fundamentals_of_radiation detection.pdf

8/14/2019 fundamentals_of_Radiation Detection.pdf

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Fundamentals

1.0 Define:

Radioactivity- That property of certain materialsspontaneously emit penetrating ionizing radiation.Radiation Interaction - Radiation loses kinetic enundergoes a change in direction or is absorbed.Radioactive Decay- The process whereby an atmore stable by emitting particulate or electromagParticulate Radiation- Radiation that has mass.Neutron, Beta, Alpha)Mass- The quantity of matter in an object measurresistance to a change in its motion.Ionization- The process by which radiation imparexcitation energy to the electrons of atoms in thesubstance to remove one or more electrons fromproducing free electrons & ions.Ion Pair- The positively charged atom and free elresulting from an ionization event.

Ion- A positively charged atom (one from which aelectron has been removed).Free Electron- An electron existing outside the oatom.Excitation- The process by which radiation impaor all of its energy to the target atoms, causing thto exist in some higher energy state.

Ato mic Exc itat ion - Raising of an atom to an excNuclear Excitation- Raising of a nucleus to an eTarget- An item or material upon which a radiatioDirect Ionizing Radiation- A radiation that carriecharge and exerts electrical forces upon the electsubstance.Indirect Ionizing Radiation- A radiation that doeelectrical charge.Kinetic Energy- Energy due to motion.Negatron - Negatively charged beta particle.Positron- Positively charged beta particle.Electromagnetic Radiation- Traveling wave mot

from changing electric or magnetic fields.Gamma- High energy, short wavelength, electroradiation emitted from the nucleus.X-ray- Penetrating electromagnetic radiation haviwavelength that is shorter than that of visible light,an excited electron.Prompt Neutron- A neutron emitted less than 1after fission.Delayed Neutron- A neutron emitted at least 1 Eafter fission.Fission- The splitting of an atomic nucleus into tsometimes, more) lighter fragments, accompaniedrelease of a large amount of energy.fissionFragments- The two (or more) lighter nuby the fissionprocess. Generally unstable due toneutron-to-proton ratio. Also called fission productFissile Material- Material in which fission can beabsorption of a thermal neutron. (U-235)Mass Defect- A measure of the loss of mass in a

nucleus. The difference between the sum of theatomic components (W) and the measured mass(M). Mass Defect = W-MBinding Energy- The energy released to assemThe energy equivalent of the Mass Defect. B.E. =(931 MeV/u)Critical Energy- The energy required to induce finucleus.

Standard Nucli de Notation- A = Neutrons

= Protons N = Neutrons

2.0 List the ionizing radiations of concernnuclear power plant and for each radiatio

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3.0 Perform mass to energy and energy tequivalent calculations.

E = mc2: E = total energy (joules) / m = mass (kil3.0 E+08 m/sec (speed of light)Example: me= 9.1093897 x 10-31 kg&1 MeV = 1.

1) Determine the mass equivalent to 1.02 MeV.Convert from MeV to Joules: (1.02MeV)(1.60E-1313J

E = mc2 (divide both sides by c2) m = E/c2

m = (1.632E-13J) / (3.0E8 m/sec)m = 1.81E-30 kg

4.0 Describe the "water drop" model of th

process, including incident and emitted rand the decay process that occur.

1) A neutron interacts with a fissile material.2) A thermal neutron is absorbed by the nucleus.3) The nucleus becomes distorted and begins to s4) The fissionfragments are separate, only residuremains, yet due to nuclear forces they are defor5) Nucleons will reshape themselves; Coulombic fbetween the two. The nucleons are in a higher enwill decay.6) Prompt neutrons and g are released as the nucto a lower energy state.7) They will begin to emit only gammas (prompt) tmore stable.8) They will undergo - decay. (And associated d9) Followed with Delayed Neutrons. (And associatdecays)10) They reach stability.

