|| RTSM Table Of Contents ||

RADIATION SAFETY TRAINING MANUAL

CHAPTER 6
PRACTICAL STEPS TO RADIATION SAFETY

CHAPTER 6 Table Of Contents

A. PRINCIPLES OF RADIATION SAFETY

1. TIME

Figure 6.1 Variation of Exposure With Time
2. DISTANCE
Figure 6.2 Variation of Exposure With Distance
3. SHIELDING
Figure 6.3 Shielding Affect on Radiation
TABLE 6.1
Figure 6.4 Half Value Layer vs Radiation Exposure

B. THE LABORATORY RADIATION SAFETY PROGRAM

Table 6.2 BASIC SHIELDING NEEDS AND METHODS

C. BECOMING AN AUTHORIZED USER OF RADIOACTIVE MATERIAL

Figure 6.5 Supplement A Form
Figure 6.6 RUA Modification Form

D. STORAGE OF RADIOACTIVE MATERIALS

Figure 6.7 RUA Summary Sheet

E. HANDLING RADIOACTIVE MATERIALS

1. PURCHASING AND RECEIVING RADIOACTIVE MATERIALS
2. PREPARING THE WORK AREA
3. PRECAUTIONS DURING THE EXPERIMENT

F. USE OF VOLATILE RADIONUCLIDES

G. SPECIAL PRECAUTIONS FOR THE USE OF RADIOACTIVE IODINE

H. TRANSPORTATION OF RADIONUCLIDES

Figure 6.8 Transfer of Radioactive Material Form
Figure 6.9 Transfer of Radioactive Material Form

I. POSTING AND LABELING REQUIREMENTS

1. POSTING
2. LABELING
Figure 6.10 Radiation Safety Labels

J. WORKING WITH RADIOACTIVE ANIMALS

Figure 6.11 Supplement B Form

The hazards of ionizing radiation and how they can be estimated have been previously discussed. In this section the principles that form the foundation for good laboratory practice when using radioactive materials are reviewed. These principles are applied to specific situations in the work place (such as storage and use of radioisotopes, ventilation requirements, transportation and waste disposal). In addition, information is provided about the radionuclides that you are likely to use, their properties and methods of containment, and the standards of behavior that you will be expected to meet.

A. PRINCIPLES OF RADIATION SAFETY

The three basic principles used to protect against external radiation are to decrease the time of exposure (See Figure 6.1), increase the distance from the radiation source (See Figure 6.2), and increase shielding between the source and detector (See Figure 6.3).

1. TIME

Figure 6.1 Variation of Exposure With Time - Graphic Under Construction

The energy imparted to tissues from external sources is proportional to the number of radioactive decay events, the energy of the emissions, and the length of exposure time. Laboratory personnel can minimize their radiation exposure by simply reducing the amount of time that they are involved in the direct use of radioactive materials. One way that this can be accomplished is by practicing a procedure using non-radioactive material. For example, if an iodination is planned with ¹²⁵I, the procedure for separating free from bound radionuclides should be practiced with non-radioactive material until it becomes routine.

 

2. DISTANCE

Figure 6.2 Variation of Exposure With Distance (Inverse Square Law)-
Graphic Under Construction

Since radiation exposure is reduced by the square of the distance from the source, very intense radioactive sources should be handled with tongs or placed into devices that will allow manipulation of the material while still providing as much distance from the source as possible.

 

For example, if a 10 mCi ⁵⁹Fe source were used, the exposure rate would be 62 Roentgen/hour at 1 cm. (See Table 5.4 to obtain the gamma factor for ⁵⁹Fe.) To reduce the exposure rate to a more acceptable level, the distance from the source would have to be increased, the source would have to be shielded, or a combination of the two would have to be used. If the principle of increasing distance is used, at what distance would be the exposure rate be reduced to 2 mR/hr? The inverse square law states that the intensity will be reduced by the square of the distance from the source.

In this case, the intensity at 1 cm is 62,000 mR/hr. The desired intensity is 2 mR/hour. Thus, the required distance is computed as the square root of 62,000/2 or approximately 176 cm.

