the fingers to estimate the hand exposure. Rings which include the metal shield with open window can be used. In many cases, a simple film disk covered with thin rubber is an effective substitute, which introduces very little inconvenience in handling laboratory tools. Strictly quantitative results are obtained only when calibrations can be made with the particular isotopes used in the laboratory. 2. Beta-Gamma Survey Meters These meters fall into two classes: 1. Sensitive detection instruments primarily used for qualitative estimation of contamination. Whenever contamination is found, it is customary to remove it, and there is consequently no need to determine the exposure, quantitatively. Geiger counters in various circuit combinations are frequently used for this purpose. The "Zeuto" survey meter is also convenient for detection purposes. 2. Quantitative survey meters consisting of ion chambers with suitable indicating circuits, for the measurement of radiation transmitted through shields, or in other cases where it is necessary to evaluate the potential radiation exposure. When properly designed, the response of these chambers is independent of the wavelength of the incident radiation over a wide range. The chambers are made optionally sensitive to both beta and gamma radiations or to gamma radiation only. This is effected by provision of a removable shield over a thin window on the chamber. Table 3 includes some of the currently available radiation meters. 3. Beta-Gamma Hand Counters and Shoe Counters The small laboratory can use the simple Geiger counter equipment for the detection of contamination on the hands and shoes of workers. Where the procedure is economically justified, it is preferred to use combinations of G. M. tubes assembled so as to register the activity on both sides of the hands and on the shoes. Ten-tube combinations are available for this purpose. Registration may be either by scaler and registers, or by multiple counting-rate meters. Whenever it is required to make a permanent record of the hand and shoe counts, the scaler-register combination is more effective, and can be made on an automatic printing basis. Alpha, beta, Beta, gamma "Shoe box" type with 1 to 2 liter Beta (alpha). Similar to Zeus circuit, but with 1 Indication of a manufacturer's name does not constitute endorsement of the instrument nor deny the superiority of other makes. 4. Dust, Gas, and Vapor Samplers (a) Dust Samplers Dust or spray may be sampled by drawing air through a filter, or by electrostatic precipitation. The filtration method is reliable, provided that leaks around the edge of the collection paper are eliminated. The activity on the sample paper is measured on standard laboratory counting equipment. Complications are introduced when the halflife of the collected material is short or comparable with the collection time. The electrostatic precipitation method permits the precipitation onto an aluminum surface which is a suitable source for the evaluation of range and energy of the deposited particles. (b) Gas and Vapor Samplers One type of sampler draws air through an ion chamber and measures the ion current with a suitable electrometer circuit. A continuous record of the activity in the atmosphere may be obtained in this manner. The method is unsuitable at low levels because of the difficulty of avoiding disturbance to the chamber insulators by friction, etc. Another method involves the collection of samples in evacuated containers which can be returned to a central location for sampling. In special cases, chemical or adsorption methods are available for specific gases or vapors. V. Hazard Monitoring 1. Inspection of Personnel The monitoring of personnel with respect to incident radiation is achieved by the use of pocket ion chambers and/or film badges worn on the person. It is standard practice to process the pocket chambers daily, and the films weekly. Where experience has shown continued low exposure, films read every 2 weeks give an adequate exposure index. Similarly, self-reading pocket chambers may be worn for an extended period if the casual leakage is insignificant. Finger film should be processed at least weekly. In general, each individual using radiosotopes should be responsible for monitoring himself against contamination. The inspection should include qualitative tests for contami nation of the clothing, hands, and other parts that may be contaminated. Hand checks shall be mandatory before leaving the work area for lunch or termination of the work day. In those cases where the risk of absorption of the isotopes through an open cut is important, hands should be inspected by the supervisor or laboratory leader at the beginning of the work day, and injured persons excluded from the program. Prompt removal of contamination, when found, is a necessary corollary of the inspection. 2. Inspection of Work Areas The beta- and gamma-ray exposures at points habitually occupied by workers should be determined periodically by properly designed ionization or counter devices, operated by qualified personnel. An instrument, or instruments, should be available to cover the range from 1 mr/hr up to 2 r/hr. Other meters for the qualitative detection of small amounts of active contamination should be available. Under laboratory conditions, each person in the laboratory should be responsible for maintaining an adequate frequency of inspection in his own work area. In larger organizations, it may be expedient to employ personnel specifically for these inspections. Continuous monitoring equipment, which may have an alarm feature, is very desirable for locations handling "curie" amounts of radioisotopes. Such meters, and many portable survey meters, give an inadequate indication of the hazard arising from contaminated surfaces. Such surfaces may give a direct contact exposure hazard, or offer a means of transfer to the body. The instrument response corresponding to a permissible level of beta contamination is a function of the active materials involved, and each laboratory should properly evaluate these levels for its own purpose. In general, if a Geiger counter of flat-plate area about 2 square inches is passed with a normal hand motion over a suspected surface, contamination is present in undesirable amounts if there is an obvious instrument response. This policy will result in the cleaning of some areas which were not specifically dangerous to personnel. This in general is offset by the easier definition of this particular limit, and the benefits arising from the maintenance of an extremely clean work area. Care must be |