Abstract
The theory governing the strong nuclear force—quantum chromodynamics—predicts that at sufficiently high energy densities, hadronic nuclear matter undergoes a deconfinement transition to a ...new phase of quarks and gluons
1
. Although this has been observed in ultrarelativistic heavy-ion collisions
2,3
, it is currently an open question whether quark matter exists inside neutron stars
4
. By combining astrophysical observations and theoretical ab initio calculations in a model-independent way, we find that the inferred properties of matter in the cores of neutron stars with mass corresponding to 1.4 solar masses (
M
⊙
) are compatible with nuclear model calculations. However, the matter in the interior of maximally massive stable neutron stars exhibits characteristics of the deconfined phase, which we interpret as evidence for the presence of quark-matter cores. For the heaviest reliably observed neutron stars
5,6
with mass
M
≈ 2
M
⊙
, the presence of quark matter is found to be linked to the behaviour of the speed of sound
c
s
in strongly interacting matter. If the conformal bound
$${c}_{\rm{s}}^{2}\le 1/3$$
c
s
2
≤
1
/
3
(ref.
7
) is not strongly violated, massive neutron stars are predicted to have sizable quark-matter cores. This finding has important implications for the phenomenology of neutron stars and affects the dynamics of neutron star mergers with at least one sufficiently massive participant.
Full text
Available for:
FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The charge particle (α) induced reactions on enriched copper (65Cu) are investigated for the production of 68Ga. The data sets of experimental cross sections are compiled, normalized and nuclear ...model analysis is done using calculational codes namely, ALICE-IPPE, TALYS 1.95 and EMPIRE 3.2. The theoretical production cross sections via alpha particle induced reactions are calculated to present a set of recommended cross sections. The calculated cross sections are utilized to deduce thick target yield (TTY) for the 65Cu (α, n) 68Ga reaction. The range of energy for production of 68Ga is suggested up to 40 MeV having least contribution of radio-impurities.
•Compilation of the excitation functions of 65Cu(α, n)68Ga reaction from all available experimental data.•Theoretical production cross sections are calculated using ALICE-IPPE, TALYS-1.95, EMPIRE-3.2.•The contributions of radio-nuclidic impurities are discussed.•Recommended cross sections have been deduced.•Thick target yield is estimated from the recommended cross sections.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Excited states have been observed for the first time in the very neutron-deficient odd-odd nucleus 57120La63. The observed γ rays have been assigned based on coincidences with lanthanum X rays ...measured with the JUROGAM 3 array and with A=120 fusion-evaporation residues measured with the MARA separator. The observed γ rays form a rotational band which decays to the ground state via a cascade of four low-energy transitions. Based on the systematic comparisons with the heavier odd-odd La isotopes we assign spin-parity 4+ to the ground state and a πh11/2⊗νh11/2 configuration to the rotational band. The nuclear shape has been investigated by the cranked Nilsson-Strutinsky model. Two quasiparticle plus triaxial rotor model calculations including the np interaction nicely reproduce the spin of the inversion between the even- and odd-spin cascades of E2 transitions, giving credit to the np interaction as an important parameter responsible for the mechanism inducing the inversion. The position of the Fermi levels, in particular for neutrons, also has a strong impact on the observed inversion in the chain of lanthanum nuclei.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The deformation mechanism of an eutectic high-entropy alloy (EHEA) AlCoCrFeNi2.1 at elevated temperature has been studied by tensile test, microstructure analysis and calculation. The ratio of the ...FCC and BCC phases has changed greatly after deformation. The formation enthalpies of L12-type Ni3Al and B2-type NiAl are calculated by using Miedema model. Testing and calculation suggest that B2Ⅱprecipitates (NiAl) have a priority in the precipitation order, which is critical to phase change. Besides, TEM results reveal that the function of B2Ⅱ precipitates in FCC matrix during deformation is similar to Orowan by-passing mechanism, and the role of L12,Ⅱ precipitates in B2 matrix is regarded as dislocation cutting. Dynamic recrystallization, occurring in the FCC matrix, reduces stress concentration caused by dislocation motion, but it may be suppressed by B2Ⅱ precipitates. It has been identified that the softening mechanism of dynamic recrystallization and precipitation strengthening have an effect on the high temperature deformation process of the AlCoCrFeNi2.1 EHEA.
Display omitted
•Eutectichigh-entropy alloy exhibits ultra high ductility at elevated temperature.•The dynamic recrystallization takes place in the FCC matrix and it plays a softening role in the deformation process.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The prescission neutron multiplicities (νpre) are studied for a systematic understanding of the influence of entrance-channel shell closure in fusion-fission dynamics. The existing νpre data are ...analyzed for reactions with a wide variety of target and projectile combinations. For completeness, the measured νpre data for the fusion-fission reactions with the doubly closed shell 16O projectile on the targets having either proton (204,206Pb) or both proton and neutron (208Pb) shell closure is reanalyzed. Although the measured νpre for 224Th disagree with the available data reported by Rossner et al. (1992) 1, our results are found to be more consistent and follow a systematic trend as described in this letter. Theoretical analysis is performed within the standard statistical model framework, where dissipation strength is used as a tunable parameter. It is observed that irrespective of the compound nuclear excitation energy, the entrance channel magicity imparts an intriguing impact on the dissipation strength. A similar entrance channel effect in the evaporation residue cross-section is also demonstrated. In conclusion, the present analysis establishes an entanglement of the exit channel observables with the entrance channel shell closure. It contradicts the hypothesis of complete equilibrium in compound nuclear reactions.
