Diploma thesis in Physics submitted by Florian Freundt born in ...

5 Results 5.5. Noble gases
3
He [% atm. air]
4
He [% atm. air]
40
Ar [% atm. air]
Aug Sep Oct Nov Dec Jan Feb Mar Apr May
110
105
100
95
90
105
100
95
90
105
100
95
90
Aug Sep Oct Nov Dec Jan Feb Mar Apr May
Date
20
Ne [% atm. air]
22
Ne [% atm. air]
36
Ar [% atm. air]
Aug Sep Oct Nov Dec Jan Feb Mar Apr May
110
105
100
95
90
105
100
95
90
105
100
95
90
Aug Sep Oct Nov Dec Jan Feb Mar Apr May
Figure 5.8: Noble gas concentrations of atmospheric air samples relative to literature values
from Porcelli et al. [2002] for 3 He, 4 He, 20 Ne, 22 Ne, 36 Ar and 40 Ar. All isotopes show an
underestimation of roughly 2 %.
tube volume than A23-I, the measured inlet pressure is actually 0.6 mbar lower, indicating a
pressure overestimation on sample A23-I. A comparison of the noble gas concentrations calculated
for these two samples shows that A23-I displays a shift relative to A23-III by roughly -2 %
on most noble gas isotopes. Samples A20-IV and A21-VIII show elevated noble gas concentrations
compared with samples from the same depth and roughly the same time as well, however
comparing samples from different sampling dates can only deliver a vague indication at best. To
quantify the observed behavior of slowly decreasing pressure readings the Keller gauge and the
inlet volume were reinstalled in the mass spectrometer preparation line and eight atmospheric
air samples were opened. This experiment was unable to replicate the previously observed effect:
the readings for those instantaneously vented samples did not decrease. However this led to the
observation that the Keller gauge is highly sensitive to its spatial orientation, showing a 1 mbar
difference when rotated by 180 ◦ , possibly adding to the observed shift in atmospheric noble gas
values.
It was deemed most likely that the reading of the inlet pressure was executed prematurely, but
consistently, leading to a systematical overestimation of sample gas amount and thereby causing
the offset displayed by the atmospheric air samples. Therefore all measured samples’ individual
noble gas isotope values discussed below (except those that vented slowly) were standardized to
the mean fitted values of the measured atmospheric air.
59
Date