 

3. SHIELDING

Figure 6.3 Shielding Affect on Radiation - Graphic Under Construction

For low energy beta-emitters, (e.g., ³H, ¹⁴C, ³⁵S, and ⁴⁵Ca), the walls of commonly used containers will completely shield the beta-particles. But ³²P is so energetic that additional shielding is necessary for protection. Nominally 1 cm of Plexiglas or weight equivalent material is sufficient to stop all of the beta-particles. However, a problem occurs if the shielding for ³²P is made of a heavy material such as lead or steel. In this case bremsstrahlung will be produced.

 

Gamma-emitters are shielded with high atomic number materials such as lead. The half value layer (HVL), discussed previously, is the thickness of a material required to reduce the radiation intensity by 50%. Each additional half-value layer will reduce the beam intensity by another 50%. (See Table 6.1 and Figure 6.4)

TABLE 6.1

Figure 6.4 Half Value Layer vs Radiation Exposure -
Graphic Under Construction

A summary of shielding needs and methods for different radioisotopes is given in Table 6.2 A useful rule of thumb is that a shielding thickness seven times the half-value layer reduces the intensity by two orders of magnitude, and ten times by three.

B. THE LABORATORY RADIATION SAFETY PROGRAM

Each Principal Investigator (PI) is responsible for ensuring that radioactive materials are used in their laboratory in conformance with University of California, San Francisco (UCSF) policies and procedures and applicable regulations. The Laboratory Supervisor is generally responsible for implementing the laboratory's Radiation Safety Program.

The purpose of the program is to ensure that the laboratory is kept free of radioactive contamination, that radiation exposures to laboratory workers and others who may visit the laboratory are kept to an absolute minimum, and that required records (such as radioisotope usage, storage, disposal, and monitoring) are properly maintained.

The Radiation Safety Office audits the laboratory's Radiation Safety Program on a periodic basis (generally every three months). Deficiencies are reported in writing to the PI. Repeated and/or serious problems may be referred to the Radiation Safety Committee (RSC).

Table 6.2 BASIC SHIELDING NEEDS AND METHODS

BASIC SHIELDING NEEDS AND METHODS

BETA EMITTERS - OPTIMUM VISIBILITY AND SHIELDING NEEDS ARE MET WITH THE USE OF LUCITE "L" BLOCKS (REMEMBER ALL SHIELDS SHOULD BE MARKED WITH THE RADIATION SYMBOL TO PREVENT ACCIDENTAL EXPOSURE). CAUTION: DO NOT USE DENSE MATERIALS SUCH AS LEAD TO SHIELD BETA EMITTERS. USE OF SUCH MATERIALS MAY CAUSE BREMSSTRAHLUNG (X-RAY) EXPOSURE.

GAMMA EMITTERS - LEAD GLASS GIVES BEST VISIBILITY, BUT LEAD SHEET OR BRICKS PROVIDE BETTER ATTENUATION. LEAD "L" BLOCKS WITH LEAD GLASS IN THE 45% ANGLE TOP PLATE ARE A GOOD COMPROMISE WHEN VISIBILITY IS THE PRIME CONCERN. ANY LEAD GLASS OR OTHER SHIELDING (SUCH AS STEEL) USED SHOULD HAVE EQUIVALENCY TO THE LEAD VALUE SPECIFIED. GENERALLY SPEAKING, 10 TIMES THE HALF VALUE LAYER IS ADEQUATE FOR MOST ISOTOPES, AS THIS WILL REDUCE THE EXPOSURE BY THREE ORDERS OF MAGNITUDE.

UCSF is committed to following established radiation safety policies and procedures. Failure to follow these procedures can result in the suspension or revocation of your "authorized user" status.

A description of the responsibilities and roles of the RSC, PIs, and authorized users may be found in Chapter 3 of the UCSF Radiation Safety Manual. Copies of the forms mentioned in this manual may be obtained from your Laboratory Supervisor or from the Radiation Safety Office.

|| Top of page || Chapter 5 || Chapter 6 Sections C-E ||Table Of Contents ||