Download BD0038

SMU-DDE-Assignments-Scheme of Evaluation
PROGRAM
SEMESTER
SUBJECT CODE &
NAME
BK ID
SESSION
MARKS
A
Describe the electrolytic method of silver recovery.
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B1061
WINTER 2015
25
Criteria
Q.No
1.
B.Sc./DIPLOMA IN MEDICAL IMAGING TECHNOLOGY
II
BD0038/DM0038– RADIOGRAPHIC PHOTOGRAPHY
In electrolytic method the used fixer contains silver.
In this reaction the thiosulphate ions will break down and the
product is silver sulphite.
This has the power to react with unexposed silver halide. If the
film is put in the fixer where the silver sulphite has formed it
will become a victim of sulphite fog. This is avoided by
violently agitation of film during silver recovery.
A silver recovery unit consists of two electrodes: the carbon
plates are anodes and stainless steel plates are cathodes upon
which the silver is deposited.
The fixer contains complex argent thiosulphate, which is -vely
charged, and migrates from the cathode.
As dissociation takes place it gives out a small proportion of
+ve silver ions. These +ve ions more towards cathode (-ve
change) and get deposited on it. Then further dissociation takes
place and again +ve silver ions are deposited on the Cathode.
Likewise a slow continuous deposition of silver takes place.
Then the cathode stripes are taken out and the deposited silver
is collected by scrubbing the strips (chipping out).
The control system allows the unit to operate from A C mains
at correct voltage and current values.
The ions involved in are -vely charged and will migrate not
towards the cathode but away from it.
Marks
(Unit 10;Pg 86-87)
10
Explain the construction of intensifying screen.
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The silver halide emulsion changes on exposure to X-rays in a
manner similar to its reaction when exposed to light.
 The absorption of radiation of incident X-rays by emulsion is
very little.
 An intensifying screen exposed to the same radiation will
absorb more radiation and convert it into emission of light.
The use of intensifying screen provides a method of
converting X-rays to another actinic radiation (light).
The Intensifying screen consists of:
 Base: This may be of polyester or cellulose acetate. It must be
radioprarent and chemically inert, showing characteristics of
toughness and flexibility and should not either curl or discolour
with age.
Total
Marks
10
(Unit 4;Pg 45-46)
2
10
6
SMU-DDE-Assignments-Scheme of Evaluation
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White pigmental layer: The base is coated first with a smooth
white pigmental layer of magnesium oxide or titanium dioxide
which serves to redirect the emitted light to film.
Fluorescent layer: Over the white pigment a uniform
homogeneous layer of Fluorescent material is coated.
Super coat: Over the fluorescent layer a thin transparent tough
and water proof layer is coated which protects the fluorescent
layer from scratching or any kind of abrasion.
Flexibility is essential as sometimes the screens are used in
curve cassettes, which are used for the examination of shoulder,
knees and hip joints.
Both screens are not identical in structure. The first screen is
thinly coated with fluorescent material and the second (back)
screen is thickly coated with fluorescent material to get equal
densities.
If the placing of the layers of screens interchanged it will create
a seriously under exposed image.
2
List the functions of gelatin as a suspension medium.
Listing any of the following 5 functions:
1. It is a suitable medium for the formation of the silver halide
crystals. The chemical reaction between the solution of silver
nitrate and alkaline halides in gelatin lead to the formation of
insoluble silver halide crystals. They remain finely dispersed
and suspended in gelatin.
2. It maintains the silver halide crystals evenly distributed within
the suspension.
3. When warmed gelatin forms a solution, which flows over the
base. When cooled it forms a firm jelly which sets on the base
and then this jelly can be dried. It is a flexible and transparent
layer on the base.
4. It allows the solution to penetrate the emulsion and the material
is chemically processed after photographic or radiographic
exposure.
5. Some of the constituents of gelatin act on silver salts as
sensitizers and increase the speed of emulsion, other
constituents act as restrainer and reduce fog.
6. On exposure to light change takes place in silver halide grains.
It is believed that the gelatin helps to prevent any reversal
change, which will reduce the effect of exposure.
(Unit 1;Pg 3)
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*A-Answer
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