Three-body effects in the Hoyle-state decay

We use a sequential $R$-matrix model to describe the breakup of the Hoyle state into three $\alpha$ particles via the ground state of $^8\mathrm{Be}$. It is shown that even in a sequential picture, features resembling a direct breakup branch appear in the phase-space distribution of the $\alpha$ particles. We construct a toy model to describe the Coulomb interaction in the three-body final state and its effects on the decay spectrum are investigated. The framework is also used to predict the phase-space distribution of the $\alpha$ particles emitted in a direct breakup of the Hoyle state and the possibility of interference between a direct and sequential branch is discussed. Our numerical results are compared to the current upper limit on the direct decay branch determined in recent experiments

Stringent upper limit on the direct 3α decay of the Hoyle state in 12C

We investigate an implication of the most recent observation of a second Jπ=2+ state in 12C, which was measured using the 12C(γ,α)8Be(g.s.) reaction. In addition to the dissociation of 12C to an α-particle and 8Be in its ground state, a small fraction of events (2%) were identified as direct decays and decays to excited states in 8Be. This allowed a limit on the direct 3α partial decay width to be determined as Γ3α<32(4) keV. Since this 2+ state is predicted by all theoretical models to be a collective excitation of the Hoyle state, the 3α partial width of the Hoyle state is calculable from the ratio of 3α decay penetrabilities of the Hoyle and 2+ states. This was calculated by using the semiclassical Wenzel-Kramers-Brillouin approach and we deduce a stringent upper limit for the direct decay branching ratio of the Hoyle state of Γ3α Γ <5.7×10−6, over an order of magnitude lower than previously reported. This result places the direct measurement of this rare decay mode beyond current experimental capabilities

Measurement of the full excitation spectrum of the 7Li(p,{\gamma}){\alpha}{\alpha} reaction at 441 keV

A current challenge for ab initio calculations is systems that contain large continuum contributions such as 8Be. We report on new measurements of radiative decay widths in this nucleus that test recent Green's function Monte Carlo calculations. Traditionally, {\gamma} ray detectors have been utilized to measure the high energy photons from the 7Li(p, {\gamma}){\alpha}{\alpha} reaction. However, due to the complicated response function of these detectors it has not yet been possible to extract the full {\gamma} ray spectrum from this reaction. Here we present an alternative measurement using large area Silicon detectors to detect the two {\alpha} particles, which provides a practically background free spectrum and retains good energy resolution. The resulting spectrum is analyzed using a many-level multi channel R-matrix parametrization. Improved values for the radiative widths are extracted from the R-matrix fit. We find evidence for significant non-resonant continuum contributions and tentative evidence for a broad 0+ resonance at 12 MeV.Comment: Accepted version. Fixed Fig. 5 ordinate label

Experimental study of the 11B(p,3α)γ^{11}\text{B}(p,3\alpha)\gamma reaction at Ep=0.5−2.7E_p = 0.5-2.7 MeV

Our understanding of the low-lying resonance structure in $^{12}$C remains incomplete. We have used the $^{11}\text{B}(p,3\alpha)\gamma$ reaction at proton energies of $E_p=0.5-2.7$ MeV as a selective probe of the excitation region above the $3\alpha$ threshold in $^{12}$C. Transitions to individual levels in $^{12}$C were identified by measuring the 3$\alpha$ final state with a compact array of charged-particle detectors. Previously identified transitions to narrow levels were confirmed and new transitions to broader levels were observed for the first time. Here, we report cross sections, deduce partial $\gamma$-decay widths and discuss the relative importance of direct and resonant capture mechanisms.Comment: 9 pages, 7 figures, 5 tables; added details on data analysi

Vascular diseases in patients with chronic myeloproliferative neoplasms:Impact of comorbidity

Background: Patients with chronic myeloproliferative neoplasms (MPNs), including essential thrombocythemia (ET), polycythemia vera (PV), and primary myelofibrosis (PMF), are at high risk of vascular complications. However, the magnitude of this is risk not well known and the possible effect of comorbidity is poorly understood. Aim: Our aim was to compare the risk of vascular diseases in patients with MPNs and matched comparisons from the general population and to study the effect modification of comorbidity. Methods: We followed 3087 patients with ET, 6076 with PV, 3719 with PMF or unspecified MPN, and age- and sex-matched general population comparisons to estimate the risks of cardiovascular diseases such as myocardial infarction and stroke. We computed 5-year cumulative incidences (risks) for vascular disease in patients with MPNs and comparisons as well as 1-year and 5-year risks, risk differences, and hazard ratios (HRs) for vascular diseases comparing rates in each group of patients with their comparison cohort by level of comorbidity based on the Charlson Comorbidity Index (CCI) [score of 0 (low comorbidity), of 1–2 (moderate comorbidity), and of >2 (severe comorbidity)], as well as other comorbid conditions. Results: The overall 5-year risk of vascular disease ranged from 0.5% to 7.7% in patients with MPNs, which was higher than the risk in the general population. In the same period, the adjusted HRs for vascular disease were 1.3 to 3.7 folds higher in patients with MPNs compared to the general population. An increase in CCI score was associated with an equally increased rate of most types of vascular diseases during the first 5 years of follow-up in both MPN and comparisons. Conclusion: Patients with MPNs have a higher risk of vascular diseases during the first 5 years than that of the general population; however, comorbidity modifies the rates similarly in MPN and in the general population

Coulomb dissociation of N 20,21

Neutron-rich light nuclei and their reactions play an important role in the creation of chemical elements. Here, data from a Coulomb dissociation experiment on N20,21 are reported. Relativistic N20,21 ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment. Using the detailed balance theorem, the N19(n,γ)N20 and N20(n,γ)N21 excitation functions and thermonuclear reaction rates have been determined. The N19(n,γ)N20 rate is up to a factor of 5 higher at