Measurement of ultraviolet Argon(II) transition probabilities

The transition probabilities of twelve Ar(II) lines around 300nm have been measured in a stationary arc experiment at 1 atm. The reported data are based on absolute intensities, calibrated by the continuum radiation of a high temperature hydrogen plasma. For two lines the maximum emission coefficient at 26500 K has been used for an immediate determination of the respective A_mn-values. These data serve for temperature measurements at lower arc currents, where the other lines are investigated. The results, the uncertainty of which should be below ±15%, agree satisfactorily with coulomb approximation calculations, but show severe discrepancies as compared with more recent NBS tables.     

Oscillator strengths of neutral and singly ionised molybdenum

Oscillator strengths of 174 Mo(I) and 58 Mo(II) lines in the range 2470–5570 Å were obtained from wall-stabilised arc and hollow cathode measurements. Sets of relative f-values were determined by a combination of hook and emission measurements requiring no assumptions concerning the plasma state. The sets have been enlarged considerably by evaluating spectra recorded with a Fourier spectrometer. The relative Mo(I) f-values were converted to an absolute scale by means of radiative lifetimes measured by P. Zimmermann and his group. The overall uncertainties are within 10–35%. Since lifetimes of Mo(II) levels are not yet available, only relative Mo(II) f-values are presented.     

Measurement of Ar(I) and Ar(II) transition probabilities in LTE ARC plasmas

The transition probabilities of two Ar(I) lines and one Ar(II) line have been measured in emission on wall-stabilized argon arc plasmas (0·5×10⁵?p, Nm^-2?3×10⁵; 10,000?T, K?20,000; 10²²?N_e, m^-3?5×10²³) using the “method of best fit (MBF)”. The results (without line-wing correction) are for Ar(I) at 714·7 nm, A_nm=5·66×10⁵ s^-1±5%; for Ar(I) at 430·0 nm, A_nm=3·40×10⁵ s^-1±5%; for Ar(II) at 480·6 nm, A_nm=8·82×10⁷ s^-1±7%. These values were not influenced by deviations from LTE, which have been observed at electron number densities n_e?10²³ m^-3. The small uncertainties were achieved after careful corrections of different sources of error.     

Transition probabilities of some lines of Ne(I)

Relative transition probabilities for twenty-four spectral lines belonging to 3p-3d transition array of neutral neon have been determined by means of emission line-intensity measurements. The lifetime of the 3d(3/2)₂ level has been measured by the delayed coincidence method obtaining a value of 20.5±2.0 ns. With this lifetime value and taking into account the 3887.1 Å forbidden line, the transition probabilities of the lines with origin in the 3d(3/2)₂ level were put on an absolute scale. The experimental values of the present work are compared with theoretical calculations obtained by use of the Coulomb approximation and intermediate coupling scheme.     

Electron paramagnetic resonance and thermodynamic measurements on a phase transition of tris(acetylacetonato)aluminium(III) and tris(acetylacetonato)cobalt(III)

Pure Al(acac)₃ and Co(acac)₃ exhibit a first-order phase transition at 140 ± l K and 30 ± l K respectively. At the phase transition the unit cell triples, but the space-group remains P₂₁c. The unit cell dimensions at 90 K and at room temperature in parenthesis are: a = 41.17 (14.07) Å; $\text{b = 7.42 (7.57)}\text{A}\text{?}\text{;}$$\text{c = 22.70 (23.20)}\text{A}\text{?}\text{; β = 135.7 (135.8)}$. From epr measurements on Cr doped Al(acac)₃ and Co(acac)₃ it appeared that at the phase transition the molecules in the lattice are rotated over small angles towards new orientations. The paramagnetic parameters showed small deviations from those at room temperature, except for the rhombic parameter E. By calorie methods the transition enthalpy of Al(acac)₃ was determined to be 36.8 ± 0.4J mol^?1. From the T, X phase diagram of the binary system Al(acac)₃-Co(acac)₃ as determined by means of epr measurements for Co(acac)₃ a transition enthalpy of 17.4 ± 4.8J mol^?1 was estimated. The use of a paramagnetic ion as a probe for solid-solid phase transitions may have conceivable wider applications.     

