2241-4 Neutron Meter

Ludlum Measurements

Features

• 22.9 cm (9 in.) Moderated Neutron Detector
• Range: 0 to 100 mSv/h (0 to 10,000 mrem/hr)
• Gamma Rejection up to 0.1 Sv/h (10 R/hr)
• Ratemeter with Built-in Scaler Function
• Autoranging
• Independent Adjustable Alarms for Ratemeter & Scaler Modes
• RS-232 Connection

The Model 2241-4 is a portable neutron REM meter. This instrument combines Ludlum's microprocessor-based digital Scaler-Ratemeter Model 2241 electronics with a Model 42-31H Neutron Detector. This system is sensitive to neutrons from thermal to 12 MeV with a response approximating the inverse RPG curve for neutron dose.

Data is presented on a four-digit LCD with a moving decimal point. Two additional digits are employed for the Scaler mode. A three-position switch labeled Off/Ratemeter/Scaler selects the desired operating mode for the instrument. Other controls include Audio On/Off switch, Fast/Slow Response switch, LCD Backlight pushbutton, Count Reset pushbutton, and Scaler Count/Stop pushbutton.

This instrument incorporates independent adjustable alarms for the ratemeter and scaler operating modes. Audible alarms may be silenced (acknowledged) by depressing the RESET switch. The scaler count time, alarm values, and backlight on time are pre-programed values. This instrument can be programmed via its RS-232 port, which can also be used to output readings at two-second intervals.

Medical Applications

NCRP Report #151 redefines the need to evaluate not only new Linac installations but also equipment that has been upgraded for higher energies and broader capabilities, like IMRT and rotational beam systems, which may be beyond what original shielding designs had recommended.

Specifications

Detector: ³ He tube (LND 25185 or equivalent)
Moderator: 22.9 cm diameter cadmium-loaded polyethylene sphere
Measurement Range: 0 to 10,000 mrem/hr
Sensitivity (moderated ²⁵²Cf): Typically 10 cpm per µSv/h (100 cpm per mrem/hr) (bare AmBe neutrons)
Energy Response: Provides appropriate inverse RPG curve for neutrons from thermal through 7 MeV, provides response up to 12 MeV
Gamma Rejection (¹³⁷Cs): < 10 cpm through 10 R/hr
Display: 4-digit LCD with 1.3 cm height, plus two 0.5 cm digits used for overflow counter (scaler mode) and exponential powers (parameter setup)
Controls:

• Off / Ratemeter / Scaler three-position operation switch
• Audio on/off switch
• Fast/Slow response switch
• LCD backlight pushbutton
• Count reset pushbutton
• Scaler count pushbutton on the handle

Alert/Alarm: Pre-programmed alarms for ratemeter and scaler modes
Audio: Built-in audio speaker with audio on/off switch, greater than 60 dB at 0.6 m
Scaler Time: Adjustable from 1 to 999,999 seconds, can display seconds or minutes
Operating Voltage: Approximately 1200 Vdc
Input Sensitivity: -2 mV
Temperature Range: -20 to 50 °C (-4 to 122 °F)
Environmental Rating: IP rating of 53
Power: Two each “D” cell batteries housed in an externally accessible sealed compartment
Battery Life: Typically 200 hours, low battery symbol alert (instrument will operate for approximately 24 hours after symbol first appears)
Detector Connector: Series “C” (others available)
RS-232: “D” type connector, used for programming instrument and outputting data at two-second intervals, baud rate from 150 to 19,200 bps
Size:

• Meter: 16.5 x 8.9 x 21.6 cm
• Detector: 26.2 x 22.9 x 22.9 cm

Weight: Meter: 1.6 kg, Detector: 6.56 kg