Neutron Dose Ratemeter - Model 2241-4

Introduction

The Model 2241-4 is a portable neutron REM meter. This instrument combines Ludlum's microprocessor-based digital Ratemeter/Scaler 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 utilized to output its readings at two-second intervals.

Medical Application

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

Spezification

Meter Specifications

DISPLAY: LCD with programmable backlight on time
POWER: two each "D" cell batteries
BATTERY LIFE: typically 200 hours
CONTROLS: Off/Ratemeter/Scaler three-position operation switch, audio on/off switch, fast/slow response switch, LCD backlight pushbutton, count reset pushbutton, and a scaler count pushbutton on the handle
AUDIO: built-in audio speaker with audio on/off switch, greater than 60 dB at 0.6 meters (2 ft)
SCALER TIME: adjustable from 1-999999 seconds, can display seconds or minutes
ALERT/ALARM: pre-programmed alarms for ratemeter and scaler modes
RS-232: "D" type connector, used for programming instrument and outputting data at two-second intervals, baud rate from 150-19.2k bps
SIZE: 16.5 x 8.9 x 21.6 cm (6.5 x 3.5 x 8.5 in.) (H x W x L)
WEIGHT: 1.6 kg (3.6 lb)

Detector Specifications

DETECTION RANGE: thermal to approximately 12 MeV
ENERGY RESPONSE: approximately follows the inverse of the radiation protection guide curve for neutron dose
DETECTOR: 2 Atm ³He tube LND 25185 or equivalent
MODERATOR: 22.9 cm (9 in.) diameter cadmium-loaded polyethylene sphere
SENSITIVITY: typically 100 cpm/mrem/hr (²⁴¹AmBe fast neutrons)
GAMMA REJECTION: typically 10 cpm or less through 100 mSv/h (10 R/hr) (¹³⁷Cs)
OPERATING VOLTAGE: ≈1200 Vdc
THRESHOLD: -2 mV
CONNECTOR: series "C" (others available)
TEMPERATURE RANGE: -20 to 50 °C (-4 to 122 °F)
SIZE: 26.2 x 22.9 x 22.9 cm (10.3 x 9.0 x 9.0 in.) (H x W x D), including brackets
WEIGHT: 6.6 kg (14.5 lb)