Search results for "nucleus"
showing 10 items of 1803 documents
Superdeformation in the Doubly Magic NucleusC2040a20
2001
A rotational band with seven gamma -ray transitions between states with spin 2 (h) over bar and 16 (h) over bar has been observed in the doubly magic, self-conjugate nucleus Ca-40(20)20. The measured transition quadrupole moment of 1.80(-0.29)(+0.39)eb indicates a superdeformed shape with a deformation beta (2) = 0.59(-0.07)(+0.11). The features of this band are explained by cranked relativistic mean field calculations to arise from an 8-particle 8-hole excitation.
Steady state shocks in accretion disks around a Kerr black hole
1994
Results of numerical simulations of shock solutions in a geometrical thin accretion disk around a Kerr black hole (BH) are presented. Using the smoothed particle hydrodynamics (SPH) technique, the influence of the central object is included by means of an effective potential, We first present the theory of standing shock formation in accretion disks around a Kerr black hole, and show that the results of our numerical simulation agree very well with the theoretical results. We find that the shocks in an inviscid flow are very stable. We also remove the ambiguity prevalent regarding the location and stability of shocks in adiabatic flows. Finally we sketch some of the astrophysical consequenc…
QPOs expected in rotating accretion flows around a supermassive black hole
2006
AbstractIt is well known that rotating inviscid accretion flows with adequate injection parameters around black holes could form shock waves close to the black holes, after the flow passes through the outer sonic point and can be virtually stopped by the centrifugal force. We numerically examine such shock waves in 2D accretion flows with 10−5 to 106 Eddington critical accretion rates around a supermassive black hole with 106M⊙. As the results, the luminosities show QPO phenomena with modulations of a factor 2–3 and with quasi-periods of a few to several hours.
Individual Estimates of the Virial Factor in 10 Quasars: Implications on the Kinematics of the Broad Line Region
2020
Assuming a gravitational origin for the Fe III$\lambda\lambda$2039-2113 redshift and using microlensing based estimates of the size of the region emitting this feature, we obtain individual measurements of the virial factor, $f$, in 10 quasars. The average values for the Balmer lines, $\langle f_{H\beta}\rangle={\bf 0.43\pm 0.20}$ and $\langle f_{H\alpha}\rangle={\bf 0.50\pm 0.24}$, are in good agreement with the results of previous studies for objects with lines of comparable widths. In the case of Mg II, consistent results, $f_{Mg II} \sim {\bf 0.44}$, can be also obtained accepting a reasonable scaling for the size of the emitting region. The modeling of the cumulative histograms of indi…
Total photoabsorption cross section for4He from 200 to 800 MeV
1997
The total photoabsorption cross section for ${}^{4}$He has been measured for the first time over a wide photon energy range (200 MeV$l~{E}_{\ensuremath{\gamma}}l~$800 MeV). By using the large acceptance detector DAPHNE at the tagged photon facility of the MAMI microtron in Mainz high precision results with small systematic errors were obtained. This measurement shows that ${}^{4}$He has a behavior similar to heavy nuclei and, in particular, a reduction of the cross section with respect to the lighter nuclei is found for ${E}_{\ensuremath{\gamma}}g$600 MeV.
Fission fragment angular distributions in the capture reactions 50Ti, 56Fe + 208Pb
2008
The analysis of %-ray mult ip l ic i t ies measured I in coincidence with capture fission events in reactions of 26Mg through 54Cr, 58Fe, and 64Ni with 208pb in terms of Ko and~eff revealed1 that the resulting values of ~ /~e f f were rather independent of for a given system and, in a compound nucleus picture, were more in agreement with the 'shape of the non-rotating saddle than with the actually expected rotating saddle I f non-compound systenmhave to be considered these values of ~/J~ff__ shapes. suggested at least that the captured systems near the turning point from the inward radial motion to symmetric fragmentation had reached a remarkable compactness.
Unified description of structure and reactions: implementing the Nuclear Field Theory program
2015
The modern theory of the atomic nucleus results from the merging of the liquid drop (Niels Bohr and Fritz Kalckar) and of the shell model (Marie Goeppert Meyer and Axel Jensen), which contributed the concepts of collective excitations and of independent-particle motion respectively. The unification of these apparently contradictory views in terms of the particle-vibration (rotation) coupling (Aage Bohr and Ben Mottelson) has allowed for an ever increasingly complete, accurate and detailed description of the nuclear structure, Nuclear Field Theory (NFT, developed by the Copenhagen-Buenos Aires collaboration) providing a powerful quantal embodiment. In keeping with the fact that reactions are…
New Insight into the Cluster Structure of $^9$Be by Reactions with Deuteron Beam
2018
International audience; Angular distributions of protons, deuterons, tritons, and alpha particles emitted in the reaction 2H+9Be at Elab=19.5, 25, and 35 MeV were measured to study the structure of 9Be, especially to shed light on the internal clusters and possible cluster transfer of 5He. The experiments were performed at sufficiently high energies to ensure suppression of compound nucleus contribution. Thus, the direct reaction mechanism should be mainly responsible for the measured five-nucleon transfer cross section. The analysis suggests a significant contribution of simultaneous five-nucleon transfer in the reaction channel 9Be (d,4He) 7Li.
Chirality of $^{135}$Nd reexamined: Evidence for multiple chiral doublet bands
2019
One new pair of positive-parity chiral doublet bands have been identified in the odd-$A$ nucleus $^{135}$Nd which together with the previously reported negative-parity chiral doublet bands constitute a third case of multiple chiral doublet (M$\chi$D) bands in the $A\approx130$ mass region. The properties of the M$\chi$D bands are well reproduced by constrained covariant density functional theory and particle rotor model calculations. The newly observed M$\chi$D bands in $^{135}$Nd represents an important milestone in supporting the existence of M$\chi$D in nuclei.
Spectral Variability of the Nucleus of M33 in aChandra/ACIS Observation
2002
We have analyzed a 90 ksec long observation of the bright nucleus of M33 made with Chandra/ACIS. We detected low-amplitude (~sim10%) highly significant variability on timescales of ~5000 sec. We also find associated spectral variability. The two main spectral components (a power-law with \Gamma~2 and a multicolor disk -MCD- with kT~0.9-1.2 keV) vary in relative flux. The MCD temperature also increases with increasing MCD flux. The pattern of variability is reminiscent of (but not identical to) galactic black hole binaries. A ~5 M$_{\odot}$ accreting black hole may explain this source.