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Model 42-49 Neutron Detector

Technical Manual

Section 5

Ludlum Measurements, Inc.

Page 5-1

December 2017

Calibration

To calibrate the detector, the following items are needed:



Counting instrument: Ludlum Model 2200 Scaler/Ratemeter



241

AmBe neutron source or equivalent



137

Cs gamma source for gamma rejection check

Operating Voltage Plateau

Connect the Model 42-49 to a Model 2200.

Set Model 2200 input sensitivity to -2 mV.

Expose the detector to a 20 mrem/hr

241

AmBe neutron source.

“Run a plateau” as follows: Taking one-minute counts, record the

count rate for 25-volt incremental steps from 1000 volts through a
region in which the count rate steadily increases, becomes relatively

constant (“flattens out”), and then increases again. (A typical range
will be 1000-1250 volts.) The flattest portion of this region is the

desired plateau. The value in the middle of this region is the assumed
operating voltage of the detector, subject to the sensitivity and the

gamma rejection checks.

Calculate the sensitivity (cpm/mrem/hr) for the assumed operating

voltage as follows:

Rate

Equivalent

Dose

Rate

Count

Sensitivit





Section

Содержание 42-49

Страница 1: ...LUDLUM MODEL 42 49 NEUTRON DETECTOR December 2017 ...

Страница 2: ...LUDLUM MODEL 42 49 NEUTRON DETECTOR December 2017 ...

Страница 3: ...Repacking 2 Connecting to an Instrument 2 1 Specifications 3 Safety Considerations 4 Environmental Conditions for Normal Use 4 1 Cleaning Instructions and Precautions 4 1 Calibration 5 Calibration 5 1 Operating Voltage Plateau 5 1 Gamma Rejection Check 5 2 Conversion Chart 5 3 Parts List 6 ...

Страница 4: ...ese gamma rays in the detection process A common reaction for the conversion of slow neutrons into directly detectable particles is n 3 He 3 H 1 H 0 764 MeV The Ludlum Model 42 49 utilizes this reaction in the form of helium 3 3 He which fills the gas proportional tube of the detector The Model 42 49 is designed to be used with portable counting instruments and has a top bracket that allows for co...

Страница 5: ...lManual Section1 Ludlum Measurements Inc Page 1 2 December 2017 Note The detector does not contain any consumable materials Note If the detector is used in a manner not intended by the manufacturer the detector may not function properly ...

Страница 6: ...calibration provide sufficient packing material to prevent damage during shipment Every returned instrument must be accompanied by an Instrument Return Form which can be downloaded from the Ludlum website at www ludlums com Find the form by clicking on the Support tab and selecting Repair and Calibration from the drop down menu Then choose the appropriate Repair and Calibration division where you ...

Страница 7: ... mV input sensitivity Sensitivity 100 cpm mrem hr 241 AmBe fast neutrons Gamma Rejection 10 cpm or less through 10 R hr 100 mSv hr 137 Cs Detection Range thermal to approximately 12 MeV Energy Response thermal to 12 MeV follows the radiation protection guide curve for neutron dose Input Sensitivity 2 mV Operating Voltage approximately 1200 V Connector series C others available Temperature Range 20...

Страница 8: ...less than 95 non condensing Pollution Degree 2 as defined by IEC 664 Normally only nonconductive pollution occurs Temporary conductivity caused by condensation is to be expected Cleaning Instructions and Precautions The detector may be cleaned externally with a damp cloth using only water as the wetting agent Do not immerse the instrument in any liquid Observe the following precautions when cleani...

Страница 9: ...em hr 241 AmBe neutron source Run a plateau as follows Taking one minute counts record the count rate for 25 volt incremental steps from 1000 volts through a region in which the count rate steadily increases becomes relatively constant flattens out and then increases again A typical range will be 1000 1250 volts The flattest portion of this region is the desired plateau The value in the middle of ...

Страница 10: ...ly 120 cpm mrem hr Gamma Rejection Check With the Model 42 49 connected to the Model 2200 adjust the Model 2200 HV to the assumed operating voltage determined above Remove the Model 42 49 detector from the moderator and place in a 10 R hr 137 Cs gamma radiation field Take a one minute count If more than 10 counts are observed for the one minute period decrease the operating voltage until the count...

Страница 11: ...0 mrem hr Take a one minute count and record the value including the range scale setting of counting instrument Repeat for the dose equivalent rates shown in Table 1 The values in Table 1 and their corresponding measured values represent a conversion chart for use in relating other measured values to actual dose equivalent rates Table 1 Ref Point mrem hr Reading cpm Range Scale 400 200 80 20 8 2 ...

Страница 12: ...05 060 7 7 inch SPHERE 7014 858 2 EA INSERT E Z LOK 6 32 20 9066 8 EA 8 INCH HDPE ROD 29 9985 MODEL 42 49 DET MODERATOR 47 4059 1 EA O RING 2 116 16 8293 1 EA O RING 2 148 16 8340 2 EA SCREW 8 32 X 5 8 SOC SET 17 8765 MODEL 42 49 PROBE ASSY 4014 587 3 He TUBE 25185 2 ATM 01 5793 CONNECTOR UG706 U 4478 011 TUBE BODY ASSY 2014 595 MODEL 42 30 42 31 DETECTOR SPACER 7005 056 CONNECTOR END 7014 598 CBL...

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