T.O. 33B-1-1
6-126
Table 6-22 lists several instruments that are suitable for measuring exposure rates resulting from NDI operations. The
table differentiates between older instruments that have been used historically for this purpose, as well as newer
instruments that make suitable replacements. Included with the table is the relative response of each instrument as a
function of the x-ray or gamma ray energy being detected. The relative response is defined as the indicated exposure
rate divided by the true exposure rate. A brief description of each type of instrument follows the Table 6-22.
Table 6-22. RECOMMENDED INSTRUMENTS FOR SURVEYS AND THEIR RELATIVE ENERGY
RESPONSE.
Relative Response
Effective Energy (keV)
22
32
70
120
170
663(a)
Older Instruments (no longer available)
Victoreen Model 440
NSN 6665-00-938-6806
0.94
1.04
11.6
1.18
1.16
1.0
Heat Pipe Corp. Model VR-10
Cap Off
NSN 6665-00-581-0220
1.06
1.16
1.03
1.0
1.03
0.82
Nuclear Research Corp. Model SM400
Cap
Off
NSN 6665-01-157-3780
1.00
1.05
1.08
1.08
1.07
0.96
External Probe Cap On
--
0.34
1.35
1.94
1.34
1.0
Internal Probe
--
0.01
2.22
2.1
2.0
1.0
New Instruments (currently available)
Victoreen Model 450B
Bottom Off
Bottom Cap Off
0.93
0.58
0.98
0.80
1.06
1.12
1.08
1.12
1.05
1.06
-
0.93
Victoreen Model 450P
Bottom oriented field
0.55
0.88
1.06
1.04
1.03
1.03
Victoreen Model RPO-50
Bottom Cap Off
Bottom Cap On
Instrument Suitable in RF Fields
Victoreen 440 RF/D
(a)
Note that the 663 keV response was obtained from Cs-137, which is commonly used for calibration.
6.9.10.4
Descriptions and Operating Characteristics of Specific Instruments.
6.9.10.4.1
Common Instruments: Models 440, SM400 And VR-10 Survey Meters.
CAUTION
The VR-l0 survey meter may reflect a false reading when near an RF environment.
reading is stray RF energy being generated by the X-ray control panel components
and is not hazardous radiation. Caution should be exercised using this meter at this
location; however, the aforementioned does not preclude its use.
The Victoreen Model 440, Nuclear Research Corporation SM400 and the Heat Pipe Model VR-10 survey meters have
been standard instruments authorized for use in the Air Force in TA-455 for industrial radiography. These instruments
are no longer available from the manufacturer. Suitable replacement instruments are listed in the above table and
described briefly in the following section. When monitoring radiation fields with these instruments, their front caps
SHALL be removed. The thin mylar cover at the end of the ionization chamber is easily punctured. If it is punctured,
the instrument is inoperative and must be repaired.