The application of some beam-foil measurements for Co I and Co II to the cobalt photospheric abundance

The mean lives of a number of energy levels in Co I and Co II have been measured. Particular attention has been paid to the energy loss incurred by the ions in the foil, which was found to be somewhat larger than the loss forecast by Lindhard's theory.A-values derived for Co I (using relativegA-values from the literature) are found to be significantly lower than those reported previously by other authors. Fair agreement is obtained for Co II with theA-values forecast by Warner. The Co IA-values indicate that the cobalt solar abundance given by Goldberget al. (LogN _Co=4.64) should be increased to about 4.9.     

Stark broadening of some C(I) and N(I) vacuum ultraviolet lines

Stark widths of 11 C(I) lines and 3 N(I) multiplets were measured in the wavelength range 1310 Å ⩽ λ ⩽ 2583 Å. Gas mixtures (Ar+CO₂, Ar+N₂ and Ar+CO₂+N₂) were used for production of plasmas in a wall-stabilized arc under atmospheric pressure. Results were provided by five experiments (T varies from 13,370 to 13,950 K and N_e from 1.13 x 10¹⁷ cm^-3 to 1.35 x 10¹⁷ cm^-3. Stark shifts were measured for 2 C(I) lines and the ion-broadening parameter A was evaluated for 7 C(I) lines using different methods. The Stark widths and shifts are generally in reasonable agreement with other experimental or theoretical values, while the estimated A values are much higher than those predicted by Griem's theory.     

Spectroscopic study of microwave discharge as a radiation source for transition probability measurements

The optical properties of a discharge in a mixture of helium (200 torr) and hydrogen (0.1 torr) were investigated. Line intensities were measured photoelectrically. Partial LTE is demonstrated by the linearity of plots of log(Iλ/gA) vs E. The temperatures T_He = 3300 and T_H = 3400 K are obtained from the slopes of the plots for He and H, respectively. Relative A-values for the hydrogen Balmer lines derived from the helium temperature agree with theoretical values within ±20 per cent. The uncertainties (≤ 7 per cent) estimated from the discrepancy between the temperatures are smaller than those (±10 per cent) due to errors in the observed line intensities.     

The S34 (p, γ) Cl35 reaction and energy levels of the Cl35 nucleus

A method is presented to eliminate quantitatively the decay time of the radioactive source and all systematic errors caused by the instability of the associated electronics. The essential part of this procedure is a versatile method to measure the random coincidences together with the sum of true and random coincidences under the same experimental conditions for both quantities. The proposed method is applied toγ-γ-directional correlation measurements with a five detector apparatus. The construction and function of the device is illustrated. Test measurements with⁶⁰Co prove the usefulness of the method and the capability of the apparatus. The investigation of twoγ-γ-cascades in the decay of¹²⁴Sb gives the following values for the coefficients of the correlation function 1,69-0,603 MeV-cascade:A ₂=?0,065±0,003A ₄=+0,001±0,005 2,09-0,603 MeV-cascade:A ₂=?0,056±0,008A ₄=+ 0,006±0,008     

Shock tube measurements of Y I and Y II oscillator strengths

Yttrium-silicon spectra have been photographed in the 3400- to 6200-Å region using a 3.4-m Ebert-type spectrograph. The light source was a helium-driven shock tube containing a mixture of powdered YSi₂ in an Ar carrier gas. A high-speed mechanical shutter and a Garton-type coaxial flashtube were used to record essentially simultaneous emission and absorption spectra for each shock. This procedure resulted in the testing for and removal of a number of systematic errors during reduction of the data, yielding relative oscillator strengths for 255 Y I lines and 90 Y II lines. These relative oscillator strengths have been placed on an absolute scale using the published gf-values of Hannaford et al. and the 3906-Å line of Si I. A comparison of these results with those of previous workers shows general agreement, although significant differences are seen in several cases.     

