Film Badge Dosimetry in Atmospheric Nuclear Tests (1989) / Chapter Skim
Currently Skimming:
2 Basic Principles of Film Badge Dosimetry
2 Basic Principles of Film Badge Dosimetry
Pages 10-23
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 10... ...
Even before Roentgen's discovery of x-rays in 1895, fogging of unknown origin was observed in photographic emulsions by researchers who were unknowingly producing x-rays during their research with evacuated discharge tubes. Among the first to apply photographic emulsions to radiation protection was William H
|
From page 11... ...
After two weeks, this film was to be developed and the degree of blackening correlated with radiation exposure in terms of skin erythema dose (Pfahler 1922~. Four years later, Edith Quimby, a New York medical physicist, proposed the first true film badge, incorporating a system of metallic filters to compensate for the energy dependence of the film sensitivity (Quimby 1926)
|
From page 12... ...
B PERSONNELDOSIMETRY FILMS Films used for personnel dosimetry are basically the same as ordinary black and white photographic film or x-ray films, consisting of a layer of gelatin emulsion containing a specified quantity of silver halide laid on top of a sheet of supporting structure known as the film base (Figure 2-29.
|
From page 13... ...
The first step is the precipitation of silver halide in a gelatin solution. This is accomplished by addition of an aqueous solution of silver salts, primarily silver nitrate, to a gelatin solution containing an excess of alkali halide under controlled conditions.
|
From page 14... ...
Basically, the Gurney-Mott theory proposes that all or a portion of the incident energy of a photon or charged particle is transferred to one or more valence band electrons in the silver halide crystal, raising them into the conduction band, where they are free to migrate through the crystal. These electrons will either recombine with positive holes (i.e., a deficiency of electrons)
|
From page 15... ...
The final washing is usually carried out for an hour in running water, perhaps containing a wetting agent, to ensure complete removal of chemical residues. The wetting agent helps prevent the occurrence of water marks which may affect subsequent optical density measurement.
|
From page 16... ...
F RESPONSE CHARACTERISTICS OF FILM The optical density of an exposed film is usually plotted as a semilogarithmic function of the radiation exposure and is characterized by a curve of the form shown in Figure 2-3.
|
From page 17... ...
For photographic emulsions used for personnel dosimetry in the normally expected occupational exposure range, a typical film sensitivity is 0.5 NOD units per 400 mR exposure. For films with this sensitivity, the lower limit of detection is about 10-20 mR for photon energies above a few hundred keV.
|
From page 18... ...
The effect is most pronounced in the photon energy region below a few hundred kilovolts, peaking as shown in Figure 2~. A reasonable solution to the problem of photon energy dependence is to use filters to obtain a response for the film that is reasonably independent of photon energy and approximates that of soft tissue.
|
From page 19... ...
On a practical level, the high-, filter is selected to provide an essentially flat response over the widest possible energy range. An appropriate thickness, e.g., 0.5 mm (0.020 inch)
|
From page 20... ...
H OTHER SOURCES OF ERROR IN FILM BADGE DOSIMETRY Although the intrinsic accuracy of personnel dosimetry films to suitable reference levels of radiation is quite good (Brodsky 1963; Brodsky and Kathren 1963;
|
From page 21... ...
Because the planar geometry of film and badge-f~lter combination cause angular dependence, the angle of incidence of the exposing radiation will affect the response. Photons or beta particles incident at oblique angles will pass through a proportionately larger thickness of overlying filter.
|
From page 22... ...
Usually, a few percent of the processing batch should be unexposed controls to establish the background fog level for that particular processing batch; similarly, each batch should contain one or more films exposed to a predetermined level in the usable portion of the H and D curve (e.g., 100 mR to 1 R referenced to air for a typical personnel dosimetry film)
|
From page 23... ...
The most common track inducing process is from proton recoils produced by the (n,p) reaction in the emulsion, film base, and low-, material (e.g., paper wrappings)
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.