Dose to Lens of Eye - STD-1128-98master0193

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

6.3.5

Dose to Lens of Eye

The dose to the lens of the eye is not generally a problem in plutonium facilities because

whole body exposures are generally the limiting case. Dosimeters to measure the dose to

the lens of the eye are seldom used. However, shallow doses at depths of 3 mm can be

appreciable in cases where there is an abundance of low-energy photons, such as during

visual inspection of machined plutonium pieces on laminar-flow tables or other situations

where the plutonium is not shielded. In these cases, the eyes are generally protected by

requiring safety glasses to be worn.

6.3.6

Spectrometry Measurements

Personnel neutron dosimeters used at DOE plutonium facilities include TLD-albedo and

nuclear track detectors. The response per unit dose equivalent for TLD-albedo

dosimeters is a sensitive function of incident neutron energy (see Figure 6.2). These

dosimeters are typically calibrated under low-scatter conditions in a calibration

laboratory, such as the facility at PNL used for exposing dosimeters for DOELAP

accreditation. The dosimeters are calibrated to a fission spectrum from 252Cf or a

degraded fission spectrum from D2O-moderated 252Cf. However, the neutron energy

spectrum of the workplace is significantly different from that of the calibration facility

and the response per unit dose equivalent is also different, primarily because of the

number of low-energy neutrons produced by scatter within process equipment, glove

boxes, and the walls and floor of the facility. To achieve accurate results, the TLD-

albedo dosimeter results must be corrected for the specific neutron energy spectrum in

which they are exposed. One method to achieve accuracy is to expose neutron

dosimeters on a phantom in the workplace in neutron fields where the dose equivalent

rate has been carefully measured using neutron spectrometers.

There are several neutron energy spectrometers available to make accurate neutron

spectrum measurements and dose equivalent estimations, as outlined in the document A

Field Neutron Spectrometer for Health Physics Applications (Brackenbush et al., 1992).

Neutron spectrometers that are useful for dose equivalent determinations in plutonium

facilities include:

-- Multisphere or Bonner sphere spectrometers

-- tissue equivalent proportional counters (to determine LET spectra)

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