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RADIATION BASED DENSITY SENSGamma

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PRINCIPLES OF OPERATION

Gamma-based density gauges consist of a sealed source in a source holder and a

detector. The source holder is mounted on the side of a pipe or chute with the detethe opposite side. A focused beam of gamma radiation is transmitted from the sourthe pipe and process material to the detector.

As the density of the material in the pipe changes, the amount of radiation reachingdetector changes. The greater the density of the material, the lower the radiation fidetector; the lower the density of the material, the higher the radiation field at the d

When the radiation strikes the scintillation crystal, pulses of light are emitted which a

detected by a photomultiplier tube. The photomultiplier tube outputs a signal propothe number of light pulses received. The electronics monitors this signal and generascaled 4 to 20 mA or other useable process signal

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TECHNICAL APPLICATIONS

PROCESS TEMPERATURE COMPENSATED DENSITYWith input from a temperature probe, the density can be calculated to a refeprocess temperature.

PERCENT SOLIDS MEASUREMENT

When the carrier fluid remains stable, nuclear density gauges provide highly ameasurement of percent solids for most slurries.

MASS FLOW MEASUREMENT

When used in conjunction with a flow meter, nuclear density gauges providemass flow monitoring.

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INDUSTRIAL APPLICATIONS

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SCINTILLATION DETECTOR

Radiation interaction in scintillator produces light (may bvisible range)

Quantification of output requires light amplification anddetection device(s)

This is accomplished with the: Photocathode

Photomultiplier tube

Both components are placed together as one unit

optically coupled to the scintillator

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SCINTILLATION DETECTOR

Gamma rayScintillationevent

Reflector housing

Fluor crystal NaI (Tl)

Photocathode

Photoelectrons

Dynodes

Photomultiplier tube

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SCINTILLATION DETECTOR

Main components - Photocathode material

Dynodes electrodes which eject additional electrons after being struck by an electron

Multiple dynodes result in 106 or more signal enhancement

Collector accumulates all electrons produced from final dynode

Resistor collected current passed through resistor to generate voltage pulse

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SCINTILLATION DETECTOR

Scintillation material with a high light outputis preferred for all sapplications.

Emission wavelength should be matched to the sensitivity of thdetection device that is used (PMT of photodiode).

Scintillation light pulses (flashes) are usually characterized by aof the intensity in time (pulse rise time) followed by an exponendecrease.

Decay timeof a scintillator is defined by the time after which tthe light pulse has returned to 1/e of its maximum value.

Most scintillators are characterized by more than one decay tiusually, the effective average decay time is given

The decay time is of importance for fast counting and/or timin

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SCINTILLATION DETECTOR

NaI(Tl) is one of the most important scintillants. Can only be used in hermetically se

Material Density [g/cm3]Emission

Max [nm]

Decay

Constant (1)Refractive Index (2)

Conversion

Efficiency (3)

NaI(Tl) 3.67 415 0.23 ms 1.85 100

CsI(Tl) 4.51 550 0.6/3.4 ms 1.79 45

CsI(Na) 4.51 420 0.63 ms 1.84 85

CsIundoped 4.51 315 16 ns 1.95 4 - 6

CaF2 (Eu) 3.18 435 0.84 ms 1.47 50

6LiI (Eu) 4.08 470 1.4 ms 1.96 35

6Li - glass 2.6 390 - 430 60 ns 1.56 4 - 6

CsF 4.64 390 3 - 5 ns 1.48 5 - 7

(1) Effective average decay time Forg-rays.

(2) At the wavelength of the emission maximum.(3) Relative scintillation signal at room temperature forg-rays when coupled to photomultiplier tube with a B

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SCINTILLATION DETECTOR

Oscilloscope

Scaler

Multi-

Channel

Analyzer

DiscriminatorAmplifierPre-

Amp

High

Voltage

Detector

(Crystal &

Photomultiplier)

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SCINTILLATION DETECTOR

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GAMMA RADIATION SOURCES

Radioactive isotopes are used as gamma radiation soulevel, density and interface measurement as well as for limit detection.

The gamma source radiates equally in all directions. Forradiometric measurements, however, only radiation pasthrough the tank or pipe is of interest.

All other radiation is superfluous and must be shielded othis reason, the radioactive source is mounted in a specsource container which affords the necessary protectioproviding a defined, practically unattenuated, narrow bin one direction only.

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GAMMA RADIATION SOURCES

Features and Benefits Point source in special source container ensures simple

handling and easy installation

Specially constructed source capsule conforms to strictsafety requirements, Class 66646 to ISO 2919

Choice of source type and activity ensures optimized dfor your application

The radioactive sources, both 137Cs and 60Co, are sealed in a double-walled, weldesteel capsule. The encapsulation corresponds to Performance Class C 66646 as per ISOproviding maximum protection against temperature, external pressure, impact, vibratpuncture.

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GAMMA RADIATION

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GAMMA RADIATION SOURCEShttp://www.end

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SENSOR SET UP

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SENSOR SET UP

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