Abstract
Two new unitsthe ‘rutherford’ and the ‘roentgen-per-hour at the metre’ for the measurement of radioaetitily, have recently been recommended by the Natinal Bureau of Standards, at the suggestion of the Committee on Radioactivity of the National Research Council. The Radiology Congress in Brussels in 1910 defined the curie as “the amount of radon in equilibrium with one gram of radium”. Therefore, strictly speaking, the curie can only be used to represent the disintegration-rate of radium or its equilibrium products. As is pointed out by E. U. Condon and L. F. Curtiss (Rev. Sci. Instr., 17, 249; June 1946. Also Phys. Rev., 69, 672; June 1946), it has, however, become the custom to use the curie, quite erroneously, as the unit of strength of all radioactive sources. The disintegration-rate, which correctly specifies the strength of a radioactive source, is a pure number, and is determined by the decay constant and the number of atoms of the radioactive isotope in the source. All that is required, therefore, to establish a proper unit, is to choose a suitable number, preferably a multiple of ten. The number 106, with the name ‘rutherford’, abbreviated to ‘rd.’, is recommended. No confusion can arise when dealing with the radium family, as the curie and rutherford are sufficiently different in magnitude. Apart from that of definition, the rutherford has other advantages over the curie. The rutherford is a definite unit, whereas the curie is uncertain to at least 4 per cent, and also, the new unit does away with the necessity for measuring radio-isotopes in terms of a standard. For the intensity of gamma-ray sources, it is recommended that a roentgen-per-hour at one metre be used in place of the curie. The abbreviation, ‘r.h.m.’, pronounced ‘rum’, is suggested. A gamma-ray source of one r.h.m. has a gamma-ray strength of the same order of magnitude as that of one curie of radium.
Article PDF
Rights and permissions
About this article
Cite this article
New Units for the Measurement of Radioactivity. Nature 158, 373 (1946). https://doi.org/10.1038/158373b0
Issue Date:
DOI: https://doi.org/10.1038/158373b0