THERMALIZATION OF HIGH-FREQUENCY PHONONS IN SILICON SINGLE CRYSTALS

Heat pulses generated by means of small constantan heaters were transmitted through long silicon single crystals. Despite isotope scattering we find the transmitted energy to depend linearly on the applied heater power for heater temperatures between 5 K and 30 K. We obtain evidence that rapid thermalization of the phonon pulse takes place in the vicinity of the heater

Propagation of high-frequency phonons in thin SiO films at 60 mK

By means of a superconducting tunnel junction we study the propagation of heater generated high-frequency phonons through a thin evaporated SiO film. The experiments suggest that SiO contains two-level systems with energies above 360 μeV. Extremely long transit times and saturation of the phonon absorption are observed.A l'aide d'une jonction tunnel supraconductrice, nous étudions la propagation de phonons de haute fréquence engendrés par un émetteur de chaleur, à travers une couche mince de SiO déposée sous vide. Les expériences montrent que le SiO contient des systèmes à deux niveaux d'énergie supérieure à 360 μeV. On observe des temps de transit extrêmement longs et une saturation de l'absorption des phonons

Transient field measurements of g-factors for 28Si and 30Si

Transient field precession measurements have been performed on the first excited Jπ = 2+ states of 28Si and 30Si with the IMPAC technique on recoil in magnetized iron. The results were analyzed with empirically adjusted Lindhard-Winther predictions. This yields g-factors of g = +0.56 ± 0.09 and G = +0.56 ± 0.16 for 28Si and 30Si, respectively. In the present cases the influence of static hyperfine fields is negligible due to the very short mean lives for 28Si and 30Si of 0.68 and 0.35 ps, respectively. The results are compared with theoretical calculations. Previous results for 26Mg(21+) were reanalyzed with the more recent lifetime of τm = 0.72 ± 0.03 ps. The value of the g-factor becomes g = +0.82 ± 0.16

Anomalously large transient field through polarized electron capture

The measured precession for 28Si(21+) recoiling into magnetized Fe shows an anomalous increase with initial recoil velocity. This is explained quantitatively by capture of polarized Fe electrons into 2s vacancies in the moving ion

Transient field measurements of g-factors for 28Si and 30Si

Transient field precession measurements have been performed on the first excited Jπ = 2+ states of 28Si and 30Si with the IMPAC technique on recoil in magnetized iron. The results were analyzed with empirically adjusted Lindhard-Winther predictions. This yields g-factors of g = +0.56 ± 0.09 and G = +0.56 ± 0.16 for 28Si and 30Si, respectively. In the present cases the influence of static hyperfine fields is negligible due to the very short mean lives for 28Si and 30Si of 0.68 and 0.35 ps, respectively. The results are compared with theoretical calculations. Previous results for 26Mg(21+) were reanalyzed with the more recent lifetime of τm = 0.72 ± 0.03 ps. The value of the g-factor becomes g = +0.82 ± 0.16

Anomalously large transient field through polarized electron capture

The measured precession for 28Si(21+) recoiling into magnetized Fe shows an anomalous increase with initial recoil velocity. This is explained quantitatively by capture of polarized Fe electrons into 2s vacancies in the moving ion

Transient field measurements of g-factors for 24Mg AND 26Mg

The g-factors of the first-excited Jπ = 2+ states of 24Mg and 26Mg have been measured with the ion-implantation perturbed angular correlation technique (IMPAC). The precession of the spins of nuclei recoiling into a magnetized iron backing is predominantly caused by the transient magnetic field for these very light and short-lived (τm ≈ 1 ps) nuclei. The transient field, which attains a value of 200 T for the Mg isotopes, is present only during the slowing-down of the recoiling nucleus and results in average precession angles of about 1.5 mrad. The experimental results are treated in the framework of the transient field theory of Lindhard and Winther. This yields g-factors of G = +0.42b ± 0.09 and G = +1.3 ± 0.3 for 24Mg and 26Mg, respectively. The results are compared with theoretical predictions and for 24Mg also with a recent time-differential deorientation experiment

Recoil-distance measurements of g-factors for 24Mg(21+) and 20Ne(21+)

Time-differential recoil-into-vacuum measurements have been performed with a plunger on the first-excited Iπ = 2+ states of 24Mg and 20Ne. The states were populated by the reactions 12C(16O, α)24Mg and 12C(12C, α)20Ne. The measured anisotropy of the α-γ angular correlation was greatly increased by means of a vertical slit on the annular particle detector. Values of ¦g¦= 0.51 ± 0.02 and 0.54 ± 0.04 have been deduced for the 24Mg and 20Ne g-factors, respectively. The mean lives of these states have been determined as τm = 2.09 ± 0.13 ps and 0.8 ± 0.2 ps, respectively. Various theoretical calculations are discussed and compared with the measured g-factors. The analysis of the measurement also yields values for the populations of electronic states contributing to the hyperfine interaction. For 20Ne the populations of the different electronic configurations are compared with the results of a separate time-integral measurement, in which the correlations were measured for each ionic state separately. Large fractions of two-electron excited states are found to contribute