Fluid Scintillation Counter And Contamination Monitoring Training

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Points. What is Liquid Scintillation?QuenchingCalibration of Liquid Scintillation CounterOperating Procedure for Liquid Scintillation CounterContamination Monitoring. Partner Director, Radiation and Biosafety Lois Sowden-Plunkettext. 3058 lsowden@uottawa.caRadiation Compliance SpecialistAli Shoushtarianext. 3057ashousht@uottawa.caRadiation Safety Program Web Page http://www.uottawa.ca/s

Presentation Transcript

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Fluid Scintillation Counter And Contamination Monitoring Training Presented by: Ali Shoushtarian Office of Risk Management October 2009

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Topics What is Liquid Scintillation? Extinguishing Calibration of Liquid Scintillation Counter Operating Procedure for Liquid Scintillation Counter Contamination Monitoring

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Assistant Director, Radiation and Biosafety Lois Sowden-Plunkett ext. 3058 lsowden@uottawa.ca Radiation Compliance Specialist Ali Shoushtarian ext. 3057 ashousht@uottawa.ca Radiation Safety Program Web Page http://www.uottawa.ca/administrations/ehss/ionizing.htm

Slide 4

What is Scintillation Counter? A glitter counter measures ionizing radiation The sensor, called a scintillator, comprises of a straightforward precious stone, for the most part phosphor that fluoresces when struck by ionizing radiation. A touchy photomultiplier tube (PMT) measures the light from the precious stone. The PMT is joined to an electronic speaker and other electronic hardware to tally the signs delivered by the photomultiplier.

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Scintillation counter mechanical assembly When a charged molecule strikes the scintillator, a glimmer of light is delivered. Each charged molecule delivers a blaze. At the point when a charged molecule goes through the phosphor, a portion of the phosphor's iotas get energized and discharge photons. The power of the light blaze relies on upon the vitality of the charged particles. Cesium iodide (CsI) in crystalline shape is utilized as the scintillator for the recognition of protons and alpha particles; sodium iodide (NaI) containing a little measure of thallium is utilized as a scintillator for the location of gamma waves.

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Liquid shine numbering Samples are broken down or suspended in a "cocktail" containing a sweet-smelling dissolvable and little measures of different added substances known as fluors. Beta particles discharged from the example exchange vitality to the dissolvable atoms, which thus exchange their vitality to the fluors; the energized fluor particles disseminate the vitality by emanating light. Along these lines, every beta emanation brings about a beat of light

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Liquid shine tallying Counting efficiencies under perfect conditions go from around 30% for H-3 (a low-vitality beta emitter) to almost 100% for P-32, a high-vitality beta emitter.

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Liquid glimmer checking The counter has two photomultiplier tubes associated in an incident circuit. The happenstance circuit guarantees that honest to goodness light heartbeats, which achieve both photomultiplier tubes, are tallied, while different heartbeats (because of clamor, for instance), which would just influence one of the tubes, are overlooked .

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Summary of Scintillation Counter Scintillation Cocktail contains dissolvable and fluor (or solute) atoms. Dissolvable is great at catching vitality of -molecule (electron), however regularly does not create light. A fluor atom enters an energized state taking after communication with energized dissolvable. The energized fluor particle rots to ground state by discharging light (as a rule in blue wavelength) Blue light is distinguished by photomultiplier tube (generally two PMT are utilized to limit PMT blunders.

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-Energy and Light Intensity Stronger  emitters produce more grounded beats of light, so that 3 H , 14 C, and 32 P can all be recognized and numbered in the meantime. The stature of the beat can be resolved as a voltage and is corresponding to the measure of light which communicates with photocathode. In this manner, the beat tallness at the yield of the PMT is relative to the vitality of the molecule.

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Quenching inside an example alludes to any system which lessens the measure of light being discharged from the vial. Diminishing the measure of light achieving the PMT's outcomes in a decrease of the beat stature. Any variable, which lessens the effectiveness of the vitality exchange or causes the assimilation of photons (light), brings about extinguishing in the example.

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Quenching Chemical Quenching Chemical extinguish happens amid the exchange of vitality from the dissolvable to the scintillator. Synthetic specialists (e.g. water and different solvents) added to the mixed drink with the radioactive specimen meddle with the exchange of active vitality between the dissolvable and the fluor(s). The outcomes are: Reduction and loss of light Reduced tallying proficiency Color Quenching Color extinguishing is a lessening of the photon of light. The photons delivered are consumed or scattered by the shading in the arrangement, bringing about decreased light yield accessible for estimation by the PMT's.

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Summary of Quenching

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Effects of Quenching A move in the beat stature range of the particles to lower vitality A decrease in the deliberate CPM of the example (loss of checking productivity). This impact happens particularly with low vitality particles.

