Experimental Transition Probabilities Research Articles

Potential description of the positive- and negative-energy properties of the alpha + 40Ca system and alpha -cluster structure of 44Ti.

The \ensuremath{\alpha}-cluster structure of the $^{44}\mathrm{Ti}$ nucleus is investigated within a local potential model description, starting from the unique optical potential which describes elastic $^{40}\mathrm{Ca}$(\ensuremath{\alpha},\ensuremath{\alpha}) scattering on broad angular and energy ranges, and which has recently been shown to describe the broad oscillations seen in the low energy fusion excitation function as well. It is found that the various \ensuremath{\alpha}-cluster states group into quasirotational bands whose properties are not dissimilar to those of the well-understood $^{20}\mathrm{Ne}$ nucleus. The lowest lying band is composed of states of even parity with moderate cluster character at low spin; it agrees within a few MeV's in absolute energy with the $^{44}\mathrm{Ti}$ experimental ground state band, and the experimental intraband quadrupole transition probabilities are reproduced with good accuracy. The potential supports an excited positive parity band with strong cluster character, starting a few MeV's above the \ensuremath{\alpha}${+\mathrm{}}^{40}$Ca threshold; the states of this band with spins ranging from 6 to 12 are responsible for the oscillations observed in the fusion excitation function. It supports, in addition, a negative parity band starting just above the threshold and composed of narrow states with intermediate cluster character; the latter has up to now no experimentally known counterpart. The states of higher lying bands are very broad and overlapping but they play an important role in enhancing the $^{40}\mathrm{Ca}$(\ensuremath{\alpha},\ensuremath{\alpha}) backward angle cross section. Our results are discussed in terms of the available experimental evidence and of the various, often conflicting theoretical interpretations which have been put forward to describe the $^{44}\mathrm{Ti}$ \ensuremath{\alpha}-cluster spectroscopy.

Experimental transition probabilities of infrared lines belonging to the 4 p-3 d transition array of Ar(I)

Relative transition probabilities for the lines belonging to the Ar(4 p-3 d) transition array and coming from the six upper levels 3 d( 7 2 ) 1, 3 d( 3 2 ) 1, 3 d( 5 2 ) 2, 3 d′( 5 2 ) 2, 3 d′( 3 2 ) 2, 3 d′( 3 2 ) 1 ( jK notation) have been determined from emission line-intensity measurements of optically-thin light sources. Absolute transition probabilities were obtained by using the Coulomb approximation. The present results are compared with previously published theoretical and experimental data.

Low-energy excitations in odd-mass barium nuclei

The experimental systematics of the low-lying states of 131-137Ba nuclei with N=75-81 are discussed in terms of the semi-microscopic particle-vibrational model taking into account anharmonicity of the even-even core. Good agreement between the experimental and theoretical energies, magnetic dipole moments and spectroscopic factors is obtained. The approach used here presents a test for the experimental quadrupole moments and transition probabilities of adjacent even-even Ba nuclei.

Parameterization of 4f-4f transition intensities in Eu 3+-doped lanthanum oxychloride

The Simulation of the line-to-line transition intensities of the 5 D 0, 1 M → 7 F JM transitions in Eu 3+-doped lanthanum oxychloride has been carried out according to the Judd-Ofelt theory. Emphasis is placed upon explaining the high intensities of the “hypersensitive” 5D 0 → 7F 2 and the “forbidden” 5D 0 → 7F 0 transitions. The nine, non-zero B( λkq) parameters reproduce the experimental transition probabilities reasonably well. The parameter set is characterized by a large value of the “linear” B(210) term. This is in accordance with electrostatic point charge calculations which yielded a large A 0 1 value. The high B(210) value, together with the strong mixing of the 7F JM wave functions with the 7F 00 function explains the intense 5D 0 → 7F 0 transition. The intensity of the 5D 0 → 7F 2 transitions is also mainly controlled by the B(210) parameter.

