United States Air Force
Radiac Set


Radiac Set  /  NSN 6665-01-120-5978
Measures 0 - 500 milliroentgens per hour over 4 scales.
Measures gamma radiation from 80 kev - 2 mev. Detects Beta / Uses 2 Geiger Mueller Tubes
This unit uses two BA-30 or BA-3030/U ("D" size) 1½ volt batteries, it is complete and working.

Manufacturer: Nuclear Research Corporation - Warrington, Pennsylvania
 Contract F41608-81-D-0065  / Serial Number: 1836

Set as received includes:
CY-777A/PDR-27T Carry Case
IM-238A/PDR-27T Radiacmeter
DT-613A/PDR-27T Probe
H43B/U Headphones / ST-123 Carrying Strap / BK-101 Arctic Battery Kit
The AN/PDR-27T set is also supposed to inclued a spare 5979 and 5980 GM tube, manual and a
radiation test sample of Cesium-137. I did not receive these spare tubes, manual  or check source.

A copy of the manual was supplied to me by Jay S. Boggess ... Thank you Jay!

IM-238A/PDR-27T Radiacmeter with: DT-613A/PDR-27T Probe
To the left of the handle is a "XB" connection that is for the external Arctic Battery Kit
(see more on this kit below). It is next to the battery box cover.
The headphone jack is also visible in this photograph. The switch for the meter lamp is at the end
of the handle.
Dimensions for this unit: 7" High x 4½" Wide x 8½" Long
Click here for a diagram of top panel controls.

IM-238A/PDR-27T Radiacmeter meter face and control panel.
The scales on the meter change and are color coded as follows:
0 - 500 Milliroentgens Per Hour = Yellow
(shown above)
0 - 50 Milliroentgens Per Hour = White
0 - 5 
Milliroentgens Per Hour = Lime Green
0 - 0.5
Milliroentgens Per Hour = Blue
The battery check scale is white.

The meter is illuminated by a momentary switch on the handle, for low light situations.

Headset - Carry Strap - Probe Connecting Cable
The H-43B/U headset provides an aural indication of radiation intensity. The ST-123 carry strap is
 made of non-absorbent plastic with clips that snap into holes on each end of the radiacmeter.

DT-613A/PDR-27T Probe with Connecting Cable
Two tubes (JAN-5980), and (JAN-5979) are mounted together and attach to the front of the
IM-238A/PDR-27T via a spring clip.
The larger tube (JAN-5979) is used for the two lower ranges of  0 - 5 m/R & 0 - .5 m/R per hour.
This tube is a mica window, which is covered by a movable beta shield. The mica is 0.0005 inches thick.
The smaller tube (JAN-5980) is used for the two higher ranges of  0 - 50 & 0 -500 m/R per hour.

Nameplate and Arctic Battery Kit
The Arctic Battery Kit is an external battery pack for holding (2) BA-30 or BA-3030/U ("D" size)
1½ volt batteries. The kit is to be used when temperatures are below 21º F. Place the batteries in the
cradle and the cradle in the pouch with the connector cable running to the "XB" connection on the meter.
The pouch is placed in the pocket or other warm place. The internal batteries are to be removed from
the radiacmeter when using this kit.

IM-238A/PDR-27T Radiacmeter inside views.
The housing is made of cast aluminum with a gasket between the two sections.
Operating Limits:
Altitude up to 50,000 Feet / Temperature -40
º C to +60º C

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