First Direct Measurement of an Astrophysical p-Process Reaction Cross Section Using a Radioactive Ion Beam

We have performed the first direct measurement of the ^{83}Rb(p,γ) radiative capture reaction cross section in inverse kinematics using a radioactive beam of ^{83}Rb at incident energies of 2.4 and 2.7A  MeV. The measured cross section at an effective relative kinetic energy of E_{cm}=2.393  MeV, which lies within the relevant energy window for core collapse supernovae, is smaller than the prediction of statistical model calculations. This leads to the abundance of ^{84}Sr produced in the astrophysical p process being higher than previously calculated. Moreover, the discrepancy of the present data with theoretical predictions indicates that further experimental investigation of p-process reactions involving unstable projectiles is clearly warranted.

Erratum: Direct Observation of Proton Emission in ^{11}Be [Phys. Rev. Lett. 123, 082501 (2019)]

This corrects the article DOI: 10.1103/PhysRevLett.123.082501.

Direct Observation of Proton Emission in ^{11}Be

The elusive β^{-}p^{+} decay was observed in ^{11}Be by directly measuring the emitted protons and their energy distribution for the first time with the prototype Active Target Time Projection Chamber in an experiment performed at ISAC-TRIUMF. The measured β^{-}p^{+} branching ratio is orders of magnitude larger than any previous theoretical model predicted. This can be explained by the presence of a narrow resonance in ^{11}B above the proton separation energy.

Novel ΔJ=1 Sequence in ^{78}Ge: Possible Evidence for Triaxiality

A sequence of low-energy levels in _{32}^{78}Ge_{46} has been identified with spins and parity of 2^{+}, 3^{+}, 4^{+}, 5^{+}, and 6^{+}. Decays within this band proceed strictly through ΔJ=1 transitions, unlike similar sequences in neighboring Ge and Se nuclei. Above the 2^{+} level, members of this sequence do not decay into the ground-state band. Moreover, the energy staggering of this sequence has the phase that would be expected for a γ-rigid structure. The energies and branching ratios of many of the levels are described well by shell-model calculations. However, the calculated reduced transition probabilities for the ΔJ=2 in-band transitions imply that they should have been observed, in contradiction with the experiment. Within the calculations of Davydov, Filippov, and Rostovsky for rigid-triaxial rotors with γ=30°, there are sequences of higher-spin levels connected by strong ΔJ=1 transitions which decay in the same manner as those observed experimentally, yet are calculated at too high an excitation energy.

Nuclear Force Imprints Revealed on the Elastic Scattering of Protons with ^{10}C

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.

Scattering of the Halo Nucleus ^{11}Be on ^{197}Au at Energies around the Coulomb Barrier

Angular distributions of the elastic, inelastic, and breakup cross sections of the halo nucleus ^{11}Be on ^{197}Au were measured at energies below (E_{lab}=31.9  MeV) and around (39.6 MeV) the Coulomb barrier. These three channels were unambiguously separated for the first time for reactions of ^{11}Be on a high-Z target at low energies. The experiment was performed at TRIUMF (Vancouver, Canada). The differential cross sections were compared with three different calculations: semiclassical, inert-core continuum-coupled-channels and continuum-coupled-channels ones with including core deformation. These results show conclusively that the elastic and inelastic differential cross sections can only be accounted for if core-excited admixtures are taken into account. The cross sections for these channels strongly depend on the B(E1) distribution in ^{11}Be, and the reaction mechanism is sensitive to the entanglement of core and halo degrees of freedom in ^{11}Be.

Decay and Fission Hindrance of Two- and Four-Quasiparticle K Isomers in ^{254}Rf

Two isomers decaying by electromagnetic transitions with half-lives of 4.7(1.1) and 247(73) μs have been discovered in the heavy ^{254}Rf nucleus. The observation of the shorter-lived isomer was made possible by a novel application of a digital data acquisition system. The isomers were interpreted as the K^{π}=8^{-}, ν^{2}(7/2^{+}[624],9/2^{-}[734]) two-quasineutron and the K^{π}=16^{+}, 8^{-}ν^{2}(7/2^{+}[624],9/2^{-}[734])⊗8^{-}π^{2}(7/2^{-}[514],9/2^{+}[624]) four-quasiparticle configurations, respectively. Surprisingly, the lifetime of the two-quasiparticle isomer is more than 4 orders of magnitude shorter than what has been observed for analogous isomers in the lighter N=150 isotones. The four-quasiparticle isomer is longer lived than the ^{254}Rf ground state that decays exclusively by spontaneous fission with a half-life of 23.2(1.1) μs. The absence of sizable fission branches from either of the isomers implies unprecedented fission hindrance relative to the ground state.