Time-of-flight spectroscopy of high-overtone mode-selective vibrational excitation of CF4 and SF6 in collisions with H+(D+) at energies between 10 and 28 eV

Time-of-flight spectra for H+(D+)–CF4 and SF6 collisions have been measured with an improved resolution and at higher collision energies (10≤Elab ≤28 eV) compared to earlier work. In the low energy region (≤13 eV) new distinct peaks are resolved for both molecules corresponding to small contributions from the second infrared active ν4 mode in addition to the dominant ν3 mode observed previously. Reexamination of experimental vibrational transition probabilities reveals an almost perfect agreement with a Poisson distribution for both modes up to the n=6 overtone transition of ν3. A simple straight line theory is used to calculate the energy transfer in small angle scattering from the long-range potential in good agreement with a full classical trajectory calculation. With this theory dipole moment derivatives can be determined directly from the observed energy transfers and are found to agree well with previous infrared measurements. At larger collision energies (≥16 eV) an additional low intensity vibrational distribution is identified in the high energy loss tail of the spectra which can be attributed to small impact parameter collisions which probe the repulsive region of the potential. The observed energy transfers are also in good agreement with trajectory calculations indicating that the forced oscillator model is also applicable in the repulsive potential region for the present systems. A closer examination of the high energy loss tail reveals resolved structure which has been assigned to discrete states of the ν3 mode in CF4 up to the n=14 overtone. These new results demonstrate that H+(D+) energy loss scattering can provide spectroscopic information not readily available from other experiments.

Comment on probabilities of the 2p53p-2p53s transitions in NeI

Experimental absolute transition probabilities in the NeI 3p-3s fine-structure array are discussed in respect to the accuracy of the measurements and their evaluation.

Phenomenological weak-coupling analysis on N = 81 isotones

A phenomenological np weak-coupling model is applied to N = 81 isotones. The energy spectra, stripping spectroscopic factors and electromagnetic transition probabilities are calculated and compared with experimental data. It is shown that the energy spectra and the spectroscopic factors can be reproduced quite well. The structures of the wave functions are analyzed. The discrepancies between the calculated and experimental transition probabilities suggest that the configuration mixings of the calculated wave functions are too small. The results of the calculation indicate that this model is a very efficient truncation scheme and suggest that its domain of applicability may be extended.

Experimental transition probabilities and lifetimes of some 2 p43 p levels of Ne(II)

Relative transition probabilities for 21 ( 3 P)3 p-( 3 P)3s lines of Ne(II) have been determined from emission line-intensity measurements. The lifetimes of the ( 1 D)3 p 2 F 7 2 and ( 1 D)3 p 2 F 5 2 levels of singly-ionized Ne have been measured by the delayed coincidence method; possible cascade transitions that may repopulate these levels have been studied. Comparisons are made with other experimental and theoretical values.

Transition probabilities for lines arising from levels belonging to the 3p5np (n = 4, 5, 6) configurations of Ar I

Abstract Lifetimes of thirteen levels belonging to the 3p5np (n = 5, 6) configurations of Ar I have been measured by means of the delayed coincidence method. Relative transition probabilities for sixty-seven 4s-np (n = 4, 5, 6) lines have been found. For twenty-six intense (4s-4p) lines the experimental absolute transition probabilities are given. From cascade components of the 5p levels, decay lifetime values for 4d and 6s levels have been inferred. Seven of these results are original, as well as the lifetimes of the 6p( 1 2 )1 and the 6pv( 1 2 )0 levels. The lifetimes of the last two levels are 324±14 and 190±10 n s, respectively.

Measurement of lifetimes and transition probabilities of Kr II

The lifetimes of ten levels belonging to the 4p45p configuration of Kr II have been measured by the delayed coincidence method. Relative transition probabilities for lines arising from the 4p45p configuration are given. Theoretical calculations of the transition probabilities in LS coupling have been performed taking the energy level data of Minnhagen et al. into account. For seven intense lines the experimental absolute transition probabilities are shown.

