Data on diurnal variations of radon and thoron decay product concentrations in the surface layer of the atmosphere in the Moscow region are given. It is noted that the maximum of radon exhalation from the soil occurred at night. (Measurements were carried out in summer in dry weather.) The strongest upset of radioactive equilibrium between radon daughter products was observed in the first half of night and in the day-time.From the degree of non-equilibrium between RaA:RaB:RaC during the rain the constant of their washout from the lower layer of the troposphere was estimated. The effect of radon and thoron exhalation variations on variations of their concentrations in the surface layer of the atmosphere is theoretically considered.

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The gating circuit used is a hybrid integrated analogue the switch drive and switch contacts. A negative 0.5 v bias switch (Fairchild SH3001) which uses metal-oxide-is applied to the trigger amplifier to prevent its firing on semiconductor transistors providing good isolation between noise produced in the transducer circuit. To prevent overdriving the switch ampmers, the trigger signal is limited to 5 v by 1 * 5 kQ series resstor.Each magnetic transducer signal is fed into a separate gating circuit (shaper and analogue switch). The output signal from the single photomultiplier tube is fed into, each gating circuit and is separated into four outputs and identified by the transducer trigger pulses for recording purposes.The instrument uses only one detector and one amplifier in place of four of the previous one. Spectral selection and dynamic range control can be achieved by using appropriate filters. Fillters of 1.) in. diameter will cover the aperture of the polarizing prism assembly and are readily available. Rapid spectral selection can be done by using the reference transducer pulse to trigger a stepper motor drive circuit. Since the light beam is continuously chopped, the problem of d.c. drift in the amplifiers is negligible. The aperture disk can be rotated at any desired speed up to a maximum of 400revmin-' which is fast enough even for measurements from an aircraft. Further details of the instrument will be published elsewhere.

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