Low energy fission of 234,235,236,238U and 237,238Np radioactive beams, provided by the GSI/FRS facility, has been studied using the R3B/SOFIA setup. The latter allows, on an event-by-event basis, to ...simultaneously identify, in terms of their mass and atomic numbers, the fissioning nucleus in coincidence with both fission fragments after prompt-neutron emission. This presentation reports on new results on elemental, isobaric and isotopic yields.
Many neutron star properties, such as the proton fraction, reflect the symmetry energy contributions to the equation of state that dominate when neutron and proton densities differ strongly. To ...constrain these contributions at suprasaturation densities, we measure the spectra of charged pions produced by colliding rare isotope tin (Sn) beams with isotopically enriched Sn targets. Using ratios of the charged pion spectra measured at high transverse momenta, we deduce the slope of the symmetry energy to be 42<L<117 MeV. This value is slightly lower but consistent with the L values deduced from a recent measurement of the neutron skin thickness of ^{208}Pb.
In the past two decades, pions created in the high density regions of heavy ion collisions have been predicted to be sensitive at high densities to the symmetry energy term in the nuclear equation of ...state, a property that is key to our understanding of neutron stars. In a new experiment designed to study the symmetry energy, the multiplicities of negatively and positively charged pions have been measured with high accuracy for central 132Sn+124Sn, 112Sn+124Sn, and 108Sn+112Sn collisions at E/A=270 MeV with the SπRIT Time Projection Chamber. While individual pion multiplicities are measured to 4% accuracy, those of the charged pion multiplicity ratios are measured to 2% accuracy. We compare these data to predictions from seven major transport models. The calculations reproduce qualitatively the dependence of the multiplicities and their ratios on the total neutron and proton number in the colliding systems. However, the predictions of the transport models from different codes differ too much to allow extraction of reliable constraints on the symmetry energy from the data. This finding may explain previous contradictory conclusions on symmetry energy constraints obtained from pion data in Au+Au system. These new results call for still better understanding of the differences among transport codes, and new observables that are more sensitive to the density dependence of the symmetry energy.
The Reactions with Relativistic Radioactive Beams (R3B) collaboration of the Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, has constructed an experimental setup to perform ...fundamental studies of nuclear matter, using as a probe reactions with exotic nuclei at relativistic energies. Among the various detection systems, one of the most recent upgrades consists of the installation of a large area, around 2 m2, multi-gap Resistive Plate Chamber (RPC). The chamber is equipped with twelve 0.3mm gaps and readout by 30mm pitch strips, exhibiting a timing precision down to 50 ps and efficiencies above 98% for minimum ionizing particles in a previous characterization of the detector. The RPC was part of the setup of the FAIR Phase 0 experiment that focused on measuring for the first time, in spring 2022, nucleon–nucleon short-range correlations (SRC) inside an exotic nucleus (16C). The excellent timing precision of this detector will allow the measurement of the forward emitted proton momentum with a resolution of around 1%. In beam measurements show an RPC efficiency above 95% and a time precision better than 100 ps (including the contribution of a reference scintillator and the momentum spread of the particles) for forward emitted particles.
The first γ-ray spectroscopy of 52Ar, with the neutron number N = 34, was measured using the 53K(p, 2p) one-proton removal reaction at ~210 MeV/u at the RIBF facility. The 2+1 excitation energy is ...found at 1656(18) keV, the highest among the Ar isotopes with N > 20. This result is the first experimental signature of the persistence of the N = 34 subshell closure beyond 54Ca, i.e., below the magic proton number Z = 20. Shell-model calculations with phenomenological and chiral-effective-field-theory interactions both reproduce the measured 2+1 systematics of neutron-rich Ar isotopes, and support a N = 34 subshell closure in 52Ar.
The one-neutron knockout from 52Ca in inverse kinematics onto a proton target was performed at similar to 230 MeV/nucleon combined with prompt 7 spectroscopy. Exclusive quasifree scattering cross ...sections to bound states in 51Ca and the momentum distributions corresponding to the removal of 1f7=2 and 2p3=2 neutrons were measured. The cross sections, interpreted within the distorted-wave impulse approximation reaction framework, are consistent with a shell closure at the neutron number N = 32, found as strong as at N = 28 and N = 34 in Ca isotopes from the same observables. The analysis of the momentum distributions leads to a difference of the root-mean-square radii of the neutron 1f7=2 and 2p3=2 orbitals of 0.61(23) fm, in agreement with the modified-shell-model prediction of 0.7 fm suggesting that the large root-mean-square radius of the 2p3=2 orbital in neutron-rich Ca isotopes is responsible for the unexpected linear increase of the charge radius with the neutron number.
