Gas Samplers

DOE-HDBK-1129-99

or a Q-Tip. The filter paper or Q-Tip is then placed in a scintillation cocktail, and the quantity of

tritium is measured by counting the light flashes that occur in the scintillation cocktail as the

tritium decays. The surface contamination is then calculated in units of dpm/100 cm2.

For liquid measurement, a sample of the liquid to be measured is placed in the liquid

scintillation cocktail and measured. The tritium concentration of the liquid is calculated in

Ci/mL. For solid measurement, a known weight of a material is dissolved to produce a liquid

and then the liquid is sampled and measured in the scintillation counter. The quantity of tritium

is then calculated in units of Ci/g of the original solid.

Gas Samplers -- Many different types of gas samplers have been developed and used for

measuring very small quantities of tritium in very large volumes of gas. These samplers are

used to measure quantities of tritium released through a facility stack and for environmental

monitoring at a site. Stack exhaust gas monitoring systems generally use an ionization

chamber to measure the tritium in the stack gases and a gas sampler to measure the

extremely low levels of tritium that cannot be measured by an ionization chamber.

Most of the stack gas samplers are patterned after the ethylene glycol sampling system

developed at Mound Laboratories. A commercial version of this system is now available. In

this system, a sample of gas from the stack is circulated through six ethylene glycol bubblers in

series. The first three bubblers remove tritium in the form of HTO, DTO, and T2O. The gas

stream is passed through a heated catalytic reactor where tritium in the form of HT, DT, T2, and

CHxTy, is cracked and oxidized to form water. This sample is then passed through three more

ethylene glycol bubblers to remove the tritium gas, which is now in the form of water. After a

period from a few hours to days, a sample of the ethylene glycol from each bubbler is removed

and counted using a scintillation counter to determine the quantity of tritium in each bubbler.

Tritium recovered from the first three bubblers is proportional to the tritium in liquid form

contained in the stack gases and the tritium recovered in the last three bubblers is proportional

to the quantity of tritium in gaseous form contained in the exhaust gases.

Due to the extremely small quantity of tritium contained in the atmospheric gases surrounding a

tritium facility, the environmental gas samplers use higher flow rate sampler systems than

those required for stack monitoring, and, in general, collect the water on molecular sieve traps.

The water collected on the molecular sieve traps is then recovered from the trap and the tritium

concentration of the gas passing through the trap is calculated from the tritium concentration of

the collected water, the gas flow rate through the trap, and the sampling time.

Portable Room Air Monitors -- There are several hand held portable room air monitors on the

market and their capabilities and ranges vary as a function of the different manufacturer and

the purpose for which they were designed. It is convenient in some activities to have the

capability to connect a small hose to the monitor so that it may be used to detect tritium leaks

around equipment.

Fixed Station Room Air Monitors -- Fixed station monitors are designed to be installed in fixed

locations and to be used to monitor the room air tritium concentrations. Depending upon the

manufacturer they may have several ranges and are equipped with one or two alarm set points

and audible as well as visual alarms.