ASTM E1165-92(1996)E1
(Test Method)Standard Test Method for Measurement of Focal Spots of Industrial X-Ray Tubes by Pinhole Imaging
Standard Test Method for Measurement of Focal Spots of Industrial X-Ray Tubes by Pinhole Imaging
SCOPE
1.1 This test method provides instructions for determining the length and width dimensions of line focal spots in industrial X-ray tubes (see Note 1). This determination is based on the measurement of an image of a focal spot that has been radiographically recorded with a "pinhole" projection/imaging technique.
Note 1—Line focal spots are associated with vacuum X-ray tubes whose maximum voltage rating does not generally exceed 500 kV.
1.2 This test method may not yield meaningful results on focal spots whose nominal size is less than 0.3 mm (0.011 in.). (See Note 2.)
Note 2—The X-ray tube manufacturer may be contacted for nominal focal spot dimensions.
1.3 This test method may also be used to determine the presence or extent of focal spot damage or deterioration that may have occurred due to tube age, tube overloading, and the like. This would entail the production of a focal spot radiograph (with the pinhole method) and an evaluation of the resultant image for pitting, cracking, and the like.
1.4 Values stated in SI units are to be regarded as the standard. Inch-pound units are provided for information only.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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e1
Designation: E 1165 – 92 (Reapproved 1996) An American National Standard
Standard Test Method for
Measurement of Focal Spots of Industrial X-Ray Tubes by
Pinhole Imaging
This standard is issued under the fixed designation E 1165; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Section 10 was updated editorially in December 1996.
1. Scope
1.1 This test method provides instructions for determining
the length and width dimensions of line focal spots in industrial
X-ray tubes (see Note 1). This determination is based on the
measurement of an image of a focal spot that has been
radiographically recorded with a “pinhole” projection/imaging
technique.
NOTE 1—Line focal spots are associated with vacuum X-ray tubes
FIG. 1 Pinhole Diaphragm Design
whose maximum voltage rating does not generally exceed 500 kV.
1.2 This test method may not yield meaningful results on
focal spots whose nominal size is less than 0.3 mm (0.011 in.). 3.1.1 actual focal spot—the X-ray producing area of the
(See Note 2.) target as viewed from a position perpendicular to the target
surface (see Fig. 2).
NOTE 2—The X-ray tube manufacturer may be contacted for nominal
3.1.2 effective focal spot—the X-ray producing area of the
focal spot dimensions.
target as viewed from a position perpendicular to the tube axis
1.3 This test method may also be used to determine the
in the center of the X-ray beam (see Fig. 2).
presence or extent of focal spot damage or deterioration that
3.1.3 line focal spot—a focal spot whose projected pinehole
may have occured due to tube age, tube overloading, and the
image consists primarily of two curved lines (see Fig. 3).
like. This would entail the production of a focal spot radio-
graph (with the pinhole method) and an evaluation of the 4. Significance and Use
resultant image for pitting, cracking, and the like.
4.1 One of the factors affecting the quality of a radiographic
1.4 Values stated in SI units are to be regarded as the
image is geometric unsharpness. The degree of geometric
standard. Inch-pound units are provided for information only.
unsharpness is dependent upon the focal size of the radiation
1.5 This standard does not purport to address all of the
source, the distance between the source and the object to be
safety concerns, if any, associated with its use. It is the
radiographed, and the distance between the object to be
responsibility of the user of this standard to establish appro-
radiographed and the film. This test method allows the user to
priate safety and health practices and determine the applica-
determine the focal size of the X-ray source and to use this
bility of regulatory limitations prior to use.
result to establish source to object and object to film distances
appropriate for maintaining the desired degree of geometric
2. Referenced Documents
unsharpness.
2.1 ASTM Standards:
E 999 Guide for Controlling the Quality of Industrial Ra-
5. Apparatus
diographic Film Processing
5.1 Pinhole Diaphragm—The pinhole diaphragm shall con-
form to the design and material requirements of Table 1 and
3. Terminology
Fig. 1.
