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.