External Dose Reduction

DOE-STD-1128-98

Recently, neutron energy spectrometers have been fabricated from

superheated drop detectors. Each type of superheated drop detector

responds to neutrons with energies above a certain threshold. By using a

combination of detectors with different thresholds and appropriate

unfolding algorithms, it is possible to determine approximate neutron

energy spectra from simple measurements. Commercially available units

currently tend to suffer from quality control problems; i.e, the sensitivity

per unit neutron fluence varies too much to make highly accurate spectral

measurements. (The sensitivity varies with the degree of superheat and

ambient temperature.) However, this technique offers great promise as a

very simple, relatively inexpensive method for neutron spectrometry and

dose determinations, particularly in facilities with a constant temperature.

6.4

EXTERNAL DOSE REDUCTION

The traditional methods of using time, distance, and shielding are typically employed in

plutonium facilities to reduce exposures to ALARA levels. However, other considerations

may be just as important. Good housekeeping practices are vital to keep dose rates low.

Even invisible dust layers on the interior surfaces of glove boxes can create gamma

radiation fields of 10 mrem/h or more, especially through lightly shielded glove ports. The

practice of pulling gloves outside for storage should not be condoned in operations that

generate dust or powders. Dose rates of 30 mrem/h have been measured in facilities

processing high-exposure oxide powders. A factor of 30 reduction in dose rate was

achieved by merely storing the gloves inside the glove box when not in use and placing

lightweight "pie plate" shields over the glove-port openings.

6.4.1

Time

Obviously, reducing the time a worker is exposed in a radiation field will reduce

the dose. Any operation which involves high dose rates (more than a few

mrem/hour) or long exposures should be reviewed for possible reductions in a

worker's exposure time. For example, a worker should minimize the time spent

near a fluorination operation. After the equipment has been set up, the worker

should leave the area during the actual fluorination step.

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