Measurement of 23Na(α,p)26Mg at Energies Relevant to 26Al Production in Massive Stars

26Al is an important radioisotope in astrophysics that provides evidence of ongoing nucleosynthesis in the Galaxy. The 23Na(α, p)26Mg reaction has been identified by a sensitivity study as being one of the most important reactions for the production of 26Al in the convective C/Ne burning shell of massive stars. Owing to large uncertainties in previous experimental data, model calculations are used for the reaction rate of 23Na(α, p)26Mg in this sensitivity study. Current experimental data suggest a reaction rate a factor of ∼40 higher than model calculations. However, a new measurement of this reaction cross section has been made in inverse kinematics in the energy range E(c.m.)=1.28-3.15  MeV at TRIUMF, and found to be in reasonable agreement with the model calculation. A new reaction rate is calculated and tight constraints on the uncertainty in the production of 26Al, due to this reaction, are determined.

Fission barrier of superheavy nuclei and persistence of shell effects at high spin: cases of 254No and 220Th

We report on the first measurement of the fission barrier height in a heavy shell-stabilized nucleus. The fission barrier height of 254No is measured to be Bf=6.0±0.5  MeV at spin 15ℏ and, by extrapolation, Bf=6.6±0.9  MeV at spin 0ℏ. This information is deduced from the measured distribution of entry points in the excitation energy versus spin plane. The same measurement is performed for 220Th and only a lower limit of the fission barrier height can be determined: Bf(I)>8  MeV. Comparisons with theoretical fission barriers test theories that predict properties of superheavy elements.

Measurements of fusion reactions of low-intensity radioactive carbon beams on 12C and their implications for the understanding of X-ray bursts

The interaction between neutron-rich nuclei plays an important role for understanding the reaction mechanism of the fusion process as well as for the energy production through pycnonuclear reactions in the crust of neutron stars. We have performed the first measurements of the total fusion cross sections in the systems (10,14,15)C+(12)C using a new active target-detector system. In the energy region accessible with existing radioactive beams, a good agreement between the experimental and theoretical cross sections is observed. This gives confidence in our ability to calculate fusion cross sections for systems which are outside the range of today's radioactive beam facilities.

Measurement of the survival probabilities for hot fusion reactions

We have studied the fission-neutron emission competition in highly excited (274)Hs (Z=108) (where the fission barrier is due to shell effects) formed by a hot fusion reaction. Matching cross bombardments ((26)Mg+(248)Cm and (25)Mg+(248)Cm) were used to identify the properties of first chance fission of (274)Hs. A Harding-Farley analysis of the fission neutrons emitted in the (25)Mg,26+(248)Cm was performed to identify the prescission and postscission components of the neutron multiplicities in each system. (Γn/Γt) for the first chance fission of (274)Hs (E*=63  MeV) is 0.89±0.13; i.e., ∼90% of the highly excited nuclei survive. The high value of that survival probability is due to dissipative effects during deexcitation. A proper description of the survival probabilities of excited superheavy nuclei formed in hot fusion reactions requires consideration of both dynamic and static (shell-related) effects.

Direct measurement of the (23)Na(α,p)(26)Mg reaction cross section at energies relevant for the production of galactic (26)Al

The 1809-keV γ ray from the decay of (26)Al(g) is an important target for γ-ray astronomy. In the convective C/Ne burning shell of massive presupernova stars, the (23)Na(α,p)(26)Mg reaction directly influences the production of (26)Al. We have performed a direct measurement of the (23)Na(α,p)(26)Mg reaction cross section at the appropriate astrophysically important energies. The stellar rate calculated in the present work is larger than the recommended rate by nearly a factor of 40 and could strongly affect the production of (26)Al in massive stars.

Study of nsLTPs in Lotus japonicus genome reveal a specific epidermal cell member (LjLTP10) regulated by drought stress in aerial organs with a putative role in cutin formation

The cuticle is the first defense against pathogens and the second way water is lost in plants. Hydrophobic layers covering aerial plant organs from primary stages of development form cuticle, including major classes of aliphatic wax components and cutin. Extensive research has been conducted to understand cuticle formation mechanisms in plants. However, many questions remain unresolved in the transport of lipid components to form cuticle. Database studies of the Lotus japonicus genome have revealed the presence of 24 sequences classified as putative non-specific lipid transfer proteins (nsLTPs), which were classified in seven groups; four groups were selected because of their expression in aerial organs. LjLTP8 forms a cluster with DIR1 in Arabidopsis thaliana while LjLTP6, LjLTP9, and LjLTP10 were grouped as type I LTPs. In silico studies showed a high level of structural conservation, and substrate affinity studies revealed palmitoyl-CoA as the most likely ligand for these LTPs, although the Lyso-Myristoyl Phosphatidyl Choline, Lyso-myristoyl phosphatidyl glycerol, and Lyso-stearyl phosphatidyl choline ligands also showed a high affinity with the proteins. The LjLTP6 and LjLTP10 genes were expressed in both the stems and the leaves under normal conditions and were highly induced during drought stress. LjLTP10 was the most induced gene in shoots during drought. The gene was only expressed in the epidermal cells of stems, primordial leaves, and young leaflets. LjLTP10 was positively regulated by MeJA but repressed by abscisic acid (ABA), ethylene, and H2O2, while LjLTP6 was weakly induced by MeJA, repressed by H2O2, and not affected by ABA and ethylene. We suggest that LjLTP10 is involved in plant development of stem and leaf cuticle, but also in acclimation to tolerate drought stress in L. japonicus.

