Proton Distribution Radii of

The root mean square radii of the proton density distribution in ^{16-24}O derived from measurements of charge changing cross sections with a carbon target at ∼900A MeV together with the matter radii portray thick neutron skin for ^{22-24}O despite ^{22,24}O being doubly magic. Imprints of the shell closures at N=14 and 16 are reflected in local minima of their proton radii that provide evidence for the tensor interaction causing them. The radii agree with ab initio calculations employing the chiral NNLO_{sat} interaction, though skin thickness predictions are challenged. Shell model predictions agree well with the data.

Two-Neutron Halo is Unveiled in

We report the measurement of reaction cross sections (σ_{R}^{ex}) of ^{27,29}F with a carbon target at RIKEN. The unexpectedly large σ_{R}^{ex} and derived matter radius identify ^{29}F as the heaviest two-neutron Borromean halo to date. The halo is attributed to neutrons occupying the 2p_{3/2} orbital, thereby vanishing the shell closure associated with the neutron number N=20. The results are explained by state-of-the-art shell model calculations. Coupled-cluster computations based on effective field theories of the strong nuclear force describe the matter radius of ^{27}F but are challenged for ^{29}F.

First Spectroscopy of the Near Drip-line Nucleus

One of the most exotic light neutron-rich nuclei currently accessible for experimental study is ^{40}Mg, which lies at the intersection of the nucleon magic number N=28 and the neutron drip line. Low-lying excited states of ^{40}Mg have been studied for the first time following a one-proton removal reaction from ^{41}Al, performed at the Radioactive Isotope Beam Factory of RIKEN Nishina Center with the DALI2 γ-ray array and the ZeroDegree spectrometer. Two γ-ray transitions were observed, suggesting an excitation spectrum that shows unexpected properties as compared to both the systematics along the Z=12, N≥20 Mg isotopes and available state-of-the-art theoretical model predictions. A possible explanation for the observed structure involves weak-binding effects in the low-lying excitation spectrum.

Investigation of the

This Letter reports a study of the highly debated ^{10}Li structure through the d(^{9}Li,p)^{10}Li one-neutron transfer reaction at 100 MeV. The ^{10}Li energy spectrum is measured up to 4.6 MeV and angular distributions corresponding to different excitation energy regions are reported for the first time. The comparison between data and theoretical predictions, including pairing correlation effects, shows the existence of a p_{1/2} resonance at 0.45±0.03 MeV excitation energy, while no evidence for a significant s-wave contribution close to the threshold energy is observed. Moreover, two high-lying structures are populated at 1.5 and 2.9 MeV. The corresponding angular distributions suggest a significant s_{1/2} partial-wave contribution for the 1.5 MeV structure and a mixing of configurations at higher energy, with the d_{5/2} partial-wave contributing the most to the cross section.

Nuclear Force Imprints Revealed on the Elastic Scattering of Protons with

How does nature hold together protons and neutrons to form the wide variety of complex nuclei in the Universe? Describing many-nucleon systems from the fundamental theory of quantum chromodynamics has been the greatest challenge in answering this question. The chiral effective field theory description of the nuclear force now makes this possible but requires certain parameters that are not uniquely determined. Defining the nuclear force needs identification of observables sensitive to the different parametrizations. From a measurement of proton elastic scattering on ^{10}C at TRIUMF and ab initio nuclear reaction calculations, we show that the shape and magnitude of the measured differential cross section is strongly sensitive to the nuclear force prescription.

Proton Distribution Radii of

Proton radii of ^{12-19}C densities derived from first accurate charge changing cross section measurements at 900A MeV with a carbon target are reported. A thick neutron surface evolves from ∼0.5 fm in ^{15}C to ∼1 fm in ^{19}C. The halo radius in ^{19}C is found to be 6.4±0.7 fm as large as ^{11}Li. Ab initio calculations based on chiral nucleon-nucleon and three-nucleon forces reproduce the radii well.

