reaction on 232Th. Thus the ratio of rare earth to Sc or Th determines the sensitivity with which the lanthanides can be determined in any particular material. For a short irradiation, the most prominent activity is &6Mnwhich causes an important background correction in the neighborhood of the l65Dy photopeak. The effect of the Sc/l,a ratio is conveniently illustrated by an inspection of the results for the limestone and the garnet (Table IV). The concentration of lanthanides in the limestone sample is three to five times less than that found in basalts; however, the Sc/La ratio is much more favorable, being 0.5 or less for the limestone (for the lanthanides Sm to Yb) and about 10 for basalts. Thus, the gamma photopeaks in the limestone spectrum are more prominent than in the basalt spectrum. The garnet has the highest concentration of scandium of any sample measured. Background effects caused by 46Sc are so large that they cbscure the photopeaks due to cerium and europium. Results for the heavy lanthanides were obtained only because they are strongly concentrated in the garnet structure. Advances in the technology of the fabrication and uses of Ge(Li) detectors are such that the background caused by Compton scattering can be sharply reduced. Detectors with
a volume at least 20 times that used in this study can now be made (14). Crystals of this size should greatly increase counting efficiency and contribute to an improvement in the Compton background. Some attention has also been paid to the use of an anti-coincidence ring around Ge(Li) detectors to subtract the Compton scattered photons (15). Results of this study include most of the common rock types, but only one mineral, garnet, has been investigated. Concentrations of lanthanides in separated minerals (3,5)are such that they should be within the range of measurement of this technique in most cases. In some iron-rich minerals, such as biotite and hornblende, the sensitivity limit may be set by the presence of radiation from 59Fe.
RECEIVED for review August 1, 1966. Accepted November 2,1966. Research performed under the auspices of the U.S. Atomic Energy Commission. (14) H. L. Malm and I. L. Fowler, IEEE T r a m Nucl. Sci., NS13, 62 (1966). (15) J. Kantele, 0. J. Marttila, and J. Hattula, Nucl. Inst. Methods, 39, 194 (1966).
~~~
~
~~~
~~
~
S pectrophotomet ric Determination of Hyd rogen Perox ide with 8-Quin01 in01 SIR: The presence of peroxy-type substances in photochemical smog is mentioned quite often in the chemical literature. Although total oxidant concentration is routinely reported as an air pollution component, there is a definite need for more sensitive, specific colorimetric methods for detecting and determining the pollutants with peroxidic linkage. The method described here is quite specific for hydrogen peroxide and is sensitive enough for analysis at low concentrations. The increase in sensitivity compared to the titanous sulfate method reported by Eisenberg ( I ) and Pobiner ( 2 ) is somewhat similar to that achieved in Gardiner’s determination of titanium (3). Essentially, the method involves the reaction of titanium(1L’) and 8-quinolinol with microgram quantities of hydrogen peroxide. The results of this preliminary investigation support the suggested formation of a peroxidized titanium 8-hydroxyquinolate. EXPERIMENTAL