5.0 Define:

Curie- The unit of radioactivity. 1 Ci = 3.7E10 dpdpmDisintegration- A radioactive decay event.Isotopes- Same # of protons, different # of neutr(Horizontal to element on chart)Stable Nuclide- A nuclide which has not been obundergo spontaneous radioactive

decay or whose half-life is very long (~5 x 108 yeaby gray shading on the chart.Decay Constant- A statistical expression of theunit time in a large sample.

= .693 / T is expressed in reverse time units

AlphaRadiation

BetaRadiation

NeutronRadiation

Classify it asparticulate or

electromagnetic.Particulate Particulate Particulate

Classify it asdirectly orindirectlyionizing.

DirectlyIonizing

DirectlyIonizing

IndirectlyIonizing

Identify itsrelative mass.

4 timesmass of

proton

Equal inmass to an

electron

Slightly >than a proton

Identify itscharge.

+2 Charge

-1 Charge(Negatron)+1 Charge(Positron)

Zero Charge

Identify itsorigin.

UnstableNucleus

UnstableNucleus

FissioningNucleus

and unstablenucleus

Identify itsrelative range intissue-equivalent

materials.

Lowest Low High

Classify it as aninternal or

external hazard.Internal

InternalExternal to

skin &eyes

External

Identify typicalshielding

materials.

PaperOther light

materials

Plastics,cloth,

cardboard(low-Z

materials)

Water,Polyethylene,borated poly,

concrete




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h-1...)

Half-life- The amount of time required for a samp of its original activity.Parent Nucli de- The original nucleus which undeprocess.Decaying Nucleus- The original nucleus which udecay process.Decay Produ ct- The nucleus which results fromdecay process.Daughter Product- The nucleus which results frdecay process.

Decay Daughter- The nucleus which results fromdecay process.Resulting Nucleus- The nucleus which results frdecay process.Isotones- Same # of neutrons, different mass nucolumns to element on chart)Isobars- Nuclides with same mass #, but differen

along 45diagonal to element)

Isomers- 2 or more nuclides that have the samemass #, but whose nuclei are at different levels ofMetastable State- A state of nuclear excitation whalf-life.

6.0 List two characteristics that identify a

1) The # of protons in the nucleus and 2) the # ofnucleus.

7.0 Discuss the "Curve of Stability" inclusignif icance of the curve and the range ththe neutron-to-proton ratios that the curvencompasses.

Unstable radionuclides undergo decay processesnucleus to get closer to the line of stability. Startsratio and finishes with ~1.6 -to1 neutron to proton

8.0 Identify stable and uns table nuclidesof the Nuclides.

Gray shading in the elements block denotes that icolored shading indicates unstable.

9.0 Identify a nuclides half-lif e, includingfrom the Chart of the Nuclides.

The half-life is stated directly under the elementson the Chart.Time Units: ms - microseconds, ms - milliseconds,m - minutes, h - hours, d - days, a - years.

10.0 Perform radioactive decay calcu latioincluding:

Decay constant, atoms remaining and activity remgiven amount of time.

Decay Constant - = .693/T# of atoms - N=N

oe-

11.0 Identify nuc lides' ground states andstates.

On the Chart of Nuclides, metastable states are in

division of the nuclide block into 2 or more areas.always appear below and to the right of other iso

12.0 Identify and describe each type of radecay i ncluding the following:

1. net effect on the nucleus2. radiations absorbed or emitted3. whether emissions are discreet or spectral in na4. factors affecting the probability of the decay pro5. examples of nuclides that undergo the processBeta minus decay (-):1. A neutron is changed into a proton, the Z increaremains constant.




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2. radiations emit a continuous distribution of enEmaxw/ Eave being 1/3 of Emax.

