Liquid Scintillation Counting - Nuclear Regulatory Commission
Liquid Scintillation Counting6/21/20111
General9/8/20082
IntroductionA scintillating liquid, referred to as the “cocktail,” serves asthe detector.The cocktail (perhaps 10 ml) is inside a plastic or glass vialthat is transparent to the light emitted by the cocktail.Ideally, the sample (eIdeally(e.g.,g 1 ml) is dissolved in the cocktailcocktail.Failing that, the sample might be suspended as an emulsionor suspended in a gel. In some cases, a large solid sample(e.g., a smear) is simply placed into the cocktail with noattempt at dissolving it.3
IntroductionLiquid scintillation counting is primarily used to quantify purebeta emitters, e.g., H-3Ni-63C-14S-35P-32It is also used to quantify alpha emitters and nuclides thatdecay by electron capture (e.g., Fe-55, Cr-51, I-125).LSC incorporates elements of spectroscopy, but it is rarelyused to identify radioactive material. As a rule, LSC is usedto quantify the activity of a known nuclide.4
Important Characteristics of LSC9/8/20085
Important Characteristics of LSCThree Important Characteristics of LSC:1.High counting efficiency: 100% for many nuclides.Efficiencies as high as 70% for H-32.No backscatter3.Low background6
Important Characteristics of LSC1. High Counting EfficiencyThere are two reasons for the high counting efficiency: There is no window through which the radiation mustpass in order to reach the sensitive part of the detector The system employs a “four pi” geometry. No matterwhich direction the radiation is emitted in, it will interactwith the cocktail (assuming we are talking about chargedparticle radiation).7
Important Characteristics of LSC2. No BackscatterWhen proportional counters or GM detectors count betaparticles, backscatter directs some betas towards the detectorthat otherwise would have gone in a different direction.DETECTORSOURCESOURCE SUPPORTWhile this increases the detector counting efficiency, it makesour estimate of the counting efficiency less certain!LSC involves no source support in which backscatter canoccur.8
Important Characteristics of LSC3. Low BackgroundThe LSC vials (glass or plastic) are made of materials withvery low levels of naturally occurring radionuclides.When positioned inside the counting chamber, the LSC vialis shielded from background gamma raysrays. OtherwiseOtherwise, thesegamma rays could interact with the vial wall or the cocktail(primarily via Compton scattering) and transfer their energyto electrons which could produce a signal indistinguishablefrom that produced by the betas being counted.The shield might be passive (e.g., lead) or active (e.g., ananticoincident BGO guard detector)9
Important Characteristics of LSC3. Low BackgroundLSC systems use coincidence counting to reduce thenumber of spurious counts produced by electronic 10
Important Characteristics of LSC3. Low BackgroundWhen a beta particle is emitted in the cocktail, a singlescintillation event (flash) occurs in which light photons areemitted in all directions.The two photomultiplier tubes react to the scintillation at thesame momentt ini timeti(i coincidence)(ini id) andd eachh PMTgenerates a pulse that travels to the coincidence andsummation circuits.The coincidence circuit “recognizes” that this represents alegitimate decay event and it sends a logic pulse to thesummation circuit telling it to sum the two pulses and openits electronic gate to allow the resulting pulse through.11
Important Characteristics of LSC3. Low t(Gate Closed)PMT12
Important Characteristics of LSC3. Low mationCircuit(Gate Closed)PMT13
Important Characteristics of LSC3. Low t(Gate Closed)PMT14
Important Characteristics of LSC3. Low t(Gate Closed)PMT15
Important Characteristics of LSC3. Low t(Gate Closed)PMT16
Important Characteristics of LSC3. Low tionCircuit(Gate Closed)PMT17
Important Characteristics of LSC3. Low t(Gate Open)PMT18
Important Characteristics of LSC3. Low BackgroundPMTVialSummed PulseCoincidenceCircuitSummationCircuitPMT19
Important Characteristics of LSC3. Low BackgroundElectronic noise from the PMTs (random fluctuations in thevoltage) is a potentially significant source of backgroundcounts. Although such noise “pulses” consists of smallvoltage fluctuations, they still might be mistaken for smalllegitimate pulses of the sort produced by tritium.tritiumOnly infrequently are “noise pulses” produced by the twoPMTs in coincidence. As such, in the absence of legitimatepulses, the coincidence circuit rarely produces the logicpulses required to open the summation circuit’s gate. If thelatter is kept closed, spurious noise pulses will not get pastthe summation circuit for analysis.20
