Scattering of $^8$He from $^4$He has been performed through the coincident detection of the scattered particles using a silicon array within a helium-4 gas volume with a $^8$He beam. This permitted ...the reconstruction of the interaction probability as a function of position within the gas and hence the excitation function to be calculated together with the angular distribution of the products. These measurements also enabled the reconstruction of the two-neutron transfer to $^6$He + $^6$He. The measurements provide the first characterisation of the scattering of the α+4n , $^8$He, halo nucleus from $^4$He and the 2n-transfer to populate the symmetric final state. The results indicate the presence of a L=4 component at excitation energies of 14–15 MeV, consistent with a broad ( ∼1 MeV ) $J^π$=4$^+$ resonance. These measurements would agree with generalized two-centre cluster model (GTCM) calculations indicating a cluster, or molecular, structure predicted at this energy.
The three-axis Dalitz plot has been applied to the breakup of a nucleus into unequal mass fragments for the first time. The Dalitz plot allows clear identification of the various breakup channels ...of9Be → 2α + n process. The method has allowed the branching ratio for the 6.38 MeV level in9Be to be provisionally calculated when examining the9Be(4He, α)ααn reaction. The effects of non-uniform angular distributions on the Dalitz plot must still be properly investigated along with the effects of contaminant reaction channels. It is proposed that this method could be used to determine the breakup branching ratio of a newly-measured level in this nucleus.
The 12C(13C,α)21Ne reaction has been measured with a 13C beam energy of 20 MeV. States in 21Ne have been populated between 0 and 12 MeV with a resolution of ~350 keV (FWHM). A coincidence experiment ...has been performed in which either the bound 21Ne nucleus or the 20Ne nucleus produced via neutron decay is detected. This permitted the 21Ne states undergoing gamma decay and neutron decay to the ground and first excited states in 20Ne to be determined. The current measurements suggest several errors in the current compilation for 21Ne.
Measurements of the helium-cluster breakup and neutron removal cross-sections for neutron-rich Be isotopes 10–12,14Be are presented. These have been studied in the 30 to 42 MeV/nucleon energy range ...where reaction measurements are proposed to be sensitive to the cluster content of the ground-state wave-function. These measurements provide a comprehensive survey of the decay processes of the Be isotopes by which the valence neutrons are removed revealing the underlying α–α core-cluster structure. The measurements indicate that clustering in the Be isotopes remains important up to the drip-line nucleus 14Be and that the dominant helium-cluster structure in the neutron-rich Be isotopes corresponds to α–Xn–α.
Variegate porphyria (VP), a low-penetrant autosomal dominant inherited disorder of haem metabolism, is characterised by photosensitivity (Fig. 1) and a propensity to develop acute neuropsychiatric ...attacks with abdominal pain, vomiting, constipation, tachycardia, hypertension, psychiatric symptoms and, in the worst cases, quadriplegia. Acute attacks, often precipitated by inappropriate drug therapy, are potentially fatal. While earlier workers thought the distal haem biosynthetic enzyme ferrochelatase may be involved in the genesis of VP, it was shown in the early 1980's, and is now accepted, that VP is associated with decreased protoporphyrinogen oxidase activity (PPO) (E.C.1.3.3.4). VP prevalence is much higher in South Africa than elsewhere; probably due to a founder effect with patients descending from a 17th century Dutch immigrant. PPO cDNAs from Bacillus subtilis, Myxococcus xanthus, human placenta and mouse liver have been cloned, sequenced and expressed. Human and mouse cDNAs consist of open reading frames 1431 nucleotides long, encoding a 477 amino acid protein. The human PPO gene contains thirteen exons, spanning approximately 4.5 kb. We have identified a C to T transition in codon 59 (in exon 3) resulting in an arginine to tryptophan substitution (R59W). A protein expressed from an in vitro-mutagenized PPO construct exhibits substantially less activity than the wild type. The R59W mutation was present in 43 of 45 patients with VP from 26 of 27 South African families investigated, but not in 34 unaffected relatives or 9 unrelated British patients with PPO deficiency. Since at least one of these families is descended from the founder of South African VP, this defect may represent the founder gene defect associated causally with VP in South Africa.
Simplicity from Complexity Freer, M; Almaraz-Calderon, S; Carter, J ...
Journal of physics. Conference series,
01/2012, Letnik:
381, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The emergence of clustering in light nuclear systems is explored using the deformed harmonic oscillator as a starting point. The experimental evidence for various geometrical arrangements of clusters ...in carbon-12 is discussed.
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