ASTM E803-91(2002)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: E 803 – 91 (Reapproved 2002)
Standard Test Method for
Determining the L/D 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.
1. Scope and constitutes a numerical definition of the geometry of the
neutron beam. The L/D ratio required for a specific neutron
1.1 This test method defines an empirical technique for the
radiographic examination is dependent upon the thickness of
measurement of the effective collimation ratio, L/D, of neutron
the specimen and the physical characteristics of the particular
radiography beams. The technique is based upon analysis of a
element of interest. Use of this test method allows the
neutron radiographic image and is independent of measure-
radiographer and the user to determine and periodically check
ments and calculations based on physical dimensions of the
the effective collimation ratio.
collimator system.The values derived by this technique should
be more accurate than those based on physical measurements,
5. Apparatus
particularly for poorly defined apertures.
5.1 NU Device (seeFigs.2(a),2(b),and3)employsneutron
2. Referenced Documents absorbing rods positioned at various distances from the image
plane. In practice this device consists of cadmium and nylon
2.1 ASTM Standards:
rodslocatedinV-groovesaccuratelymachinedinthesurfaceof
E 748 Practices for Thermal Neutron Radiography of Ma-
analuminumchannelsectionsetata45 6 ⁄4°angletotheside
terials
support plate. Near the image plane end the V-grooves are
E 1316 Terminology for Nondestructive Examinations
machined on 0.283-cm centers. After 21 V grooves, counting
3. Summary of Test Method one on the end, the grooves are machined on 0.707-cm centers
to the source end. The 0.64-mm diameter cadmium and nylon
3.1 Determination of neutron beam L/D ratio using the NU
rods are laid into the V-grooves and secured with neutron
(no umbra) technique is accomplished by radiographing the
transparent adhesive tape. The aluminum channel is supported
NU device with the neutron beam to be measured and
by side plates to maintain the 45 6 ⁄4 ° angle relative to the
subsequently analyzing the radiograph by one of three meth-
image plane. While cadmium rods with diameters other than
ods. Each of the three methods is based upon the determination
0.64 mm may be used, the exact rod diameter must be known
of that point at which the umbral shadow width reaches zero.
and the depth of the V grooves must be adjusted accordingly.
See Fig. 1. A key feature of the NU technique is that L/D can
5.2 A single A unit as shown in Fig. 2(b) is used for L/D
be determined accurately without the need for expensive
values expected to be less than 150.Alternately, a singleAunit
instrumentation. Neutron radiography practices are discussed
used with appropriate spacers may be used to accommodate a
in Practices E 748 and the terms are defined in Terminology
wide range of L/D values.
E 1316.
6. Procedure
4. Significance and Use
6.1 Place the NU device against the cassette with the finely
4.1 The quality of a neutron radiographic image is depen-
spaced rods nearest the cassette.
dent upon many factors. The L/D ratio is one of those factors
6.2 Align the plane of the cassette perpendicular to the axis
of the neutron beam.
This test method is under the jurisdiction of Committee E07 on Nondestructive
6.3 Expose the single-emulsion film and NU device for a
Testing and is the direct responsibility of Subcommittee E07.05 on Radiology
time span that will produce a nominal background film density
(Neutron) Method.
of 2.5 6 0.4.
Current edition approved May 15, 1991. Published July 1991. Originally
published as E 803 – 86. Last previous edition E 803 – 86.
6.4 Process the exposed film in accordance with the manu-
Annual Book of ASTM Standards, Vol 03.03.
facturer’s recommendations.
Newacheck, R. L., and Underhill, P. E., “The NU Method for Determining L/D
6.5 Analyze the resultant image in accordance with one or
Ratio Of Neutron Radiography Facilities,” Aerotest Operations, Inc., Report A.O.
77-27, June 1977. more of the three methods outlined in Section 7.
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E 803 – 91 (2002)
FIG. 1 Diagram of Zero Umbra Image Configuration
NOTE 1—Rods at “A” positions are 1 cm each side of center line (22 ea.)
NOTE 2—Rods at “B” positions are 2 cm each side of center line (9 ea.)
NOTE 3—Rods at “C” positions are 2.5 cm each side of center line (1 ea.)
NOTE 4—All dimensions from base line to reduce accumulative errors
NOTE 5—Rod arrangement shown for single system device. For an add-on device, to form a double system, extend the 11 spaces for 7.78 cm to 19
spaces for 13.43 cm and eliminate the close spacing (20 for 5.65 cm)
NOTE 6—Rods held tightly in position with one layer of transparent tape
2(a) Support Channel Subassembly with Rod Spacing
E 803 – 91 (2002)
2(b) L/D Apparatus Assembly
7. Data Analysis 7.2 Microdensitometric Analysis—The second data analysis
method is based on a microdensitometric scan across the
7.1 Visual Analysis—Avisualdeterminationofthe L/Dratio
cadmium rod images beginning with the “0” position rod
can be made directly from the neutron radiograph. When
nearest the film. A typical scan is shown in Fig. 4. A
observing the individual rod images, the umbral image can be
densitometer aperture of 20 3 300 µm and no horizontal
recognized as the “white” line along the center of the rod
expansion is suggested for this method. The value of b is
image. This “white” line will decrease in width for the rods
obtained from the intersection of a straight line originating
located farther and farther from the film. At some point the
from the tip (low film density) of the scan of the “0” rod and
umbral images will disappear. Beyond this point a less intense
a curved line through the tips of the remaining wave forms as
whitelinewillappearandincreaseinwidthwithincreasingrod
shown in Fig. 4. This method gives the best results for L/D
distance. Use of a 5 to 10-power magnifier will aid in
ratios up to a few hundred. Higher L/D ratios cannot be
determining the point at which the “white” line disappears and
determinedbythismethodduetotheinabilitytoobtainastable
thenincreasesinwidthwithadecreasedintensity.Basedonthe
visual observation, determine the rod with zero umbral width wave form for large values of b.
and then determine its distance (b) from the cassette. The L/D
7.3 Alternative Microdensitometric Analysis—This method
ratio is as follows:
also uses scanning microdensitometric traces for L/D ratio
determinations and is applicable for both high and low L/D
L/D5~b/rod diameter!
ratios. For this method the recommended microdensitometer
E 803 – 91 (2002)
FIG. 3 NU Device Pictorials
settings are: 20 3 300-µm aperture and 503 (or more) chart
where:
recording expansion. These settings will produce individual
U = umbral width of a rod near the image plane,
wave forms as shown in Fig. 5. At least two wave forms must
U = umbral image width of a rod near the d
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