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.

Improved limit on direct α decay of the Hoyle state

The current evaluation of the triple-α reaction rate assumes that the α decay of the 7.65 MeV, 0+ state in 12C, commonly known as the Hoyle state, proceeds sequentially via the ground state of 8Be. This assumption is challenged by the recent identification of two direct α-decay branches with a combined branching ratio of 17(5)%. If correct, this would imply a corresponding reduction in the triple-α reaction rate with important astrophysical consequences. We have used the 11B(3He,d) reaction to populate the Hoyle state and measured the decay to three α particles in complete kinematics. We find no evidence for direct α-decay branches, and hence our data do not support a revision of the triple-α reaction rate. We obtain an upper limit of 5×10(-3) on the direct α decay of the Hoyle state at 95% C.L., which is 1 order of magnitude better than a previous upper limit.

Precise determination of the unperturbed 8B neutrino spectrum

A measurement of the final state distribution of the (8)B β decay, obtained by implanting a (8)B beam in a double-sided silicon strip detector, is reported here. The present spectrum is consistent with a recent independent precise measurement performed by our collaboration at the IGISOL facility, Jyväskylä [O. S. Kirsebom et al., Phys. Rev. C 83, 065802 (2011)]. It shows discrepancies with previously measured spectra, leading to differences in the derived neutrino spectrum. Thanks to a low detection threshold, the neutrino spectrum is for the first time directly extracted from the measured final state distribution, thus avoiding the uncertainties related to the extrapolation of R-matrix fits. Combined with the IGISOL data, this leads to an improvement of the overall errors and the extension of the neutrino spectrum at high energy. The new unperturbed neutrino spectrum represents a benchmark for future measurements of the solar neutrino flux as a function of energy.

Fusion reactions with the one-neutron halo nucleus (15)C

The structure of (15)C, with an s(1/2) neutron weakly bound to a closed-neutron shell nucleus (14)C, makes it a prime candidate for a one-neutron halo nucleus. We have for the first time studied the cross section for the fusion-fission reaction (15)C+(232)Th at energies in the vicinity of the Coulomb barrier and compared it to the yield of the neighboring (14)C+(232)Th system measured in the same experiment. At sub-barrier energies, an enhancement of the fusion yield by factors of 2-5 was observed for (15)C, while the cross sections for (14)C match the trends measured for (12,13)C.

Measurement of the two-halo neutron transfer reaction (1)H((11)Li, (9)Li)(3)H at 3A MeV

The p((11)Li, (9)Li)t reaction has been studied for the first time at an incident energy of 3A MeV at the new ISAC-2 facility at TRIUMF. An active target detector MAYA, built at GANIL, was used for the measurement. The differential cross sections have been determined for transitions to the (9)Li ground and first excited states in a wide range of scattering angles. Multistep transfer calculations using different (11)Li model wave functions show that wave functions with strong correlations between the halo neutrons are the most successful in reproducing the observation.

Bacterial translocation is favored by the preservation of the ileocecal valve in experimental short bowel with total parenteral nutrition

Sepsis in short-bowel syndrome (SBS) is in part due to bacterial translocation (BT). Parenteral nutrition (PN) is often necessary in SBS and promotes BT. The aim of this study was to asses the effect of the presence or absence of ileocecal valve (ICV) on BT in parenterally-fed rats with massive intestinal resection. Sixty-five adult Wistar rats underwent central venous cannulations and were randomly assigned to one of five groups receiving for ten days five treatment regimes: Sham (n = 17) standard rat chow + i.v. saline. PN (n = 17) fasting + PN. Res-Sham (n = 10) standard rat chow + i.v. saline + 80% gut resection. Res-PN (n = 11) fasting, PN + 80% gut resection. Res-ICV-PN (n = 10) fasting, PN + 80% gut resection including ICV. At the end of the experiment they were euthanized and mesenteric lymph nodes (MLN), spleen and peripheral and portal blood specimens were recovered and cultured. BT was found in 47% of PN animals, 91% of Res-PN rats, 100% of Res-Sham group and 60% of Res-ICV-PN animals, but not in Sham ones. 97% of BT+ animals had positive cultures in MLN and/or portal blood, whereas germs beyond liver were detected in 30% of Res-Sham, 37% of PN, 50% of Res-PN and 0% of Res-ICV-PN rats. The present study confirms that both massive intestinal resection and PN promote BT. In addition, it shows that animals deprived of ICV have lower incidence of BT in this setting than those with it and that the germs do not reach in them peripheral blood in the same proportions as in ICV-intact animals. These results suggest that the presence of an intact ICV favor BT in parenterally-fed rats with massive intestinal resection.