•Dissipation transiently drives the fission degree of freedom and delays the journey of CN across the fission barrier.•A systematic analysis of the existing prescission neutron multiplicity data is performed.•Systematic analysis reveals an evident impact of entrance channel magicity on neutron emission.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We examine the thermodynamic properties of mass A∼200 nuclei utilizing angular momentum (J) gated nuclear level densities (NLDs) extracted in the excitation energy range of 2–15 MeV. Interestingly, ...the experimental NLDs are in good agreement with the results of a microscopic approach, which is derived based on the exact pairing plus the independent-particle model at finite temperature (EP+IPM), whereas the conventional Hartree–Fock BCS (HFBCS) and Hartree–Fock–Bogoliubov plus combinatorial method (HFBC) fail to describe these data. Consequently, the thermodynamic properties of those nuclei at finite angular momentum have been extracted using the EP+IPM NLDs. While the heat capacities of 200Tl, 211Po and 212At (near spherical nuclei) follow the trend as expected in odd–odd and even–odd masses, surprisingly an S-shaped heat capacity is found in odd–odd deformed nucleus 184Re. It has been shown that this S-shaped heat capacity observed in 184Re is caused by not only the breaking of nucleon Cooper pairs but also the change of pairing induced by deformation.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The fourth version of the Japanese Evaluated Nuclear Data Library has been produced in cooperation with the Japanese Nuclear Data Committee. In the new library, much emphasis is placed on the ...improvements of fission product and minor actinoid data. Two nuclear model codes were developed in order to evaluate the cross sections of fission products and minor actinoids. Coupled-channel optical model parameters, which can be applied to wide mass and energy regions, were obtained for nuclear model calculations. Thermal cross sections of actinoids were carefully examined by considering experimental data or by the systematics of neighboring nuclei. Most of the fission cross sections were derived from experimental data. A simultaneous evaluation was performed for the fission cross sections of important uranium and plutonium isotopes above 10 keV. New evaluations were performed for the thirty fissionproduct nuclides that had not been contained in the previous library JENDL-3.3. The data for light elements and structural materials were partly reevaluated. Moreover, covariances were estimated mainly for actinoids. The new library was released as JENDL-4.0, and the data can be retrieved from the Web site of the JAEA Nuclear Data Center.
Full text
Available for:
BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
High-spin states of the N = 83 nucleus 142Pr have been observed for the first time using the 138Ba(7Li, 3n) reaction at a beam energy of 38 MeV. A total of 40 new transitions and 22 new levels have ...been identified, leading to a considerable extension of the level scheme of 142Pr. The experimental level structures of 142Pr are compared with its neighboring N = 83 isotones 144Pm and 146Eu. Shell model calculations employing the jj56pna interaction reproduce the experimental findings and provide guidance in the interpretation of the observed high-spin level structures.
Activation cross-sections of the nuclear reactions
Ba(p,x)
La,
Ba and
Ce(p,x)
Pr,
Ce have been measured experimentally at the MGC-20 cyclotron, Cairo, Egypt, from their respective threshold energies ...up to about 14.7 MeV. Stacked foil irradiation technique and high-resolution gamma-ray spectroscopy were used. A comparison between the experimental and theoretical data derived from the nuclear model codes EMPIRE and TALYS (in the form of the TENDL library) was performed. The agreement in the low-energy region is fairly good. Integral yields of the produced radioisotopes were estimated from the present cross-section data and the results are discussed in terms of their production possibilities.
A fully microscopic model for the description of nuclear level density (NLD) in spherical nuclei is proposed. The model is derived by combining the partition function of the exact pairing solution ...plus the independent-particle model at finite temperature (EP+IPM) with that obtained by using the collective vibrational states calculated from the self-consistent Hartree-Fock mean field with MSk3 interaction plus the exact pairing and random-phases approximation (SC-HFEPRPA). Two important factors are taken into account in a fully microscopic way, namely the spin cut-off and vibrational enhancement factors are, respectively, calculated using the statistical thermodynamics and partition function of the SC-HFEPRPA without any fitting parameters. The numerical test for two spherical 60Ni and 90Zr nuclei shows that the collective vibrational enhancement is mostly dominated by the quadrupole and octupole excitations. This is the first microscopic model confirming such an effect, which was phenomenologically predicted long time ago and widely employed in several NLD models. In addition, the influence of collective vibrational enhancement on nuclear thermodynamic quantities such as excitation energy, specific heat capacity and entropy is also studied by using the proposed model.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
