Model 451P Ion Chamber (Pressurized) SPECIFICATIONS

Radiation Detected

Beta above 1 MeV, Gamma and X-rays above 25 keV

Operating Ranges

0-500 ÁR/h or 0-5 ÁSv/h
0-5 mR/h or 0-50 ÁSv/h
0-50 mR/h or 0-500 ÁSv/h
0-500 mR/h or 0-5 mSv/h
0-5 R/h or 0-50 mSv/h

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

Detector Chamber: 300 cc volume pressurized air ionization chamber to 6 atmospheres

Controls ON/OFF and MODE

Automatic Features Auto-zeroing, auto-ranging, and auto-backlight

Response Time 

Analog response time from 10% to 90% of reading for a full scale step increase is dependent on operating range. Response time for a step increase in radiation exposure rate from background:

Step increase,

Step increase, background to

Time to reach 90% of final value (seconds)

400 ÁR/h 4.8
4 mR/h  3.3
10 mR/h 4.3
40 mR/h 4.5
100 mR/h 2.7
1 R/h 2
4 R/h  2.7

The following table shows time measured from 10% to 90% of final value for a step increase or decrease in exposure rate such that a range change does not occur. These values are the response times for the various ranges:

Range 10% - 90% (seconds)
0-500 ÁR/h (5 ÁSv/h) 5
0-5 mR/h (50 ÁSv/h) 2
0-50 mR/h (500 ÁSv/h) 1.8
0-500 mR/h (5 mSv/h) 1.8
0-5 R/h (50 mSv/h) 1.8

Power Two 9-volt alkaline, 200 hours operation

Display LCD analog/digital with backlight

Analog 100 element bar graph 2.5 in (6.4 cm) long. Bar graph is divided into five major segments, each labeled with the appropriate value for the range of the instrument 

Digital 2 1/2 digit display zero digit depending on the operating range of  the instrument. The units of measurement are indicated on the display at all times. Digits are 1/4 in (6.4 mm) high. Low battery and freeze indicators are also provided on the display

Warm-Up Time Less th an two minutes for initial operation when the instrument is in equilibrium with ambient temperature


Temperature Range - 20░C to + 50░C

Relative Humidity 0 to 100%

Geotropism Negligible

Typical Energy  Dependence  Nitrogen gamma rays are 110% to 120% of indicated readings as determined at the University of Lowell

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

Weight 2 lb 6 oz (1.07 kg)

451P Models

Model 451P-RYR 451P w/standard chamber 

Model 451P-YGG 451P w/standard chamber

Model 451P-DE-SI-RYR 451P w/Dose Equivalent chamber

Model 451P-DE-SI-YGG 451P w/Dose Equivalent chamber

Options Model 451EXL Excel add-in for Windows « and RS-232 interface cable

Model 190HPS Single Unit Carrying Case

Model 190HPC Multiple Unit Carrying Case

Model 62-103 137 Cs 10 ÁCi Check Source

Modes 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