Absolute Excitation Energies Research Articles

Single step links of the superdeformed band in 194Pb: a measure of the absolute excitation energy, spin and parity of the superdeformed states

The EUROGAM array has been used to investigate the decay out of the yrast superdeformed (SD) band in 194Pb. Six single step decays from the lowest observed SD states to low-lying states at normal deformation (ND) have been identified. From this observation, the excitation energy of the SD band in 194Pb is established at 4877 ± 1.5 keV for the 6 + SD state. The most probable spins and parities of all members of the SD band are also deduced assuming that the SD states have even spin and positive parity.

An efficient polarization propagator approach to valence electron excitation spectra

A practical polarization propagator method devised for the treatment of valence electron excitations in atoms and molecules is presented. This method, referred to as (second-order) algebraic-diagrammatic construction (ADC(2)), allows for a theoretical description of single and double excitations consistently through second and first order, respectively, of perturbation theory. The computational scheme is essentially an eigenvalue problem of a Hermitian secular matrix defined with respect to the space of singly and doubly excited configurations. The configuration space is smaller (more compact) than that of comparable configuration interaction (CI) expansions and the method leads to size-consistent results. The performance of the ADC(2) method is tested in exemplary applications to Ne, Ar and CO, where detailed comparison can be made with experiment and previous theoretical results. While the accuracy of the absolute excitation energies is only moderate, a very satisfactory description is obtained for the relative energies and, in particular, for the spectral intensities. Aspects related to the Thomas-Reiche-Kuhn sum rule and the equivalence of the dipole-length and dipole-velocity forms of the transition moments are discussed. Due to the relatively small computational expense and the possibility of a direct ADC(2) formulation this method should prove particularly useful in applications to large molecules.

Shape coexistence in 185Tl and 187Tl — investigation of the deformed minima

Abstract High spin gamma-ray spectroscopy of 185 Tl and 187 Tl has been performed with the reactions 154 Gd( 35 Cl, 4n) and 159 Tb( 32 S, 4n). Positive γ-ray identification with the thallium isotopes was made via X-ray coincidences, and supported by mass selected γ-ray spectra, the latter obtained with the reactions 154 Gd( 36 Ar, p4n) and 155 Gd( 36 Ar, p3n). Rotational bands associated with both prolate and oblate shape were observed. The bandheads of the proposed oblate 13 2 + [606] states were found to be isomeric, with meanlives of 12 ± 2 ns in 185 Tl and 1.0 ± 0.2 ns in 187 Tl. Prolate deformed i 13 2 bands were observed in both nuclei, while in 187 Tl, bands due to h 9 2 and f 7 2 protons coupled to the prolate shape are also assigned. An h 9 2 band is tentatively assigned in 185 Tl. The observation of these rotation-aligned bands at low excitation energy implies that the development of prolate deformed minima in the odd nuclei is not necessarily blocked by occupation of a single deformation-driving orbital. Equilibrium deformation calculations for intrinsic states in a range of thallium nuclei are presented. Experimental trends with mass number are reproduced, but absolute excitation energies, and energy differences between the prolate and oblate states are not, continuing the persistent discrepancy between theory and experiment in the mercury region. Theoretical calculations of intruder orbital occupation probabilities show a correlation between prolate deformation and h 9 2 and f 7 2 proton pair population, in particular of the 1 2 − [541] orbital from the h 9 2 proton shell. They also show that blocking of the 1 2 − [541] orbital significantly suppresses the prolate deformation. Implications for the structure of the prolate deformed mercury and thallium isotopes are considered, leading to the conclusion that the prolate mercury core nuclei consist of a mixture of low-Ω proton intruder excitations.

Observation of the decay out of the superdeformed band in 143Eu

Connections between the superdeformed and normaldeformed states in 143Eu have been established by measuring energy sums of two consecutive γ-ray transitions in the linking cascade. Six decay paths have been observed connecting discrete states in the two potential wells. The absolute excitation energy and the most likely spin of a superdeformed band have been determined directly for the first time.

Linking transitions from the superdeformed band in 143Eu.

Connections between the superdeformed and normal-deformed states in $^{143}\mathrm{Eu}$ have been established by measuring energy sums of two consecutive \ensuremath{\gamma}-ray transitions in the linking cascade. Six decay paths have been observed connecting discrete states in the two potential wells. The absolute excitation energy and the most likely spin of the superdeformed band have been determined directly for the first time.

Absolute excitation energies for the 2p53s3p and 3d configurations in core-excited Na-like sulfur and chlorine

Using the beam-foil technique we have investigated the 2p63l 2L-2p53s3l 2,4L transitions which connect the normal and core-excited termsystems in Na-like S VI and Cl VII. From the observed wavelengths absolute excitation energies have been derived for some core-excited levels. The analysis is greatly facilitated by combining the results from theoretical calculations with measurements utilizing the unique time-resolution of the beam-foil method. We also present an overview of the absolute energies along the isoelectronic sequence.

