Intensification Of Underexposed Radiographs
Every industrial radiographic department occasionally encounters a radiograph that has been underexposed, either through an oversight or because of insufficient machine capacity. If the radiograph cannot be repeated because the time required for proper exposure would be prohibitively long, or if the item is no longer available, the underexposed negative can in many cases be salvaged. Chemical intensification of the completely processed film may, under certain circumstances, result in a speed gain of a factor of 5 to 7, while still retaining acceptable radiographic quality.
Films may be intensified immediately after fixation, or after they have been fully washed and dried. In either case, the films are washed in running water for 5 to 10 minutes, hardened in KODAK Special Hardener SH-1 (formula given below), and again washed for 5 minutes.
KODAK Special Hardener SH-1
|
||
Avoirdupois, U.S. Liquid
|
Metric
|
|
Water
|
16 fl oz
|
500 mL
|
KODAK
Formaldehyde, about
37% solution by
weight
|
21/2 fl oz
|
10.0 mL
|
KODAK
Sodium Carbonate (Monohydrated)
|
90 grains
|
6.0 grams
|
Water to make
|
32 fl oz
|
1.0 litre
|
They are then treated, one at a time, for up to 10 minutes in KODAK Intensifier In-6. The working intensifier is mixed from the stock solutions (formulas given below) by taking one part of Solution A, and adding in succession two parts of Solution B, two parts of Solution C, and finally one part of Solution A. The order of mixing is important and should be followed. The hardening and intensification can conveniently be done in trays. The film should be agitated frequently during intensification, after which it is washed for 20 to 30 minutes in running water and dried normally.
Warning
Always add the sulfuric acid to the water slowly, stirring constantly, and never the water to the acid; otherwise, the solution may boil and spatter the acid on the hands and face, causing serious burns.
The water used for mixing the solutions for the intensifier should not have a chloride content greater than about 15 parts per million (equivalent to about 25 parts sodium chloride per million); otherwise, the intensification will be impaired. If in doubt as to chloride content, use distilled water.
KODAK
Quinone-Thiosulfate Intensifier In-6
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||
Avoirdupois, U.S. Liquid
|
Metric
|
|
Solution A
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||
Water
|
96 fl oz
|
750 mL
|
Sulfuric acid (concentrated)
|
4 fl oz
|
30.0 mL
|
KODAK Potassium Dichromate
(anhydrous)
|
3 ounces
|
22.5 grams
|
Water to make
|
1 gallon
|
1.0 litre
|
Solution B
|
||
Water
|
96 fl oz
|
750 mL
|
KODAK
Sodium Bisulfite (anhydrous)
|
1/2 ounce
|
3.8 grams
|
KODAK
Hydroquinone
|
2 ounces
|
15 grams
|
KODAK PHOTO-FLO
200 Solution
|
1/2 fl oz
|
3.8 mL
|
Water to make
|
1 gallon
|
1.0 litre
|
Solution C
|
||
Water
|
96 fl oz
|
750 mL
|
KODAK
Sodium Thiosulfate (Hypo)
|
3 ounces
|
22.5 grams
|
Water to make
|
1 gallon
|
1.0 litre
|
The intensification may be carried out in room light. During treatment, the film may be viewed on an illuminator and the process stopped at any time that the results suit the operator. Intensification in In-6 produces a rather grainy, yellowish image, which is not quite as permanent as a properly fixed and washed silver image. However, sufficient improvement is made in the radiographic sensitivity of underexposed radiographs to make these drawbacks relatively minor.
Because the intensified image is destroyed by acid hypo, under no circumstances should the intensified negatives be placed either in a fixing bath or in wash water contaminated with fixing bath. Films to be intensified should be handled as little as possible, and then only by the edges or corners.
The stock solutions from which the intensifier is mixed will keep in stoppered bottles for several months, and the mixed intensifier is stable for 2 to 3 hours. The bath should be used only once and then be discarded because a used bath may produce a silvery scum on the surface of the image.