Keeping Track of Everyone’s Radiation Exposure (Group Dosimetry) in the Bomb Shelter

Keeping Track of Everyone’s Radiation Exposure (Group Dosimetry) in the Bomb Shelter

The radiation hazard will be worst throughout the first 24 hours after each fallout cloud arrives. It is important to start keeping track of everyone’s radiation exposure right away, as soon as fallout begins to arrive.

In most bomb shelters the radiation levels will be different as you move from one place to another. In these bomb shelters each Unit Leader should have a dosimeter. The readings on the Unit Leader’s dosimeter will be used to fill out the radiation exposure record of each member of the unit. For this reason, every member of the unit should stay close to the leader, especially during the first 24 hours after fallout arrives. This method of estimating individual exposures is called Group Dosimetry.

If any member of the unit needs to make an urgent trip to some area where the radiation level is higher and for a length of time such tat the person’s radiation exposure might be a few roentgens higher than the rest of the unit, special arrangements should be made. The bomb shelter Manager and RM should be consulted if the trip is unusual. An extra entry should be made on the individual’s radiation exposure record for such trips.

Trips to restrooms and drinking fountains in areas of higher radiation levels should be limited in number and length. The Unit Leader should make about the same number of trips as other unit members at about the same times for the same length of time. The dosimeter should be worn by the Unit Leader on these trips to get an idea of how much exposure is received during these trips. If some members need to make additional trips, the extra exposure should be estimated by the Unit Leader, with help from the RM if necessary, and entered on the members’ radiation exposure records.

You, the RM, should very carefully monitor your own exposure and make forecasts on your future exposures so you will not exceed the limit of exposure set in Row A of the Penalty Table (below). Your experience and training make you very valuable to the occupants of the bomb shelter.

A dosimeter hung on the wall or a post at eye level or higher will show a higher radiation exposure than a dosimeter carried on a person in the same area. The person’s body shields the dosimeter from some of the gamma radiation. If the person wearing the dosimeter is surrounded by many people who are standing up, the reading on that person’s dosimeter will be even lower because of the gamma shielding provided by the people’s bodies.

During the first 24 hours after fallout begins to come down, entries should be made every 4 hours in each person’s radiation exposure record. The Unit Leader should check each entry on each record kept in his unit. The RM should spot-check records throughout the bomb shelter and look for entries which seem too high or too low. Such entries may be due to faulty instruments or to shielding conditions which the RM should know about. It is important that these situations be corrected as soon as possible.

Sample radiation exposure records from the apartment example (earlier) are shown in the Figures below. The radiation exposure record in the the first Figure shows what a dosimeter would read if it were mounted at location 1, where survey meter readings were taken earlier. The radiation exposure record taken from dosimeters clipped to the clothing of adults on the edges of Room G would have entries which may be less than 75 percent of the entries in the first figure, due to the shielding effect of their own bodies and others. The entries on records of those in the interior of the room would be even lower.

In the second Figure the radiation exposure record is shown for John Doe, an infant. His radiation sensitivity category is “Child”, as listed in the Radiation Sensitivity Category Table near the beginning of this Chapter.

This record was maintained by his father, James Doe, who was made the leader of the bomb shelter unit in which the Doe family was placed. The radiation levels in the apartment started to climb a second time at 1645 hr on July 5, 1989, as shown by the survey meter readings in the first Figure, indicating the arrival of another cloud of fallout.

By 1745 hr the radiation level had reached 5 R/hr at location 1 and was still climbing. It was decided that human body shielding would be used to protect those in the first two radiation sensitivity categories. This special shielding, involving all the people in the bomb shelter, began at 1800 hr, as shown on the radiation exposure records in the second Figure, and reduced John Doe’s exposure to less than half of what it would have been without this special shielding.

On the second day, 24 hours after fallout arrived, special shielding was terminated, but partial shielding for John Doe was provided by the members of his bomb shelter unit. The next 13 entries were made on a daily basis instead of every four hours. On July 18, the occupants of the apartment were relocated to a bomb shelter in an area with much lighter fallout.

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