Determination of transition probabilities for singly ionized vanadium

Transition probabilities of 211 spectral lines of VII, in the wavelength range 2340–4200 Å, have been determined by emission spectroscopy using a wall-stabilized arc as source. The lines studied belong to the transition arrays 3d⁴, 3d³4s-3d³4p (199 lines) and 3d³4p-3d³4d, 3d³5s (12 lines). Vanadium was introduced into the helium-arc discharge as the liquid VOCl₃. An important feature of this work is the determination of transition probabilities for many lines from a wide spectral range with a uniform absolute scale. The absolute A_ki values were obtained by normalizing relative A_ki values to an absolute scale set by ionic lifetime for the level y³H⁰₄. These results are compared with other experimental as well as theoretical results.     

Diffusion-weighted imaging versus superparamagnetic iron oxide (SPIO)-enhanced MRI: exclusive and combined values in the assessment of hepatic metastases

Purpose

The purpose was to validate diffusion-weighted imaging (DWI) in the assessment of hepatic metastases compared with superparamagnetic iron oxide (SPIO)-enhanced magnetic resonance imaging.

Materials and Methods

For 21 consecutive patients with 160 metastases from extrahepatic malignancy and 25 benign focal lesions, two radiologists evaluated four separate review sessions (I, SPIO-enhanced T2?-weighted images; II, precontrast DWI; III, SPIO-enhanced T2?-weighted images and precontrast DWI; IV, SPIO-enhanced T2?-weighted images plus precontrast and SPIO-enhanced DWI) and assigned confidence levels using a five-grade scale for each hepatic lesion.

Results

The A_z values after receiver operating characteristic curve analysis for Reader 1 and Reader 2 were 0.80 and 0.75 on session I, 0.91 and 0.91 on session II, 0.97 and 0.96 on session III and 0.96 and 0.96 on session IV, respectively. The A_z value of session II was significantly higher than that of session I (Reader 1, P=.004; Reader 2, P<.001), and that of session III was significantly higher than that of session I (P<.001 for each reader) or session II (Reader 1, P=.004; Reader 2, P=.003). Although there was no significant difference of A_z value between session III and session IV (Reader 1, P=.231; Reader 2, P=.878), the sensitivity improved for session IV compared with that for session III (Reader 1, P=.031; Reader 2, P=.039).

Conclusion

In the assessment of hepatic metastases, DWI can provide more accurate information than can SPIO-enhanced images. Diagnostic accuracy can be increased even more through the combination of both techniques.     

Atomic transition probabilities for Sn(I), Sn(II) and Cl(I) lines in the 5300–6850 Å wavelength range

Absolute transition probabilities for fifteen Sn(I) lines, nine Sn(II) lines and six Cl(I) lines have been measured in the spectral range 5400–6850 Å by using a wall-stabilized arc. The elements were introduced to the arc chamber as gas mixtures containing small amounts of SnCl₄ in argon. Plasma diagnostic was carried out by line-intensity measurements and by numerical solution of the equations for a perfect gas.Measured transition probabilities are compared with theoretical calculations and other experimental values. Discrepancies have been found to be greater than the experimental uncertainties. However, for two Sn(II) lines, agreement is satisfactory.     

Determination of the oscillator strengths of Sn(I) in the ultraviolet (2400–4000 Å)

The emission spectrum of Sn(I) generated in a direct current arc plasma (Ar-SnCl₄ mixture) has been studied. The relative socillator strengths were obtained in the u.v. spectral range (2400–4000 Å) from measurements of branching ratios and from the study of radial temperature distribution and radial emission coefficients obtained by side-on measurement. These relative oscillator strengths were converted to an absolute scale by using as reference the lifetime determination of the ³P₁⁰ state. The results are compared with other absolute measurements.     

