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Vol. 14, No. 2 (1958)

1958-01-20
Topics
CONTENT
THE PROCESS OF DECOMPOSITION OF MARTENSITE DURING THE FIRST STAGE OF TEMPERING
SZE SHIH-YUAN
1958, 41 (2): 95-105. doi: 10.7498/aps.14.95
Abstract +
The process of decomposition of supersaturated tetragonal martensite during the first stage of tempering is investigated by considering the characteristics of motion of a carbon atom from one interstitial position to another within the martensite matrix. It is evident that not all the carbon atoms take part simultaneously in the process of precipitation, some remain in solution for a longer time, others shorter, some mobile, others stationary. By assuming that each transition from one state of motion to another has a definite probability, which is independant of time and carbon concentration but dependant on temperature and the nature of crystalline matrix, it can be shown that an isothermal decomposition curve can be expressed as a series with exponential terms, the coefficients of which are related to the distribution of carbon atoms in different states of motion. The agreement between this expression and the existing experimental data is satisfactory. The general tendancy of the variation of the coefficients with temperature is just what should be expected.
CALCULATION OF THE COHESIVE ENERGY OF METALS BY THE FERMI-THOMAS METHOD
CHENG KAI-CHIA
1958, 41 (2): 106-113. doi: 10.7498/aps.14.106
Abstract +
Slater and Krutter have attempted to solve the problem of cohesive energy of metals by using the Fermi-Thomas method. They treated the valence electrons and the electrons in the ion core on the same footing. In a way similar to Seitz's cellular method, a sphere with a volume equal to that of a unit cell was drawn and periodic boundary conditions were applied on the surface. Furthermore another boundary condition was imposed in their calculation, namely, on the ground that the sphere as a whole is electrically neutral, the potential energy of an electron on the surface should be equal to zero. Then it was expected that there existed a minimum of the total energy versus the interatomic distance. However, actual computation gave no such a minimum at all. This discrepancy was ascribed to the neglect of the correlation energy of the electrons.It now appears to the present author that the failure to find a minimum is the result of an incorrect boundary condition imposed by the previous authors. In view of the fact that each electron is only acted by all the other electrons except the one being considered, obviously an electron on the surface on the average receives a potential energy-e2/R. Using this boundary condition we can calculate the total energy by numerical integration of the equation, in which the data of Feynman, Metropolis and Teller are adopted. A minimum of the energy versus the interatomic distances is found. The calculated interatomic distances for the minimum for various elements together with the observed ones are tabulated and compared. For the multivalent heavy elements the agreement is remarkably good. For the monovalent light elements, e.g. for the alkali metals, the agreement is not so satisfactory, giving only an order of magnitude. This, however, is expected from the statistical nature of the present method, which certainly is not adquate for the description of the single valence electrons, e.g. those in the alkali metals.For the cohesive energy of the metals, the total energy of the system is subtracted by the energy of the free atoms. We use the Fermi-Thomas model for the free atoms also. In view of the fact that for the free atoms the Fermi-Thomas model is accurate only within 1%, the result of the subtraction would introduce an error which is about hundred times that of the total cohesive energy. Hence the absolute value of the cohesive energy up to the present stage is not reliable. The author believes that this method can be extended to the calculation of the energy of formation of alloys, where the total energy of a free atom is not necessarily known. It is hoped that this programm will be carried out in the near future.
COINCIDENCES CAUSED BY COMPTON BACKSCATTERING OF GAMMA-RAYS
HSU YUNG-CHANG, CHENG LIN-SHENG
1958, 41 (2): 114-120. doi: 10.7498/aps.14.114
Abstract +
With slight improvement of ordinary Rossi circuit, a coincidence circuit of resolving time of 1.5×10-7 sec. has been built. Using this instrument, the annihilation radiations of small component β+-rays emitted by Zn65 have been investigated under various experimental conditions. The experiments demonstrate that the 0.21 Mev γ-rays found previously by some authors in Zn65 may be the backscattered γ-rays due to large component 1.12 Mev γ-rays of Zn65. Moreover, the coincidence rate of collimated annihilation radiations gives the percentage of β+-decay of Zn65 per total disintegration as (1.56 ±0.16)%.