Measurement of Excitation Spectra in the

Excitation spectra of ^{11}C are measured in the ^{12}C(p,d) reaction near the η^{'} emission threshold. A proton beam extracted from the synchrotron SIS-18 at GSI with an incident energy of 2.5 GeV impinges on a carbon target. The momenta of deuterons emitted at 0° are precisely measured with the fragment separator (FRS) operated as a spectrometer. In contrast to theoretical predictions on the possible existence of deeply bound η^{'}-mesic states in carbon nuclei, no distinct structures are observed associated with the formation of bound states. The spectra are analyzed to set stringent constraints on the formation cross section and on the hitherto barely known η^{'}-nucleus interaction.

Evidence of soft dipole resonance in

The first conclusive evidence of a dipole resonance in ^{11}Li having isoscalar character observed from inelastic scattering with a novel solid deuteron target is reported. The experiment was performed at the newly commissioned IRIS facility at TRIUMF. The results show a resonance peak at an excitation energy of 1.03±0.03 MeV with a width of 0.51±0.11 MeV (FWHM). The angular distribution is consistent with a dipole excitation in the distorted-wave Born approximation framework. The observed resonance energy together with shell model calculations show the first signature that the monopole tensor interaction is important in ^{11}Li. The first ab initio calculations in the coupled cluster framework are also presented.

Observation of a p-wave one-neutron halo configuration in (37)Mg.

Cross sections of 1n-removal reactions from the neutron-rich nucleus (37)Mg on C and Pb targets and the parallel momentum distributions of the (37)Mg residues from the C target have been measured at 240 MeV/nucleon. A combined analysis of these distinct nuclear- and Coulomb-dominated reaction data shows that the (37)Mg ground state has a small 1n separation energy of 0.22(-0.09)(+0.12) MeV and an appreciable p-wave neutron single-particle strength. These results confirm that (37)Mg lies near the edge of the "island of inversion" and has a sizable p-wave neutron halo component, the heaviest such system identified to date.

Proton radii of (12-17)B define a thick neutron surface in ¹7B.

The first determination of radii of point proton distribution (proton radii) of (12-17)B from charge-changing cross sections (σ(CC)) measurements at the FRS, GSI, Darmstadt is reported. The proton radii are deduced from a finite-range Glauber model analysis of the σ(CC). The radii show an increase from ¹³B to ¹7B and are consistent with predictions from the antisymmetrized molecular dynamics model for the neutron-rich nuclei. The measurements show the existence of a thick neutron surface with neutron-proton radius difference of 0.51(0.11) fm in ¹7B.

11Li Breakup on 208 at energies around the Coulomb barrier.

The inclusive breakup for the (11)Li + (208)Pb reaction at energies around the Coulomb barrier has been measured for the first time. A sizable yield of (9)Li following the (11)Li dissociation has been observed, even at energies well below the Coulomb barrier. Using the first-order semiclassical perturbation theory of Coulomb excitation it is shown that the breakup probability data measured at small angles can be used to extract effective breakup energy as well as the slope of B(E1) distribution close to the threshold. Four-body continuum-discretized coupled-channels calculations, including both nuclear and Coulomb couplings between the target and projectile to all orders, reproduce the measured inclusive breakup cross sections and support the presence of a dipole resonance in the (11)Li continuum at low excitation energy.

Do halo nuclei follow Rutherford elastic scattering at energies below the barrier? The case of 11Li.

The first measurement of the elastic scattering of the halo nucleus 11Li and its core 9Li on 208Pb at energies near the Coulomb barrier is presented. The 11Li+208Pb elastic scattering shows a strong reduction with respect to the Rutherford cross section, even at energies well below the barrier and down to very small scattering angles. This drastic change of the elastic differential cross section observed in 11Li+208Pb is the consequence of the halo structure of 11Li, as it is not observed in the elastic scattering of its core 9Li at the same energies. Four-body continuum-discretized coupled-channels calculations, based on a three-body model of the 11Li projectile, are found to explain the measured angular distributions and confirm that the observed reduction is mainly due to the strong Coulomb coupling to the dipole states in the low-lying continuum of 11Li. These calculations suggest the presence of a low-lying dipole resonance in 11Li close to the breakup threshold.

