Document 6w2DMdD7kQzZ14xjbX1awv239

Ionizing Radiation tOO nR perhr FlC 44-17 --The effect of time on radiation expo sure is easy to understand If we are in an area when the radiation level from penetrating external radiation is 100 mR/hr, then in 1 hr we would get 100 mr (millirems) If we stayed 2 hr, we would get 200 mr, and so on From U S Atomic Energy Commission, "Lining With Radiation, Part 1--Fundamentals " Functions of a Radiation Safety Staff A radiation safety program must be con cerned with establishing safe working dis tances, detecting and measuring radiation, making surveys, decontamination, laboratory and other special services, and record-keep ing Establishing safe distance and times Work involving external sources of radi ation is often done where permanent barners and shielding protect personnel from harmful exposure But it is possible that certain operations may occasion some ex posure of employees In these cases, all un necessary subjection to radiation should be avoided, even to the extent of barring per sonnel, including technicians, from active areas during exposure time, such as during use of X-ray equipment (see Fig 44-20) Maintaining a safe distance is especially critical for employees who must work near portable sources of radiation or inadequately shielded nonportable sources (See Fig 44-21 ) In such cases, a radiation survey should be made with an appropriate survey meter by a qualified health physicist or tech nician m order to provide information to establish minimum safe distances that per sonnel must abide by A safe distance is the distance nonoper ating personnel must maintain from the ra diation source in order to receive no more exposure than that specified in the Radiation Protection Guides even if personnel were to remain at that distance continually (see pre vious discussion under "Regulation and Con trols") The distances specified for a given job may not necessanly remain constant if the radiation m use is modified Hazardous areas indicated by the protec tion survey must be barricaded or roped off to form a restricted section which must not be entered by nonoperating personnel or bystanders Large signs bearing the stand ard radiation symbol, and worded in accord ance with 10-CFR-20, should be posted Shielding* The radiation level from a source is reduced by a factor of 1 divided by the square of the distance placed between a worker and the source If the radiation level is 1 0 roentgen per hour (R/hr) at a distance of 1 foot from a source and you move 2 feet away, the radiation level will drop by a factor of 7/ or 'U (0 25 R/hr) If you move 3 ft away the level will be re duced by a factor of 1 or 7 Thus, by simply putting 3 ft of space be tween a worker and the source, the radiation level has reduced a factor of almost ten Shielding is commonly used to protect against radiation from radioactive sources The more mass placed between a source and a person, the less radiation the person will receive If the mass is concentrated, as in lead, the barner thickness required for the same degree of protection will be less than it would be for a less dense material such as packed earth This introduces another important term -- half value layers (HVL) Tables of HVL are given in radiation handbooks and tvpical values for two radioactive materials, cobalt60 and cesium-137, are given in this table Cobalt-60_____ Cesium-137 Lead . Copper Iron Zinc Concrete 0 49 in 083 0 87 1 05 26 0 25 in 065 068 081 21 1476