摘要:

The room‐temperature emission in CdS:Te is a single broad band whose half‐width and peak position provide a simple means of estimating the tellurium concentration in the range 2×1018−5×1019atoms cm−3with a precision of 15%. Of the two discrete bands (at 2.1 and 1.7 eV) seen at low temperatures, only the higher‐energy emission can be described by a simple configuration coordinate model. The nophonon line energy, not observed experimentally, is 2.36±0.05 eV, the exciton being bound to the tellurium atom by 0.22 eV. At high tellurium concentrations the exciton can be trapped at pairs or larger groupings of tellurium atoms sited on nearest‐neighbor sulfur sites, the binding energy increasing correspondingly. The emission intensity from the 2.1‐eV band is reduced by a factor of about 100 as the temperature is increased from near 0° to 300°K. The quenching behavior cannot be described in detail by a single decay process but the effective activation energy is about 0.20±0.03 eV. The drastic temperature quenching above 200°K restricts the usefulness of CdS:Te as a room‐temperature scintillation device but can be reduced by the addition of donors. The relative efficiency at 300°K to that at low temperature increases from less than 1% in undoped material to 15%–20% in CdS:Te containing about 1018donors cm−3. Chlorine, bromine, or iodine appear to serve equally well as donors. Donor‐doped crystals exhibit two components in decay lifetime measurements at 300°K but only one (&tgr;∼250±50 nsec) at low temperature. The extra radiative decay time (500±100 nsec) may arise from free‐electron to bound‐hole transitions at high donor concentrations. Energetically one expects such a process to be near degenerate with the trapped exciton decay and no obvious change occurs in the broad emission band. Hall data show a reduction in the donor binding energy roughly proportional toND1/3, whereNDis the donor concentration. Pulse heights detected after nuclear excitation of CdS:Te are increased about fivefold when 5×1017donors cm−3are added, chlorine giving the cleanest pulse shapes.

ISSN:0021-8979    

DOI:10.1063/1.1658501

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

An experimental investigation was made to determine in detail an NMR ground state transition lineshape function of a two‐level system (spin 1/2). The optically pumped vapor of199Hg was selected as an investigative medium because of the narrow bandwidth (∼1 Hz) and large maximum signal‐to‐noise power ratio (>60 dB at an observation bandwidth of 1 Hz) of the associated NMR. The shape at 1.0 kHz, under the conditions of the experiment, for199Hg was found to be describable within experimental error over a 750 linewidth spectral region using only simple combinations of Lorentzian functions. In addition, the saturation properties were found to agree with the prediction of modified Bloch susceptibility equations.

ISSN:0021-8979    

DOI:10.1063/1.1658502

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The magnetic properties of the cubic RCu5compounds TbCu5, DyCu5, HoCu5, ErCu5, and TmCu5are reported for temperatures between 2.1° and 300°K. In the paramagnetic region the susceptibility follows a Curie‐Weiss law. The type of ordering at low temperatures changes with increasing atomic number from antiferromagnetic (R = Tb) to ferromagnetic (R = Ho, Er, Tm), while DyCu5is metamagnetic. The Knight shifts of the63Cu NMR in these compounds have been measured between 100° and 300°K. The results are discussed in terms of the Ruderman‐Kittel‐Kasuya‐Yosida theory.

ISSN:0021-8979    

DOI:10.1063/1.1658503

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Light propagating in a ``cubic magnetic crystal'' perpendicular toMis subject to a linear magnetic birefringence. The origin and representation of this birefringence is discussed. In the ferrimagnetic garnets several mechanisms may be identified, but the overwhelming part is apparently associated with the magnetostrictive distortion. Measurements are presented for each of the rare‐earth iron garnets at 77° and 300°K.

ISSN:0021-8979    

DOI:10.1063/1.1658504

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A theoretical investigation is made of the forces on a current ring moving in a conducting tube. The ring carries constant current and moves with constant speed along the tube. The ring is coplanar with the circular cross section of the tube, with the center of the ring displaced downward from the axis of symmetry of the tube so that the asymmetric image currents provide a lift force on the ring. The wall of the tube has finite thickness and finite conductivity. The lift and drag forces exerted on the ring by the wall currents are calculated. The minor radius of the ring is neglected, and within this approximation, the calculations are exact.

