Initial Screening Evaluation

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

-- a method to determine the activity of 24Na in blood and 32P in hair; and

-- a method to correct dosimeter results for actual spectrum (if known).

7.4.2.1 Initial Screening Evaluation

A nuclear accident dosimetry program should provide absorbed dose information

within 24 hours after the incident. A nuclear accident dosimetry program shall include

a method to conduct initial screening of personnel involved in a nuclear accident to

determine whether significant exposures to radiation have occurred (10 CFR

835.1304)[also see ANSI N13.3 (ANSI, 1969b)]. Discussions on initial screening

evaluations to segregate exposed from unexposed individuals (sometimes referred to

as "quick sort techniques") are found in several references (Moe, 1988; Delafield,

1988; Petersen and Langham, 1966; Hankins, 1979; Swaja and Oyan, 1987).

A common initial screening method is to provide all workers in areas requiring

nuclear accident dosimetry with an indium foil in their personnel dosimeter or security

badge. During a criticality excursion the foil will become activated by neutrons per

the 115In(n, gamma)116mIn reaction and can be measured with a portable beta-gamma

survey instrument or ion chamber. The 116mIn has a 54-min half-life and releases a

1-MeV beta (maximum energy) and a 1.3-MeV gamma (80% of the time).

An alternate screening is to measure body activity due to neutron activation of the

sodium in the blood via the 23Na(n, gamma)24Na reaction. Sodium-24 has 15-hour

half-life and releases a 1.4-MeV beta (maximum energy) and two gammas (1.37 MeV

and 2.75 MeV). A beta-gamma survey meter is used to measure the 24Na activity in

the blood by placing the detector probe against the individual's abdomen and having

the individual bend forward to enclose the detector (Moe, 1988). Alternatively, the

probe can be positioned under the armpit with the open window facing the chest area.

Moe (1988) noted that this method is less sensitive than the use of indium foils and

even a small reading can indicate a significant exposure. An approximate equation to

calculate worker dose (D) based on body weight and instrument reading is shown in

Equation 7.1:

( instrument reading in mR / h )

D ( Gy )

Body weight ( lb )

(7.1)

Differences in incident neutron energy spectrum, orientation, and measurement

techniques relative to conditions used to develop activity-dose correlations can cause

significant errors in estimated radiation dose based on quick-sort surveys. Swaja and

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