Activities observed in iridium after neutron bombardment. Remarks on a paper by H. H. Hennies and A. Flammersfeld
Recently Hennies and Flanunersfeld (Naturwissenschaften, 47: 11(1960)) reported ths observation of a new 47-sec activity produced by irradiating Ir powder with slowed-down neutrons. The activity was tentatively assigned to Ir/ sup 194//sup m/. Beta activities, previously ascribed to Ir/sup 192//sup m/, were reassigned to Ir/sup 194//sup m/. A repetition of the experiment on the bombardment of Ir/sup 193/ with slow neutrons (Phys. Rev. Lettens, 3: 4S(1959)) confirmed the previous conclusions and ruled out a 47-sec period in Ir/sup 192/ or Ir/sup 19 / 4>s. It was suggested that the Hennies and Flammersfeld results may be partly ascribed to a Rh impurity and partly to the effect of fast neutrons. (J.S.R.)
TRIPLE ISOMERISM IN Ir$sup 19$$sup 2$
In studying an iridium specimen irradiated for one month in the BNL Reactor and then allowed to cool, a gamma spectrum identical with Ir/sup 192g/ was obtained, but corresponding to a source strength of 2820 plus or minus 140 disintegrations per sec. As Ir/sup 192/ g is known to have a 1.45minute isomer, decaying mainly by a 58-kev isomeric (E3) transition to the 74-day ground state, it was concluded that the observed activity stems from a third, longer lived isomer of Ir/sup 192/. Afar various studies on the isomer a lower limit of T 1/2 > 5 yr was set. (W.D.M.)
VLA stereoscopy of solar active regions. 2: Altitude, relative motion, and center-to-limb darkening of 20 centimeter emission
A newly developed method of stereoscopic correlation is applied to solar radio maps at a wavelength of 20 cm. On the basis of stereoscopic correlations between radio maps obtained on 6 different days we establish the presence of 66 radio source components associated with 22 active regions. We find the following statistical results for active region source structures at 20 cm: 1. The observed lifetime is consistent with an exponential distribution having an e-folding time scale of greater than 18 days. 2. The average altitude of 20 cm sources is 25 +/- 15 Mm; 90% of the sources are found in heights less than 40 Mm. 3. The average diameter of discrete source structures is 48 +/- 15 Mm, implying a vertical/horizontal aspect ratio of q(sub A) approx. = 0.5. 4. No significant source motion has been found with respect to the standard differential rotation rate of Omega = 13.45 deg - ((3 deg (sin(exp 2)B)). 5. We find a statistical limb darkening, which can be described by the relation (T(sub B)(alpha))/T(sub B)(0)) = 0.4 + ((0.6(cos(exp 2) alpha)) for sources with T(sub B) greater than 0.5 MK. 6. The degree of source polarization is 15% +/- 10% and is independent of source location. 7. Bright sources (greater than or approximately equal to 0.5 MK), or equivalently, long-lived sources (greater than or approximately equal to 5 days) show a systematic variation of their altitude as function of the center-limb distance.