1,422 research outputs found
Lifetime measurement of excited low-spin states via the ) reaction
In this article a method for lifetime measurements in the sub-picosecond
regime via the Doppler-shift attenuation method (DSAM) following the inelastic
proton scattering reaction is presented. In a pioneering experiment we
extracted the lifetimes of 30 excited low-spin states of Ru, taking
advantage of the coincident detection of scattered protons and de-exciting
-rays as well as the large number of particle and -ray
detectors provided by the SONIC@HORUS setup at the University of Cologne. The
large amount of new experimental data shows that this technique is suited for
the measurement of lifetimes of excited low-spin states, especially for
isotopes with a low isotopic abundance, where ) or - in
case of investigating dipole excitations - ()
experiments are not feasible due to the lack of sufficient isotopically
enriched target material
Possible experimental signature of octupole correlations in the 0 states of the actinides
= 0 states have been investigated in the actinide nucleus
Pu up to an excitation energy of 3 MeV with a high-resolution (p,t)
experiment at = 24 MeV. To test the recently proposed = 0
double-octupole structure, the phenomenological approach of the
spdf-interacting boson model has been chosen. In addition, the total 0
strength distribution and the strength fragmentation have been compared
to the model predictions as well as to the previously studied (p,t) reactions
in the actinides. The results suggest that the structure of the 0 states
in the actinides might be more complex than the usually discussed pairing
isomers. Instead, the octupole degree of freedom might contribute
significantly. The signature of two close-lying 0 states below the
2-quasiparticle energy is presented as a possible manifestation of strong
octupole correlations in the structure of the 0 states in the actinides.Comment: 6 pages, 5 figures, published in Phys. Rev. C 88, 041303(R) (2013
Octupole correlations in positive-parity states of rare-earth and actinide nuclei
In this contribution, further evidence of the importance of multiphonon-octupole excitations to describe experimental data in the rare earths and actinides will be presented. First, new results of a (p, t) experiment at the Q3D magnetic spectrograph in Munich will be discussed, which was performed to selectively excite J(pi) = 0(+) states in Pu-240. spd f interacting boson model (IBM) calculations suggest that the previously proposed double-octupole phonon nature of the J(pi) = 0(2)(+) state is not in conflict with its strong (p, t) population. Second, the framework of the IBM has been adopted for the description of experimental observables related to octupole excitations in the rare earths. Here, the IBM is able to describe the signature splitting for positive- and negative-parity states when multi-dipole and multi-octupole bosons are included. The present study might support the idea of octupole-phonon condensation at intermediate spin (J(pi) = 10(+)) leading to the change in yrast structure observed in Nd-146
Octupole correlations in positive-parity states of rare-earth and actinide nuclei
In this contribution, further evidence of the importance of multiphonon-octupole excitations to describe experimental data in the rare earths and actinides will be presented. First, new results of a (p, t) experiment at the Q3D magnetic spectrograph in Munich will be discussed, which was performed to selectively excite J(pi) = 0(+) states in Pu-240. spd f interacting boson model (IBM) calculations suggest that the previously proposed double-octupole phonon nature of the J(pi) = 0(2)(+) state is not in conflict with its strong (p, t) population. Second, the framework of the IBM has been adopted for the description of experimental observables related to octupole excitations in the rare earths. Here, the IBM is able to describe the signature splitting for positive- and negative-parity states when multi-dipole and multi-octupole bosons are included. The present study might support the idea of octupole-phonon condensation at intermediate spin (J(pi) = 10(+)) leading to the change in yrast structure observed in Nd-146
The pygmy quadrupole resonance and neutron-skin modes in Sn-124
We present an extensive experimental study of the recently predicted pygmy quadrupole resonance (PQR) in Sn isotopes, where complementary probes were used. In this study, and experiments were performed on 124Sn. In both reactions, states below an excitation energy of 5 MeV were populated. The E2 strength integrated over the full transition densities could be extracted from the experiment, while the experiment at the chosen kinematics strongly favors the excitation of surface modes because of the strong α-particle absorption in the nuclear interior. The excitation of such modes is in accordance with the quadrupole-type oscillation of the neutron skin predicted by a microscopic approach based on self-consistent density functional theory and the quasiparticle-phonon model (QPM). The newly determined γ-decay branching ratios hint at a non-statistical character of the E2 strength, as it has also been recently pointed out for the case of the pygmy dipole resonance (PDR). This allows us to distinguish between PQR-type and multiphonon excitations and, consequently, supports the recent first experimental indications of a PQR in 124Sn
Mixed-symmetry octupole and hexadecapole excitations in N=52 isotones
