Neutron-upscattering enhancement of the triple-alpha process.

The neutron inelastic scattering of carbon-12, populating the Hoyle state, is a reaction of interest for the triple-alpha process. The inverse process (neutron upscattering) can enhance the Hoyle state's decay rate to the bound states of 12C, effectively increasing the overall triple-alpha reaction rate. The cross section of this reaction is impossible to measure experimentally but has been determined here at astrophysically-relevant energies using detailed balance. Using a highly-collimated monoenergetic beam, here we measure neutrons incident on the Texas Active Target Time Projection Chamber (TexAT TPC) filled with CO2 gas, we measure the 3α-particles (arising from the decay of the Hoyle state following inelastic scattering) and a cross section is extracted. Here we show the neutron-upscattering enhancement is observed to be much smaller than previously expected. The importance of the neutron-upscattering enhancement may therefore not be significant aside from in very particular astrophysical sites (e.g. neutron star mergers).

Mirror-symmetry violation in bound nuclear ground states.

Conservation laws are deeply related to any symmetry present in a physical system1,2. Analogously to electrons in atoms exhibiting spin symmetries3, it is possible to consider neutrons and protons in the atomic nucleus as projections of a single fermion with an isobaric spin (isospin) of t = 1/2 (ref. 4). Every nuclear state is thus characterized by a total isobaric spin T and a projection Tz-two quantities that are largely conserved in nuclear reactions and decays5,6. A mirror symmetry emerges from this isobaric-spin formalism: nuclei with exchanged numbers of neutrons and protons, known as mirror nuclei, should have an identical set of states7, including their ground state, labelled by their total angular momentum J and parity π. Here we report evidence of mirror-symmetry violation in bound nuclear ground states within the mirror partners strontium-73 and bromine-73. We find that a J π = 5/2- spin assignment is needed to explain the proton-emission pattern observed from the T = 3/2 isobaric-analogue state in rubidium-73, which is identical to the ground state of strontium-73. Therefore the ground state of strontium-73 must differ from its J π = 1/2- mirror bromine-73. This observation offers insights into charge-symmetry-breaking forces acting in atomic nuclei.

Factors influencing mortality in perforated duodenal ulcer following emergency surgical repair.

Duodenal perforation is a common abdominal catastrophe with excellent outcome if prompt resuscitation and surgical repair of perforation are done. The aim of this study was to identify factors associated with death after surgery in patients with duodenal perforation. One hundred and forty-five patients who underwent Graham's patch repair for perforated duodenal ulcer between 14 April 2002 and 31 December 2004 were studied. The mean age was 45.99 years and 61 patients (42.07 %) were referrals. There were 124 (85.52 %) males and 21 (14.48 %) females. There were 10 deaths (6.9 %). The mean time delay was 2.46 days. It was 2.37 days in survivors, 3.7 days in non-survivors. The time delay was 3.25 days for females and 3.13 days for patients referred from another hospital. The mortality was significantly associated with time delay between perforation and operation (p<0.01), presence of co-morbid conditions (P<0.04), respiratory rate (p<0.02), raised blood urea (p<0.01) and serum creatinine (p<0.001), size of perforation (p<0.005), amount of peritoneal fluid (p=0.003) and requirement of postoperative intensive care unit support (p=0.003). Time delay between perforation and operation, preoperative blood urea and serum creatinine, size of perforation and amount of peritoneal fluid, presence of co-morbid conditions and need for post operative ICU support are the important predictors of outcome after emergency surgery for duodenal perforation.