Important Characteristics of LSC3. Low Background“Noise Gate Closed)PMT21
Important Characteristics of LSC3. Low t(Gate Closed)PMT22
Important Characteristics of LSC3. Low t(Gate Closed)PMT23
Important Characteristics of LSC3. Low t(Gate Closed)PMT24
Important Characteristics of LSC3. Low t(Gate Closed)PMT25
Important Characteristics of LSC3. Low tPMT26
Maximizing Light CollectionA given scintillation event (flash) consists of many individuallight photons. But even a high energy beta emitter such as P32 emits some low energy betas that produce weakscintillations.With the low energy beta emitter tritium (H-3), the brightestscintillations produced by its 1818.66 keV betas consist of 200 –250 photons. The average energy betas of H-3 only producescintillations involving 70 – 100 photons.Because these scintillations can be so weak, the LSC systemis designed to maximize the transmission of light from thesample vial to the PMTs. It does so via reflectors positionedaround the vial and PMTs. There might even be a reflectivefoil inside the cap of the sample vial itself!27
Typical LSC SystemCourtesy of PerkinElmer, Inc. 940 Winter Street, Waltham, MA.28
The Liquid Scintillation VialThe most common size of LSC vial is 20 ml (intended to hold10 mls of cocktail). Smaller sizes include 6, 7, 8 ml. Glass (borosilicate). Lowpotassium versions areavailable. Transparencyallows visual inspectionof cocktail for color,inhomogeneity, etc. Plastic(polyethylene).Less expensive, lowerbackground, butpermeable to toluene,xylene and benzene29
The LSC Cocktailand theEnergy Transfer Process9/8/200830
The Liquid Scintillation CocktailThe two major components of the LSC cocktail are the: Solvent - dissolves sample and fluor Fluor - emits light31
SolventThe solvent makes up 60-99% of the cocktail by volume.Solvents are almost always aromatic organics.Properties of an ideal solvent: good solubility for sampleg flash ppointhighlow vapor pressurelow toxicitybiodegradablegood solubility for fluorlow photo and/or chemoluminescencehigh counting efficiency (tritium)chemical and color quench resistant32
SolventSolvents can be characterized as: Aqueous solvent – for samples soluble in water Non-aqueous solvent – for samples not soluble inwater MultipurposeMltisolventlt – forf samplesl ththatt are solublel blor insoluble in waterSecondary Solvents - these might be added to theprimary solvent to improve the solubility of the sample(sometimes referred to as a solubilizer).33
Older Solvents TolueneBenzeneDioxaneXylenePseudodocumeneModern Biodegradable/DisposablegpSolvents Linear alkyl benzene (LAB), e.g., Packard’s OptiFluor, RPI’s Bio-Safe Di-isopropylnaphthalene (DIN), e.g., Packard’sUltima Gold, Wallac’s Optiphase Hi-Safe Phenylxylylethane (PXE), e.g., Beckman’sReadySafe34
FluorThe fluor (aka, scintillator) might make up 0.3 to 1.0% of thecocktail by volume.Its purpose is to absorb excitation energy from the solventand emit some fraction of this energy as light.There are two categories of fluors: Primary Fluor – most primary fluors emit light in theUV range with wavelengths shorter than 400 nm Secondary Fluor (wave shifter) – the presence of thesecondary fluor increases the wavelength of theemitted light to one more efficiently absorbed by thephotomultiplier tubes.35
Primary FluorNThe most common primaryfluor is 2,5 diphenyloxazole(PPO) whose peak emissionwavelength is at 357 nm.OPPOSecondary FluorThe most common secondary fluors:CH3CHCH3CHCHCH1,4 bis[2-methylstyryl] benzene (Bis-MSB)NONO1,4-bis[5-phenyloxazol-2yl] benzene (POPOP)36
Energy Transfer Process in the CocktailRadioactive decay in the cocktail results in the emission of acharged particle (e.g., beta particle) that travels (a few mm atmost) through the cocktail.Pi electrons in the aromatic rings of the solvent moleculesclose to the charged particle tract are excited.These excited solvent molecules collide with other solventmolecules and transfer the excitation energy to them.Eventually a primary fluor molecule picks up the excitationenergy from an excited solvent molecule – this does notrequire a physical collision but can occur at some distance.By some mechanism, not completely understood, this energycan be transferred to a secondary fluor molecule which de37excites and emits a light photon.
