IM-160D/PDR-56 Alpha Scintillator Survey Meter (ca. late 1960s, 1970s)

The AN/PDR-56 is a ZnS alpha scintillator that replaced the AN/PDR-10 alpha air proportional meter for alpha contamination surveys. It has since been replaced by the AN/PDR-77. This example of the IM-160D/PDR-56 was manufactured by Gulf Aerospace Corporation of Houston Texas.

Quoting the Directory of Radiac Equipment (NAVSHIPS 94200.5, ca. 1960): "Radiac set AN/PDR-56 detects and measures alpha radiation having energies greater than 3 MeV. Its primary purpose is to monitor radiation hazards. The radiation sensing element is a scintillating crystal located in a probe. The radiac set is portable (by hand) and is comprised of a radiacmeter with auxiliary probe, a shoulder harness, a headset, a probe handle extension, and a carrying case. The radiacmeter receives pulses from the probe and converts them in a discriminator and rate meter circuit to a meter reading… The probe uses Phosphor Zinc Sulphide to convert the alpha radiation to light pulses which are focused onto the photocathode of a photomultiplier with a light pipe."

IM-160D/PDR-56 Alpha Scintillator

Unfortunately, the radiacmeter is the only component of the set in the ORAU collection. The auxlliary probe mentioned in the description is much smaller than the standard probe. It was intended to survey in small areas and the surface of irregularly shaped objects. The primary purpose of the probe extension handle was to allow the user to scan the floor/ground without having to bend over.

IM-160D/PDR-56 Alpha Scintillator

This photograph shows the bottom of the alpha probe. The aluminized mylar window can be seen through the six diagonal slots.

IM-160D/PDR-56 Alpha Scintillator

This photograph shows the inside of the probe. Note the curved multilayered clear plastic light pipe. The end of the photomultiplier tube would face down onto the flat upper surface of the light pipe.

For many years, the AN/PDR-56 has been the military's primary instrument for alpha contamination surveys (e.g., surveys for depleted uranium and plutonium contamination). The AN/PDR-27 was the instrument of choice for beta contamination surveys.

Detector: ZnS alpha scintillator in detachable probe

Range: 0-1,000 (yellow), 0-10,000 (pink), 0-100,000 (orange) and 0-1,000,000 (red) counts per minute

Size: 4” x 8" x 9" (including probe and handle)

Batteries: Two 1 1/2 volt D cells

Weight: ca. 7 1/2 lbs

Manufacturers: Tracerlab, Nuclear Research Corp., Electro-Neutonics, Gulf Aerospace

Estimated date of first manufacture: 

  • AN/PDR-56 1960
  • AN/PDR-56A 1962, 1963
  • AN/PDR-56B 1963, 1964
  • AN/PDR-56C 1964, 1965
  • AN/PDR-56D 1967, 1968
  • AN/PDR-56E early 1970s


  • Directory of Radiac Equipment NAVSHIPS 94200.5, no date, ca. 1961-62.
  • Defense Atomic Support Agency, List of Military and Civil Defense Radiac Devices. DASA 1243 revised, 1966.
  • Defense Atomic Support Agency, List of Military and Civil Defense Radiac Devices. DASA 1243 revised, 1969.
  • Naval Electronic Systems Command List of Radiacs in the Navy Program P-9670-1, February 1975.