Coulomb and nuclear breakup of a halo nucleus 11Be

Breakup reactions of the one-neutron halo nucleus 11Be on Pb and C targets at about 70 MeV/u have been investigated by measuring the momentum vectors of the incident 11Be, outgoing 10Be, and neutron in coincidence. The relative energy spectra as well as the angular distributions of the 10Be+n center of mass have been extracted for both targets. For the breakup on Pb target, the selection of forward scattering angles is found to be effective to extract almost purely the first-order E1 Coulomb breakup component, and to exclude the nuclear contribution and higher-order Coulomb breakup components. This angle-selected energy spectrum is thus used to deduce the spectroscopic factor for the 10Be(0+) 2s_1/2 configuration in 11Be which is found to be 0.72+-0.04 with B(E1) up to Ex=4 MeV of 1.05+-0.06 e2fm2. The energy weighted E1 strength up to Ex=4 MeV explains 70+-10% of the cluster sum rule, consistent with the obtained spectroscopic factor. The non-energy weighted sum rule is used to extract the root mean square distance of the halo neutron to be 5.77(16) fm, consistent with previously known values. In the breakup with C target, we have observed the excitations to the known unbound states in 11Be at Ex=1.78 MeV and 3.41 MeV. Angular distributions for these states show the diffraction pattern characteristic of L=2 transitions, resulting in J^pi =(3/2,5/2)+ assignment for these states. We finally find that even for the C target the E1 Coulomb direct breakup mechanism becomes dominant at very forward angles.Comment: 14 pages, 7 figures, accepted for publication on Physical Review

Projectile fragmentation reactions and production of nuclei near the neutron drip-line

The reaction mechanism of projectile fragmentation at intermediate energies has been investigated observing the target dependence of the production cross sections of very neutron-rich nuclei. Measurement of longitudinal momentum distributions of projectile-like fragments within a wide range of fragment mass and its charge was performed using a hundred-MeV/n $^{40}$Ar beam incident on Be and Ta targets. By measurement of fragment momentum distribution, a parabolic mass dependence of momentum peak shift was observed in the results of both targets, and a phenomenon of light-fragment acceleration was found only in the Be-target data. The analysis of production cross sections revealed an obvious enhancement of the target dependence except target size effect when the neutron excess is increased. This result implies the breakdown of factorization (BOF) of production cross sections for very neutron-rich nuclei near the drip line.Comment: 16 pages, 18 figures, submitted to Phys. Rev.

Measurement of two-halo neutron transfer reaction p(11^{11}Li,9^{9}Li)t at 3AA MeV

The p(\nuc{11}{Li},\nuc{9}{Li})t reaction has been studied for the first time at an incident energy of 3$A$ MeV delivered by the new ISAC-2 facility at TRIUMF. An active target detector MAYA, build at GANIL, was used for the measurement. The differential cross sectionshave been determined for transitions to the \nuc{9}{Li} ground andthe first excited states in a wide range of scattering angles. Multistep transfer calculations using different \nuc{11}{Li} model wave functions, shows that wave functions with strong correlations between the halo neutrons are the most successful in reproducing the observation.Comment: 6 pages, 3 figures, submitted to Physical Review Letter

A new DNA-cloning vector for Haemophilus influenzae Rd

A new, high-efficiency, DNA-cloning vector pJ1-8 was derived in two steps from the chimeric plasmid pD7 consisting of RSF 0885(ampr) and Haemophilus influenzae chromosomal DNA. pJl-8 has only one EcoRI site and a molecular weight of only 2.5×106. No detectable ampr transformation was obtained with pJl-8 DNA. However, ampr transformation increases markedly if Haemophilus influenzae chromosomal DNA segments are spliced into it, providing a very facile assay for detecting inserts

