Fig. 3.

The initial remote spectra were obtained by using a home-built probe containing two coils separated by 2.5 cm, center to center, and by a copper sheet, which serves as an radio frequency shield. A 1/4-inch Pyrex tube with a 180° bend passes through both coils. The tubing in the larger lower coil (1/2-inch i.d.) holds aerogel crystal fragments. The smaller upper tubing section is empty of aerogel fragments and is centered within a 1/4-inch i.d. coil. The two coils are controlled by separate x- and y-channels of a Varian Infinity Plus spectrometer tuned to 83.25 MHz.