.1OUl•N,r. oF G•.orztvsxcxz. R•.s]•,]•c]• Vo•,u•. 66, No. 10 Ocrorca 1961 On the Radioactivity of the Bruderheim Chondrite IV[. W. ROWE AND M. A. V•.N DILLA Los Alamos Scientific Laboratory, University o• Calqornia Los Alamos, New Mexico Abstract. A sample of the Bruderheim chondrite (fell March 4, 1960) has been examined with a •-ray spectrometer, K% A1 •, Mn% and Na 22 having been identified and quantitatively assayed. The concentrations found were 0.089per cent potassium, 57 disintegrations per minute per kilogram A1 •, 82 disintegrationsper minute per kilogram Mn% and 90 disintegrations per minute per kilogram Na •, which are in good agreement with values found by other workers for this and other meteorites. Introduction. The T-ray spectrum of a 2.15- kilogram sample of the Bruderheim chondrite (fell March 4, 1960, in Alberta, Canada) has beeninvestigated usinga NaI (T1) scintillation spectrometer technique previously described by Van Dilla, Arnold, and Anderson [1960]; it is shown in Figure 1. The technique has been ex- tended to make it more quantitative. The problemhas beenthe proper way of accounting for y-ray scattering and absorption effects and geometry. Our solution hasbeento make a thin, hard shellthe sameshape as the meteoriteand then fill it with iron powderthoroughly mixed with an accurately known amount of the radio- activity to be quantitatively assayed. Experimentalprocedure. The shell (Fig. 2) is fabricated by covering the meteorite with aluminum foil, pressed tightly againstthe sur- face to conformclosely to its shape. A molding compound, Rezolin,Epoxy F (Rezolin L-933A Epo•, Resin 'F,' Rezolin, Inc., Santa Monica, California), is then painted on the aluminum- coated meteorite in two halves with an unpainted strip about X/sinch wide around the middle. After the compound hardens, the two halves are pulled apart from the meteorite and then 'glued' togetherwith more moldingcompound to form the completed shell. The composition of each filling, shown in Table 1, was chosen so that the resultant electron density was very close to chondritic;the average atomicnumber is low enough to make Compton effect the dom- inant interaction. The Bruderheim composition used was that of Baadsgaard and Stelmach (private commu- nication) (seeTable 2). On this basis, the Bru- 14, m > 12 o BRUDERHEIM CHONDRITE (2.15 Kg) 0.51Mev B42580-842.378 Ai26+ Ne EE At = 960 MIN. II DEC. 1960 K40 1.46 Mev Mn 54 0.84, Mev •\ I28 Mev /• • AlE6 ß / '• , ,' ß 1.85 Mev •..,•-' -•.,,.,•'-.• 0 I0 20 30 40 50 60 70 80 90 I00 CHANNEL NUMBER Fig. 1. •-Ray spectrum of the Bruderheim chon- drite. derheim electron density was 2.92 X 10 • elec- trons per gram and that of the mock-up 2.85 to 2.88 X 10 • electrons per gram. After count- ing each mock-up in the same geometry as the meteorite, direct comparison of photopeak areas yielded the quantitative meteorite radioactivity. Results. The Na •2 and Mn • solutions were both calibrated at the National Bureau of Standards with an accuracy estimated at +--2 per cent. The AF • was calibrated by comparing the positronannihilationpeak of A1 • with that of the NBS-calibrated Na •'• and also by com- paring the 1.83-Mev peak of A1 • with a known 1.46-Mev K •ø peak and making small corrections for photofraction, peak width, and self-absorp- tion. The two resultswere within 7 per cent of each other. An accurately weighed amount of KC1 constitutedthe potassium standard. The AP • content of the meteorite was also 3553