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.
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.
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.