ASTM E803-91

Standard Test Method for Determining the L/D Ratio of Neutron Radiography Beams

General Information

• Status: Historical
• Publication Date: 31-Dec-1990
• Technical Committee: E07 - Nondestructive Testing
• Drafting Committee: E07.05 - Radiology (Neutron) Method

Standards Content (Sample)

ASTM E803 73 0757530 0075872 3 =
d[Tb Designation: E 803 - 91
AMERICAN SOCIETY FOR TESTINGAND MATERIALS
1916 Race St Philadelphia, Pa 19103
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
If not Ilsted in the current combined index, will appear in the next edMon.
Standard Method for
Determining the LID Ratio of Neutron Radiography Beams’
This standard is issued under the fixed designation E 803; 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.
5. Apparatus
1. Scope
1.1 This method defines an empirical technique for the NU Device (see Figs. 2, 2A, and 3) employs neutron
5.1
measurement of the effective collimation ratio, L/D, of absorbing rods positioned at various distances from the
neutron radiography beams. The technique is based upon
image plane. In practice this device consists of cadmium and
analysis of a neutron radiographic image and is independent nylon rods located in V-grooves accurately machined in the
of measurements and calculations based on physical dimen- surface of an aluminum channel section set at a 45 f 1/4O
sions of the collimator system. The values derived by this angle to the side support plate. Near the image plane end the
technique should be more accurate than those based on V-grooves are machined on 0.283-cm centers. After 21 V
physical measurements, particularly for poorly defined aper- grooves, counting one on the end, the grooves are machined
tures. on 0.707-cm centers to the source end. The 0.64-mm
diameter cadmium and nylon rods are laid into the V-
grooves and secured with neutron transparent adhesive tape.
2. Referenced Documents
The aluminum channel is supported by side plates to
2.1 ASTM Standards:
maintain the 45 f V4” angle relative to the image plane.
E 748 Practices for Thermal Neutron Radiography of
While cadmium rods with diameters other than 0.64 mm
Materials2
may be used, the exact rod diameter must be known and the
E 13 16 Terminology for Nondestructive Examinations*
depth of the V grooves must be adjusted accordingly.
5.2 A single A unit as shown in Fig. 2 (b) is used for L/D
values expected to be less than 150. Alternately, a single A
3. Summary of Method
unit used with appropriate spacers may be used to accommo-
3.1 Determination of neutron beam L/D ratio using the
date a wide range of L/D values.
NU (no umbra) technique3 is accomplished by radio-
graphing the NU device with the neutron beam to be
6. Procedure
measured and subsequently analyzing the radiograph by one
of three methods. Each of the three methods is based upon 6.1 Place the Nu device against the cassette with the
the determination of that point at which the umbral shadow finely spaced rods nearest the cassette.
width reaches zero. See Fig. 1. A key feature of the NU
6.2 Align the plane of the cassette perpendicular to the
technique is that L/D can be determined accurately without
axis of the neutron beam.
the need for expensive instrumentation. Neutron radiog- 6.3 Expose the single-emulsion film and NU device for a
raphy practices are discussed in Practices E748 and the time span that will produce a nominal background film
terms are defined in Terminology E 13 16. f 0.4.
density of 2.5
6.4 Process the exposed film in accordance with the
manufacturer’s recommendations.
4. Significance and Use
6.5 Analyze the resultant image in accordance with one or
4.1 The quality of a neutron radiographic image is de-
more of the three methods outlined in Section 7.
pendent upon many factors. The L/D ratio is one of those
factors and constitutes a numerical definition of the geom-
7. Data Analysis
etry of the neutron beam. The L/D ratio required for a
specific neutron radiographic test is dependent upon the 7.1 Visual Analysis-A Visual determination of the L/D
ratio can be made directly from the neutron radiograph.
thickness of the specimen and the physical characteristics of
the particular element of interest. Use of this method ailows When observing the individual rod images, the umbral image
the radiographer and the user to determine and periodically can be recognized as the “white” line along the center of the
check the effective collimation ratio. rod image. This “white” line wiil decrease in width for the
rods located farther and farther from the film. At some point
the umbral images will disappear. Beyond this point a less
I This method is under the jurisdiction of Committee E-7 on Nondestmctive
intense white line will appear and increase in width with
Testing and is the direct responsibility of Subcommittee E07.05 on Neutron
increasing rod distance, Use of a 5 to 10-power magnifier will
Radiography.
aid in determining the point at which the “white” line
Current
...