ISSN:0021-8979    

DOI:10.1063/1.1658505

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A generalized equation is proposed for the relative elastic moduli of composite materials. By the introduction of a generalized Einstein coefficient and a function which considers the maximum volumetric peaking fraction of the filler phase, the moduli of many types of composite systems can be calculated.

ISSN:0021-8979    

DOI:10.1063/1.1658506

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

It has been shown that the &ggr;‐radiation‐induced hardening of NaCl is strongly dependent on temperature [between liquid‐nitrogen temperature (LNT) and room temperature (RT)] for low irradiation doses, but it is essentially independent of it for doses ≳6×106R. For very low doses ≲1×106R the experimental data can be analyzed in terms of a rapid solution hardening mechanism of the type proposed by Fleischer. For higher doses this model is not adequate and one should think of a precipitation (Orowan) hardening mechanism.

ISSN:0021-8979    

DOI:10.1063/1.1658507

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Information theory formalism has been applied to the scanning electron microscope. A theoretical model of two‐dimensional secondary electron noise has been derived and the maximum capacity content per picture element of the S.E.M. has been computed as a function of its geometrical resolving power. According to the theory, it is shown that the maximum number of grey levels on the picture varies between 2 and 8 (varying with the maximum secondary electron yield) with a resolving power of 200 Å for a S.E.M. equipped with a tungsten filament gun, and 30–40 Å is equipped with a lanthanum‐hexaboride gun. However, these figures are established with the assumption that the object does not present any redundant properties. The knowledge of the statistics of a general class of objects will permit the use of adapted coding to increase the information content in the object area of interest.

ISSN:0021-8979    

DOI:10.1063/1.1658508

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Niobium‐selenium compounds in the composition range NbSe2&sngbnd;Nb1.14Se2can form layered crystals which are readily cleaved in a direction perpendicular to thecaxis. For compositions in the range NbSe2&sngbnd;Nb1.05Se2, two structures, a high‐temperature &zgr; phase and a lower‐temperature &egr; phase may be formed. Single crystals of &egr;‐NbSe2, &egr;‐Nb1.04Se2, &zgr;‐NbSe2, and &zgr;‐Nb1.04Se2were grown by the vapor transport technique and the optical absorption spectra of thin‐cleaved specimens in the visible and near infrared regions were studied. An infrared absorption spectrum to &lgr; = 15 &mgr; was also obtained for &egr;‐NbSe2. Accurate values of the absorption coefficient &agr; were measured at 10 nm intervals in the spectral region 400–620 nm. For all crystal types, &agr; was found to have peak value ∼4.5×105cm−1at &lgr; = 460 nm, decreasing steadily to ∼1.3× 105cm−1at &lgr; = 620 nm. The values of &agr; for &egr;‐NbSe2, along with bulk reflectivitiesR0measured on basal plane cleavage surfaces of opaque sections of &egr;‐NbSe2, have been used to calculate the optical constantsnandk. The most notable feature of the visible and near infrared studies is the similarity of the gross features of the absorption spectra of all four crystal types. This indicates that the absorption is governed principally by a mechanism operating largely within the Se&sngbnd;Nb&sngbnd;Se ``layer molecules'' and relatively independent of structure or the presence of interstitial excess metal. An absorption minimum centered about &lgr; = 1.2 &mgr; has been attributed to plasma oscillation of the conduction electrons, and calculations based on this assumption have yielded a valuem*≤5.9 m for the effective mass of these electrons.

ISSN:0021-8979    

DOI:10.1063/1.1658509

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The fluorescence intensity and photoelectric current in polystyrene under excitation with radiation in the vacuum ultraviolet are strongly enhanced by the presence of naphthalene vapor and application of an electric field.

ISSN:0021-8979    

DOI:10.1063/1.1658510

出版商:AIP    

年代:1970

数据来源: AIP