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This section will discuss methods for both categories. The measurements techniques for
tritium can be grouped in the three general areas: composition measurements, thermal mea-
surements, and tritium concentration measurements.
Composition measurements determine the actual concentration determination for each
atomic/molecular species. This method can be used for gases only. Thermal methods
(calorimetry) rely on the radioactive heat of decay of tritium. For 1 g of tritium ~0.333 W is gen-
erated by decay. The temperature increase or heat generation is measured. Calorimetry can be
used for tritium in any form: solid, liquid, or gas. The only radioactive material present must be
tritium because other radioactive materials will contribute to the thermal properties of the
sample. The final method determined the total tritium concentration by the measurement of the
products or the effects of the products of the radioactive decay. The beta particle can cause
scintillation effects or ionization effects. These effects can be measured and the concentration of
tritium determined. The following methods are used or proposed to be used for measurement of
tritium: Pressure/Volume/Temperature/Composition (PVTC), using either a mass spectrometer
or laser RAMAN spectrometer for the composition measurement; Beta scintillation counter; Self-
assaying tritium storage beds; Scintillation Counting; and Ion Chamber.
Most of the techniques discussed here are batch samples, however some techniques can
be used for "on-line/real time" measurements.
a. Composition Measurements. PVTC measurement is used for measurement of
gaseous samples only. A representative sample of the gas is taken. The gas that is to
be measured must be mixed well. The volume, pressure, and temperature must be
measured accurately. The temperature is difficult to measure accurately because of
temperature gradients caused by the heat of decay of tritium. The composition of the
gas in the sample is then measured using a mass spectrometer or a laser RAMAN
The mass spectrometer will measure all gas species. A high-resolution mass spec-
trometer is required to distinguish between different molecules with the same mass
number. For example HT and D2 have the same mass number, but must be sepa-
rated to determine the tritium concentration. All species that can contain tritium must
be measured. This includes, water as HTO, methane as C(H,D,T)4, ammonia as
N(H,D,T)3, etc. The sum of all the species containing tritium can then be determined.
If the approximate gas composition is unknown, the use of the mass spectrometer
may be difficult.
The laser RAMAN spectrometer is a relatively new system that can be used to mea-
sure molecular concentrations in a gas mixture. The sample is placed in a cell with
optical windows. The laser excites the rotational or vibrational atomic levels in the gas
molecules. The light emitted as the excited levels decay back to the ground state is
detected using a photodetector system. The measurement is absolute in that the fre-
quency spectrum of each molecule is unique. The intensity is proportional to the
amount of gas present. The disadvantages of the RAMAN method are that the amount
of inert gases cannot be determined. Common inert gases at a fusion facility are the

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