Measurement of the ¹⁸Ne(α,p)²¹Na reaction rate, and its implications for Nuclear Astrophysics

• Main Author: Bradfield-Smith, William
• Published: University of Edinburgh 1999
• Subjects: 520
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.641869

Experimental work has been carried out at Louvain-la-Neuve to study the reactions <SUP>13</SUP>N(α,p)<SUP>16</SUP>O and <SUP>18</SUP>Ne(α,p)<SUP>21</SUP>Na in inverse kinematics with a gaseous helium target. The experimental method devised was tested using the reaction <SUP>13</SUP>N(α,p)<SUP>16</SUP>O, as the cross section was calculable from data on <SUP>16</SUP>O(p,α)<SUP>13</SUP>N[1,2,3,4], the inverse reaction. This test experiment showed that the experimental error obtainable in the deduction of the cross section resonance strength's was 30%, making the technique of practical use in the investigation of (α,p) reactions of interest to Nuclear Astrophysics. The reaction <SUP>18</SUP>Ne(α,p)<SUP>21</SUP>Na, which is important as a break-out mechanism from the hot CNO cycle into the rp-process during explosive hydrogen burning, has been investigated, and values for the cross sections resonance strengths have been extracted from the experimental data. A stellar reaction rate, based only upon the observed resonances, has been calculated and compared with theoretical predictions[5]. A good agreement was obtained at and above a temperature of 2.5 10<SUP>9</SUP><I>K</I>, whilst at lower temperatures the experimentally reaction rate obtained fell rapidly below the calculated value. This discrepancy was due to the fact that the theoretical calculation of the stellar reaction rate used resonances at energies below 2.5 MeV, not observed experimentally. At low temperature the reaction flux through these resonances dominates the stellar reaction rate. The experimental stellar reaction rate, though only a lower limit, has been applied to a one mass zone X-ray burst model[6]. This network calculation has shown that break-out via <SUP>18</SUP>Ne(α,p)<SUP>21</SUP>Na is sufficient to trigger the burst for a type I X-ray burster, and allow mass to flow from the CNO region to the mass 100 region via the rp-process.