33 research outputs found
Statistical properties of Pu, and Pu(n,) cross section calculation
The level density and gamma-ray strength function (gammaSF) of 243Pu have
been measured in the quasi-continuum using the Oslo method. Excited states in
243Pu were populated using the 242Pu(d,p) reaction. The level density closely
follows the constant-temperature level density formula for excitation energies
above the pairing gap. The gammaSF displays a double-humped resonance at low
energy as also seen in previous investigations of actinide isotopes. The
structure is interpreted as the scissors resonance and has a centroid of
omega_{SR}=2.42(5)MeV and a total strength of B_{SR}=10.1(15)mu_N^2, which is
in excellent agreement with sum-rule estimates. The measured level density and
gammaSF were used to calculate the 242Pu(n,gamma) cross section in a neutron
energy range for which there were previously no measured data.Comment: 9 pages, 8 figure
Search for Nova Presolar Grains: γ -Ray Spectroscopy of Ar 34 and its Relevance for the Astrophysical Cl 33 (p,γ) Reaction
The discovery of presolar grains in primitive meteorites has initiated a new era of research in the study of stellar nucleosynthesis. However, the accurate classification of presolar grains as being of specific stellar origins is particularly challenging. Recently, it has been suggested that sulfur isotopic abundances may hold the key to definitively identifying presolar grains with being of nova origins and, in this regard, the astrophysical Cl33(p,γ)Ar34 reaction is expected to play a decisive role. As such, we have performed a detailed γ-ray spectroscopy study of Ar34. Excitation energies have been measured with high precision and spin-parity assignments for resonant states, located above the proton threshold in Ar34, have been made for the first time. Uncertainties in the Cl33(p,γ) reaction have been dramatically reduced and the results indicate that a newly identified ℓ =0 resonance at Er=396.9(13) keV dominates the entire rate for T=0.25-0.40 GK. Furthermore, nova hydrodynamic simulations based on the present work indicate an ejected S32/S33 abundance ratio distinctive from type-II supernovae and potentially compatible with recent measurements of a presolar grain
Search for Nova Presolar Grains: γ -Ray Spectroscopy of Ar 34 and its Relevance for the Astrophysical Cl 33 (p,γ) Reaction
The discovery of presolar grains in primitive meteorites has initiated a new era of research in the study of stellar nucleosynthesis. However, the accurate classification of presolar grains as being of specific stellar origins is particularly challenging. Recently, it has been suggested that sulfur isotopic abundances may hold the key to definitively identifying presolar grains with being of nova origins and, in this regard, the astrophysical Cl33(p,γ)Ar34 reaction is expected to play a decisive role. As such, we have performed a detailed γ-ray spectroscopy study of Ar34. Excitation energies have been measured with high precision and spin-parity assignments for resonant states, located above the proton threshold in Ar34, have been made for the first time. Uncertainties in the Cl33(p,γ) reaction have been dramatically reduced and the results indicate that a newly identified ℓ =0 resonance at Er=396.9(13) keV dominates the entire rate for T=0.25-0.40 GK. Furthermore, nova hydrodynamic simulations based on the present work indicate an ejected S32/S33 abundance ratio distinctive from type-II supernovae and potentially compatible with recent measurements of a presolar grain
Collectivity in ¹⁹⁶,¹⁹⁸Pb isotopes probed in Coulomb-excitation experiments at REX-ISOLDE
The neutron-deficient ¹⁹⁶,¹⁹⁸Pb isotopes have been studied in Coulomb-excitation experiments employing the Miniball γ-ray spectrometer and radioactive ion beams from the REX-ISOLDE post-accelerator at CERN. The reduced transition probabilities of the first excited 2⁺ states in ¹⁹⁶Pb and ¹⁹⁸Pb nuclei have been measured for the first time. Values of B (E2) = 18.2₋₄,₁⁺⁴,⁸ W.u. and B (E2) = 13.1₋₃,₅⁺⁴,⁹ W.u., were obtained, respectively. The experiment sheds light on the development of collectivity when moving from the regime governed by the generalised seniority scheme to a region, where intruding structures, associated with different deformed shapes, start to come down in energy and approach the spherical ground state
The spectroscopic quadrupole moment of the 21+ state of 12C : A benchmark of theoretical models
The spectroscopic quadrupole moment of the first 2+ state of 12C has been measured employing the Coulomb-excitation re-orientation technique. Our result of Qs(21+)=+9.3−3.8+3.5efm2 suggests a larger oblate deformation than previously reported. Combining this with the consistently re-analyzed adopted value, we present the most precise value to date of Qs(21+)=+9.5(18)efm2, which is consistent with a geometrical rotor description. This simple outcome is compared to state-of-the-art shell-model, mean-field, ab initio calculations, cluster-based and geometrical-like theories, which show varying degrees of emergent quadrupole collectivity
Superdeformed and Triaxial States in Ca 42
Shape parameters of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in ^{42}Ca were determined from E2 matrix elements measured in the first low-energy Coulomb excitation experiment performed with AGATA. The picture of two coexisting structures is well reproduced by new state-of-the-art large-scale shell model and beyond-mean-field calculations. Experimental evidence for superdeformation of the band built on 0_{2}^{+} has been obtained and the role of triaxiality in the A∼40 mass region is discussed. Furthermore, the potential of Coulomb excitation as a tool to study superdeformation has been demonstrated for the first time
Quadrupole and octupole collectivity in the semi-magic nucleus 80206Hg126
The first low-energy Coulomb-excitation measurement of the radioactive, semi-magic, two proton-hole nucleus 206Hg, was performed at CERN's recently-commissioned HIE-ISOLDE facility. Two γ rays depopulating low-lying states in 206Hg were observed. From the data, a reduced transition strength B(E2;21+→01+)=4.4(6) W.u. was determined, the first such value for an N=126 nucleus south of 208Pb, which is found to be slightly lower than that predicted by shell-model calculations. In addition, a collective octupole state was identified at an excitation energy of 2705 keV, for which a reduced B(E3) transition probability of 30−13+10 W.u. was extracted. These results are crucial for understanding both quadrupole and octupole collectivity in the vicinity of the heaviest doubly-magic nucleus 208Pb, and for benchmarking a number of theoretical approaches in this key region. This is of particular importance given the paucity of data on transition strengths in this region, which could be used, in principle, to test calculations relevant to the astrophysical r-process
Decay of the I π = 8 − isomeric state in Nd 134 and Pt 184 studied by electron and γ spectroscopy
International audienceThe properties of the K-isomer decays in the 134 Nd and 184 Pt nuclei have been investigated. Measurements were carried out in e-γ and γ-γ coincidence modes using electron spectrometers coupled to the central European Array for Gamma Levels Evaluations at the Heavy Ion Laboratory of the University of Warsaw. Internal conversion coefficients were obtained for transitions relevant to the decay of the isomeric states, allowing the determination of multipolarities and mixing ratios as well as hindrance factors. Two possible causes of the weakening of the K forbiddenness, namely rotational K mixing (Coriolis interaction) and triaxiality, are briefly discussed using schematic theoretical models