Evidence for prevalent Z = 6 magic number in neutron-rich carbon isotopes.

The nuclear shell structure, which originates in the nearly independent motion of nucleons in an average potential, provides an important guide for our understanding of nuclear structure and the underlying nuclear forces. Its most remarkable fingerprint is the existence of the so-called magic numbers of protons and neutrons associated with extra stability. Although the introduction of a phenomenological spin-orbit (SO) coupling force in 1949 helped in explaining the magic numbers, its origins are still open questions. Here, we present experimental evidence for the smallest SO-originated magic number (subshell closure) at the proton number six in 13-20C obtained from systematic analysis of point-proton distribution radii, electromagnetic transition rates and atomic masses of light nuclei. Performing ab initio calculations on 14,15C, we show that the observed proton distribution radii and subshell closure can be explained by the state-of-the-art nuclear theory with chiral nucleon-nucleon and three-nucleon forces, which are rooted in the quantum chromodynamics.

Pneumococcal nasopharyngeal colonization in young South Indian infants.

BACKGROUND: Streptococcus pneumoniae is the most frequent bacterial cause of morbidity and mortality in young children. Bacteria carried in the nasopharynx of healthy children reflect the prevalent strains circulating in the community. METHODS: We recruited 464 newborns from a rural area in South India with endemic vitamin A deficiency. Nasopharyngeal specimens were collected from each infant at ages 2, 4 and 6 months. RESULTS: Fifty-four percent of study infants were colonized by age 2 months, with 64.1 and 70.2% carriage prevalence at ages 4 and 6 months, respectively. The odds of carriage at 2 months were significantly increased in female infants, infants living in a household in which 20 or more cigarettes were smoked each day, infants whose mothers had less than 1 year of schooling and infants fed colostrum. At age 4 months infants having 2 or more siblings <5 years of age were at significantly increased risk of carriage. At age 6 months none of the potential risk factors examined achieved statistical significance, but maternal night blindness increased the risk of colonization 3-fold. The odds of carrying a PncCRM197 vaccine serotype were increased among infants born to mothers who experienced night blindness during pregnancy. The most prevalent serogroups/types during the first 6 months of life were 6, 9, 10, 11, 14, 15, 19, 23 and 33, accounting for 76.7% of all serotyped isolates. CONCLUSIONS: South Indian infants experience high rates of pneumococcal carriage during the first 6 months of life, which may partially explain their increased risk for pneumonia.

Corneal perforation due to Acinetobacter junii: a case report.

Acinetobacter spp. is emerging as a common cause of nosocomial infections. Community acquired ocular infections due to Acinetobacter are rare. Only one case of perforation of cornea has been reported previously, where old nomenclature was used to describe the causal agent. We report a case of corneal perforation due to Acinetobacter junii for which a therapeutic penetrating keratoplasty was conducted and the patient eventually recovered.

Serotype distribution & antimicrobial resistance in Streptococcus pneumoniae causing invasive & other infections in south India.

BACKGROUND & OBJECTIVES: Streptococcus pneumoniae continues to be a major cause of morbidity and mortality in developing countries. The emerging resistance to some common antibiotics compounds the problem. There arises a need to monitor the resistance pattern and map serotype distribution in different geographic locations. The present study was undertaken to determine the serotype prevalence and antibiotic susceptibility of clinically significant S. pneumoniae isolated from a tertiary care hospital in south India. METHODS: A total of 150 clinical isolates from invasive and other clinically significant pneumococcal infections were serotyped and screened for susceptibility to commonly used antibiotics by standard and modified laboratory procedures. RESULTS: Majority (59.3%) of the isolates belonged to one or other of the serotypes 1, 6, 19, 5, 23 and 7. Serotype 1 was the commonest isolate from patients of meningitis and empyema followed by pneumonia. Nineteen isolates (12.6%) were nonvaccine type. Eleven (7.3%) isolates were relatively resistant to penicillin (minimum inhibitory concentration was between 0.1 and 1 microgram/ml) and 64 were resistant to one or more antibiotics. Resistance was distributed equally among the predominant serotypes. INTERPRETATION & CONCLUSION: The common serotypes responsible for significant infections were similar to those reported in some other studies from India, with minor variations. Resistance to cotrimoxazole and tetracycline was predominant followed by chloramphenicol. Low level resistance to penicillin was observed but no isolate had absolute resistance. This calls for monitoring of resistance and mapping of serotype distribution from various parts of India.

