Differential Diffusion of Helium Isotopes in Glass, Quantum-tunneling 3He Enrichment, and Portable 3He/4He Monitoring of Mantle Processes

Abstract

While studying the scientific and engineering aspects of a field-portable 3He/4He ratio detector, we found elevated ratios at comparatively lower temperatures that appear to result from differential diffusion of these isotopes in pure quartz glass. The 3He enrichment relative to 4He in lab air, expressed as the ratio R and normalized to the accepted 3He/4He ratio of 1.40 E-06 (Ra), ranges from peak values of about 200 to 600 in dry static samples. Even at the maximum classical 3He/4He diffusivity ratio of 1.15, the expected R would be only 1.61 E-06. Within a narrow temperature window, the air value in our experimental set up with pure quartz glass can range from about 2.70 to 8.20 E-04, or nearly 1000 times the expected enrichment based upon classical fractionation. When plotted versus temperature, the narrow 3He net partial pressure peak reveals at least three sharper embedded peaks that may be quantized vibrational entrance states in quartz glass which are temperature specific. This discovery has implications for relatively low-energy industrial enrichment of scarce 3He from natural sources on Earth, and for radiogenic and cosmogenic helium dating assumptions in natural glasses. It also has bearing upon designs for field portable 3He/4He ratio detectors aimed at earthquake and volcanic eruption studies, and monitoring of nuclear sites.

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“…Three prototype instruments have been made and utilized to date. “Albert” is a largely manually-operated bench-top unit, with a larger, 2.5-inch diameter cylindrical quartz adapter flange and sample chamber 15,16 . The “Edward” and “Lyle” instruments are identical, relatively compact field-portable versions of the Albert instrument, with smaller 1.5-inch diameter cylindrical quartz adapter flange and sample chamber (Fig.…”

“…Albert is a bench-top unit, with a larger, 2.5-inch diameter cylindrical quartz adapter flange and sample chamber. Edward and Lyle are intended as identical, relatively compact field-portable units with smaller 1.5-inch diameter cylindrical quartz adapter flange and sample chamber 15,16 .**We use a linear correction of y’ = (y/1.83) − 2.45 to correct the net integral results of the heat ramps, set to 100 sample scan averages past the beginning of the ramp. This linear correction was produced by an earlier regression analysis using the HESJ, Salton Sea, and Lab Air as standards run on Albert.***Air contamination corrections were made based upon assumed dry air values for N 2 , O 2 and Ar of 78.09, 20.95, and 0.93% (source: ref.…”

“…Corrections involve normalization of the calculated PPs for the variable filament emission and electron multiplier gains used in the TIMS method 17 as described in ref. 16 .…”

“…Albert is a bench-top unit, with a larger, 2.5-inch diameter cylindrical quartz adapter flange and sample chamber. Edward and Lyle are intended as identical, relatively compact field-portable units with smaller 1.5-inch diameter cylindrical quartz adapter flange and sample chamber 15,16 .…”

“…A discussion of the reliability of this isobaric separation can be found in the Supplementary Information of ref. 16 . We routinely collect over 100 approximately 1-minute scan averages during a sample heat ramp.…”