PHYSICS

A. K. LAVRUKHINA, T. V. MALYSHEVA, and B. A. KHOTIN

A NEW ISOTOPE Ir$^{183}$

(Presented by Academician A. P. Vinogradov, 10 X 1960)

In separating daughter osmium from the iridium fraction formed in the spallation of gold by protons with an energy of 660 MeV, an activity with a half-life of 12 hours, belonging to Os$^{183}$ ($^{1,2}$), was detected. This fact indicates the formation, among the spallation products of gold, of a new neutron-deficient isotope of iridium with mass number 183. The present work is devoted to determining the half-life of Ir$^{183}$.

Metallic gold in an amount of $\sim 0.5$ g was irradiated in the internal beam of the synchrocyclotron of the Joint Institute for Nuclear Research with protons of energy 660 MeV for 0.5–1 hour. Radiochemically pure iridium from the gold spallation products was obtained by the procedure described in work ($^3$). Then, from the iridium, at equal time intervals, daughter osmium was systematically separated (the accumulation time varied in different experiments from 1.5 to 4 hours). For this purpose, 20 mg of osmium in the form of Na$_2$OsO$_4$ was added to the radioactive iridium solution. OsO$_4$ was distilled off with hydrochloric acid and trapped in 10% NaOH. Then osmium sulfide was precipitated and ignited to the metal in a stream of hydrogen. The completeness of the separation of osmium was monitored by weighing the metallic osmium. The chemical yield was 95–98%.

Fig. 1. Decay curves of the activity of daughter osmium: a—4th separation, b—7th separation

Fig. 2. Change in the activity of daughter osmium, 9th separation

The decay of the activity of daughter osmium was measured with an end-window counter of a standard counting setup. Figure 1 gives the decay curves of the osmium activity accumulated over 1.5 hours for the 4th and 7th separations. Half-lives of 10 min, 12 hours, and 90 days were found. It is evident that the activity due to Os$^{183}$ constitutes a considerable fraction of the total activity of osmium. In the osmium separated 12 hours after the start of the iridium separation (9th separation, see Fig. 2), the 12-hour activity was not detected.

Fig. 3. Change in the amount of Os$^{183}$ activity ($T = 12$ hours) as a function of the time of separation of daughter osmium: a—every 4 hours, b—every 1.5 hours

The change in the amount of activity of \(\mathrm{Os}^{183}\) as a function of the separation time (Fig. 3) gives a half-life of \(\mathrm{Ir}^{183}\) equal to \(1 \pm 0.1\) h. Activity with a half-life of \(1 \pm 0.15\) h was also found in the decay curve of the total activity of the iridium fraction.

The longer-lived activity with a half-life of \(\sim 90\) days (Figs. 1 and 2) is due to the formation of \(\mathrm{Os}^{185}\) from the 15-hour \(\mathrm{Ir}^{185}\). The shorter-lived activity, decaying with a half-life of \(10 \pm 2\) min, belongs to the osmium isomer \(\mathrm{Os}^{190m}\).

Institute of Geochemistry and Analytical Chemistry
named after V. I. Vernadsky
Academy of Sciences of the USSR

Received
23 IX 1960

REFERENCES

1. V. I. Baranov, K. Ya. Gromov et al., Izv. AN SSSR, ser. fiz., 24, No. 9, 1079 (1960).
2. Yu. A. Sukhov, G. M. Chernov et al., same issue, p. 1119.
3. A. K. Lavrukhina, T. V. Malysheva, B. A. Khotin, Third Conference on Neutron-Deficient Isotopes, Dubna, 1960.