Hyperfine structure investigations of some odd levels of Co I by level crossing and optical methods

Using the level crossing technique the ratios and absolute values of the hyperfine structure (hfs) constants of the levelsz ⁴F_9/2 andz ⁴F_7/2 of the configuration 3d ⁷4s4p of Co I were measured:z ⁴ F _9/2: ¦A¦=(811±12)MHz; ¦B¦=(48±93) MHz;B/A=?0.06±0.11 A>0; B<0z ⁴ F _7/2: ¦A¦ = (659 ±11)MHz; ¦B¦=(33±84)MHz;B/A=?0.05±0.13 A>0; B<0. In addition the hfs constants of three other excited levels of Co I could be determined by optical methods:z ⁴ F _9/2:A=525±26 MHz;B=200 MHzy ⁴ F _9/2:A=300±30 MHz;B=?500 MHzy ⁴ G _11/2:A=315±20 MHz;B=400 MHz. The experimental results are compared with known experimental and also with theoretical values which where calculated using the parametric potential method.     

Measurement of the oscillator strengths of transitions of titanium(I) in the region 3600–4500 Å

The emission spectrum of an arc discharge stabilized by a rotating radial magnetic field, operated at high pressure in an Ar-TiCl₄ mixture, has been analyzed under the assumption that local thermodynamic equilibrium is established in the arc. The temperature distribution was determined from absolute radial emission coefficients of the 4158 Å-4200 Å Ar(I) lines.Relative transition probabilities of 52 titanium lines have been obtained in the range 3600–4500 Å and converted to an absolute scale using absolute values for the three resonance transitions at 3635, 3981 and 3998 Å.     

Transition probabilities of lines with origin in the 3d′(5/2)2, 3d′(5/2)3 and 3d′(3/2)1 levels of Ne(I).

Relative transition probabilities for twenty near-i.r. electric dipole lines and for three forbidden lines of Ne(I) with origin in the 3d′(5/2)₂, 3d′(5/2)₃ and 3d′(3/2)₁ levels have been measured. The calculated lifetime in jK coupling of the 3d′(5/2)₂ and 3d′(5/2)₃ levels was used to put on an absolute scale the transition probabilities of fourteen lines. The values of the present work are compared with theoretical calculations obtained by use of the Coulomb approximation and the intermediate-coupling scheme.     

Electron-nuclear-double-resonance of the VAl center in MgO

An ENDOR study of a hole center in MgO with g_|=2.0032±0.0001 and g_⊥=2.0385±0.0001 reveals that the hole interacts with an axial aluminum ion with A_⊥=±0.178±0.008 MHz, A_⊥=±0.074±0.008 MHz, and P= ±0.366±0.002 MHz. The structure of the center is consistent with the label, V_Al. It is suggested that the V_Al center may have been mistaken in the past for the V^- center because of the similarity of their g-values, method of production, and thermal properties.     

Spectrum and energy levels of Cr3+ ions and exchange-coupled Cr3+ pairs in lanthanum aluminate

From the optical spectra the energy levels of the Cr³⁺ ion in LaAlO₃ were determined. In the cubic field approximation we obtained with the parametersDq=1750cm^-1,B=661 cm^-1, andC=2908 cm^-1 a good agreement between the calculated and measured energies. For higher Cr³⁺ concentrations the fluorescence spectrum of the exchange-coupled first nearest (1N) Cr³⁺ pairs was separated from the vibronic fluorescence spectrum of the single ions by selective excitation. From the experimental data the energy level scheme of the 1N pairs is constructed for the states ¦⁴ A ₂·⁴ A ₂〉 and ¦⁴ A ₂·² E〉. In the ground state the pairs are ordered antiferromagnetically due to an isotropic exchange interaction with an exchange integralJ=(?68 ± 1) cm^-1. From the fluorescence decay the intrinsic lifetimes of the fluorescent states of the single ions, the 1N and the 2N pairs were determined to be equal to (86± 4) msec, (1.75± 0.25) msec, and (31 ± 5) msec respectively. The fluorescence decay shows an energy transfer between the single ions and the pairs.     

Impurity lattice dynamics of Fe in Cr from precision Mössbauer fraction measurements

Precision 〈x²〉-values and their anharmonicity been measured for ⁵⁷Fe in Cr between 80 K and 600 K. At 294 K. $\text{? = 0.798 ± 0.005}$. A theoretical analysis based upon Cr neutron scattering data yields 0.8 for the impurity/host force constant ratio.