Energy Transfer Process in the Cocktail* Excitation energyCharged ParticlePMTSolvent *Solvent38
Energy Transfer Process in the Cocktail* Excitation energyCharged ParticleSolvent *SolventPMTSolvent *Solvent39
Energy Transfer Process in the Cocktail* Excitation energyCharged ParticleSolvent *SolventSolvent *SolventPMTSolvent *Solvent40
Energy Transfer Process in the Cocktail* Excitation energySolvent *Solvent *SolventSolventSolvent *Solvent *SolventSolventSolvent *Solvent *SolventSolventPMT41
Energy Transfer Process in the Cocktail* Excitation energySolvent *10 Fluor *Solvent10 FluorSolvent *10 Fluor*Solvent10 FluorSolvent *10 Fluor *Solvent10 FluorPMT42
Energy Transfer Process in the Cocktail* Excitation energyShort wavelength light photon10 Fluor *20 Fluor *10 Fluor20 Fluor10 Fluor *20 Fluor *10 Fluor20 Fluor10 Fluor *20 Fluor *10 Fluor20 FluorPMT43
Energy Transfer Process in the Cocktail* Excitation energyLong wavelength light photon20 Fluor *20 Fluor20 Fluor *20 FluorPMT20 Fluor *20 Fluor44
Energy Transfer Process in the CocktailShort wavelength light photon* Excitation energyLong wavelength light photonCharged ParticleSolvent *Solvent *10 Fluor *20 Fluor *SolventSolvent10 Fluor20 FluorSolvent *Solvent *10 Fluor20 Fluor *SolventSolvent10 Fluor20 FluorSolvent *Solvent *10 Fluor *20 Fluor *SolventSolvent10 Fluor20 FluorPMT45
Energy Transfer Process in the CocktailThe greater the energy of the charged particle, the greaterthe number of excited solvent moleculesThe greater the number of excited solvent molecules, thegreater the number of light photons emitted by the cocktail.The more light photons emitted by the cocktail, the greaterthe size of the pulse produced by the PMT.A given beta emitting radionuclide emits beta particles with arange of energies up to some maximum value.46
Beta SpectrumThe beta spectrum looks something like this:Number of Pulses(Number of Betas)AverageBeta EnergyPulse Size(Beta Energy)MaximumBeta Energy47
Problems to beAddressed9/8/200848
Problems to be AddressedThere are several potential problems that must beaddressed in LSC: Getting the sample into solution Static Electricity Photoluminescence Chemiluminescence Quenching- Optical- Color- Chemical49
Getting the Sample in SolutionThe goal is to get the sample completely dissolved in thecocktail or uniformly dispersed throughout the cocktail as anemulsion or gel.In addition, the solution should be clear, colorless and of aneutral pH.If the radioactive component of the sample is not in intimatecontact with the cocktail, the emitted betas may lose someor all of their energy before the energy can be transferred tothe solvent molecules. As such, phase separation of thecocktail components would be a major problem.50
Getting the Sample in SolutionIf the sample is not completely dissolved in the cocktail, thecounts may go up over time as the radioactive material isgradually “taken up” by the cocktail.If this might be a problem, a small amount (e.g., 500microliters) of a solution that the sample is known to besoluble in can be added to the sample before the latter goesinto the cocktail. Ideally this solution should produce minimalquenching. Water, ethanol, acetonitrile, ethyl acetate,hexane are relatively good in this regard.A more thorough mixing of the sample in the cocktail (e.g.,via ultrasonication) might help in some cases.51
Getting the Sample in SolutionOrganic samples are fairly easy to get into solution becausethe cocktail solvents are organic molecules. With suchsamples, the best efficiencies are obtained with cocktails thatare only intended for organics.Aqueous samples require cocktails employing emulsifiers.These cocktails can also be used for organic samplessamples, andfor convenience they might be used for all types of samples.With aqueous samples, the trade off is between countingefficiency and the sample capacity, i.e., the amount of waterthe cocktail can hold.52
