The cross sections of nuclear reactions between the radioisotope Be7 and deuterium, a possible mechanism of reducing the production of mass-7 nuclides in big-bang nucleosynthesis, were measured at ...center-of-mass energies between 0.2 and 1.5 MeV. The measured cross sections are dominated by the (d,α) reaction channel, towards which prior experiments were mostly insensitive. A new resonance at 0.36(5) MeV with a strength of ωγ=1.7(5) keV was observed inside the relevant Gamow window. Calculations of nucleosynthesis outcomes based on the experimental cross section show that the resonance reduces the predicted abundance of primordial Li7, but not sufficiently to solve the primordial lithium problem.
This experimental study of high-spin structure near
N
=
Z
=
20
nuclei was focused on
41
K, but will also mention three newly observed
γ
transitions in
41
Ca observed in the same reaction. High-spin ...states were populated using the
26
Mg(
18
O,
p
2
n
γ
)
41
K and
26
Mg(
18
O,
3
n
γ
)
41
Ca reactions. The experiment was carried out at an incident beam energy of 50 MeV at the Florida State University (FSU) John D. Fox Superconducting Linear Accelerator Laboratory and used the FSU high-purity germanium detector array. The
41
K level scheme was extended to 12325 keV, possibly with J
π
= 25/2
-
or 27/2
+
, by means of 25 new transitions and that of
41
Ca to 9916 keV. Linear polarization and a measure of angular distribution results are also reported and used to provide information on the spins and parities of several states in the
41
K level scheme. The results have been compared to the
spsdpf
cross-shell FSU shell model interaction calculations. The theoretical results from configurations involving no or one additional nucleon promoted from the
sd
to the
fp
shell agree relatively well with the energies of known states, while those that involve multi-particle excitations paint an interesting and complex picture of interplay between single-particle excitations, collective pairing, and deformation. This presents an interesting challenge for future theory.
The 18Ne(α,p)21Na reaction plays a significant role in Type-I X-ray bursts. It is a major path in the breakout from the hot-CNO cycles to the synthesis of heavier elements in the αp- and ...rp-processes. An experiment to determine the cross section of this reaction was performed with the ANASEN active-target detector system, determining the cross section at energies between 2.5 and 4 MeV in the center-of-mass frame. The measured cross sections for reactions populating the ground state in 21Na are consistent with results obtained from the time-inverse reaction, but significantly lower than the previously published experimental data of direct measurements. The total cross sections are also compared with those derived from indirect methods and statistical-model calculations. Furthermore, this experiment establishes a new experimental data set on the excitation function of the 18Ne(α,p)21Na reaction, revealing the significance of the excited states' contributions to the total reaction cross section and allowing us to separate the contribution of the (α,2p) reaction. The impact of the measured cross section on thermal reaction rates is discussed.
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