Stop Bath Acidity

T.O. 33B-1-1 6-83 reason, no screens of any kind are used and all the sheets of film that will be required should be exposed simultaneously in the same cassette. For instance, at 80 kilovolts, using an aluminum step tablet, three sheets may be exposed in the same cassette without introducing significant differences in the densities of the top and bottom films. At l80 kilovolts, using a steel tablet, five sheets may be exposed at once. At 1000 kilovolts, a steel tablet having steps l/4-to l/2-inch high can be used, and five sheets of film exposed at once. When this penetrating radiation is used, two extra films are included, and the top and bottom films are discarded after exposure. The exposed films should be stored in as cool and dry a place as possible (ideally, at 70°F and 50 percent relative humidity, or below). Any exposed films not used at the end of two to three weeks should be discarded. In processing test strips, they should be developed dark end down on regular film-processing hangers in the center of the tank and be given the same development time and agitation that will be used in practice. When a new batch of developer is put into use, one or more strips are processed and preserved as the standard for comparison throughout the useful life of the developer. Thereafter, a strip should be processed, say, after every 50, 14 by 17-inch films, or equivalent, processed per 5 gallons of developer. If the densities of the test strip are less than those of the strip processed in the fresh solution, the rate of addition of replenisher should be increased. On the other hand, if the densities of the test strips are too high, the rate of addition of replenisher should be decreased. The stepped wedge method of testing developer activity is also useful in cases where the temperature of the processing solutions cannot be exactly controlled. Strips are developed for a series of times, and the development time that a strip matching the one developed at 68°F in the fresh solution is used for routine work. 6.7.15.1 Stop Bath Acidity. The stop bath acidity is not as critical as developer activity, but a check can be made with litmus paper to assure the bath is acidic and capable of neutralizing the alkaline developer. 6.7.15.2 Fixer Bath Activity. The diminished activity of the fixer solution with use in manual processing can be readily noted by the extended time required for clearing of the film emulsion. Fixer time can be increased to compensate for deterioration of the chemicals or chemicals may be replenished by addition of the chemical constituents of the fixer. 6.7.16 Automatic Film Processing. The advantages of automatic processors are speed and control of the development process. Automatic processing is particularly advantageous when large volumes of film need to be processed. Automatic processing also provides for greater uniformity of development, thus providing more consistent results. The quality level of these results is determined by chemical and equipment condition, and conscientiousness of the operator. However, because the cycle is faster and the chemical temperatures are higher in automatic processing than they are with manual processing, the use of automatic processing will produce a more narrow (high) latitude radiograph and has a noticeable effect on the radiograph technique. Therefore, apparent film characteristics will be significantly altered by the use of automatic processing. As a result, film quality, when automatic processing is used, is generally lower than that which is obtainable with manual processing. However, the advantage of speed of processing, lower manpower requirements, and consistency of development generally are felt to be more important in the decision to use automatic processing. The general arrangement of a darkroom, where an automatic processor is used, is illustrated in Figure 6-40. The loading end of the processor is located in the dry area of the darkroom and is under safelight illumination. The output end of the processor is generally located on the outside of the darkroom wall under ambient illumination. In processing film in the automatic processor, the film is unloaded from the cassette film holder as in manual processing. However, it is then immediately fed into the loading end of the processor. After processing is completed, the film exits the other end of the processor. At this point, the film is ready for interpretation and filing as required. Cleanliness in automatic processing is essential. Lint and other contaminants, if they are allowed to enter the processor, can cause many spots as they collect on rollers and affect subsequent films.