Tritium Assay Analysis by PVT Mass Spectrometer cont'd

DOE-HDBK-1129-99

Rearranging the equation becomes

Moles of Tritium = (n(Moles Total) x m%(Tritium Per Mole Total))/100

The amount of tritium in grams is obtained by multiplying the moles of tritium obtained in the last

equation by the gram molecular weight of tritium (6.0321g).

As an example, the grams of tritium in a shipment of research grade tritium are determined

using the following process.

An analysis of a shipment of research grade gaseous tritium shows the following:

Component

Percent

99.704

0.115

0.079

0.050

0.023

0.016

0.012

0.010

0.005

The container pressure is 742 mm, temperature is 20oC, and volume is 49.348 liters. This gives

a compressibility factor (z(T2)) of 1.0006 and the constant, R, is 62.3631.

Calculating the percent tritium is as follows:

m%(Tritium Per Mole Total) = m%(T2) + m%(HT) x 1/2 + m%(DT) x 1/2

= 99.704 + (0.050 x 1/2) + (0.079 x 1/2)

= 99.704 + 0.025 + 0.0395

= 99.7685 percent

The number of moles of gas in the container is calculated by

n(Moles Total) = PV/zRT

= (742 x 49.348)/(1.0006 x 62.3631 x 293.15)

= 2.002 moles total

The amount of tritium in grams is

Grams of Tritium = (n(Moles Total) x m%(Tritium Per Mole Total) x 6.0321)/100

= (2.002 x 6.0321 x 99.7685)/100

= 12.046 grams tritium

The determination of the amount of tritium is only for the point in time that the sample was

analyzed as a result of the decay of tritium. Over time, the number of moles of the gases

containing tritium decrease. The pressure and number of moles of non-tritiated gases increase

with time due to the 3He produced and the molecules formed by the atoms of other materials

released when the tritium decays. Therefore, the mole percent and number of moles of gas in

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