We report on the emission patterns from THz plasmons propagating towards the end of cylindrical metal waveguides. Such waveguides exhibit low loss and dispersion, but little is known about the ...dynamics of the terahertz radiation at the end of the waveguide, specifically in the near- and intermediate-field. Our experimental results and numerical simulations show that the near- and intermediate-field terahertz spectra, measured at the end of the waveguide, vary with the position relative to the waveguide. This is explained by the frequency-dependent diffraction occurring at the end of the cylindrical waveguide. Our results show that near-field changes in the frequency content of THz pulses for increasing wire-detector distances must be taken into account when studying surface waves on cylindrical waveguides.
Background:The 31S(p,γ)32Cl reaction becomes important for sulfur production in novae if the 31P(p,α)28Si reaction rate is somewhat greater than currently accepted. The rate of the 31S(p,γ)32Cl ...reaction is uncertain,primarily due to the properties of resonances atEcm= 156 and 549 keV. Purpose:We precisely determined the excitation energies of states in 32Cl through high-resolutionγspectroscopy including the two states most important for the 31S(p,γ)32Cl reaction at nova temperatures. Method:Excited states in 32Cl were populated using the 10B(24Mg,2n)32Cl reaction with a 24Mg beam from the ATLAS facility at Argonne National Laboratory. The reaction channel of interest was selected using recoils inthe Fragment Mass Analyzer, and precise level energies were determined by detectingγrays with Gammasphere. Results:We observedγrays from the decay of 6 excited states in 32Cl. The excitation energies for two unbound levels at Ex= 1738.1 (6) keV and 2130.5 (10) keV were determined and found to be in agreement with a previous high-precision measurement of the 32S(3He,t)32Cl reaction 1. Conclusions:An updated 31S(p,γ)32Cl reaction rate is presented. With the excitation energies of important levels firmly established, the dominant uncertainty in the reaction rate at nova temperatures is due to the strength of the resonance corresponding to the 2131-keV state in32Cl.
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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.
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The super(19)Ne(p,gamma) super(20) Nareaction is the second step of a reaction chain which breaks out from the hot CNO cycle, following the super(15)O(alpha,gamma) super(19)Ne reaction at the onset ...of x-ray burst events. We investigate the spectrum of the lowest proton-unbound states in super(20) Nain an effort to resolve contradictions in spin-parity assignments and extract reliable information about the thermal reaction rate. The proton-transfer reaction super(19)Ne(d,n) super(2 0) Nais measured with a beam of the radioactive isotope super(19)Ne at an energy around the Coulomb barrier and in inverse kinematics. We observe three proton resonances with the super(19)Ne ground state, at 0.44, 0.66, and 0.82 MeV c.m. energies, which are assigned 3 super(+), 1 super(+), and (0 super(+)), respectively. In addition, we identify two resonances with the first excited state in super(19)Ne, one at 0.20 MeV and one, tentatively, at 0.54 MeV. These observations allow us for the first time to experimentally quantify the astrophysical reaction rate on an excited nuclear state. Our experiment shows an efficient path for thermal proton capture in super(19)Ne(p,gamma)Na super(20), which proceeds through ground state and excited-state capture in almost equal parts and eliminates the possibility for this reaction to create a bottleneck in the breakout from the hot CNO cycle.
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Retraction Kinoshita, N; Paul, M; Kashiv, Y ...
Science (American Association for the Advancement of Science),
2023-Mar-31, Volume:
379, Issue:
6639
Journal Article
Retraction Kinoshita, N; Paul, M; Kashiv, Y ...
Science (American Association for the Advancement of Science),
03/2023, Volume:
379, Issue:
6639
Journal Article
We have studied the nucleus super(14)B using the super(13)B(d,p) super(14 )B and super(15)C(d, super(3)He) super(14)B reactions. The two reactions provide complementary information about the ...negative-parity 1s sub(1/2) and 0d sub(5/2) neutron single-particle states in super(14)B. The data from the (d,p) reaction give neutron-spectroscopic strengths for these levels, and the (d, super(3)He) results confirm the existence of a broad 2' excited state suggested in the literature. Together these results provide estimates of the sd-shell neutron effective single-particle energies in super(14)B.
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