Engineering topics
Roosa, M.
Publications and source records attributed to Roosa, M..
First Experimental Test of the Ratio Method
The ratio is a new reaction observable suggested to extract accurately structure information on halo nuclei. It corresponds to the ratio of differential cross sections for scattering and breakup, which is predicted to remove the uncertainty related to the reaction dynamics. We present here the first experimental test of the method for the 11 Be + 12 C collision at E Lab = 20A MeV performed at Texas A&M University. Differential cross sections for scattering and inclusive one-neutron breakup have been measured with the new detector array BlueSTEAl. The ratio of cross sections is very smooth and independent of the projectile-target interaction, which demonstrates the validity of the ratio method. We extend our analysis to existing 11 Be + 208 Pb data, confirming that the method works well on any target.
Cluster structure of 3𝛼+𝑝 states in 13 N
Cluster states in 13 N are extremely difficult to measure due to the unavailability of 9 B +𝛼 elastic-scattering data. Using 𝛽-delayed charged-particle spectroscopy of 13 O, clustered states in 13 N can be populated and measured in the 3𝛼+𝑝 decay channel. One-at-a-time implantation and decay of 13 O was performed with the Texas Active Target Time Projection Chamber. 149𝛽3𝛼𝑝 decay events were observed and the excitation function in 13 N reconstructed. Four previously unknown 𝛼-decaying excited states were observed in 13 N at an excitation energy of 11.3, 12.4, 13.1, and 13.7 MeV decaying via the 3𝛼+𝑝 channel. These states are seen to have a [ 9 B (g.s) ⨂𝛼/𝑝 + 12 C (0$^+_2$)], [ 9 B ($\frac{1}{2}$ + ) ⨂𝛼], [ 9 B ($\frac{5}{2}$ + ) ⨂𝛼], and [ 9 B ($\frac{5}{2}$) ⨂𝛼] structure, respectively. A previously seen state at 11.8 MeV was also determined to have a [𝑝+ 12 C (g.s.)/𝑝+ 12 C (0$^+_2$)] structure. The overall magnitude of the clustering is not able to be extracted, however, due to the lack of a total width measurement. Clustered states in 13 N (with unknown magnitude) seem to persist from the addition of a proton to the highly 𝛼-clustered 12 C . Evidence of the $\frac{1}{2}$ + state in 9 B was also seen to be populated by decays from 13 N ★ .
Radiative decay branching ratio of the Hoyle state
The triple-alpha process is a vital reaction in nuclear astrophysics, characterized by two consecutive reactions [2α ⇌ 8 Be (α, γ) 12 C] that drive carbon formation. The second reaction occurs through the Hoyle state, a 7.65 MeV excited state in 12 C with J π = 0 + . The rate of the process depends on the radiative width, which can be determined by measuring the branching ratio for electromagnetic decay. Recent measurements by Kibédi et al. conflicted with the adopted value and resulted in a significant increase of nearly 50% in this branching ratio, directly affecting the triple-alpha reaction. Here, this work aims to utilize charged-particle spectroscopy with magnetic selection as a means to accurately measure the total radiative branching ratio (Γ rad /Γ) of the Hoyle state in 12 C.