The one-neutron knockout from 52Ca in inverse kinematics onto a proton target was performed at ∼230 MeV/nucleon combined with prompt γ spectroscopy. Exclusive quasifree scattering cross sections to ...bound states in 51Ca and the momentum distributions corresponding to the removal of 1f7/2 and 2p3/2 neutrons were measured. The cross sections, interpreted within the distorted-wave impulse approximation reaction framework, are consistent with a shell closure at the neutron number N=32, found as strong as at N=28 and N=34 in Ca isotopes from the same observables. The analysis of the momentum distributions leads to a difference of the root-mean-square radii of the neutron 1f7/2 and 2p3/2 orbitals of 0.61(23) fm, in agreement with the modified-shell-model prediction of 0.7 fm suggesting that the large root-mean-square radius of the 2p3/2 orbital in neutron-rich Ca isotopes is responsible for the unexpected linear increase of the charge radius with the neutron number.
Exposure to combustion-derived air pollution is associated with an early (1-2 h) and sustained (24 h) rise in cardiovascular morbidity and mortality. We have previously demonstrated that inhalation ...of diesel exhaust causes an immediate (within 2 h) impairment of vascular and endothelial function in humans.
To investigate the vascular and systemic effects of diesel exhaust in humans 24 hours after inhalation.
Fifteen healthy men were exposed to diesel exhaust (particulate concentration, 300 microg/m(3)) or filtered air for 1 hour in a double-blind, randomized, crossover study. Twenty-four hours after exposure, bilateral forearm blood flow, and inflammatory and fibrinolytic markers were measured before and during unilateral intrabrachial bradykinin (100-1,000 pmol/min), acetylcholine (5-20 microg/min), sodium nitroprusside (2-8 microg/min), and verapamil (10-100 microg/min) infusions.
Resting forearm blood flow, blood pressure, and basal fibrinolytic markers were similar 24 hours after either exposure. Diesel exhaust increased plasma cytokine concentrations (tumor necrosis factor-alpha and interleukin-6, p < 0.05 for both) but appeared to reduce acetylcholine (p = 0.01), and bradykinin (p = 0.08) induced forearm vasodilatation. In contrast, there were no differences in either endothelium-independent (sodium nitroprusside and verapamil) vasodilatation or bradykinin-induced acute plasma tissue plasminogen activator release.
Twenty-four hours after diesel exposure, there is a selective and persistent impairment of endothelium-dependent vasodilatation that occurs in the presence of mild systemic inflammation. These findings suggest that combustion-derived air pollution may have important systemic and adverse vascular effects for at least 24 hours after exposure.
The calcium isotopes are an ideal system to investigate the evolution of shell structure and magic numbers. Although the properties of surface nucleons in calcium have been well studied, probing the ...structure of deeply bound nucleons remains a challenge. Here, we report on the first measurement of unbound states in 53Ca and 55Ca, populated from 54,56Ca(p,pn) reactions at a beam energy of around 216 MeV/nucleon at the RIKEN Radioactive Isotopes Beam Factory. The resonance properties, partial cross sections, and momentum distributions of these unbound states were analyzed. Orbital angular momentum l assignments were extracted from momentum distributions based on calculations using the distorted wave impulse approximation (DWIA) reaction model. The resonances at excitation energies of 5516(41)keV in 53Ca and 6000(250)keV in 55Ca indicate a significant l =3 component, providing the first experimental evidence for the ν0f7/2 single-particle strength of unbound hole states in the neutron-rich Ca isotopes. The observed excitation energies and cross-sections point towards extremely localized and well separated strength distributions, with some fragmentation for the ν0f7/2 orbital in 55Ca. These results are in good agreement with predictions from shell-model calculations using the effective GXPF1Bs interaction and ab initio calculations and diverge markedly from the experimental distributions in the nickel isotones at Z=28.
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