3. decay emissions are spectral in nature.4. Radionuclides with Z < 82 decay by beta decay5. Sr90 and Cs137

Beta plus decay (+):1. A proton is changed into a neutron; Z decreaseremains constant.2. radiations emit a continuous distribution of en

Emaxw/ Eave being 1/3 of Emax.3. decay emissions are spectral in nature.4. Radionuclides with Z < 82 decay by beta decay5. O14 and Na22

Alp ha decay ():1. Z decreases by 2, A decreases by 4 (n decreas2. The a particle is highly ionizing w/ a short rangebetween 4-8 MeV)3. Alpha decay is a discrete emission.4. Radionuclides with Z > 82 decay by alpha. (It ispredominant mode)5. Rn222 and Pu240

Gamma Emission ():1. Atomic Number and Mass Number remain cons2. rays emitted from nucleus3. rays are discrete4. Independent of Z5. Co60 and Cs137

Isomeric Transition (IT):1. Atomic Number and Mass Number remain cons2. rays emitted from nucleus3. IT rays are discrete5. Co60m and Tc99m

Electron Capture (e):1. An orbital electron is changed into a neutron, Zone, A remains constant.5. La133 and Ba133

Internal Conversion (e-)1. Nuclear excitation is transferred directly to an owhich is ejected from the atom.Excitation energy in excess needed to eject the elas kinetic energy to the electron.

5. Xe131 and Cs123

13.0 Define the term "Att enuation" as i t aradiation physi cs.

The processes by which energy is transferred frotarget as the radiation passes through the target.

14.0 Define the term "Cerenkov Radiationexplain why this type of radiation is or isconcern to the Radiation Safety technicia

Electromagnetic radiation emitted as a charged pathrough a medium at a velocity greater than the spthe same medium.

15.0 Discuss charged particl e interactionthe mechanism by which charged particl

cause excitation, ionization and bremsstratoms of the absorber, the factors affectitheir probability of occurrence and the tysecondary radiations which may be emittthese interactions. State the difference bbremsstrahlung and internal bremsstrahl

Excitation: A beta particle passes close to an atoorbital electron to raise to a higher energy level duCoulombic forces.Ionization: A beta particle collides with an orbitalkicking it out of its orbit, creating an ion pair (the -charged atom and the free electron)Bremsstrahlung: A beta particle passes close todue to Coulombic forces it changes direction, the




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energy which is conserved with an x-ray.Factors affecting probabili ty: Z number and enSecondary radiations: and x-rays.Difference between bremsstrahlung and internbremsstrahlung: Internal is caused with an orbitaversus a beta particle ( free electron) is associatebremsstrahlung.

16.0 Define:

Ionization Potential- The amount of energy requthe least tightly bound electron in an atom of thatElectron Binding Energy- The difference betweexpended in the ionizing collision and the total enionizing particle in the collision.

Average Energy Ex pend ed per Ion Pai r(W valuEnergy + Ionization Potential.Stopping Power- Energy Lost (eV) / Path lengthSpecific Ionization- Stopping Power (eV/cm) /pair)Linear Energy Transfer (LET)- Average energyabsorber (keV/micron)Range- The average depth of penetration of a chinto an absorber before it loses all its kinetic energPath length- The total distance traveled by the rathrough all interactions.

17.0 Discuss the photon interactions. Disthree major types of interactions, which

Include the mechanism of interaction forprocess, the factors affecting the probabioccurrence and the secondary radiationsbe emitted.

Photoelectric Effect: A photon collides with an oexpending all its energy in freeing the electron.Compton Effect: A photon collides with an orbitalpart of its energy to free the electron, and proceedreduced energy.Pair Production: A photon passes close to an atconverts its energy into mass. Requires a photonof at least 1.022 MeV for production. The photon cpositron and electron of 0.511 MeV, which will collanti-particle and create an annihilation photon of 1

18.0 Define the term "Mean Free Path" asneutron and photon radiation.

The average distance a non-charged particle travinteractions in a specific target material.

