RADIOLOGICAL MONITORING

Intensity and dose measurements are required when a radiation hazard exists. Measurements should be started before the expected arrival of the fallout and continued regularly until the ship has been granted an operational clearance. At early times after the burst (emergency phase), rapid simple measurements are required. At later times (operational recovery phase), the required measurements will range from simple to very detailed. This sect ion is concerned with monitoring surveys in the operational recovery phase. However, you can usually take advantage of measurements made in the emergency phase.

Surveys aboard ship require specific techniques for measuring radiations that produce penetration doses and skin doses.

RADIATION-MONITORING PROCEDURES

The hazards of radiation and radioactive contamination are different from most ordinary hazards in that the former are usually invisible. However, instruments have been developed to measure radiation, and techniques have been developed to estimate the amount of removable contamination. Therefore, the hazards can be identified, their importance can be estimated, and they can be dealt with in a systematic fashion. This section describes techniques for measuring radiation and contamination. These measures provide the information necessary to identify the radiation hazards and bring them under control.

Radiacs provide intensity and exposure information on radiation hazards. The two basic types of radiacs used are the intensity meters and the dosimeters which were described earlier in this chapter.

Radiation measurements can be only as accurate as the radiacs used to make the measurements and the techniques used to operate the radiacs. Some radiacs detect the ionizing property of radiation, which is an electrical phenomenon. They convert this property, through electronic circuitry, to a visible indication. Other radiacs, such as the DT-60/PD dosimeter, depend on chemical changes due to ionization rather than on electrical effects.

Most radiacs with electronic circuitry are somewhat delicate and should be handled with care. Gamma-measuring radiacs are the sturdiest. Beta-detecting radiacs usually have detectors with thin glass walls. This delicate detector is visible when the beta window of the AN/PDR-27 detector probe is open. Alpha-measuring radiacs are the most delicate. The detector probe of this type of radiac has a window which is very thin. This allows the short-range alpha particles to pass through it into the detector. However, this window must be gastight to prevent the escape of the special gases used in the detector. Those who use radiacs should be well acquainted with the particular precautions to be taken with each type assigned to them.

Take precautions to avoid contaminating a radiac's detector probe. A contaminated detector probe will give high radiation readings. These readings might be interpreted incorrectly as contamination on the surface being monitored. Contamination of a detector probe can be avoided in two ways: (1) b y covering the radiac and (2) by not touching contaminated surfaces with the detector probe. Gamma radiacs can be covered by any convenient material. Transparent polyethylene bags are generally found to be most satisfactory. The instrument dial can be read and the control knobs can be operated through the bag. The bag can be changed periodically. The detector of beta radiacs can be protected from contamination by using a layer of thin plastic film, such as Mylar. The detector of an alpha radiac cannot be covered because the cover would reduce the sensitivity of the instrument too much and readings would be incorrect.

Use a standardized monitoring procedure for each type of radiation survey to ensure the maximum value of the radiation data. A uniform monitoring technique will use no more time or effort than a random procedure, and it may actually save time.

General shipboard preattack preparations for radiation monitoring surveys include these steps: . Establish monitoring points l Maintain radiacs

. Select a laboratory-type area for analyzing wipe samples l Prepare masters for data forms l Perform monitoring exercises

Establish monitoring points in compartments or areas that are vital action stations. Examples are living quarters, sick bay, messing areas, shelter compartments, and a few representative deck areas. Each point should be representative of the location of personnel occupying the compartment or area. Identify the points by a distinctive label that includes the location mark and an identifying number. (The identifying number can be the same as the compartment identification unless more than one monitoring point is in the compartment). The number of monitoring points should be the least number that will give a good sampling of the condition of vital stations. The number should also ensure that a complete monitoring survey can be made with only a few monitoring teams in about 10 minutes.

Test and maintain radiacs routinely to ensure proper functioning and to stay familiar with their operation.

Select a laboratory-type area for analyzing wipe samples and fallout samples. The area should have a desk or workbench and be located in a shielded compartment. If wipe samples are to be saved, store them apart from the analysis instrument so that they will not increase the background radiation intensity.

A ship should use training exercises to establish a pattern for calculating and reporting radiological information. When that has been done, prepare masters of data sheets for each step of monitoring, calculation, and reporting procedures (together with a small supply of copies) and keep them on file.

A shipboard or shipyard monitoring team consists of two personnel: a radiac operator (or a dosimeter reader or a wipe sampler, depending on the type of survey being made) and a recorder. The monitoring-team members should be dressed in protective clothing if they are to go into an area suspected of being contaminated. For rapid monitoring, the team should have specific monitoring points to survey. They should travel a previously practiced route (or an agreed-upon route if the previously practiced route cannot be used). The recorder should try to keep his hands and the data sheets from becoming contaminated so that the data sheets can be used in a clean office area.

A reminder list of rules and guidelines for the use of radiacs while performing monitoring surveys follows: