Radio-activity / by E. Rutherford.

  • Ernest Rutherford
Date:
1904
Catalogue details

Licence: Public Domain Mark

Credit: Radio-activity / by E. Rutherford. Source: Wellcome Collection.

    40/426 page 24
    ^ RADIO-ACTIVE SUBSTANCES ' [CH. earths, and is precipitated with them. The method of preparation of this material is the same as that employed for the separation of the rare earths. This substance is similar in radio-active be¬ haviour to thorium, but intensely active in comparison. From the method of separation, thorium itself cannot be present except' in minute quantity. The substance gives out easily absorbed and penetrating rays and also an emanation. On account of the intensity of the emanation which it emits, Giesel has termed this active material the “emanating substance.” If a piece of paper is placed in a small closed vessel containing the active material, in a short time the paper itself becomes power¬ fully active. This is especially the case if it is moistened with water. The emanation lights up a zinc sulphide screen. An electric field has a marked action on the luminosity of the screen. The action is discussed in more detail in section 186. Giesel found that the activity of the material seemed to increase slightly during the six months’ interval after separation. In this respect it is similar to radium compounds, of which the activity increases for a time after separation. Both the method of preparation and also the radiating properties of this “ emanating substance ” indicate that it is the same as the actinium of Debierne. Neither of these active substances has been studied in the same detail as uranium, thorium, or radium, and further comparative data on the nature of the radiations and emanations are necessary before any definite conclusion can be reached. The distinctive character of the radiations and ema¬ nations is of far more value in establishing the dissimilarity of two active bodies than differences in their chemical behaviour. This is especially the case where the active substance is present only in small quantity in inactive material. 22. The similarity of the chemical properties of actinium and thorium has led to the suggestion at different times that the activity of thorium is not due to thorium itself but to the presence of a slight trace of actinium. In view of the difference in the rate of decay of activity of the emanations of thorium and actinium, this position is not tenable. If the activity of thorium were due
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