Using Radioactive Radiation to Enhance Photographic Blackening

Among the intensifiers used in photography are solutions containing uranium salts (for example, uranyl azotnokislyi). In the course of intensification, uranium salts are deposited at the sites of blackening of the photoemulsion. Therefore, if a plate sensitive to α-rays is placed in contact with a photograph treated with a uranium intensifier, then, under the action of α-particles, a copy of the photographic image will be obtained.

In the work under review,^2 a photograph (from a magnetic spectrograph) with three lines of intensities 1:0.2:0.003 was intensified with a uranium solution. Ordinary uranium with its natural mixture of isotopes was used. On the copy obtained by the contact method as a result of a three-day exposure, all three spectral lines could be visually distinguished. However, the copy was weaker than the original.

Increasing the activity of the uranium absorbed by the photograph leads to enhancement of the copy. Replacing one and the same weight quantity of uranium in the natural mixture of isotopes by the isotope \(U^{234}\) (half-life \(T = 3 \cdot 10^5\)) increases the number of α-particles emitted in 1 sec by a factor of 7500. Thus, the use of enriched uranium increases many times the effectiveness of the copying method described.

The author of the work,^2 not having enriched uranium at his disposal, added to the photographic intensifier, for \(10\) mg of uranium, \(10\) μg of \(Pu^{239}\) nitrate \((T = 2.4 \cdot 10^5)\). If it is assumed that plutonium is adsorbed by the blackenings in the same way as uranium, then in this case the activity of the photograph was increased by a factor of 40. In the experiment, after half an hour of contact printing, a [[unclear: text continues on next page]]

copies turned out sharper than the original. The $\alpha$-particle counter recorded the concentration of activity in the areas of blackening of the photograph treated with the intensifier.

By using radioactive intensifiers of high activity (for this, isotopes with a shorter lifetime are needed), the effectiveness of the method can be increased. Besides uranium, it is also possible to use other radioactive isotopes of elements employed in photography, and in particular $\beta$-emitters with a soft spectrum. For greater amplification, the copy may be subjected to repeated intensification. It is possible to photometer the photograph of spectral lines with an $\alpha$-particle counter, and also to count the number of $\alpha$-tracks with the aid of a microscope.

I. E.

References Cited

1. K. Miz, Theory of the Photographic Process, 1949.
2. S. Rosenblum, Comptes Rendus 230, 1766 (1950).