The first direct measurement of ¹²C (¹²C,n) ²³Mg at stellar energies

Neutrons produced by the carbon fusion reaction ¹²C(¹²C,n)²³Mg play an important role in stellar nucleosynthesis. However, past studies have shown large discrepancies between experimental data and theory, leading to an uncertain cross section extrapolation at astrophysical energies. We present the first direct measurement that extends deep into the astrophysical energy range along with a new and improved extrapolation technique based on experimental data from the mirror reaction ¹²C(¹²C,p)²³Na. The new reaction rate has been determined with a well-defined uncertainty that exceeds the precision required by astrophysics models. Using our constrained rate, we find that ¹²C(¹²C,n)²³Mg is crucial to the production of Na and Al in Pop-III Pair Instability Supernovae. It also plays a non-negligible role in the production of weak s-process elements as well as in the production of the important galacti

Analysis of a genetically unstable region in Streptomyces lividans 66-TK64

Genetic and molecular analyses of an unstable region encompassing the gene loci cml arg and a 5.7 kb amplifiable unit of DNA were done. Spontaneous mutants from Cm1R→CmlS and the revertants from CmlS →CmlR were analysed for mutations at arg locus and amplification of amplifiable unit of DNA. Twenty-one revertants were analysed. Two of these had large-scale amplification and one of these was also Arg-. Nine of the revertants which were Arg+ had low-level or intermediate-level amplification of the 5.7 kb DNA sequence but no deletions of the flanking sequences were detected. Five of the CmIR' revertants, which were also Arg+, had lost one of the two copies from the doublet of amplifiable unit of DNA. The remaining five revertants did not show any other change. The amplifiable unit of DNA, therefore, not only undergoes amplification but can also suffer specific deletion of one copy. Thus, this region as a whole is characterized by instability and the events appear to take place at more than one locus concomitantly with a high frequency

β-delayed neutron and γ-ray spectroscopy of ^<17>C utilizing spin-polarized ^<17>B

Excited states in ^C were investigated through the measurement of β -delayed neutrons and γ rays emitted in the β decay of ^B. In the measurement, three negative-parity states and two inconclusive states were identified in ^C above the neutron threshold energy, and seven γ lines were identified in a β -delayed multiple neutron emission of the ^Bβ decay. From these transitions, the β-decay scheme of ^B was determined. In particular, a de-excitation 1766-keVγ line from the first excited state of ^C was observed in coincidence with the emitted β-delayed neutrons, and this changes the previously reported β-decay scheme of ^B and level structure of ^C. In the present work, the β-NMR technique is combined with the β-delayed particle measurements using a fragmentation-induced spin-polarized ^B beam. This new scheme allows us to determine the spin parity of β-decay feeding excited states based on the difference in the discrete β-decay asymmetry parameters, provided the states are connected through the Gamow-Teller transition. In this work, I^π=1/2^−, 3/2^−, and (5/2^−) are assigned to the observed states at E_x = 2.71(2), 3.93(2), and 4.05(2) MeV in ^C, respectively

Genetic transformation in bacteria

Certain species of bacteria can become competent to take up high molecular weight DNA from the surrounding medium. DNA homologous to resident chromosomal DNA is transported, processed and recombined with the resident DNA. There are some variations in steps leading to transformation between Gram-positive bacteria likebiplococcus pneumoniae and Gram-negative bacteria represented byHaemophilus influenzae but the integration is by single-strand displacement in both cases. Plasmid (RSF0885) transformation is low inHaemophilus influenzae but this is increased significantly if (homologous) chromosomal DNA is spliced to plasmid DNA. In Haemophilus influenzae, rec1 function is required for peak transformation with chimeric plasmids. Chimeric plasmid fixed presumably extrachromosomally undergoes frequent recombination between homologous segments contained in resident chromosome and the plasmid

An estimate of the physical distance between two linked markers in Haemophilus influenzae

Using DNA clones, the physical distance between the linked genesnov and str in Haemophilus influenzae was estimated. Although none of the cloned inserts contained both the markers, pJ1-8StrR 13 (insert of 18·7 kb) included str gene at one end and part of nov gene at the other end of the insert. By EcoRI restriction analysis and by Southern hybridization, the distance between the two EcoRI sites, cutting at which inactivates the two genes, was estimated to be 17·7 kb. A single continuous EcoRI fragment (containing 4EcoRI sites within it) carrying both the genes intact would need to be 20·4 kb in size. These estimates were confirmed independently using different clones of novr and strr alleles as probes for hybridization with BamHI-digested chromosomal DNA