19.0 Define:

Total Linear Attenuation c oefficient (): The suprobabilities for Photoelectric effect, Compton effeproduction interactions to occur.Mass Attenuation coefficient (/density): The #which interact per unit of mass.Total Linear Energy absorption coefficient (

en

of energy removed from the radiation beam (theredeposited in the absorber) per unit of distance)Mass absorption coefficient (

en) / p): The fracti

removed from a photon beam (and therefore depodensity of absorber.

20.0 Define:

Cross-section:The probability that a neutron willspecific interaction.

21.0 Define:

Fast Neutron: Neutrons having a kinetic energy oMeVSlow Neutron: Neutrons having a kinetic energyMeVThermal Neutron: Neutrons having a kinetic enereV (average of 0.025 eV)

22.0 Define:




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Moderation: The reduction of fast neutron energithermal energy values.Inelastic Scattering: The collision process in whithe kinetic energy of the incident neutron and targnot conserved.Elastic Scattering: The collision process in whichkinetic energy of the incident neutron and target nconserved.

23.0 Discuss neutron in teractions. Discutypes of neutron interactions that can oc

three different neutron energies. Includemechanisms which can cause each interfactors affecting the probability of each itaking place and the types of radiationsemitted immediately or some time later fothese process.

Inelastic Scattering: A fast neutron is absorbed bnucleus, but having too much energy a neutron ofenergy will be ejected from the compound nucleusemission to reduce excitation levels.Elastic Scattering: A fast neutron will collide withsame relative mass, and will break the atoms ionicreating a cation and an anion.Radiative Capture: A slow neutron will be absorbnucleus, the nucleus will emit a prompt "Capturereduce excitation, and some time later it will emitgammas for further Reduction in excitation energy

fission(Resonance Absorptio n): A thermal neutabsorbed by a heavy fissile nucleus, which will unin the "water drop model" emitting neutrons, protoradioactive fissionfragments and rays.

24.0 Identify t he major neutron interactioproduction of radionuclides in the reactoInclude target nuclide in the identification

The major neutron interaction for the production oin the core is the fissionof U235.235U (,f) 235U + 1 U X + Y + (X)1

25.0 List the three princip le chemical grofission products and the major radionucliconcern in each group (inc lude the half-liradionuclide.

1) Halogens - major nuclide: Iodine-131 T = 8 d2) Noble Gases - major nuclide: Krypton-85 T =3) Mixed Metals - major nuclide: Cesium-137 T

26.0 State the effects of fuel burn-up on tof short-lived and long-lived fissionproduct radionuclides in the reactor cool

Short-lived fissionproducts will reach equilibriumLong-lived fissionproducts will continually increasproduction.

27.0 List the three fission product radionthe longest half-lives that are commonlythe reactor coolant (include the half-life oradionuclide).

1) Cesium-137 30.17 years2) Strontium-90 29.1 years3) Krypton-85 10.73 years

28.0 Identify the mode of produc tion andthe activation product radionuclides typiin the reactor coolant.

Activated Corrosion Products (CRUD): 50Cr (,)p) 58Co/59Co (, ) 60Co

Activated Waterborne Products (Additives): 10B ((f, a) 3H

Activated Waterborne Products (Impurities): 40Ar41Ar/23Na (, ) 24Na

Activated Waterborne Products (Water Componen




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16N/2H (, ) 3H

29.0 Identify t he major long-li ved radionucommonly present in the reactor coolantcorrosion product (include the half-life ofradionuclide).

Cobalt-60, 1.332 and 1.173 MeV 's, 5.27 years T

30.0 List the two general areas within thecoolant system where corrosion productaccumulate.

1) Low flow areas - dead legs, pipe bend, etc.2) Crevice areas - valves, pumps, tube sheets, etc

31.0 Discuss the producti on of Nitrogen-1target element, half-life, decay radiation,resultant radionuclide, residence duringshutdown).

