ASTM E803-91(2008)
(Test Method)Standard Test Method for Determining the L/D Ratio of Neutron Radiography Beams
Standard Test Method for Determining the <span class="italic">L/D </span>Ratio of Neutron Radiography Beams
SIGNIFICANCE AND USE
The quality of a neutron radiographic image is dependent upon many factors. The L/D ratio is one of those factors and constitutes a numerical definition of the geometry of the neutron beam. The L/D ratio required for a specific neutron radiographic examination is dependent upon the thickness of the specimen and the physical characteristics of the particular element of interest. Use of this test method allows the radiographer and the user to determine and periodically check the effective collimation ratio.
SCOPE
1.1 This test method defines an empirical technique for the measurement of the effective collimation ratio, L/D, of neutron radiography beams. The technique is based upon analysis of a neutron radiographic image and is independent of measurements and calculations based on physical dimensions of the collimator system. The values derived by this technique should be more accurate than those based on physical measurements, particularly for poorly defined apertures.
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Designation:E803 −91(Reapproved2008)
Standard Test Method for
Determining the L/DRatio of Neutron Radiography Beams
This standard is issued under the fixed designation E803; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) 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
measurementoftheeffectivecollimationratio, L/D,ofneutron
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.
collimatorsystem.Thevaluesderivedbythistechniqueshould
be more accurate than those based on physical measurements,
5. Apparatus
particularly for poorly defined apertures.
5.1 NU Device (see Fig. 2(a) and (b), and Fig. 3) employs
2. Referenced Documents
neutronabsorbingrodspositionedatvariousdistancesfromthe
image plane. In practice this device consists of cadmium and
2.1 ASTM Standards:
nylon rods located in V-grooves accurately machined in the
E748Practices for Thermal Neutron Radiography of Mate-
surfaceofanaluminumchannelsectionsetata45 6 ⁄4°angle
rials
to the side support plate. Near the image plane end the
E1316Terminology for Nondestructive Examinations
V-grooves are machined on 0.283-cm centers. After 21 V
3. Summary of Test Method
grooves,countingoneontheend,thegroovesaremachinedon
0.707-cm centers to the source end. The 0.64-mm diameter
3.1 Determination of neutron beam L/D ratio using the NU
cadmium and nylon rods are laid into the V-grooves and
(no umbra) technique is accomplished by radiographing the
secured with neutron transparent adhesive tape.The aluminum
NU device with the neutron beam to be measured and
channel is supported by side plates to maintain the 45 6 ⁄4 °
subsequently analyzing the radiograph by one of three meth-
angle relative to the image plane. While cadmium rods with
ods.Eachofthethreemethodsisbaseduponthedetermination
diameters other than 0.64 mm may be used, the exact rod
of that point at which the umbral shadow width reaches zero.
diameter must be known and the depth of the V grooves must
See Fig. 1. A key feature of the NU technique is that L/D can
be adjusted accordingly.
be determined accurately without the need for expensive
instrumentation. Neutron radiography practices are discussed
5.2 A single A unit as shown in Fig. 2(b) is used for L/D
in Practices E748 and the terms are defined in Terminology
valuesexpectedtobelessthan150.Alternately,asingleAunit
E1316.
used with appropriate spacers may be used to accommodate a
wide range of L/D values.
4. Significance and Use
4.1 The quality of a neutron radiographic image is depen-
6. Procedure
dent upon many factors. The L/D ratio is one of those factors
6.1 Place the NU device against the cassette with the finely
spaced rods nearest the cassette.
This test method is under the jurisdiction of Committee E07 on Nondestructive
6.2 Align the plane of the cassette perpendicular to the axis
Testing and is the direct responsibility of Subcommittee E07.05 on Radiology
of the neutron beam.
(Neutron) Method.
Current edition approved July 1, 2008. Published September 2008. Originally
6.3 Expose the single-emulsion film and NU device for a
approved in 1986. Last previous edition approved in 2002 as E803–91 (2002).
time span that will produce a nominal background film density
DOI: 10.1520/E0803-91R08.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or of 2.5 6 0.4.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
6.4 Process the exposed film in accordance with the manu-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. facturer’s recommendations.
Newacheck,R.L.,andUnderhill,P.E.,“TheNUMethodforDetermining 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.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E803−91(2008)
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
FIG. 2(a) Support Channel Subassembly with Rod Spacing
7. Data Analysis densitometer aperture of 20×300 µm and no horizontal
expansion is suggested for this method. The value of b is
7.1 Visual Analysis—Avisualdeterminationofthe L/Dratio
obtained from the intersection of a straight line originating
can be made directly from the neutron radiograph. When
from the tip (low film density) of the scan of the “0” rod and
observing the individual rod images, the umbral image can be
a curved line through the tips of the remaining wave forms as
recognized as the “white” line along the center of the rod
shown in Fig. 4. This method gives the best results for L/D
image. This “white” line will decrease in width for the rods
ratios up to a few hundred. Higher L/D ratios cannot be
located farther and farther from the film. At some point the
determinedbythismethodduetotheinabilitytoobtainastable
umbral images will disappear. Beyond this point a less intense
wave form for large values of b.
whitelinewillappearandincreaseinwidthwithincreasingrod
distance. Use of a 5 to 10-power magnifier will aid in
7.3 Alternative Microdensitometric Analysis—This method
determining the point at which the “white” line disappears and
also uses scanning microdensitometric traces for L/D ratio
thenincreasesinwidthwithadecreasedintensity.Basedonthe
determinations and is applicable for both high and low L/D
visual observation, determine the rod with zero umbral width
ratios. For this method the recommended microdensitometer
and then determine its distance (b) from the cassette. The L/D
settings are: 20×300-µm aperture and 50× (or more) chart
ratio is as follows:
recording expansion. These settings will produce individual
L/D 5 ~b/roddiameter!
wave forms as shown in Fig. 5.At least two wave forms must
bescanned,onenearthefilmplaneandoneothernearthepoint
7.2 Microdensitometric Analysis—The second data analysis
method is based on a microdensitometric scan across the where the umbra disappears. Care must be taken not to go
beyond the point where the umbral image disappears. Mi-
cadmium rod images beginning with the “0” position rod
nearest the film. A typical scan is shown in Fig. 4.A crodensitometer settings must remain the same for
...
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