Model 451B Air Ion Chamber

With Beta Slide Shield

451B ion chamber survey meter

The Fluke Model 451B Ion Chamber is a hand-held battery operated unit designed for use in both rugged and normal environments. The Model 451B measures beta, gamma and X-ray radiation. The Model 451B Ion Chamber utilizes modern microprocessor and LCD technology and features a rugged ionization chamber with a mylar window and protective steel mesh. The beta shield serves as an equilibrium thickness for photon measurements. The ergonomic handle, features a large diameter cushioned grip and is designed to reduce fatigue associated with extended use. The case is constructed of lightweight, high strength materials and is sealed against moisture. The user must specify R or Sv when ordering. The display features an analog bar graph, 2 1/2 digit digital readout, low battery and freeze mode indicators. User controls consist of an ON/OFF button and a MODE button. The unit is auto-zeroing and auto-ranging. The display features circuitry that automatically activates the backlight in low ambient light conditions. The RS-232 interface can be connected directly to a computer for use with the Excel add-in for Windows ® , enhancing the functionality of the instrument. The software allows for data retrieval, user parameter selection and provides a virtual instrument display with audible (requires sound card) and visual alarm indication. The software may be customized by the user for specific applications.

415B Ion Chamber display

451B Specifications

Radiation detected: Alpha above 4 MeV, Beta above 100 keV, and Gamma above 7 keV

Energy Response

451B ion chamber energy response curve

Operating ranges:

0 to 5 mR/h or 0 to 50 µSv/h
0 to 50 mR/h or 0 to 500 µSv/h
0 to 500 mR/h or 0 to 5 mSv/h
0 to 5 R/h or 0 to 50 mSv/h
0 to 50 R/h or 0 to 500 mSv/h

451B Accuracy: Within 10% of reading between 10% and 100% of full scale indication on any range, exclusive of energy response. Calibration source is 137Cs


Chamber:349 cc volume air ionization

Chamber wall: 246 mg/cm2 thick phenolic

Chamber window: 1.7 mg/cm2 Mylar, protected by steel mesh, 46 cm2 detection area

Beta slide: 440 mg/cm2

Controls: ON/OFF and MODE

Automatic features: Auto-zeroing, auto-ranging, and auto-back

451B Response time:

0 to 5 mR/h (0 to 50 µSv/h) – 8 sec
0 to 50 mR/h (0 to 500 µSv/h) – 2.5 sec
0 to 500 mR/h (0 to 5 mSv/h) – 2 sec
0 to 5 R/h (0 to 50 mSv/h) – 2 sec
0 to 50 R/h (0 to 500 mSv/h) – 2 sec

Power requirements for 451B: Two 9 V alkaline, 200 hours operation

Warm-up time: One minute


Integrate mode: Operates continuously 30 seconds after the instrument has been turned on. Integration is performed even if the instrument is displaying in mR/h or R/h

Freeze mode: Will place a tick mark on the bar graph display to hold on the peak displayed value. The unit will continue to read and display current radiation values

451B Display: LCD analog/digital with backlight, Analog: 100 element bar graph 6.4 cm long. Bar graph is divided into 5 major segments, each labeled with the appropriate value for the range of the instrument, digital: 2.5 digit display is followed by a significant zero digit depending on the operating range of the instrument. The units of measurement are indicated on the display at all times. Digits are 0.25 in (6.4 mm) high. Low battery and freeze indicators are also provided on the display

Dimensions: 4 (w) x 8 (d) x 6 in (h) (10 x 20 x 15 cm)

Weight: 2.5 lb (1.11 kg):

Model # Part #
DS 451B Ion Chamber 451B-RYR
451 XL Software/Cable 451EXL