Nitrogen-16 production:16O + 1 16N + 1pNitrogen-16 decay: 16N 16O + - + 6.14 MeVTarget element: Oxygen-16/Half-Life: 7.13 secondOnly present in containment, Letdown Hx Room.

32.0 Discuss the production of tritium (in

element, half-lif e, decay radiation, energyradionuclide, residence during operationshutdown).

10B (f, 2) 3H/6Li (f, ) 3H/Ternary fission-fissi

resulting in 3 fissionfragments.Half-life: 12.3 years/Decays by emitting a 18.6 keLong-lived radionuclide will continue to increase o

33.0 Identify the main barrier containing tproducts within the fuel elements.

Fuel Cladding

34.0 State the three ways that fission prothe reactor coolant.

Diffusion - The gradual mixing of the molecules dmotion and the diffusionof the noblegases & 3H.Cladding Failures/Defects- Assumed that 1% ofhave minor defects."Tramp" uranium- Uranium impurities in the fuelreach the reactor coolant following fission.

35.0 Define 'crud burst' and state when it

Crud burst - A resuspension and redistribution ofcorrosion products within the RCS.They are caused by plant transients - Heat-ups, recontrolled bursts and chemistry changes.

36.0 Identify the most si gnifi cant group ooriginating in the RCS in terms of limitingthe environmental exposure.

The Iodine Isotopes

37.0 Identify the intended collection andholding/storage points for radioactive liqgases after release from t he reactor but prelease from the plant.

Liquid - (RCDT, RCW R&M Tanks, MW M&R Tan(Degasifier, Surge & Decay Tanks)

38.0 Describe how high activi ty fission aproduct gases are removed from the wasto release to the environment. (Include mto reduce activit y to acceptable levels).




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They are decayed for ~60 days in the Waste Gas

39.0 Describe the methods used to removand activation products from liquid wastrelease to the environment. (Include meth

reduce activity t o acceptable levels).

Natural decay of short-lived isotopes, ion exchangevaporation.

40.0 Discuss the dominant radionucl idesradioactive waste sys tem. (Include the dimeasure radionuclides)

Dominant:

Cs-137 makes up ~41%Cs-134 makes up 32%Co-58 makes up 10%Co-60 makes up 2%

Hard-to-Measure:

Ni-63 makes up 8% --BetaFe-55 makes up 2.5% --BetaPu-241 makes up 02% -- AlphaPu-238 makes up 0006% --AlphaCm-244 makes up .0006% -- Alpha

41.0 Define:

Abs olu te Eff ici ency (4 pi) assumes that all radifrom the source in ALL directions interacts in the dproduces a pulse. The # of pulses observed (couby the true # of radiation particle emitted.Geometry Refers to the position of the detectorthe source of radiation as well as distance from ththe source.Instrument Saturation Condition that occurs wionizations produced in the detector by incident rainteractions prevents detector voltage from buildinlevel required to produce another pulse.

Detector Saturation Is a desirable condition thaall of the ion pairs are being collected at the detecEnergy Window The Upper and Lower (bands)detection Use of discriminator.Gas amplification/multiplication One single ionizproduce secondary ions within the detector depapplied voltageRate meter Pulses are counted per unit of time.Scaler Accumulates total counts (NMC, Mini ScScintillation Material that converts the kinetic edeposited by incident radiation into detectable lighSemiconductor A material having electrical resbetween that of a conductor and an insulator.FluorescencePrompt emission of light from a smaterial that occurs within 1E-8 seconds followingPhosphorescence Emission of long wavelengtscintillator material that occurs in greater than 1E-following excitation.Gamma Spectroscopy The process of collectin

analyzing specific energies to determine the identiradionuclide.Scintillation Efficiency The fraction of all deporadiation energy that is converted into detectable lpulses counted divided by the true # of pulses)

42.0 Draw and label a s imple schematicrepresentation of a gas-filled ionization dInclude anode, cathode, power supply, reand counting circuitry.




