NUCOR E-1D Fast Neutron Detector (mid 1960s)

NUCOR E-1D Fast Neutron Detector (mid 1960s)
NUCOR E-1D Fast Neutron Detector (mid 1960s)

The Model E-1D fast neutron survey meter was manufactured by the Nuclear Corporation of America (NUCOR) of Denville, New Jersey. Better known as "Rudolph" because it had a red nose, it was originally manufactured (ca.1952) by Radioactive Products Inc. of Detroit Michigan. The example in the photograph was probably produced in the mid 1960s. My first reason for estimating this date is the fact that the April 1962 issue of Nucleonics carries an advertisement for the Model E-1D. My second reason is that the NAVSHIPS Directory of Radiac Equipment, references the Model E-1B, but not the E-1D, with a page date of 1960.

Rudolph used a proton recoil proportional counter to measure the absorbed dose (in millirep) from fast neutrons in the 0.2 to 10 MeV range. The detector chamber, employing a hydrogenous fill gas (methane) to provide some degree of tissue equivalency, is located at the red end of the probe. The rest of the probe houses the transistorized preamplifier.

The neutrons being detected strike the hydrogen nuclei in a couple of polyethylene radiators located inside the detector chamber. The scattered hydrogen nuclei (recoil protons) travel through and ionize the fill gas.

"Rep" is an acronym for roentgen equivalent physical. Since the term was coined by Herbert Parker, the acronym was sometimes explained as the roentgen equivalent Parker! The rep served as the predecessor to the rad. For whatever reason, the rep was used long after the introduction of the rad, at least for neutron doses. One possible explanation: it was convenient for gamma measurements to be expressed in one set of units (mR/hr), beta measurements in a second set (mrad/hr) and neutron measurements in a third set (mrep/hr).

Range: 0-5, 0-50 and 0-500 mrep/hr. In the integrate mode, it acts as a scaler and can register up to 200 counts.

Size: 5" x 10" x 4"

Batteries: Six 1.5 volt D cells

Weight: 8 pounds


  • Directory of Radiac Equipment NAVSHIPS 94200.5, page date June 1960.
  • Defense Atomic Support Agency, List of Military and Civil Defense Radiac Devices. DASA 1243 revised, 1966.
  • Defense Nuclear Agency List of Military and Civil Defense Radiac Devices HQDNA (AR) 3M Revised, August 1987.
  • Advertisement: Nucleonics April 1962, page 97.
  • Advertisement: Nucleonics May 1952, page 67.