In addition to the well-established quadrupole mixed-symmetry states, octupole and hexadecapole excitations with mixed-symmetry character have been recently proposed for the N = 52 isotones 92Zr and 94Mo. We performed two inelastic proton-scattering experiments to study this kind of excitations in the heaviest stable N = 52 isotone 96Ru. From the combined experimental data of both experiments absolute transition strengths were extracted
High-resolution (p,t) study of low-spin states in Pu 240: Octupole excitations, α clustering, and other structure features
© 2018 American Physical Society. Background: Many nuclear-structure features have been observed in actinides in recent decades. In particular, the octupole degree of freedom has been discussed lately after the successful measurement of the BE3;01+→31- reduced transition strength in Ra224. Recent results stemming from γ-spectroscopy experiments and high-resolution (p,t) experiments suggested that strong octupole correlations might be observed for some positive-parity states of actinide nuclei. Purpose: This work completes a series of (p,t) experiments on actinide nuclei by adding the data on Pu240. The (p,t) experiments allow us to study low-spin states up to Jπ=6+. Besides two-nucleon transfer cross sections, spin and parity can be assigned to excited states by measuring angular distributions, and several rotational bands are recognized based on these assignments. Methods: A high-resolution (p,t) experiment at Ep=24 MeV was performed to populate low-spin states in the actinide nucleus Pu240. The Q3D magnetic spectrograph of the Maier-Leibnitz Laboratory (MLL) in Munich (Germany) was used to identify the ejected tritons via dE/E particle identification with its focal-plane detection system. Angular distributions were measured at nine different Q3D angles to assign spin and parity to the excited states based on a comparison with coupled-channel distorted-wave Born approximation calculations. Results: In total, 209 states have been excited in Pu240 up to an excitation energy of 3 MeV. Many previously known states have also been observed and their spin-parity assignments were confirmed. However, many of the populated states have been seen for the first time, e.g., 15 new and firmly assigned Jπ=0+ states. In addition, all low-spin one-octupole phonon excitations, i.e., Kπ=0-,1-,2-,3-, could be observed and a new candidate for the K=3 projection is proposed. Furthermore, the double-octupole or α-cluster structure of the 02+ state in Pu240 has been studied in more detail. It is shown that the 02+ state in Th230 has a distinctly different structure. In addition, strongly excited 1- states have been observed at 1.5 and 1.8 MeV in Pu240. The present study suggests that similar states might be observed in Th230. Conclusions: At least two different and distinct structures for Jπ=0+ states are present in the actinides. These are pairing states and states with enhanced octupole correlations. We have shown that it is crucial to consider negative-parity single-particle states being admixed to some Kπ=02+ rotational bands to understand the α-decay hindrance factors and enhanced E1-decay rates. Based on our analysis, we have identified the double-octupole or α-cluster Kπ=0+ candidates from Ra224 to Pu240
The {\eta}'-carbon potential at low meson momenta
The production of mesons in coincidence with forward-going
protons has been studied in photon-induced reactions on C and on a
liquid hydrogen (LH) target for incoming photon energies of 1.3-2.6 GeV at
the electron accelerator ELSA. The mesons have been identified
via the decay
registered with the CBELSA/TAPS detector system. Coincident protons have been
identified in the MiniTAPS BaF array at polar angles of . Under these kinematic constraints the
mesons are produced with relatively low kinetic energy (
150 MeV) since the coincident protons take over most of the momentum of the
incident-photon beam. For the C-target this allows the determination of the
real part of the -carbon potential at low meson momenta by
comparing with collision model calculations of the kinetic energy
distribution and excitation function. Fitting the latter data for
mesons going backwards in the center-of-mass system yields a potential depth of
V = (44 16(stat)15(syst)) MeV, consistent with earlier
determinations of the potential depth in inclusive measurements for average
momenta of 1.1 GeV/. Within the experimental
uncertainties, there is no indication of a momentum dependence of the
-carbon potential. The LH data, taken as a reference to check
the data analysis and the model calculations, provide differential and integral
cross sections in good agreement with previous results for
photoproduction off the free proton.Comment: 9 pages, 13 figures. arXiv admin note: text overlap with
arXiv:1608.0607
Les Houches 2015: Physics at TeV colliders - new physics working group report
We present the activities of the 'New Physics' working group for the 'Physics
at TeV Colliders' workshop (Les Houches, France, 1-19 June, 2015). Our report
includes new physics studies connected with the Higgs boson and its properties,
direct search strategies, reinterpretation of the LHC results in the building
of viable models and new computational tool developments. Important signatures
for searches for natural new physics at the LHC and new assessments of the
interplay between direct dark matter searches and the LHC are also considered.Comment: Proceedings of the New Physics Working Group of the 2015 Les Houches
Workshop, Physics at TeV Colliders, Les Houches 1-19 June 2015. 197 page
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