Index of content:
Volume 15, Issue 7, July 1944
15(1944); http://dx.doi.org/10.1063/1.1770262View Description Hide Description
The magnetometer consists mainly of two parts: a Helmholtz‐Gaugain coil fixed on a horizontal divided circle for producing a uniform vertical magnetic field to balance the vertical component of the earth's field, and a magnet‐balance system for observing the effect of the fields. The vertical component of the earth's field is determined in terms of the coil constants and the strength of the current passing through the coil. The error due to the horizontal component of the earth field and that due to the deviation of the center of gravity of the balance system from the rotating axis are eliminated, respectively, by taking the mean value of two observations with the axis of the balance set first in one direction and then turned into the opposite direction by rotating the whole instrument through 180° about a vertical axis, and by reversing the polarity of the balance. The special features of the instrument are as follows: (1) a pair of small solenoids is fixed inside the balance chamber and the balance can have its polarity reversed in its arrested position without being taken out; and (2) by providing another pair of horizontal coils on the chamber, the magnetometer serves at the same time as a galvanometer with the magnet balance as its moving magnet (the galvanometer is needed for the determination of the current and would otherwise be provided separately). By preliminary tests the instrument is found to give consistent results. Its sensitivity is about ½ min. per γ.
15(1944); http://dx.doi.org/10.1063/1.1770263View Description Hide Description
A beta‐ray spectrometer has been constructed utilizing the chromatic aberration of a ``thin'' magnetic lens. The lens is wound of 300 pounds of copper wire and does not utilize iron. Its focal length for transmitted electrons can be varied from 25 to 50 cm and the magnification from 0.5 to 2. Circular sources varying in diameter from 0.4 to 1.6 cm are used and the solid angle subtended at the source is varied between 0.025 and 0.1 steradian. The half‐maximum width of the transmitted distribution is 0.017 to 0.06 of the momentum of the focused electrons. Larger solid angles or better resolution could probably be obtained. The focusing properties of the instrument are derived from the calculated field distribution of the lens by the method of Busch. The spectrometer has been applied to studies of radioactive disintegration schemes. Appropriate techniques are described for the measurement of discrete and continuous beta‐ray spectra, of coincidences of focused electrons with other radiations, and of gamma‐ray energies through secondary electron spectra. A special baffle system allows the separation of negatrons and positrons. The performance of the short lens spectrometer is compared with that of other types of beta‐ray spectrometer and it is concluded that it is a particularly useful tool for the investigation of disintegration schemes because of its flexibility, the use of large circular sources, and the accessibility of source and counter which are located outside the magnetic field at a distance of 100 cm from each other.