A two-crystal x-ray spectrometer for use in the wave-length region 0.030<λ<0.215A is described. Transmission and reflection of the x-rays through the body of the crystal, instead of the usual reflection from the surface, is employed. An ionization chamber containing argon at 80 atmospheres, and an FP-54 electrometer tube system is used to measure the intensity of the reflected radiation. A source of short wave-length x-rays, consisting of two specially designed induction coils and a cascade Coolidge tube, is described. Rocking curves in the (1, −1) position at 50 X.U., the K limits of lead and of uranium, and the Kα and Kβ-lines of tungsten were observed for the purpose of calibrating the spectrometer. The resolving power of the instrument with the present crystals is discussed.

The need for convenient instruments to measure soil moisture and density in place in a quick, reliable, and possibly continuous manner has long been felt by soils engineers. This paper summarizes the work done up to this time by the Civil Aeronautics Administration and Cornell University on the nuclear meters that are designed to solve the problem. The method presented here makes use of the physical principles of the scattering of neutrons and gamma rays. A source of proper radiation, radium D-beryllium or cobalt 60, is contained in cylindrical probes along with a detector of slow neutrons or of gamma rays, respectively. The probe is inserted into the soil mass through a 1-in. diameter pipe, and the radiation penetrates the nearby soil and is scattered back toward the detector, the amount and character of the scattered radiation giving a measure of the characteristics. The design and testing of such probe meters that measure soils at depth and of the related surface meters that measure thin-layered soils are described in detail. With suitable care, the probe meters measure moisture to ±1 lb of water per cu ft, and measure density to ±5 lb of soil per cu ft. The surface meters are in an earlier experimental stage and are not so accurate. The time required to take a complete set of readings is about 15 min. Further laboratory and field testing is being conducted to perfect these meters to fulfill specific requirements of different engineering projects.

An Ionization Gauge for the Detection of Molecular RaysThe essential features of this ionization gauge for the detection of molecular rays are (1) a small volume, (2) a high sensitivity, (3) a highly insulated plate, and (4) the use of a thin metal film on the wall for a plate, which permits the simultaneous outgassing of plate and wall by radiation from the grid.

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