Rapid Alpha-Monitoring Survey

The purpose of a rapid alpha survey is to obtain the data necessary to quickly detect the contaminated areas of a ship after a nuclear weapons accident. The alpha-contamination limit can be delineated at the same time. A rapid alpha survey should take place immediately after the accident and at designated intervals thereafter. The following procedure should be used to delineate the contaminated areas:

l From the nature of the accident, tentatively identify those areas that almost certainly are not contaminated and also those areas that almost certainly are contaminated.

l Take readings, beginning with the presumed uncontaminated area and working to the presumed contaminated area; space the survey points so that there will be four points between the presumed clean area and the presumed contaminated area.

. Survey first those areas where spread of contamination would be most important.

. Record results of the survey as readings are made; include time, location, meter reading, and notes on any unusual observation.

The technique for taking readings is as follows: Place the probe within one-eighth inch of the surface. Hold the probe in one position for 3 to 5 seconds to allow for the relatively slow response of the alpha radiac. Use earphones if they are available. An alpha reading cannot be taken on a wet surface.

Even though alpha-monitoring teams may be dressed in protective clothing, they should try to stay out of a highly contaminated area because they might spread alpha contamination into the clean area.

Detailed Monitoring Survey

The detailed monitoring survey is a slow, careful inspection of all accessible areas, equipment, and systems that have been exposed to contamination. This survey is generally conducted after the application of countermeasures and toward the end of the operationalrecovery phase. The purpose of this survey is to verify the radiological clearance level of various areas on a ship. These checks determine whether or not the next lower clearance level can be assigned to the area, thereby reducing radiological restrictions aboard the ship. After fallout contamination, the survey includes both a betagamma radiation survey using radiacs and a contamination survey using wipe samples. After a damaging nuclear-weapon accident, the survey includes an alpha-radiation survey using radiacs and an alpha-contamination survey using wipe samples.

When the general radiation level of the ship has been reduced by decontamination operations, read the wipe samples where they are taken rather than take them to a low-background laboratorytype area.

The detailed survey should include all accessible surfaces (both horizontal and vertical) in suspect areas of the ship. It is especially important to check surfaces and areas that tend to capture and hold dirt, such as rust spots, scuppers, caulking in wood decking, canvas covers, and manila lines. Give extra attention to compartments, such as firerooms, that were ventilated during fallout. The finer fallout particles, which can enter the ship through the ventilation system, tend to settle on horizontal surfaces. They adhere to wire screens, steel wool, and air filters (such as those on electronic equipment). Carefully monitor the ship's seawater piping systems externally, over all parts from the intake to the outlets. Remove access ports along the ventilation system and take wipe samples of interior surfaces. Take air samples, as described in the air sampling section that follows, at the outlets of any ventilation ducts suspected of being used during fallout.

This gamma monitoring procedure is slightly different from that described under Rapid Exterior Gamma-Monitoring Survey. Hold the gamma detector approximately 2 inches from the surface being monitored. By using this procedure, you can identify a contaminated area 1 foot in diameter or less. You can sometimes further localize a contaminated area by slowly moving a detector probe (with the beta shield removed) over the surface at the 2-inch distance. Identify the contaminated area by marking it with a crayon. For example, you should record the following: the location of the contamination, intensity, method of reading, and date.

Air Sampling

Air sampling has two purposes: to detect the presence of radioactive aerosols created in a contaminated area which may possibly spread to a clean uncontrolled area and to establish the requirement for respiratory protection for personnel working in a contaminated area. Air sampling is applicable to shore-based operations. However, it is also applicable to the testing of the atmosphere of compartments having ventilation intakes downwind of an alpha-contaminating incident (such as a weapon-handling accident).

An air sampler (or more properly, air-particle sampler) draws air through a replaceable filter at a nearly constant rate of flow. With some air samplers, you can read the total volume of air on a digital counter. With others, you can calculate the total volume of air by multiplying the known flow rate by the air-sampling time. You should then remove the filter from the air sampler. Then, collect and analyze the radioactivity of the air particles, using instrumentation suited to the type of contaminant suspected.

Analyze the filter papers from air samplers by the procedures given in the air-sampling instruction. If at all possible, use the type of filter paper recommended by the manufacturer of the air samplers. If that type of filter paper is unavailable, substitute other types of filter paper. However, note that air samplers might give erroneous readings if substitute filter papers are used.

Coarse filter papers will allow the finest particles to pass through. This gives low collection efficiencies as compared to the recommended paper. In addition, coarse papers absorb some of the alpha radiation from contaminated particles that have been collected. Therefore, use of other than recommended papers when sampling air for alpha aerosol contamination can result in readings having a substantial error.

Air sampling can be done in two ways, depending on the size of the operation:

. If the operation being monitored is small, take a sample during the operation, with all workers wearing respiratory protection suitable for the aerosol problem expected. After the sample is analyzed, modify respiratory protection according to the findings.

. If the operation is large, make a pilot run under conditions as realistic as possible. Analyze air samples from the pilot run and project the results to the full-scale operation. Continue air sampling through the full-scale operation, monitoring filter papers periodically as a check on the projection from the pilot run.

While monitoring the spread of contamination, set up the air sampler at a height of about 5 feet, directly downwind from the operation to be monitored but not further than the line demarking the contaminated and clean areas. To monitor the inhalation hazard to operating personnel, set up the air sampler in the highest suspected airborne contamination in which a worker may go.

Fallout Samples

Fallout samples can be taken to check the decay rate of fallout. They can also be used to predict decay better than the assumptions made when measurements are not available. Samples collected before and during the operationalrecovery phase will be most useful in planning radiological-recovery operations.

Take a fallout sample in the same manner as for a standard wipe sample except that you should take a larger sample to obtain a high-radiation reading. It is advisable to obtain a fresh sample each time the ship is decontaminated. Decontamination can selectively remove certain radioisotopes and thereby change the decay rate of the remaining mixture of radioisotopes.

Analyze samples by using laboratory counting techniques. If a laboratory counter is not available, use the procedure for analyzing wipe samples but cover the detector with the beta shield. Plot the net readings on log paper. An example of this type of plot is given in figure 8-19. Compare the plotted points with the dashed line indicating the average decay. If the slope of the plotted data is greater than average decay (as is the case with data up to about 15 hours in fig. 8-19), then the predicted intensities and exposures calculated by methods based on average decay will be greater than the actual future intensities and exposures. On the other hand, if the slope of the plotted data is less than the average decay (as is the case with data after about 20 hours in fig. 8-19) then the predicted intensities and exposures calculated by methods based on average decay will be lower than the actual future intensities and exposures. These differences may be significant for planning purposes.