madey, 
D.M. Manley, J.W. Watson, and W.M. Zhang 
Physics Depar tment ,  K e n t  S ta t e  Universi ty ,  K e n t ,  Ohio 44242 
C.C. Foster and Y. Wang 
Ind iana  Universi ty  Cyclotron Facility, Bloomington,  Inddina  4 7408 
At the high temperatures and densities present in supernovae explosions, explosive 
hydrogen burning proceeds through the hot CNO cycle (HCNO), 
At very high temperatures (T > 3 x lo8 OK), the reactions l5 0 ( a ,  y)lgNe(p, y)20Na may 
begin a sequence of rapid proton captures and beta decays which can process CNO seed nu- 
clei to form elements up to A = 56 and can increase nuclear energy generation significantly.' 
This branching may also explain over-abundances of Ne, Na, Mg, and A1 isotopes in nova 
ejecta2 and cosmic rays3 relative to solar abundmces. 
The strength of this possible breakout branching is very sensitive to resonances in 
the 'gNe+p system, i.e., states in 20Na near the proton threshold. This threshold is at 
2.199 MeV. A state has been observed at 2.6 MeV via the 20Ne(3He,t)20Na reaction by 
three separate g r o ~ ~ s . ' , ~ , ~  This state would be the first state above threshold; consequently 
its existence and properties significantly affect the strength of the branching. In an earlier 
e ~ ~ e r i m e n t , ~  we saw no evidence for such a state in the 20Ne(p,n)20Na reaction. On the 
basis of DWBA analyses of the (3He,t) experiments, it was suggested that the J" of the 
2.6 MeV state is O+ or I+, i.e., it is AL = 0. 
We performed a new experiment using the beam-swinger at the IUCF in January 
1993 in order to search more carefully for such a state. The new experiment used the 
"stripper loop" storage ring to achieve ~2 ps between beam bursts. The earlier experiment, 
performed without the stripper loop, used normal pulse suppression and had -133 ns 
between beam bursts. The longer time between beam bursts eliminates overlap background 
from earlier beam bursts and also greatly reduces backgrounds from cosmic rays (because 
the system is open for a smaller fraction of the total time). The net result is a much 
improved signal-to-background ratio (better by more than a factor of 10). Care was taken 
to obtain as good an energy resolution as possible with the swinger system. The flight 
paths to the large-volume, mean-timed neutron detectors were 128 m. We obtained an 
overall time resolution of 750 ps, which translates into an energy resolution of 260 keV. 
Our preliminary results at 0.2" are shown in Fig. 1. If there is a O+ or 1+ state at 
2.6 MeV, we would expect it to peak at 0° (AL = 0). As one can see, there is no evidence 
for a state at 2.6 MeV. The large peak seen at 1.0 MeV is a known I+ state in 20Na, as 
is the smaller state observed at 3.0 MeV.6 The very large peak seen near 3.4 MeV is the 
l2 C(p,n)12N g.s. reaction from the carbon in the Kapton entrance and exit windows of the 
0 1 2 3 4 5 
Excitation energy (MeV) 
Figure  1. Excitation-energy plot for the 20Ne(p,n)20Na reaction at 135 MeV and 0". 
gas cell. The bump observed near 2 MeV is a complex of 2-, 3-, and 3+ states.' The 
region around 2.6 MeV is seen to be quite flat with a very low background (this spectrum 
has no background subtraction). From these results, we will be able to place an upper 
limit on the existence of a O+ or 1+ state with one-particle one-hole strength. It appears 
unlikely that such a state exists with simple structure. 
These results are consistent with the recent work of Kubona, e t  al.,' who looked for 
the beta decay of 2 0 ~ g  and then observed the delayed beta decay to 20Na. They found 
that 85% of the decay went to the 1+ state at 1.0 MeV, 9% to the 1+ state at 3.0 MeV, 5% 
to the 1+ state at 3.9 MeV, 1% to a O+ state at 6.4 MeV and less than 1% to any possible 
state at 2.6 MeV. More recently, it has been suggested that the 2.6 MeV state might be a 
3+ state.8 This possibility will be considered as the data are further analyzed. 
1. M.S. Smith, e t  al., Nucl. Phys. A536, 333 (1992). 
2. M.A.M. Snijders, e t  al., Mon. Not. R. Astron. Soc. 211, 7 (1984). 
3. R.E. Williams and J.S. Gallagher, Ap. J.  228, 482 (1979). 
4. S. Kubona, e t  al., 2. Phys. A333, 359 (1988). 
5. L.O. Lamm, e t  al., Nucl. Phys. A510, 503 (1990). 
6. B.D. Anderson, e t  al., Phys. Rev. C 43, 50 (1991). 
7. S. Kubona, e t  al., Phys. Rev. C 46, 361 (1992). 
8. B.A. Brown and R. Sherr, private communication. 


Search for a State at E_x = 2.6MeV in 20-Na via the 20-Ne(p,n)20-Na Reaction and Possible Breakout from the Hot CNO Cycle

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Search for a State at E_x = 2.6MeV in 20-Na via the 20-Ne(p,n)20-Na Reaction and Possible Breakout from the Hot CNO Cycle

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