3.1 Definitions of Terms Specific to This Standard:
5.2 Camera—The pinhole camera assembly consists of the
pinhole diaphragm, the shielding material to which it is affixed,
and any mechanism that is used to hold the shield/diaphragm in
This test method is under the jurisdiction of ASTM Committee E-7 on
Nondestructive Testing and is the direct responsibility of Subcommittee E07.01 on
position (jigs, fixtures, brackets, and the like; see Fig. 4).
Radiographic Practice and Penetrameters.
5.3 Film—Industrial type extra fine grain. No intensifying
Current edition approved May 15, 1992. Published July 1992. Originally
screens are to be used. The film shall be processed in
published as E 1165 – 87. Last previous edition E 1165 – 87.
Annual Book of ASTM Standards, Vol 03.03. accordance with Guide E 999.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 1165
FIG. 2 Actual/Effective Focal Spot
NOTE 1—During the production of X-rays the electrons are accelerated from the filament to the target in two separate paths (see Sketch 1). Electrons
emitted at the front of the filament travel primarily along Path A, and electrons emitted at the backside of the filament travel primarily along Path B. Note
that these two paths intersect at a certain point; this is the point at which the target is positioned. As a result, the pinhole picture of the focal spot shows
two lines that correspond with the intersections of Paths A and B at the target (see Sketch 2).
FIG. 3 Line Focal Spot
5.4 Image Measurement Apparatus—This apparatus is used ment (see Fig. 5). The specified focal spot to pinhole distance
to measure the size of the image of the focal spot. The (FHD) for the different nominal focal spot size ranges is
apparatus shall be an optical comparator with built-in graticule
provided in Table 2. Position the pinhole such that it is within
with 0.1 mm or .001 in., or both divisions and magnification of
61° of the central axis of the X-ray beam. Fig. 6 illustrates a
5X to 10X (or equivalent).
typical focal spot exposure arrangement.
6. Procedure
NOTE 3—The accuracy of the pinhole system is highly dependent upon
the relative distances between (and alignment of) the focal spot, the
6.1 If possible, use a standard 91.44 cm (36 in.) focal spot
pinhole, and the film. Accordingly, specially designed apparatus may be
to film plane distance (FFD) for all exposures. If machine
necessary in order to assure compliance with the above requirements. Fig.
geometry or accessibility limitations will not permit the use of
7 provides an example of a special collimator that can be used to ensure
a 91.44 cm (36 in.) FFD, use the maximum attainable FFD (in
conformance with the 61° alignment tolerance. Some other standards
these instances adjust the relative distances between focal spot,
impose very stringent alignment requirements and express these require-
pinhole, and film accordingly to suit the image enlargement
ments in terms of radial tolerances. These documents do not, however,
factors specified in Table 2). The distance between the focal
address any means for assuring compliance with such tolerances. In order
spot and the pinhole is based on the nominal size of the focal
to simplify the focal spot radiography technique and to improve the
spot being measured and the desired degree of image enlarge- overall practicality of the procedure, it is considered that a workable
E 1165
A
TABLE 1 Pinhole Diaphragm Design Requirements (Dimension)
NOTE 1—The pinhole diaphragm shall be made from one of the following materials:
(1) An alloy of 90 % gold and 10 % platinum,
(2) Tungsten,
(3) Tungsten carbide,
(4) Tungsten alloy,
(5) Platinum and 10 % Iridium Alloy, or
(6) Tantalum.
Nominal Dimension of Nominal Diameter of Diaphragm Required “D” and “L” Dimensions, mm (in.)
B
Focal Spot, mm (in.) Opening, mm (in.) DL
0.3 to 1.2 (0.011 to 0.046) incl 0.030 (0.0011) 0.030 6 0.005 0.075 6 0.010
(0.0011 6 0.0002) (0.0029 6 0.0004)
>1.2 to 2.5 (0.046 to 0.097
...
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