Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A New Method of Measuring 81Kr and 85Kr Abundances in Environmental
  Samples   We demonstrate a new method for determining the 81Kr/Kr ratio in
environmental samples based upon two measurements: the 85Kr/81Kr ratio measured
by Atom Trap Trace Analysis (ATTA) and the 85Kr/Kr ratio measured by Low-Level
Counting (LLC). This method can be used to determine the mean residence time of
groundwater in the range of 10^5 - 10^6 a. It requires a sample of 100 micro-l
STP of Kr extracted from approximately two tons of water. With modern
atmospheric Kr samples, we demonstrate that the ratios measured by ATTA and LLC
are directly proportional to each other within the measurement error of +/-
10%; we calibrate the 81Kr/Kr ratio of modern air measured using this method;
and we show that the 81Kr/Kr ratios of samples extracted from air before and
after the development of the nuclear industry are identical within the
measurement error.

34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
29
The categories of this paper are: funct-an
5
The categories of this paper are: gr-qc
20
The categories of this paper are: acc-phys
23
The categories of this paper are: solv-int
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
8
The categories of this paper are: hep-ex
24
The categories of this paper are: dg-ga
32
The categories of this paper are: atom-ph
12
The categories of this paper are: nucl-th
10
The categories of this paper are: q-bio