Dose to Lens of Eye - doe-std-1128-98

DOE-STD-1128-98

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)

-- liquid scintillator spectrometers

-- proton recoil spectrometers.

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