On the use of higher-order irreducible vertex parts in the calculation of exciton spectra

The possibility to employ higher-order irreducible vertex parts (corresponding to virtual double-excitations) in the calculation of excitonic levels in infinite systems has been discussed. Numerical ab initio Hartree-Fock and correlation calculations in the Møller-Plesset partitioning have been performed on an alternating hydrogen chain. The results show that, while proper renormalization is important in the calculation of absolute excitation energies, the exciton binding energies are stronger influenced by the higher-order terms in the irreducible vertex part.

High-resolution projectile Auger spectroscopy for Li, Be, B and C excited in single gas collisions. I. Line energies for prompt decays

The ejected-electron spectra of highly excited autoionising levels of Li, Be, B and C have been studied by using the projectile electron spectroscopy method. Singly and doubly core-excited states are strongly populated in 100 to 500 keV Li+, Be+, B+ and C+ single collisions with He and CH4. High resolution is obtained by selecting a small observation angle (6.4 degrees ) with respect to the beam axis. Numerous states, previously not seen, have been resolved and identified by comparison with existing theoretical data. For a large number of core-excited states, absolute Auger transition and excitation energies are given. In particular, isoelectronic sequences for singly core-excited lithium-like (Z=2-16) and doubly core-excited helium-like (Z=1-14) autoionising states are studied.

Excitation energies of barium oxide bands measured in flames

Experiments are described that yield additional information about the excitation energy of visible barium oxide bands appearing in flames. Excitation energy differences are derived directly from the ratios of thermal band intensities as a function of temperature and agree with the value calculated from the known (relative) energy-level diagram. Absolute excitation energies are derived from the temperature dependence of the ratio of band-to-line intensity under thermal equilibrium conditions and under the assumption of a most probable value for the dissociation energy of BaO. Flames with temperatures ranging from 1911 to 2886 K were used. The excitation energy values found can be reconciled with the assumption that the lower 1∑ state of the optical transitions is the electronic ground state only if there are low-lying electronic levels that contribute at least a factor of 6 to the electronic partition function.

Excitation energies of strontium mono-hydroxide bands measured in flames

Experiments are described to yield more decisive information about the excitation energies of visible strontium monohydroxide bands appearing in flames. Excitation energy differences are derived directly from the ratio of thermal band intensities measured as a function of temperature. Absolute excitation energies are derived from the temperature dependence of the ratio of thermal band to strontium line intensity, while assuming a value for the dissociation energy of SrOH. Flames with temperatures ranging from 1907 to 2886 K were used. A level diagram is proposed for the strontium bands at 6060, 6470, 6690, and 6820 Å. From the results obtained, two conclusions may be drawn: (i) the bands considered are non-resonance bands and (ii) the uncertainty in the excitation energy as a result of the unknown molecular configuration is 0·25 eV.

Levels ofCu61,Cu64,Ga67, andGa68Excited by the (p, n) Reaction

Neutron time-of-flight techniques were used to study the ($p, n$) reaction on the nuclei $^{61}\mathrm{Ni}$, $^{64}\mathrm{Ni}$, $^{67}\mathrm{Zn}$, and $^{68}\mathrm{Zn}$. The locations of excited states in the residual nuclei were measured with an energy resolution of about 10 keV. The absolute excitation energies are accurate to \ifmmode\pm\else\textpm\fi{}2 keV for low-lying states and to \ifmmode\pm\else\textpm\fi{}5 to 7 keV for the highest states (2-3-MeV excitation). The following results were obtained: $^{61}\mathrm{Cu}$, 17 levels (0 to 2.6 MeV); $^{64}\mathrm{Cu}$, 66 levels (0 to 2.75 MeV); $^{67}\mathrm{Ga}$, 57 levels (0 to 3.3 MeV); and $^{68}\mathrm{Ga}$, 32 levels (0 to 1.6 MeV). Comparisons with other information on these nuclei indicate that the ($p, n$) reaction is a very effective tool for locating all the levels. The relative intensities of the neutron groups displayed distinctive patterns. However, quantitative yields of a succession of closely spaced proton energies showed typically 30% fluctuations. To maintain good energy resolution and yet reduce the fluctuations we averaged many individual runs in order to have more meaningful comparisons with the Hauser-Feshbach predictions. Spin assignments were made to 10-20 levels in $^{64}\mathrm{Cu}$, $^{67}\mathrm{Ga}$, and $^{68}\mathrm{Ga}$. The results are generally consistent with other available information on spin parities.