Levels in 156Gd studied in the (n, γ) reaction

Levels up to 2.3 MeV in 156Gd have been studied using the (n, γ) reaction. Energies and intensities of low-energy γ-rays and electrons emitted after thermal neutron capture have been measured with a curved-crystal spectrometer, Ge(Li) detectors and a magnetic electron spectrometer. High-energy (primary) γ-rays and electrons have been measured with Ge(Li) detectors and a magnetic spectrometer. The high-energy γ-ray spectrum has also been measured in thermal neutron capture in 2 keV resonance neutron capture. The neutron separation energy in 156Gd was measured as S n = 8535.8 ± 0.5 keV. About 600 transitions were observed of which ~50% could be placed in a level scheme containing more than 50 levels up to 2.3 MeV excitation energy. 42 of these levels were grouped into 15 excited bands. In addition to the β-band at 1050 keV we observe 0 + bands at 1168, 1715 and 1851 keV. Other positive-parity bands are: 1 + bands at 1966, 2027 and 2187 keV; 2 + bands at 1154 (γ-band) and 1828 keV; and 4 + bands at 1511 and 1861 keV. Negative-parity bands are observed at 1243 keV (1 −), 1366 keV (0 −), 1780 keV (2 −) and 2045 keV (4 −). Reduced E2 and E0 transition probabilities have been derived for many transitions. The ground band, the β- and γ-bands and the 0 + band at 1168 keV have been included in a phenomenological four-band mixing calculation, which reproduces well the experimental energies and E2 transition probabilities. The lowest three negative-parity (octupole) bands of which the 0 − and the 1 − bands are very strongly mixed, were included in a Coriolis-coupling analysis, which reproduces well the observed energies. The E1 transition probabilities to the ground band are also well reproduced, while those from the higher-lying 0 + bands to the octupole bands are not reproduced. Absolute and relative transition probabilities have been compared with predictions of the IBA model and the pairingplus-quadrupole model. Both models reproduce well the E2 transitions from the γ-band, while strong disagreements are found for the E2 transitions from the β-band. The IBA model predicts part of the decay features of the higher lying 2 + 2, 4 + 1 and 2 − 1 bands.

Interpretation of theA≈100transitional region in the framework of the interacting boson model

A detailed study of the transition between the SU(5) and O(6) limit of the interacting boson model (IBA-1) has been performed in a schematic way. A comparison of the experimental excitation energies and E2 transition probabilities for neutron-rich Ru and Pd isotopes with this calculation show that this mass region is well described in terms of this phase transition.

Two-photon excitation of xenon atoms and dimers in the energy region of the 5p56p configuration

Two-photon excitations from the xenon ground state into the region of the 6p configuration were measured with frequency-doubled light of a tunable pulsed dye laser. Experimental two-photon transition probabilities for the J = 0 and 2 states are compared with theoretical estimates. For atomic transitions populating the 6p‖1/2‖0, 6p‖3/2‖2, and 6p‖5/2‖2 states the following pressure shift parameters β/N were found: −(2.5±0.2)×10−9, −(2.7±0.2)×10−9, and −(2.8±0.2)×10−9 s−1 cm3, respectively. In addition to atomic two-photon transitions, molecular absorptions were observed. Two vibrational v′ progressions converging towards the 5d‖7/2‖3 dissociation limit could be identified. The energy difference of (19.4±1.0) cm−1 coincides with known values for the ground state vibrational separation ΔG(1/2).

Vibrational relaxation of N 2O by the spectrophone method

The optic-acoustic effect was used for measuring vibrational relaxation times of N 2O, both pure and in collisions with atoms. By exciting the (10°0) asymmetric stretching mode and assuming a rapid V- V equilibrium with the bending (01°0) mode, one obtained vibration-translation relaxation times, reduced to one atmosphere, of τ VT = 0.87, 0.14, 1.38, 6.8 and 17.7 μs. in collisions of N 2O with N 2O, He, Ne, Ar and Kr, respectively. The corresponding experimental transition probabilities are compared with theoretical predictions. Through excitation of the (00°1) mode it seems possible to conclude that the de-excitation of this energy level takes place via the (03 l 0) and/or the (11 10) levels. The obtained vibration-vibration relaxation times are τ VV = 1.84, 3.8, 6.8, 12.6 and 23 μs for, respectively, pure N 2O and mixtures with He, Ne, Ar and Kr, at one atmosphere.

