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Model 9-4RF

The Ludlum Model 9-4RF is a rugged air ionization chamber for performing beta-gamma dose rate measurements over a five-decade span ranging from 0 to 500 mSv/h (0 to 50,000 mR/hr). This variant of the Model 9-4 has improved components and shielding to pass RF susceptibility tests at military levels up to 18 GHz and is an improved replacement for old Model 440RF/D survey meters.



The ion chamber automatically compensates for changes in temperature and pressure. The chamber wall (including the instrument case) is 1000 mg/cm2. A 1000 mg/cm2 retractable beta shield allows beta measurement with a 7 mg/cm2 window.

The six-position selector switch selects Off, x10k, x1k, x100, x10 and x1. Other controls include an On/Off switch for a meter light, reset and battery test buttons, and a zero adjustment knob. An adjustable shoulder strap (included) provides a convenient and comfortable mode to carry the instrument during surveys.

The Model 9-4RF is equipped with a serial interface for calibration. An optional calibration kit supplies the necessary interface cable, software, calibration can, pressure pump, and serial-to-USB converter.

  • 5-Range Ion Chamber
  • Ranges: 0 to 500 mSv/h (0 to 50,000 mR/hr)
  • 1000 mg/cm2 Retractable Beta Shield
  • RF Immunity
  • PC-Controlled Calibration
  • Low-Battery Warning
  • High-Background Zero Capability
  • Automatic Temperature & Pressure Compensation
  • Adjustable Shoulder Strap Included
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