Getting the Sample in SolutionPrior to counting, biological material might be homogenized,macerated or combusted and then treated with a solubilizer.Solubilizers might be: alkaline (e.g., Soluene-350). These solubilizers mightbe used with blood, urine, muscle. Solubilization isaccomplished by hydrolysis of the sample. acidic (e.g., perchloric acid, nitric acid). These mightbe used with bone, cartilage. Solubilization isachieved via oxidation of the sample. some other type (e.g., sodium hypochlorite). Plantmaterial is often treated with sodium hypochlorite.Sodium hypochlorite works by oxidative bleaching. 53
Static ElectricityStatic charges on the surface of the scintillation vial canresult in the emission of random single photons. Themaximum pulse size due to such static charge events wouldequate to 10 keV betas (i.e., H-3).Plastic vials, especially the small vials in adapters, are moreprone to developing static charges than glass vials.Handling the vials in low humidity conditions with clothgloves can exacerbate the problem.Static eliminators are optional equipment for most LSCsystems.54
PhotoluminescenceExcitation of the vial or cocktail by ultra-violet light results inspurious single photon emissions that can produce pulsessimilar to those of H-3.The maximum height of photoluminescence induced pulsescorrespond to 6 keV betas. The vast majority of the pulses arein the 0 – 2 keV range.rangeFortunately, photoluminescence decays away very quickly andcan be completely gone within 5 minutes or so.Photoluminescence is independent of quenching and can bereduced somewhat by cooling the sample.55
ChemiluminescenceChemiluminescence is the spurious production of light bychemical reactions that involve various components of thesample.Unfortunately this light emission can last for up to a day ormore!Chemiluminescence is primarily a problem when: the sample is alkaline (high pH) the sample contains oxidizers the cocktail contains solubilizers56
ChemiluminescenceTo a large extend chemiluminescence, which consists ofmultiple single photon events, is minimized by the LSCcounter’s coincidence circuitry.Chemiluminescence can also be reduced by ensuring thatthe cocktail has a neutral pH. This is often accomplished byadding acetic acid (alkaline cocktails are the mostproblematic). This can compromise the sample holdingcapacity however.A simpler approach is to wait several hours to a day after thesample has been added to the cocktail to count.Some folks heat the cocktail in order to drive the chemicalreactions to completion, let it cool down, and then count. 57
QuenchingWhile quenching is a “good” thing in GM detectors, it isundesirable in liquid scintillation counting.In essence, it is an interference in the energy transferprocess that reduces the number of photons reaching thePMTs.This handout will consider three types: optical quenching color quenching chemical quenching58
Optical QuenchingThis term is usually treated as a synonymfor color quenching.As used here, the term applies to theabsorption of the emitted light bysomething other than the cocktail.For example,example putting a paper label on thewall of the vial or labeling the side of thevial (instead of the cap) with a marker.Other examples of what we call optical quenching would befingerprints on the vial wall or condensation.Vials should be handled by the cap when possible. If glovesare worn or the vial is cleaned prior to counting, it should be59done so as to minimize the generation of static.
