Isotopically altered xenon gas is of interest for research into double-beta decay
CHEMISTRY · Multi-part · AP · Chemistry · Atomic Structure and Properties · Atomic Structure and Properties
Problem
Isotopically altered xenon gas is of interest for research into double-beta decay. The natural isotopic abundances of xenon (in %) are 124Xe 0.10, 126Xe 0.09, 128Xe 1.92, 129Xe 26.44, 130Xe 4.08, 131Xe 21.18, 132Xe 26.89, 134Xe 10.44, and 136Xe 8.87.
A laboratory produced an enriched batch of xenon (Sample J). A mass spectrum of Sample J showed the following relative intensities (again scaled so that their sum equals 1000):
Isotope
Sample J intensity
124Xe
1
126Xe
1
128Xe
15
129Xe
80
130Xe
12
131Xe
70
132Xe
70
134Xe
55
136Xe
696
Assume that xenon forms only singly charged monatomic ions in the mass spectrometer.
(a) Identify all isotopes that are significantly enriched (by at least a factor of two) in Sample J relative to natural xenon. Support your answer with quantitative comparisons.
(b) Calculate the mole fraction of 136Xe in Sample J to three significant figures.
(c) Determine the enrichment factor for 136Xe, defined as (mole fraction in Sample J) ÷ (mole fraction in natural xenon). Report the value to two significant figures.
(d) Compute the average atomic mass of xenon in Sample J to four significant figures.
(e) Discuss how the altered isotopic composition would influence (i) the density of the gas at a given temperature and pressure and (ii) the neutron-capture cross section of the gas, compared with natural xenon.