Multiply resistant Haemophilus influenzae type b causing meningitis.

The isolation from patients of meningitis, of two multidrug resistant strains of H. influenzae is of relevance to the empirical treatment of meningitis patients. The isolates produced beta lactamase and had higher MICs as compared to the four H. influenzae strains sensitive to the drugs commonly used for the treatment of meningitis. The cephalosporins and gentamicin were found to be effective antibiotic agents. The occurrence of resistance to ampicillin, chloramphenicol, cloxacillin, cotrimoxazole, tetracycline, penicillin and erythromycin is of concern.

Detection of antipneumolysin in invasive childhood pneumococcal infections.

Antibody levels against pneumolysin, a virulence factor in pneumococcal infections were evaluated by a neutralization test, using crude pneumolysin. A study population of 28 hospitalised children with culture proven pneumococcal meningitis and pneumonia were tested for detection of antipneumolysin antibodies in their serum. Results were compared with age and sex matched controls who were admitted with infections other than pneumococcal. Geometric mean titer (GMT) of antipneumolysin in serum of patients with pneumococcal infections showed a significant difference when compared with controls, GMT of 196.1 and 185.2 were noted in patients with meningitis and pneumonia respectively, in contrast to a titer of 40.32 among controls. A difference of more than 4-fold antibody titers between patients and controls was considered significant. Detection of antipneumolysin in serum can therefore be considered as a useful laboratory investigation in diagnosing invasive pneumococcal infections.

Throat carriage of pneumococci in healthy school children in the Union Territory of Pondicherry.

BACKGROUND & OBJECTIVES: Colonisation of Streptococcus pneumoniae in the throat is common among children the world over. Little is known about the relationship of nasopharyngeal carriage and invasive disease or the way it spreads within the households and close confines. There is a paucity of data on the colonization of Strep. pneumoniae in the throat of healthy children in India. To determine the prevalence of pneumococcal carriage in school children of urban and rural Pondicherry, a study was undertaken. METHODS: Throat swabs of healthy school-going children between 5-10 yr of age were examined for pneumococcal carriage, by standard bacteriological techniques. RESULTS: A prevalence rate of 24.3 per cent was noted. There was no difference in the carriage rate among the rural children when compared to urban children. No age, sex or geographical predilection of pneumococcal carriage was noted. A statistically significant seasonal variation, however, was seen. Carriage rate increased during the colder months and was found to be the highest in the months of March and November. INTERPRETATION & CONCLUSIONS: Strep. pneumoniae circulates in the community among healthy children. Carriage rate is influenced by seasonal variation.

Bacterial contamination of anterior chamber during IOL surgery.

PURPOSE: To study the nature and frequency of bacterial contamination during cataract surgery. METHODS: The preoperative smears from the conjunctiva and anterior chamber (AC) fluid aspirates during extra-capsular cataract surgery (ECCE) with posterior chamber intraocular lens (PCIOL) implantation in 40 eyes were analysed for aerobic and anaerobic bacteria. Any change in the bacterial strains isolated before and after cataract surgery was also studied. RESULTS: AC fluid aspirates were positive for bacteria in 15 eyes (37.5%). Coagulase-negative Staphylococcus was the most common aerobe (39.4%) and Propionibacterium acnes the most common anaerobe. Of the 15 cases with positive AC fluid cultures, 6 showed an organism in the AC aspirate different from the conjunctival smear. CONCLUSION: Clinically there was no endophthalmitis in any of the eyes. Factors such as preoperative antibiotic use, the antibacterial properties of aqueous, or low inoculum size could explain this. The preoperative conjunctival smear may not be useful in predicting the AC fluid contamination or outcome of cataract surgery.