Vol. 8, No. 1 (1951)
1951, 16 (1): 1-13. doi: 10.7498/aps.8.1
Our bulk-visco-elastic theory is extended to the case, as recently discovered in ultrasonic absorption measurements, in which there are present more than one relaxation times. This multi-relaxational theory is applied to the study of acoustic dispersion phenomena. The bearing of our relaxational theory in general on classical hydrodynamics is further examined. Illustrative calculations from certain available experimental data are given and their indications discussed.
1951, 16 (1): 14-31. doi: 10.7498/aps.8.14
A gas discharge switch for controlling low level 3 cm-band signals was developed by modifying a iB24 TR tube. The keep-alive electrode in the tube was placed nearer to the r-f gap, and the aperture of the lower cone was made larger than that in the standard tube. It was observed that a keep-alive depth (distance from r-f gap) of 0.4 mm gave the highest attenuation. Among the various gas fillings tried, nitrogen was found to be most suitable. It gave a high attenuation and a reasonably long tube life. About 44 db attenuation was obtained at a keep-alive current of 0.4 ma with a gas rilling of 12 mm Hg of nitrogen. No detectable r-f noisc was introduced by the keep-alive discharge. A qualitative discussion is presented to account for the attenuation in terms of the motion of the electron furnished by the keep-alive discharge under an r-f field.
1951, 16 (1): 32-38. doi: 10.7498/aps.8.32
Based on the interaction between r-f field and the electrons furnished from an auxiliary d-c discharge, a gas discharge switch has been developed for controlling low level 10 cm-band signals by modifying the keep-alive electrode of a cell type 1827 TR tube. It has been found that the attenuation was considerably increased when the top of the keep-alive electrode was off-center and close to the side of the lower hollow cylindrical post. Nitrogen or argon at a pressure of about 4 mm Hg was found to be appropriate as a gas filling for such a switch. An attenuation of more than 30 db was obtained from a tube having a keep-alive depth of 0.0 mm and a distance of 0.7 mm from the keep-alive to lowcr-hollow-cone. The gas filling was nitrogen at 4 mm Hg, and the keep-alive current was 1 ma with a d-e gap voltage of about 450 volts. Such a switch has a very long life, as there was no appreciable change in the tube behavior alter operating continuously for several hundred hours.
It is shown that the divergence in the cases of pseudo-scalar mesons with pscudo-vector conpling and the charged pscudo-vector mesons with pscudo-vector coupling can be reduced to the same type as that in electrodynamics. Other types of meson theories having stronger divergence than quantum electrodynamics are also investigated. Our program of reduction is less-successful in these cases.
1951, 16 (1): 57-63. doi: 10.7498/aps.8.57
A quantum-mechanical vanational calculation is made for the molecule HF, based on the ionic model, the fluorine negative ion being polarized on the whole by the proton. Brown's numerical results for the Hartrce-Fock functions of the fluorine ion are used. The calculated results do not agree well with the experimental results, which indicates that, even for this most polar molecule, the above model serves only for a very poor representation of the motion of the electrons in the molecule.
1951, 16 (1): 64-72. doi: 10.7498/aps.8.64
This paper presents a graphical method of pre-determining the perlormance characteristics of a power oscillator. Calculated results are compared with experimental data and the agreement was found to be better than other methods known at present.
1951, 16 (1): 73-79. doi: 10.7498/aps.8.73
This paper presents an experimental method to determine the optimum grid leak resistance of a power oscillator. The effect of excitation ratio on the plate efficiency and the proper method of connection of the grid leak resistance are also discussed. The experimental results are checked against the calculated values obtained from graphical method.
UPPER LIMITS OF THE FISSION CROSS-SECTIONS OF BISMUTH, LEAD, GOLD, PLATINUM AND TUNGSTEN FOR 21 MEV NEUTRONS
1951, 16 (1): 95-110. doi: 10.7498/aps.8.95
The emulsion technique was used to set certain upper limits for the fission cross sections of some naturally occurring heavy elements bombarded with 21 Mev neutrons. It is established that the fission cross-sections for these elements (Bi, Pb. Au, Pt and W) are less than 4 X 10-5 of that of U238. These results are in disagreement with the fission threshold derived from the theory of fission based on the liquid drop model for heavy nuclei, but support a simple argument about the minimum neutron energy required to produce fission by Tsien San-Tsiang.