Non-endoscopic method to obtain Helicobacter pylori for culture

A sampling method to collect samples for Helicobacter pylori culture that is easier than endoscopy would be useful. We used a capsule attached to a highly absorbent nylon string, which is swallowed to obtain gastric secretions. Antral biopsy and string specimens, sequentially obtained from 36 adults with clinically suspected ulcer or gastric disease were cultured. 9 (25%) patients were negative in both tests; 18 (50%) were positive by both methods; 6 (17%) were biopsy positive and string-test negative; and 3 (8%) were biopsy negative and string-test positive. The new test is useful, simple, and causes little discomfort.

Rapid detection of tuberculous and non-tuberculous mycobacteria by microscopic observation of growth on Middlebrook 7H11 agar

The rate of recovery and time to the detection of mycobacteria in clinical specimens were measured in traditional egg-based media cultures and on Middlebrook 7H11 agar plate cultures using microcolony detection. In the 5438 specimens processed, a total of 293 (5.4%) clinically relevant mycobacterial isolates were detected (Mycobacterium tuberculosis, n = 231; Mycobacterium avium complex, n = 60; Mycobacterium kansasii, n = 2). Of these, 227 (77%) and 237 (81%) isolates were detected on Lowenstein-Jensen medium and Coletsos medium, respectively, and 265 (90%) isolates were detected on Middlebrook 7H11 plates examined microscopically. The detection time was shorter with the microcolony detection method. While the Lowenstein-Jensen and Coletsos media required an average of 23 and 25 days, respectively, for first detection of mycobacteria, microcolony detection on Middlebrook 7H11 required an average of only 12 days. For acid-fast, stain-positive specimens that were culture positive for Mycobacterium tuberculosis, the average interval to positivity was nine days for the microcolony method compared with 20 and 21 days for the Lowenstein-Jensen and Coletsos media, respectively. Microscopic detection on Middlebrook 7H11 agar plates is a rapid, accurate and inexpensive method of detecting Mycobacterium tuberculosis and other clinically important mycobacteria.

[The indications for the antipneumococcal vaccine in Spain]

The anti-pneumococcal vaccine, with 23 capsular polysaccharides, is an effective vaccine used in most of the developed countries, although still not commercially available in Spain. Between January 1981 and June 1992, we isolated 784 Streptococcus pneumoniae from clinical samples (excluding asymptomatic carriers), 728 of which could be serotyped (300 isolated in hemoculture and/or LCR). 91.5% of the total and 93.3% of the most invasive strains, as well as 98.1% of the penicillin-resistant strains or 98.8% of the isolated multiresistant strains, presented a serotype covered by the current vaccine. The high resistance to antibiotics of the pneumococcus in Spain makes more urgent the indication of the vaccine in our community.

[Low risk of acquiring the hepatitis C virus for the health personnel]

BACKGROUND

The hepatitis C virus (HCV) is transmitted by the same routes as that of hepatitis B (HBV) and that of the human immunodeficiency virus (HIV). Health care workers have been considered at risk although of different intensity for acquiring the HBV and HIV with the risk of acquiring the HCV being ignored.

METHODS

The presence of anti-HCV was investigated in 338 hospital workers, 110 proceeding from risk areas without direct contact with patients (laboratories and cleaning staff), 141 in direct contact and 87 with accidental risk (needle pricks or splashing of blood products) whom, at the time of the accident were anti-HCV negative. In the latter a minimum period of 6 months, which reached one year in 50% of the cases, elapsed to permit seroconversion. Three hundred seventy-seven healthy women were used as controls. The presence of anti-HCV was investigated with a second generation enzymoimmunoanalysis system confirming the results obtained with RIBA.

RESULTS

The workers in zones of risk without direct patient contact presented global seroprevalence of anti-HCV of 1.8% with no statistical difference obtained between those who attended patients directly (1.4%) or the control group (2.1%). HCV transmission was not detected in any of the workers who experienced a high risk accident.

CONCLUSIONS

The results concerning the study of the risk of health care workers to obtain hepatitis C suggest that the risk of transmission of the hepatitis C virus in these personnel is low.