Color QuenchingAs used here, the term refers to theabsorption of emitted light by color in thecocktail itself. This often a problem withbiological samples, e.g., blood, urine.A simple and effective approach is todecolor with ultraviolet radiation (UV).Exposing the samples to sunlight for a fewhours might be all that is necessary.Aqueous samples are often bleached by mixing 0.1- 0.3 ml of30% hydrogen peroxide in 1 ml of sample. The O2 that isproduced is a strong quenching agent and must be driven offby heating to 50 ºC for and shaking occasionally.60
Color QuenchingNon-aqueous samples and samplesdigested with organic solubilizers can bebleached with benzoyl peroxide.Two mls of a benzoyl peroxide/toluenesolution is used per ml of sample. Thesolution is prepared by dissolving onegram of benzoyl peroxide in five mls oftoluene.The sample is then incubated at for half an hour, allowed tocool to room temperature, and added to the cocktail.61
Chemical QuenchingChemical quenchers are components of the sample/cocktailthat absorb excitation energy from solvent molecules (ordirectly from the charged particle) but fail to transfer thisenergy to the fluor molecules.Common examples of chemical quenchers include oxygenand chloroform.chloroform62
Consequences of QuenchingQuenching reduces the number of photons reaching thePMT in a given scintillation. This reduces the size of thepulse.The result is that the spectrum shifts to the left.63
No QuenchingLSC VialPMTPulseCountsSpectrumPulse Size ((channel))QuenchingLSC VialPMTCountsSpectrumPulsePulse Size (channel)64
Consequences of QuenchingCounts1. Quenching reduces thepulse sizes and shifts thespectrum to the left.2. Quenching reducescounting efficiency becausethe very smallest pulses aremade so small that they arenot counted.Pulse Size (channel number)65
Consequences of QuenchingCountsMore quenchingLess quenchingPulse Size (channel number)66
Quench Correction9/8/200867
Quench CorrectionSince the amount of quenching affects the countingefficiency (counts per disintegration) and because theamount of quenching varies from sample to sample, thecounting efficiency can vary from sample to sample.Determining the counting efficiency for a sample is known asquench correction.correction There are several quench correctiontechniques that can be used, e.g.,1. Internal Standard method2. Channels Ratio method (or variant)3. External Standard method (or variant)68
Quench Correction1. Internal Standard MethodThis involves the use of a “spike.”i. The sample is counted and the resulting count rate is R1(cpm or cps).iiii. A standardd d ((theh spike)ik ) containingi i a kknown activityi i (Qk) offthe radionuclide of interest is added to the cocktail. The factthat the volume of the spike must be small in order tominimize quench effects means that skilled personnel arerequired. This method is particularly inconvenient if manysamples are being analyzed.iii. The sample is counted again. The resulting count rate is69R2.
