FISSION PRODUCTS OVER THE PACIFIC NORTHWEST 429 The height of the tropopause over the Washington area is usually low enough to permit sampling of the lower stratosphere aiso with this aircraft. EXPERIMENTAL PROCEDURES The increase in the '“C content of the atmosphere from nuclear tests has made this nuclide an important atmospheric tracer. In an at- tempt to measure the level of '“C produced during nuclear tests in the atmosphere, a stainless-steel sampler was deSigned which exposes a maximum surface area of Ascarite (sodium hydroxide on asbestos) to the airstream. The sampler (see Fig.1) was machined to fit the celestial- navigation-sextant mount of the aircraft. The sampler was designed to withstand speeds approaching Mach 1 and to penetrate above the bound- ary layer of the aircraft. ees WIRE SCREEN SCREENED FRONT AND REAR FACES ASCARITE WIRE SCREEN p——— SUCTION SLOTS FUSELAGE SEXTANT MOUNT Fig. 1—Stainless-steel air sampler inserted into the sextant mount of au, S, Navy TA-3B twin-jet trainer.