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43.0 Identify the function of the major coa gas-fill ed ionization detector: Include acathode, power supply, resistance and ccircuitry.

Ano de- Positively charged electrode that collectsCathode- Negatively charged electrode that colleions.Power Supply- provides the motive force to pull ielectrodes.Resistor- Provides Load resistance between thesupply and the anode across which the signal voltdeveloped.Counting Circuitry- Receives current or pulse siby radiation interactions within the detector and prreadout in units of detection per unit time (rate me

counted (Scaler)

44.0 List 2 processes that compete for iowithin the sensitive volume of a gas-filled

- Recombination and Collection.

45.0 Draw and Label a simple representationization current/pulse height versus devoltage curve (the six-region curve) for adetector the axes, each curve region, satthreshold and volt age, and the Geiger-Muthreshold.

A) RecombinationB)IonizationC) ProportionalD)Limited Proportional

E) Geiger-MuellerF) Continuous DischargeG) Saturation ThresholdH) Saturation VoltageI) Geiger-Mueller Threshold

46.0 Identify whichregions of the 6-region cu rve are useful foperation and those which are not.

Useful: Ionization Region, Proportional Region anMueller Region.Not Useful:Recombination, Limited Proportional,Continuous Discharge Region.

47.0 Define sensitiv ity as it is used in dof radiation counting systems. Discussioinclude three factors that affect the sensi

radiation counting s ystems.

Sensitivity: The indicated exposure rate divided bexposure rate. Factors which effect sensitivity are:1) Discriminator Setting2) Detector Volume3) Detector Voltage4) System Time Constant5) Background Radiation6) Window Thickness

48.0 Discuss current mode of operation Pulse mode of operation ; include the dibetween pulse and curr ent modes of ope




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Current Mode: The detector is designed to recordcurrent produced from multiply ionization events.Pulse Mode: The detector is designed to count eaevent occurring in the detector. Pulse mode detecgreater sensitivity and provides more informationinteractions.

49.0 Describe the pri nciple of operation odiscriminator circuit.

A discriminator is a portion of the circuitry used toabove a minimum energy level or with a certain en(energy window).

50.0 Define and discuss dead time, recovresolving time; include when resolving tiare of greatest concern (in terms of counthe affect of discriminator setting on reso

Dead Time- the time period starting at ionizationthe time at which another pulse starts to be develRecovery Time- measured from the point at whicis starting to the point at which detector voltage harestored to its original value.Resolving Time- the time period starting at ionizlasting until detector voltage has built to a level atpulse can be counted. (Resolving Time = Dead TiTime) When resolving time losses are of greatest

When counting high activity/count rates. The effecdiscriminator: A low discriminator set point reducetime.

51.0 Define and discuss pulse pile-up, incsituation (in t erms of count rate) where pigreatest concern.

A condition that occurs when the time between puthe same as or less than the resolving time of thesystem. Greatest concern when counting high acti

52.0 Describe the mechanism by which inoperating in the Geiger Mueller region crpulses than would be created in an ionizainstrument located in the same radiation

The high voltage potential applied across a G-M d

cause a Townsend avalanche which would causeavalanches until the entire anode is sheathed in elcausing one large pulse as opposed to a one ionizone electron pair collected ratio in the ionization re

53.0 Identify the regions of operation on theight vs. volt age curve for each gas-fillesurvey ins trument used at Nuclear Plants

Ionization Region:RO-2, RO-2A, RO-20, RO-4, aProportional Region: NMC, PM-6, PCM-1B, MatTrash/Laundry Monitor, Rem Ball (Ludlum-12)Geiger-Mueller Region: E-520, RM-14, And the(6112B & D)

54.0 Explain the need to generate a secoparticle in neutron detection; include neuinteractions and target materials.

Neutrons are uncharged; therefore, direct ionizatipossible. Neutrons must undergo scatter or absorinteractions with nuclei, these interactions will emiparticle, which will under go an interaction freeingelectron that can be detected (It produces a pulseinteraction is in the Bonner Sphere (BF-3) A fast nslowed or thermalized, by a hydrogenous materialabsorbed by a Boron-10 atom within the sphere,a particle to reach stability,leaving a Lithium-7 atom. The a will undergo ionizinteractions, which can be detected.