Quench Correction1. Internal Standard Methodiv. The efficiency is calculated as follows:v. The activity in the sample is then calculated as follows:70
Quench Correction2. Channels Ratio MethodThis technique employs a standard containing a knownactivity of the radionuclide of interest to determine therelationship between the counting efficiency and the shapeof the beta spectrum.Once we know this relationship, we then use the shape of abeta spectrum to determine a samples counting efficiency.The shape of the spectrum is described via the “channelsratio” (CR).Similar correction methods describe the spectrum shape viadifferent parameters, e.g., the spectral index of the sample.71
Quench Correction2. Channels Ratio MethodIn the Channels Ratio method we divide the spectrum intotwo “channels”: A and B.Channel BCountsChannel APulse Size72
Quench Correction2. Channels Ratio Methodi.A set of standards is counted. Each of these contains theradionuclide of interest (e.g., H-3) at the same knownactivity (Qk).The standard vials and, if possible, the cocktail, should beidentical to those that willill be usedsed to countco nt the samples in.inSince each standard contains a different amount of aquenching agent, the spectra of these standards will havedifferent shapes.The greater the amount of quenching agent, the fewer thecounts (i.e., the lower the counting efficiency) and thefurther to the left the spectrum is shifted.73
Quench Correction2. Channels Ratio MethodCouuntsABMore QuenchLess quenchPulse Size74
Quench Correction2. Channels Ratio Methodii. We integrate the counts in Channel A and Channel B. Foreach spectrum we calculate two values:An efficiency (E)A channels ratio (CR)The efficiency and channels ratios could be defineddifferently. The key is that we standardize the definitions.75
Quench Correction2. Channels Ratio MethodIn general, as quench is added: the count in Channel B decreases the efficiency (E) decreases the channels ratio (CR) decreases76
Quench Correction2. Channels Ratio Methodiii. We then plot efficiency (E) as a function of the channelsratio (CR). This is our quench correction curve.Efficiency(E)Channels Ratio (CR)The channels ratio (CR) describes the spectrum shape.77
Quench Correction2. Channels Ratio Methodiv. We then acquire a spectrum for our sample, andcalculate the channels ratio:BCountsAPulse Size78
Quench Correction2. Channels Ratio Methodv. On the quench correction curve, we find the efficiencythat corresponds to the channels ratio for the sample.Efficiency forsampleEfficiency(E)CR calculatedfor sampleChannels Ratio (CR)79
Quench Correction2. Channels Ratio Methodvi. Using the efficiency (E) obtained from the quenchcorrection curve, we determine the activity of thesample:80
Quench Correction2. Channels Ratio MethodThe Spectral Index of the Sample (SIS) technique is verysimilar to the channels ratio method.The difference is that the shape of the spectrum is describedvia the “spectral index of the sample” rather than thechannels ratio.ratio As such,such the quench correction curve is aplot of the counting efficiency as a function of the SIS.Mathematically, the calculation of the SIS is somewhat morecomplicated than the calculation of the CR since it involvesthe processing and weighting of each individual pulse.An advantage is that the SIS method is more sensitive thanthe CR method. Nevertheless, neither method is suitable for81low activity (e.g., 500 dpm) samples.
Quench Correction3. External Standard MethodDespite the name, this technique is unrelated to the internalstandard method discussed earlier.What it does is employ a clever “trick” to make accurateevaluations of the amount of quenching and the countingefficiency even when the sample activities are low andcounting statistics are poor.i. The sample is counted but no attempt is made toevaluate the spectral shape.ii. A gamma emitting source (e.g., Ba-133 or Cs-137) isautomatically brought into position underneath thesample vial and the sample is counted again.82
Quench Correction3. External Standard MethodThe low energy gamma rays/x-rays from the “externalstandard” interact with the vial and cocktail via Comptonscattering. The resulting Compton scattered electronstravel through the cocktail mimicking beta particles.iii. The counting efficiency is then determined from theshape of the spectrum generated by the Comptonscattered electrons via a quench correction curve. Thiscurve was produced using the same type of standardsused in the CR and SIS methods to generate quenchcorrection curves.83
Quench Correction3. External Standard MethodSecondCount ofSampleFirst Countof SampleLow Counts (A1 and B1)CR B1 /(A1 B1 )Large uncertainty in channelsratio means large uncertaintyin efficiency (E1).Ba-133SourceHigh counts (A2 and B2)CR B2 /(A2 B2 )Little uncertainty in channelsratio means little uncertainty inefficiency (E2).Sample Activity B1 /E284
Quench Correction3. External Standard MethodBecause of the high count rates associated with theCompton scattered electrons, the spectral shape evaluationand efficiency determination can be highly accurateirrespective of the sample activity.Some LSC systems use a “quench indicating parameter”known as the “transformed Spectral Index of the ExternalStandard” (t-SIE) to describe the spectral shape. In thesesystems, the quench correction curve plots countingefficiency as a function of the t-SIE value which rangesfrom 0 – 1000. Like the CR and SIS values, the t-SIEvalues decrease with increasing quenching.85
Cerenkov Counting9/8/200886
Cerenkov CountingCerenkov radiation, the blue light produced when electronstravel faster than light in a transparent medium, can be usedto assay high energy ( ca. 500 keV) beta emitters.The sample is simply dissolved in a transparent solution suchas water or alcohol.Although Cerenkov counting can be used to count any highenergy beta emitter, its primary application has been to assaySr-90/Y-90.Advantages of Cerenkov counting: Low backgroundNo chemiluminescenceNo chemical quenching87
A scintillating liquid, referred to as the "cocktail," serves as the detector. The cocktail (perhaps 10 ml) is inside a plastic or glass vial that is transparent to the light emitted by the cocktail. Ideally the sample (e g 1 ml) is dissolved in the cocktail 3 Ideally, the sample (e.g., 1 ml) is dissolved in the cocktail.
