K-selection Rule Research Articles

Recombination without k-selection rules in dense electron-hole plasmas in high-purity GaAs lasers

The low-temperature emission spectra of high-purity GaAs exhibit an intense new emission line at high optical pumping levels, which is due to band-to-band recombination within an electron-hole plasma. The experimentally determined gain spectra of this laser transition are fitted to calculated line-shape curves, which shows that the recombination takes place without k-selection rules.

Theory of two-phonon absorption processes in liquid paraffins

Calculated absorption spectra are given for linear C8H18, C10H22, C16H34 and C20H42 chains, based on the assumption of a two-phonon absorption mechanism. In the present work the normal modes of vibration of different finite chains are computed directly, without recourse to the Pitzer sampling approximation and without the assumption of strict k-selection rules. The calculated spectra are found to be much more sensitive to chain length than the experimental spectra. A possible explanation of the relative insensitivity of the observed spectra is suggested in terms of a characteristic chain segment length common to all the chains. Ironically, the apparent importance of chain segmentation in the two-phonon absorption suggests that one-phonon transitions may also play a significant role in the absorption process.

Raman Spectrum of Graphite

Raman spectra are reported from single crystals of graphite and other graphite materials. Single crystals of graphite show one single line at 1575 cm−1. For the other materials like stress-annealed pyrolitic graphite, commercial graphites, activated charcoal, lampblack, and vitreous carbon another line is detected at 1355 cm−1. The Raman intensity of this band is inversely proportional to the crystallite size and is caused by a breakdown of the k-selection rule. The intensity of this band allows an estimate of the crystallite size in the surface layer of any carbon sample. Two in-plane force constants are calculated from the frequencies.

Das gyromagnetische Verh�ltnis des 137 keV Rotationsniveaus von Os185

The rotation of the angular correlation of the 631 keV-137keVγ-γ-cascade in the decay of Re186 in an external magnetic field of 53 500 gaus was determined to:ωτ=0·098 ± 0·008. The half life of the 137 keV level was measured as: T1/2=(0·84 ± 0·03) · 10−9 sec. The coincidences between the 137 keVγ-radiation and theβ-group of 927 keV maximum energy were used in connexion with a time to pulse height converter circuit. The coefficients of the angular correlation of the 631 keV-137 keV γ-γ-cascade were found as: A2=− 0·073 ± 0·010; A4=+ 0·310 ± 0·014. These values imply corrections for 3·9% admixture of internal bremsstrahlung and a 1 % contribution by K-X-radiation. The solid angle-corrections were done according to the formula given by E.Rose. The comparison with the theoretical coefficients for a (2+ 2+ 0+)-cascade shows that the multipolarity of the 631 keV radiation is pure E2, the M1 admixture being less than 0· 1%. This result is in agreement with the K-selection rule. There is no appreciable attenuation by internal fields. The comparison with the theoretical angular correlation gives for the integral attenuation factor: G4=0·95±0·04; Assuming only attenuation by electric quadrupole interaction one gets for: G2=0·92±0·07; The nuclear g-factor of the 137 keV rotational state was derived from these results without any further correction as: gR= + 0·316±0·028.

Levels in Gd 156 excited in the decay of 5.6 d Tb 156

The decay of 5.6 day Tb 156 has been studied by means of a six gap β-ray spectrometer, scintillation spectrometers, and coincidence techniques. Conversion electron and γ-ray coincidence measurements have been used extensively for obtaining quantitative estimates of γ-ray intensities. A description of the electronic equipment is given, including a scaler and gate unit, which improves the performance of a relatively slow ( τ = 700 μsec) multichannel analyzer. 24 transitions are assigned to Tb 156. Multipole orders are given in most cases. The following levels are proposed and their quantum numbers ( K, I, π) given in parenthesis: 89 keV (0, 2 +), 199 keV (0, 4 +), 584 keV (0, 6 +) 1126 keV (tentative), 1152 keV (2, 2 +), 1246 keV (2, 3 +), 1507 keV (4, 4 +), 1620 keV (4, 5 +), 1931 keV (3 −), and 2042 keV (4 −). Violation of K-selection rules and significant deviations from the expected branching ratios for transitions to a rotational band are observed. These features are discussed in terms of a probable mixing of the rotational bands.

On anomalous conversion coefficients of dipole transitions

General aspects of the problem of anomalous nuclear-structure-dependent contributions to the internal-conversion process are considered in conjunction with highly retarded electric or magnetic dipole transitions. Formulas for an elementary theory of anomalous internal conversion for E1 transitions are given. Selection rules for the relevant nuclear matrix elements are given in the quantu, numbers appropriate to spheroidally deformed nuclei (K, N, n z, Λ, ⩞) . Similar selection rules for M1 transtions are given on the basis of the anomalous operators previously derived by Church and Weneser. The experimental data on dipole conversion coefficients of retarded transitions for odd-mass spheroidal nuclei are surveyed. It is noted that where retardation is ascribable to K-forbiddenness (up to retardation from the single-proton rate by a factor of 10 9) no detectable anomalies are found, but where transitions are allowed by K-selection rules detectable conversion-coefficient anomalies may generally be found at retardations greater than 10 5 to 10 6 and are not found at lesser retardation. There are some exceptions to this general rule, though. From the present meager data the utility of selection rules in the asymptotic quantum numbers, N, n z , Λ and Σ, for anomalous -conversion matrix elements may be open to question, although their utility in qualitatively explaining retardation of the radiative transitions is very evident. The simple E1 theory is applied in an attempt to explain quantitatively the very anomalous 85-keV transition in Pa 231. Values of the two parameters in the simple theoretical expressions can be found to explain all three L-subshell conversion coefficients. The magnitude of one parameter, the nuclear matrix element 〈 r 3 Y 1〉, is consistent with estimates from the single-particle model. However, the magnitude required of the other parameter is such as to suggest that in the intranuclear process terms of higher order in the electromagnetic field than treated here may be of importance.

A New Band System of Copper Hydride

A BAND system consisting of six band-heads has been found in the region λλ2900–2200. It is different in nature from the two systems previously known for the molecule. The bands are double-headed, indicating that their emitter consists of an odd number of electrons, and thus they have been attributed to the ionised copper hydride (CuH+) molecule. The band structure has been analysed. It consists of nine branches, namely, six main branches and three satellites, and the branch lines obey the K-selection rule. From the intensity relations of the branch lines for low quantum values, it is found that Q>R>P. Thus the system has been assigned a 2II→2∑ transition. The 2II level is inverted. From the vibrational quantum analysis, ω0′ = 1874 cm.-1. This is in good agreement with the value as calculated from the relation given by Kratzer, namely, ω02= - 4B03/D0. The values of B0′ and D0′ are 3.30 cm.-1 and -4.16 × 10-5 respectively.