55.0 Identify the purpose of a moderatorin neutron detection.




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A fast neutron is slowed or thermalized (through escattering), by a hydrogenous material surroundinSphere, to allow detection.

56.0 Identify the advantage given by the sgeometry of a Bonner Sphere.

The spherical shape provides a non-directional (odirectional) dose rate reading that is free of angle-effects.

57.0 Describe the func tion of each of thecomponents of a typical detection circuit

Detector: Converts energy deposited by radiationPreamplifier: Magnifies the pulse (proportionatelypulse height).

Ampli fier: Magnifies the pulse (proportionately inheight).Discriminator: Sorts the pulse according to energPulse Height A nalyzer: Separates and accumulaaccording to energy level.Scaler: Provides a readout in total counts.Rate meter: Provides a readout in counts per unit

58.0 Identify 1 disadvantage associatedselection of a rate meter time constant thshort or long.

Too Short:The detector circuitry may loose the aseparate individual pulses and therefore may notpulses.Too Long:More than one pulse may be countedcircuitry as a single pulse and/or the meter may shresponse.

59.0 Describe the purpose of pul se heighanalysis/gamma spectroscopy.

Used to determine the total number of pulses whofalls within selected energy band throughout a givto identify the pulses within the energy bands for ridentification.

60.0 Describe the condit ions under whichbackground radiation has the largest effecounting results.

The greatest effect is when the sample has low acbackground count rate is high. Also the greatest sis introduced when the background count time iscount time.

61.0 Identify three means of reduci ng baceffects on counting system results.

1) Use shielding2) Increase background and samtimes3) Count sample closer to detector.

62.0 Identify and descr ibe the functions othe following components of a scintil latio

Light Reflector- Reflectslight back into the scintillatorand toward the

photocathode.Optical coupler- Collectsand channels light fromreflector into thephotocathode.Photocathode- Absorbslight and emitsphotoelectrons into photomultiplier tube.Photomultiplier Tube- Increases the size of themultiplying the amount of electrons from the photoScintillator - Converts energy deposited by incideinto detectable light.

63.0 List four desirable characteristics ofscintillator for radiation detection.




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- The scintillator should convert incident radiation ilight with a good efficiency.- The light yield should be proportional to the radiadeposited over a wide energy range.- The scintillator should not self-absorb the light pr- The emission time should be short so that fast sican be generated.- The scintillator should be good optical quality anmanufacture.- The optical characteristics should be near that ofpermit efficient transmission of the scintillation ligh

photomultiplier tube.- Only a small portion of the energy deposited is clight. The amount not converted is dissipated as mvibration and heat.

64.0 Identify at least one instrument availNuclear Plants representing each of the fdetector types:

Scintillation Detector: AC-3 ( contamination probSAC-4, m-R meter, SAM-9, & the WBC.Semiconductor: Chemistry's lithium-drifted germa(GeLi).

65.0 Identify a major advantage of the s cidetector over a gas-fill ed detector. Descrireasons.

1) Low resolving times - consequently higher activcan be counted without dead time loss.2) Efficiency for scintillation much higher due to Hidensity of the Fluorescence material.

66.0 Describe the pri nciple of operation osemiconductor detector.

a) Incident radiation causes ionization within the dregion.b) When the electron is removed from orbit by ionileaves a "hole"c) The electron-hole pairs are collected by the seapplying a strong electrical potential across the p-semiconductors, usually 1000 volts.d) The collected charge passes through the circuitand produces a voltage pulse according to ohm's l

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