principles 1.1 radioactive emissions 1.2 measurement of radiation and isotope quantitation 1.3 mechanism of liquid scintillation counting 1.4 liquid scintillation signal interpretation 1.5 the complete scintillation cocktail 1.6 chemilumi
Ultima Gold is a safer liquid scintillation cocktail for a wide range of aqueous and non-aqueous samples. This multipurpose LSC cocktail has a high counting efficiency and provides superior detection efficiency for samples that exhibit severe quench in conventional cocktails. Extremely high counting efficiency: up to 56% for 3H
Guide for Nuclear Medicine NUCLEAR REGULATORY COMMISSION REGULATION OF NUCLEAR MEDICINE. Jeffry A. Siegel, PhD Society of Nuclear Medicine 1850 Samuel Morse Drive Reston, Virginia 20190 www.snm.org Diagnostic Nuclear Medicine Guide for NUCLEAR REGULATORY COMMISSION REGULATION OF NUCLEAR MEDICINE. Abstract This reference manual is designed to assist nuclear medicine professionals in .
Nuclear Chemistry What we will learn: Nature of nuclear reactions Nuclear stability Nuclear radioactivity Nuclear transmutation Nuclear fission Nuclear fusion Uses of isotopes Biological effects of radiation. GCh23-2 Nuclear Reactions Reactions involving changes in nucleus Particle Symbol Mass Charge
Addition Anno’s Counting House Anno, Mitsumasa Climate Cactus Desert, Arctic Tundra Silver, Donald Climate Tropical Rain Forest Silver, Donald Counting 26 Letters and 99 Cents Hoban, Tana Counting Anno’s Counting Book Anno, Mitsumasa Counting Let’s Count Tana Hoban Counting The Great Pe
Step 1- Counting nickels and dimes by 5 and 10 and counting quarters (25, 50, 75, 100) Step 2- Counting dimes and nickels (start with the dimes) Step 3- Counting dimes and pennies and nickels and pennies Step 4- Counting on from quarters (25/75) with nickels and dimes Coin Cards (Use
A formal Regulatory Management System [RMS] can help with: reduction of regulatory burden on citizens and firms improvement of regulatory quality identification of best choice of policy options Comprised of four elements: 1. regulatory quality tools 2. regulatory processes 3. regulatory institutions 4. regulatory policies 16
Days 1 to 5 PREDNISOLONE 40 mg/m2 PO daily. (Give first dose before rituximab as pre-med). * Vincristine 1 mg in patients over 70 years of age. Pretreatment with steroids: Some older patients may benefit from a steroid pre-phase consisting of 7 days of oral prednisolone at a dose of 50-100 mg daily. G-CSF primary prophylaxis: Consider if patient is over 70 years of age or is immunosuppressed .
