T.O. 33B-1-1
6-92
6.8.5
Density.
Radiographic density is the blackening or darkening produced on the radiograph resulting from the metallic silver
deposits remaining on the film after exposure and processing. Density is measured in terms of visible light
transmission. The accepted scale of density measurement is the logarithm of the ratio of incident light to transmitted
light as given by the following equation:
D = log
I
I
o
E
Where:
D
=
density
Io
=
intensity of incident light
It
=
intensity of transmitted light
6.8.5.1
Measurement of radiographic density SHALL be done with electronic direct-reading type densitometers. The electronic
direct-reading type densitometer is more accurate than the visual type. This densitometer SHALL be capable of
measuring the light transmitted through a radiograph with a film density up to 4.0 with a density unit resolution of
0.02. When film densities greater than 4.0 are required to perform a radiographic inspection a densitometer applicable
to film densities up to maximum density is necessary. A photographic or radiographic-calibrated reference density
strip, traceable to the National Institute of Standards and Technology (NIST), SHALL be used to calibrate the
densitometer prior to determining the density of a radiograph. These calibrated density strips shall be replaced
whenever they are physically damaged (i.e., scratched, crimped, or become wet by any fluid) to such an extent that it
may influence their effectiveness. The carbon, dot printed, etc. density strips SHALL NOT be used even though they
may be NIST traceable. These strips are not able to correlate the densitometer directly to Air Force radiographic needs.
Each type of calibrated reference density strip will calibrate the densitometer to a different standard level. The
restrictive use of only the photographic or radiographic calibration reference density strip will better enable the
standardization of all densitometers to a single calibration value establishing a common (H and D units) density for a
given radiographic inspection. The aperture of the densitometer SHALL be black in color. If it is not, it may be
darkened with a black magic marker or other indelible ink.
6.8.5.1.1
While performing the densitometer calibration procedure, the following SHALL apply:
a. Follow manufacturer's instructions, substituting the calibration strip supplied with the instrument with
the NIST traceable radiographic calibration reference density strip.
b. The calibration reference density strip SHALL be removed from its protective cover during the
calibration procedure and maintained in its protective cover when not in use.
c. The calibration reference density strip SHALL NOT be pulled or slid when it is between the aperture
and stage diffuser. The aperture SHALL be raised so that it is not in contact with the density strip when
the strip is being repositioned or removed from the densitometer.
d. Calibrated reference density strip measurements SHALL be determined from the center of the steps that
are used for the calibration procedure.
e. While reading the density of a radiograph, DO NOT pull or slide it between the aperture and stage
diffuser. When repositioning or removing the radiograph from the densitometer the aperture SHALL
be raised.
6.8.5.1.1.1
The density of a radiograph is important. Densities less than 0.5 show very little of the object due to three factors: (1)
the density of the emulsion base, (2) the basic "fog" of the film and (3) the lack of uniform response of the film at low