Solar and meteoritic abundance of silicon

Recent lifetime measurements on excited electronic states of neutral silicon ( Becker et al., Phys. Lett. In press, 1980) lead to a reassessment of widely used experimental transition probabilities Garz, Astron. Astrophys., 26, 471–477, 1973 of Si I lines. This translates into a 25% downward revision of the Si abundance determined from the solar spectrum. A solar atomic ratio, Si/Ca = 15.5 is inferred. This value coincides with that found in carbonaceous chondrites, but contrasts with ordinary and enstatite chondrites.

Experimental transition probabilities of 5s-np (n=5,6) transitions of Kr I

The lifetimes of the 5p(5/2)2, 6p(5/2)3 and 6p'(1/2)1 levels of Kr I have been measured by the delayed coincidence method. Relative transition probabilities for eight 5s-5p lines and for twenty-seven 5s-6p lines have been found and for six 5s-5p transitions, absolute values are given. Comparison is made with experimental and theoretical values.

An interferometric and spectroscopic study on a high-current argon arc

The plasmas under investigation have been generated in a 4 mm bore wall-stabilised arc operating at atmospheric pressure with currents in the range 20 to 100 A in argon as well as in a mixture of argon and hydrogen. The electron density was determined with a statistical error of less than 1% by means of 2 lambda interferometry at lambda 632.8 nm and lambda 1152.3 nm. Possible systematic uncertainty caused by excited atoms was estimated to be less than 3% for the electron density range 1.89*1016 cm-3<or=Ne<or=1.64*1017 cm-3. Under the assumption of local thermodynamical equilibrium, experimental transition probabilities were obtained for the Ar I 430.0 nm line (Anm=3.2*105 s-1+or-7%) and the Ar II 480.6 nm line (Anm=7*107 s-1+or-14%). The values are not line-wing corrected. For the considered electron density range, the experimental half and quarter widths (in the reduced wavelength scale) of the Hbeta line were found to be constant within the limits of the experimental accuracy. In addition, it is shown that the experimental data of the Ar I 1430.0 nm line transition probabilities given in the literature can be brought to a common value by considering the present reduced widths of the Hbeta line profile.

Experimental transition probabilities and Stark broadening for singly-ionized bismuth

Absolute strengths and Stark broadening parameters of the prominent (4200–6900 Å) lines of Bi(II) have been measured in emission using a gas-driven shock tube. Thermodynamic and photometric variables were determined redundantly. Comparison of the experimental ⨍ values (accuracies of 27–50%) with literature data on the homologous structure sequence N(II), P(II) discloses systematic behavior similar to trends reported for the C(II), Si(II), Ge(II), Sn(II), and Pb(II) sequence. Parameters for Stark-effect broadening (accuracies of 25–30%) are compared with predictions of a semi-empirical model.

Experimental Transition Probabilities for Intercombination Lines in N IV, O V and F VI

Lifetime measurements using the beam-foil method are reported for the 2s3p 3P0, 1, 2 levels in N IV, O V and F VI. The 3P1 level lifetime is significantly shorter than those for 3P0 and 3P2. This is due to the 2s2 1S0-2s3p 3P1 intercombination transition. From careful lifetime measurements at several ion energies we obtain transition probabilities of (3.3 ± 2.7) × 106, (22 ± 6) × 106 and (88 ± 9) × 106 s-1 for this spin-forbidden transition in N IV, O V and F VI, respectively. These results are supported by theoretical analyses.

Single particle nature of the yrast line at high angular momentum in 152Dy

Linear polarization and Doppler shift recoil-distance decay curves for γ-ray transitions deexciting very high spin yrast states up to spin 36ħ in 152Dy were measured with a delayed-promt γ-γ coincidence technique via the reactions 122Sn ( 34S, 4n) and 124Sn( 32S, 4n), at 150 MeV incident beam energy. The deduced experimental transition probabilities are consistent with those obtained for non-rotational nuclei indicating that the yrast angular momentum originates mainly from the alignment of individual particle spins.