摘要:

The collective model of the giant resonances is described. The dipole vibrations are discussed in greater detail and applied to both spherical and deformed nuclei. In a consistent expansion of the model the collective-charge vibrations are coupled to the low-energy nuclear-surface vibrations. The implications of this dynamical treatment on the photoabsorption cross section are discussed and compared with the experiments. The properties of other kinds of collective motions such as spin waves and spin-isospin waves are reviewed. Finally the connection between the collective picture of charge vibrations and the shell-model treatment of the giant resonances is pointed out.

ISSN:0002-9505    

DOI:10.1119/1.1974224

出版商:American Association of Physics Teachers    

年代:1967

数据来源: AIP

摘要:

The path traced out by the terminus of the magnetization vector for a spin-1 nucleus subjected to a nonvanishing electric-field gradient is calculated quantum mechanically. Certain special combinations of angular momentum operators are used to simplify the work.

ISSN:0002-9505    

DOI:10.1119/1.1974225

出版商:American Association of Physics Teachers    

年代:1967

数据来源: AIP

摘要:

After briefly reviewing the theory of abrupt semiconductor heterojunctions, we consider a semiconductor whose composition gradually changes from that of a small-band-gap material at one end to that of a large-band-gap material at the other. From general theoretical aspects of the energy-level structure of nonuniform semiconductors, we clarify the sense in which the system has a graded band gap. In order to separate the effect of the graded band gap on electronic charge transport from the effect of the electric field originating from space charges, we consider a graded-band-gap semiconductor which is doped inhomogeneously with donors and acceptors so that there is no space charge. Electronic transport is analyzed by a novel method which is based on intraband transitions between eigenstates of the complete Hamiltonian. In addition to the normal diffusion term, another term is obtained which is linear in the gradient of the band edge for each type of carrier. In previous work this term was ascribed to a “quasifield”; we show that it originates from asymmetric diffusion. The transport equations for both types of carriers are presented.

ISSN:0002-9505    

DOI:10.1119/1.1974226

出版商:American Association of Physics Teachers    

年代:1967

数据来源: AIP

摘要:

An elementary mathematical method is introduced for evaluating the average energy-state occupation numbers of a system of noninteracting particles in thermal equilibrium. Conceptualization of the problem is identical with that of Darwin and Fowler; but the execution avoids, without sacrifice of rigor or generality, the use of their profound analytic-function-theoretic machinery. The case of Maxwell-Boltzmann statistics is initially handled separately, but a more general unified treatment is also provided for Fermi-Dirac, Bose-Einstein, and Maxwell-Boltzmann systems as special cases. The three familiar distribution functions, with a known general formula for their mean-square fluctuations, are derived. The methods are also applied to mixtures of systems, with and without the possibility of combination and dissociation.

ISSN:0002-9505    

DOI:10.1119/1.1974227

出版商:American Association of Physics Teachers    

年代:1967

数据来源: AIP

摘要:

A simplified treatment of polarization effects in scattering of spin-one particles is presented. The analogy between spin moments and electric multipole moments is exploited. Elementary physical arguments illustrating the mechanism of polarization are given for two specific interactions.

ISSN:0002-9505    

DOI:10.1119/1.1974228

出版商:American Association of Physics Teachers    

年代:1967

数据来源: AIP

摘要:

A standard way to measure the mass of the neutron is to measure the energy of the capture-gamma ray from hydrogen. Careful measurement with a lithium-drifted Ge detector offers reasonable accuracy in determination of this energy. The measurement has been made using student-type equipment, and resulting in a mass of 1.0086654 ± 0.0000008 amu. It is proposed that this is a suitable experiment for an advanced physics laboratory.

ISSN:0002-9505    

DOI:10.1119/1.1974229

出版商:American Association of Physics Teachers    

年代:1967

数据来源: AIP

摘要:

An alternative calculational procedure for quantum theory is presented, employing three features which differ from the corresponding features of orthodox quantum theory. These are: (1) the state vector is never to be “reduced”; (2) quantum theory only makes predictions about ensembles of identical experiments (not about individual experiments); and (3) the measuring apparatus must always be included in the state vector. What is new about this alternative theory is the demonstration that Features 2 and 3 (which have hitherto been discussed separately) can be consistently combined to yield an interpretation of quantum theory which has the additional advantage of Feature 1. It is shown that alternative and orthodox theories yield identical predictions for any practical experiment. However, two classes of experiments (which are impractical) for which the orthodox and alternative theories yield different predictions are described. Therefore, it is, in principle, possible to decide which theory Nature has chosen to obey. It is concluded that there is no reason, based upon experimental evidence, for preferring one theory over the other.

ISSN:0002-9505    

DOI:10.1119/1.1974230

出版商:American Association of Physics Teachers    

年代:1967

数据来源: AIP

摘要:

The distortion of a distribution function due to the resolution of the experimental apparatus used to measure it is discussed, and the mathematical formalism connecting an “ideal” distribution with the corresponding measured distribution is presented. The approach is based on the use of a resolution function, which can be measured experimentally, to describe the distortion effects of the apparatus. The formalism is examined in general, and examples are used to illustrate some typical characteristics of distortion. The treatment given here can be usefully exploited in introducing this subject to the student.

ISSN:0002-9505    

DOI:10.1119/1.1974231

出版商:American Association of Physics Teachers    

年代:1967

数据来源: AIP

摘要:

A low-cost experimental and demonstration microwave system operating in the x band is described. Some of the features of operational radars are preserved for use in a laboratory situation. Other aspects of service radars (such as the scanning antenna) are lost. The resulting system is a blending of the good features of operational superheterodyne radars with the low-power laboratory x-band signal generator. Many uses for the system are suggested including antenna-pattern studies, radar cross section measurements, demonstrations of standing waves, measurement of wavelength, etc.

ISSN:0002-9505    

DOI:10.1119/1.1974232

出版商:American Association of Physics Teachers    

年代:1967

数据来源: AIP

摘要:

Rutherford scattering experiments are traditionally performed in the college physics laboratory with an alpha source and some suitable scattering foil. Simple calculations based on reasonable source strengths, geometry, and cross section show that it is very difficult to measure the complete Rutherford angular distribution by this method. The reason for this difficulty is, of course, that the cross section can decrease by a factor of105from the forward to the back angles. The purpose of this paper is to show that the Rutherford angular distribution can be measured in a reasonable laboratory period with a low-energy Cockcroft-Walton accelerator. Many universities have these accelerators or plan to add them to their lists of capital equipment. To date, these machines are used almost exclusively as neutron generators with theT(d,n)4HeorD(d,n)3Hereactions. These accelerators can easily be modified to include charged-particle experiments. In this report, the general format is given for measuring the Rutherford angular distributions for 150-keV protons for the following reactions:12C(p,p)12C,58Ni(p,p)58Ni, ,11B(p,p)11B, and197Au(p,p)197Au. At Oak RidgeAssociatedUniversities, we have performed charged-particle experiments similar to those outlined with many undergraduate physics students, as well as their professors. The results have been most gratifying.

ISSN:0002-9505    

DOI:10.1119/1.1974233

出版商:American Association of Physics Teachers    

年代:1967

数据来源: AIP