CMA Radiation Sensor User guide

RADIATIONSENSORML69M

USER’SGUIDE



CENTRE FOR MICROCOMPUTER APPLICATIONS

http://www.cma-science.nl

2|ML69mRadiationSensorUser’sGuide

Shortdescription

TheRadiationsensorML69msensesalpha,betaandgammaradiation.

Alpha,beta,gammaradiationionizematerial theystrikeorpassthrough.Theamount

of radiation is generally determined by measuring the resulting ionization. The

Radiation sensor uses a Geiger‐Müller tube to detect this radiation. The GM tube

consistsofan

anode(positiveelectrode)pos itionedinthecenterofa tubularcathode

(negativeelectrode)filledwithamixtureofneonandhalogen.Thecathodeisathin‐

walledmetalliccylindersealedat eachendwithaninsulatingdisktocontainthegas.

The anode is a wire that extends into the

cylinder. A high voltage is applied to the

electrodes to create an electrical field within the chamber. When radiation passes

throughthechamberandionizesthegas,itgeneratesapulseofcurrent.Thesensor

electronically processes these pulses to display the radiation level in counts per

minute.Aclickingsound

isemittedforeachdetectedradiationevent(foreachcount).

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TheendoftheGMtubehasathinmicawindow.Itallowsalphaparticlesto reachthe

GMtubeandbedetected.Themicawindowwillalso senselowenergybetaparticles

andgammaradiationthatcannotpenetratetheplastic caseorthesideofthetube.



Fortheshortamountoftime theGMtubeisdetectingoneparticle,itisnotableto

detectanotherradioactiveparticleifitentersthetube.Thisiscalledthesensor’sdead

time.ThemaximumdeadtimefortheGMtubeis90microseconds(or90μs).



Todetectradiation,pointthesensortowardthesourceofradiation.Todetectalpha

radiation put the sensor close to the source, this is because alpha particles do not

travelfarthroughair.



The Radiation sensor is an I2C digital sensor, which gives calibrated values of the

measured quantity. This sensor can only be connected to special interfaces that

supportI2CdigitalsensorsliketheCMAMoLabinterface.

Sensorspecifications

Radiation sensor ML69m is a digital sensor that converts the number of counted

detectedpulsestoadigitalvalueofcountsperminute.Themaximalsamplingrateof

thesensoris1Hz.

Collectingdata

This Radiation sensor works only with specific interfaces. The sensor will be

automaticallydetectedwhenconnectedto suchaninterface.Fordetailedinformation

aboutmeasurementswithsensorsconsulttheUserManualsoftheinterfaceandthe

Coach6software.

ML69mRadiationSensorUser’sGuide |3

Calibration

TheRadiationsensorissuppliedwithafactorycalibrationincountsperminute(cpm). 

TheCoach 6 program allows shiftingthe pre‐defined calibration if needed. The user

calibrationisstoredinnon‐volatileusersensormemory.

Suggestedexperiments

1. Monitoringbackgroundradiation

If the  radiation sensor is set up far away from any radioactive sources, it still

detectspulsesoccasionally.Thisisdueto thebackgroundradiationthatisaresult

of radiation that occurs naturally from cosmic radiation, geophysical radiation,

inherent material radiation, etc. Normal background radiation levels

 vary at

different locations, according to altitude and other factors, such as types of

mineralsintheground.Thelevelofbackgroundradiationisusuallyverylow.

Sincethebackgroundradiationispresentinallexperiments,itshouldbemeasured

andsubtractedfromtheexperimentalreadingsforthesetobe

reliable.

2. Monitoringradiationofcommonradioactivematerials

Herethenaturalsourceofradiationsuchas potassiumsaltsorlanternmantelscan

be used.In such experiments the random nature of  the radiation can be

presented.

3. Radioactivedecayandhalf‐lifedetermination

The radiation sensoroffers thepossibility to measure

 radioactive decay rate and

half‐life time. In such experiments isotope generators, like a Protactinium

generator(withahalf‐lifetimeof72seconds)oraBa137mg enerator(withahalf‐

lifetimeof153seconds)areidealradioactivesourcesfortheseexperiment.

4. Radiationlevelversusshielding

In this

experiment the radiation level is recorded when absorbers of different

thickness are placed between the sensor and radiation source. As absorber an

aluminumsheet(s)forbetaradiationoraleadsheet(s)forgammaradiationcanbe

used. In this experiment you  can also compare the effect of different types of

materials

toshieldalpha,betaorgammaradiation.

5. Monitorradiationfromanalpha,betaorgammaradiationsourceasafunctionof

thedistancebetweenthesourceandtheradiationsensor

In this experime nt the radiation level is recorded when a sensor is placed at

differentdistancesfromtheradiation

source.



4|ML69mRadiationSensorUser’sGuide

TechnicalSpecifications



Sensorkind Digital16‐bitsresolution

(on‐sensordigitalconversion)

communicationviaI2C

Sensitiveto Alpha,beta,gammaradiation

Measuringrange 0..20,000countsperminute

Resolution 1countperminute

Accuracy

Typical±10%at25℃

Maximalsamplingrate

1Hz

Temperaturerange

0‐50℃

GMtube Neon‐HalogenquenchedGM‐tube

Cathodematerial

446StainlessSteel

Cathodewallthickness 0.25mm

Micawindow

Effectivediameter9.1cm

Arealdensity1.5–2.0mg/cm



Gammasensitivity

ReferencedtoCobalt60

18cps/mr/hr

Operatingvoltage 500V

MinimumDeadTime 90μs

Audiooutput Clickingsoundforeachcount

Connection 5‐pinsminijackplug



Warranty:

The Radiation sensor ML69m is warranted to be free from defects in materials and

workmanshipfor a periodof12months fromthedateofpurchaseprovidedthatithas

been used under normal laboratory conditions. This warranty does not apply if the

sensorhasbeendamagedbyaccidentormisuse.





Note:Thisproductisto beusedforeducationalpurposesonly.Itisnotappropriatefor

industrial,medical,research,orcommercialapplications.    

Rev. 10/06/2012

CMA Radiation Sensor User guide

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