1,504 research outputs found
Direct proton decay of the isoscalar giant dipole resonance in 208Pb
The excitation and subsequent proton decay of the isoscalar giant dipole
resonance (ISGDR) in Pb have been investigated via the
Pb(Tl reaction at 400 MeV. Excitation
of the ISGDR has been identified by the difference-of-spectra method. The
enhancement of the ISGDR strength at high excitation energies observed in the
multipole-decomposition-analysis of the singles
Pb() spectra is not present in the excitation
energy spectrum obtained in coincidence measurement. The partial branching
ratios for direct proton decay of ISGDR to low-lying states of Tl have
been determined and the results are compared with predictions of continuum
random-phase-approximation (CRPA) calculations.Comment: 12 pages, 4 figures; accepted for publication in Physics Letters
pairs from a nuclear transition signaling an elusive light neutral boson
Electron-positron pairs have been observed in the 10.95-MeV decay
in O. The branching ratio of the ee pairs compared to the
3.84-MeV decay of the level is deduced to be
. This magnetic monopole (M0) transition cannot proceed by
-ray decay and is, to first order, forbidden for internal pair
creation. However, the transition may also proceed by the emission of a light
neutral or boson. Indeed, we do observe a sharp peak in the
angular correlation with all the characteristics belonging to the
intermediate emission of such a boson with an invariant mass of 8.5(5)
MeV/c. It may play a role in the current quest for light dark matter in the
universe.Comment: 6 page
Observation of Anomalous Internal Pair Creation in Be: A Possible Signature of a Light, Neutral Boson
Electron-positron angular correlations were measured for the isovector
magnetic dipole 17.6 MeV state (, ) ground state
(, ) and the isoscalar magnetic dipole 18.15 MeV (,
) state ground state transitions in Be. Significant
deviation from the internal pair creation was observed at large angles in the
angular correlation for the isoscalar transition with a confidence level of . This observation might indicate that, in an intermediate step, a
neutral isoscalar particle with a mass of 16.70 (stat)
(sys) MeV and was created.Comment: 5 pages, 5 figure
Transmission resonance spectroscopy in the third minimum of 232Pa
The fission probability of 232Pa was measured as a function of the excitation
energy in order to search for hyperdeformed (HD) transmission resonances using
the (d,pf) transfer reaction on a radioactive 231Pa target. The experiment was
performed at the Tandem accelerator of the Maier-Leibnitz Laboratory (MLL) at
Garching using the 231Pa(d,pf) reaction at a bombarding energy of E=12 MeV and
with an energy resolution of dE=5.5 keV. Two groups of transmission resonances
have been observed at excitation energies of E=5.7 and 5.9 MeV. The fine
structure of the resonance group at E=5.7 MeV could be interpreted as
overlapping rotational bands with a rotational parameter characteristic to a HD
nuclear shape. The fission barrier parameters of 232Pa have been determined by
fitting TALYS 1.2 nuclear reaction code calculations to the overall structure
of the fission probability. From the average level spacing of the J=4 states,
the excitation energy of the ground state of the 3rd minimum has been deduced
to be E(III)=5.05 MeV.Comment: 6 pages, 8 figure
Proton decay from the isoscalar giant dipole resonance in Ni
Proton decay from the 3 isoscalar giant dipole resonance (ISGDR)
in Ni has been measured using the () reaction at a
bombarding energy of 386 MeV to investigate its decay properties. We have
extracted the ISGDR strength under the coincidence condition between
inelastically scattered particles at forward angles and decay protons
emitted at backward angles. Branching ratios for proton decay to low-lying
states of Co have been determined, and the results compared to
predictions of recent continuum-RPA calculations. The final-state spectra of
protons decaying to the low-lying states in Co were analyzed for a more
detailed understanding of the structure of the ISGDR. It is found that there
are differences in the structure of the ISGDR as a function of excitation
energy.Comment: Minor changes after review. Accepted for publication in Phys. Rev. C.
19 pages; 7 figure
Reaction fronts in stochastic exclusion models with three-site interactions
The microscopic structure and movement of reaction fronts in reaction
diffusion systems far from equilibrium are investigated. We show that some
three-site interaction models exhibit exact diffusive shock measures, i.e.
domains of different densities connected by a sharp wall without correlations.
In all cases fluctuating domains grow at the expense of ordered domains, the
absence of growth is possible between ordered domains. It is shown that these
models give rise to aspects not seen in nearest neighbor models, viz. double
shocks and additional symmetries. A classification of the systems by their
symmetries is given and the link of domain wall motion and a free fermion
description is discussed.Comment: 29 pages, 5 figure
Hybrid molecules of protoflavones and spirooxindole derivatives with selective cytotoxicity against triple-negative breast cancer cells
The combination of compounds with complementary bioactivities into hybrid molecules is an emerging concept in drug discovery. In this study, we aimed to synthesize new hybrid compounds based on p53-MDM2/X protein-protein interaction spiropyrazoline oxindole-based inhibitors and ataxia telangiectasia and Rad3-related (ATR) protoflavone-based inhibitors through copper(i) catalysed azide-alkyne cycloaddition. Five new hybrids were prepared along with three representative reference fragments. The compounds were tested against human breast cancer cell lines MCF-7 (hormone-dependent, wild-type p53) and MDA-MB-231 (triple-negative, mutant p53). Most of the new hybrids were more cytotoxic than their reference fragments and several showed 2-4 times selective toxicity against MDA-MB-231 cells. Relevant pharmacological benefit gained from the hybrid coupling was further confirmed by virtual combination index calculations using the Chou method. Compound 13 modulated doxorubicin-induced DNA damage response through inhibiting the ATR-dependent activation of Chk-1, while increasing the activation of Chk-2. Our results suggest that the new hybrids may serve as new leads against triple negative breast cancer
Systematic investigation of the elastic proton-deuteron differential cross section at intermediate energies
To investigate the importance of three-nucleon forces (3NF) systematically
over a broad range of intermediate energies, the differential cross sections of
elastic proton-deuteron scattering have been measured at proton bombarding
energies of 108, 120, 135, 150, 170 and 190 MeV at center-of-mass angles
between and . Comparisons with Faddeev calculations show
unambiguously the shortcomings of calculations employing only two-body forces
and the necessity of including 3NF. They also show the limitations of the
latest few-nucleon calculations at backward angles, especially at higher beam
energies. Some of these discrepancies could be partially due to relativistic
effects. Data at lowest energy are also compared with a recent calculation
based on \chipt
Low-lying GT(+) strength in Co-64 studied via the Ni-64(d,He-2)Co-64 reaction
The Ni-64(d,He-2)Co-64 reaction was studied at the AGOR cyclotron of KVI, Groningen, with the Big-Bite Spectrometer and the EuroSuperNova detector using a 171-MeV deuteron beam. An energy resolution of about 110 keV was achieved. In addition to the J(pi) = 1(+) ground state, several other 1(+) states could be identified in Co-64 and the strengths of the corresponding Gamow-Teller transitions were determined. The obtained strength distribution was compared with theoretical predictions and former (n,p) experimental results and displayed a good agreement. Due to the good energy resolution, detailed spectroscopic information was obtained, which supplements the data base needed for network calculations for supernova scenarios
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