THE DEVELOPMENT OF RECRYSTALLIZATION TEXTURE OF COLD-ROLLED COPPER STRIPS
YEN MING-KAO, CHOU PANG-HSIN
1958, 41 (2): 121-135. doi: 10.7498/aps.14.121
Abstract +
The rolling texture of electrolytic copper after a reduction of thickness 88.7% can be described as (110) [112], (112) [111] and a texture (3,6,11) [533]. During annealing at lower temperature, the recrystallization texture was found to be (100) [001] + (358) [352] plus a (122) [212] texture which is a twin position with respect to (100) [001] texture. Together with the raising of the annealing temperature, a decrease of (358) [352] texture and on increase of (100) [001] texture was observed. When annealing temperature reached to 900℃, a nearly perfect cubic texture was developed.During annealing at higher temperature (900℃), grains having (100) [001] oriention appeared first. Then, an overall "recrystallization in situ" took place and the (100) [001] grains tended to grow selectively at the expense of the others. Finally, a concentrated (100) [001] texture was produced.The geometric relationship between the rolling texture and the recrystallization texture was investigated. In general, the change from the rolling texture to the recrystallization texture may be suggested as a rotation of 45°, 22°, 38° about a common [111] axis. The ideal pole-figures, constructed according to the above relationship were found to be in good agreement with the experimental results.It was found that the different rate of heating and the different annealing procedures produced no signeficant effect on the final recrystallization texture. The temperature of annealing, however, was the main factor contributing to the development of the recrystallization texture.
ON THE DECOMPOSITION OF QUENCHING GAS IN G-M COUNTERS
LI TEH-PING, KIU SHIH-HUA
1958, 41 (2): 136-138. doi: 10.7498/aps.14.136
Abstract +
Measurements of the pressure-rise in G-M counters filled with argon and alcohol indicate that, corresponding to each ion pair produced in the discharge, the increase in number of gaseous molecules due to alcohol decomposition, lies between 5 to 10. This number increases as the overvoltage is lowered. Thus the counting life of a counter can not be expressed merely in terms of quantity of electric charge passing through it.Some possible explanations are discussed.
INITIAL ENERGY DISTRIBUTION AND ANGULAR DISTRIBUTION OF PHOTOELECTRONS
WU CHUAN-TEH
1958, 41 (2): 139-152. doi: 10.7498/aps.14.139
Abstract +
In the present paper, the Nottingham's Empirical Formula of the transmission coefficient is used to develop the DuBridge's theory of initial energy distribution of photoelectrons from metal. Owing to the detailed considerations of refraction effect for an electron passing through the potential barry of the surface, we discuss not only the energy distribution and the normal energy distribution of photoelectrons, but also the angular distribution. All discussions are based on the following assumptions:(1) The surface is ideal;(2) The energy distribution of electrons in the metal is according to the Fermi-Dirac distribution;(3) The intensity of incident monochromatic light is constant and the incident light is unpolarized.The obtained formula of initial energy distribution of photoelectrons is very simple, but it is more satisfactory than the other theories shown in this paper. The curve of angular distribution of photoelectrons is like an egg with its large end outward. If there is no refraction effect, the angular distribution satisfies Lambert's law. The spectral distribution, the theoretical formula of volt-ampere characteristic under the retarding field of a spherical condenser with a small photocathode as one electrode at centre, the normal energy distribution, and the theoretical volt-ampere characteristic of ideal parallel plate condenser are also discussed in this paper.
ON THE SLOWING-DOWN OF NEUTRONS IN TWO ADJACENT MEDIA
HUANG TSXI-CHIA
1958, 41 (2): 153-162. doi: 10.7498/aps.14.153
Abstract +
We have calculated the slowing-down densities of neutrons in two adjacent media of different slowing-down properties according to the age theory. The outer medium is extended to infinity. The inner medium consists of a sphere of radius a, and contains a monoenergetic fast neutron-source in the form of a concentric spherical shell of radius R.The method of Laplace transformation is used in solving the problem. The results are given by the expansions (25), (25′), (28) & (28′), which converge rapidly for those cases we usually meet with.For a concrete case where the two media are heavy water and graphite, and the fast neutron-source is of energy 2 Mev, numerical results for the slowing-down densities at thermal energy are obtained and compared with those obtained by the usual two-group approximation (Fig. 1, 2 & 3).