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The Absolute Activity Calculation All specimens arranged in the research center are extinguished to some degree with a specific end goal to express the information in units that permit exact correlation. It is important to change over the deliberate CPM to Disintegrations Per Minute (DPM). Checking Efficiency = CPM/DPM DPM= CPM/Counting Efficiency

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Calibration of LSC proficiency relies on upon the level of extinguishing, the nature of the example, the scintillator utilized and the readiness technique. In spite of the fact that there are a few techniques by which LSCs can be aligned, the outer standard strategy is the most generally utilized strategy for effectiveness adjustment.

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Set of 3H Quenched Standards A 10 vial standard set each containing a similar measure of radioactivity (i.e., dpm ) yet blended with expanding measures of an extinguishing specialist is utilized. Extinguishing operators assimilate the radiation vitality Thus, the more extinguished the example, the less the include identified the coveted channel.

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Set of 3H Quenched Standards Each vial contains 194,433 dpm - 3H The extinguished guidelines are set into a LSC plate which is then put into the LSC. Set the channel # for Beckman LSCs , and start numbering. Since all benchmarks contain a similar measure of action, the effectiveness, the proportion cpm/dpm, of the counter for each of the different levels of extinguishing can be plotted as in the chart

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Beckman LSC Considerations All LSCs work in a similar way, however extraordinary producers may utilize distinctive phrasing or offer a greater number of alternatives than others. On the off chance that you are utilizing a Beckman tallying framework, for the most part the channel choice is the default choice for the window setting. Beckman checking frameworks have 1000 channels and the vitality is identified with the condition: Channel # = 72 + 280 log10 (Emax) where Emax is in keV. In this way the channel settings on a Beckman LSC to recognize the most extreme conceivable beta vitality for 3H, 14C/35S and 32P would be roughly 400, 670 and 1000 separately.

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Operating Procedures for LS Counters Read the instruments working manual to pick up recognition with the controls and working attributes of the machine. Put tests into LSC vials and include the right measure of fluid glitter mixed drink (e.g., 5 or 20 ml, as suitable). Incorporate a foundation vial which contains shine mixed drink and a non-radioactive example Place your specimen vials with foundation vial into the LSC plate and place into the LSC. Set number time, taking note of that shorter tally times give poor checking measurements. Set the proper channel and start your tallying.

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LSC Overall Summary Run your Standards ordinary to ensure your LSC is aligned Create a log sheet Remember, Energy of your isotopes (keV) is vital keeping in mind the end goal to pick the right channel

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Contamination Monitoring Basic Operation Principles Function Check Battery check Visual check (physical condition, wires, and so forth) Foils/Windows Audio reaction Calibration date Background check Low reaction Vs Fast reaction

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Contamination Monitoring 2) Parameters of enthusiasm for defilement screens Efficiency Not all rot discharges Are recognized! Locator Covering Detector Volume Efficiency: 1) Distance: 1/r2 2) Beta Absorption 3) Size of window Surface

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Contamination Monitoring Contamination Criteria < Class A: 3.0 Bq/cm 2 Class B: 30 Bq/cm 2 Class C: 300 Bq/cm 2 Decommissioning Criteria < Class A: 0.3 Bq/cm 2 Class B: 3.0 Bq/cm 2 Class C: 30 Bq/cm 2

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Contamination Monitoring 3) Calculating Efficiency Eff (%) = ((CPS Source – CPS Background )/Source Activity (Bq)) X 100 Example: Source movement : 1kBq Background: 50 cpm Counts: 15000 cpm Note: 1 cps= 60 cpm Eff % = (250 – 0.8)/1000 X100 = 24.9%

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Contamination Monitoring 4) Calculating Minimum Detection Activity (MDA) Calculating the littlest measure of defilement a screen can identify with 95% certainty MDA = (4.66 √B+3)/Kt [ MDA = (4.66 √B+3)/Eff X time] K= figure including effectiveness, change into Bq, and synthetic or physical yield for inspecting procedures. t= test number time and foundation check time B= Background

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Contamination Monitoring Example: Surface territory is 15 cm 2 Eff is 2.6% Time 7 sec (moderate reaction) Background = 50 cpm = 0.83 cps MDA = (4.66√B+3)/Eff X time = (4.66√0.83X7)+3/0.026 X7X15 = 5.1 Bq/cm 2 in view of a 7 seconds reaction time

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Contamination Monitoring 5) Converting cpm comes about into Bq/cm 2 for GM flapjack Bq/cm 2 = (Cpm – Bkg)/Ec X Ew X 60 X A where Cpm = tallies every moment for the wipe, Bkg = checks every moment of the foundation channel, Ec = sparkle counter productivity (see note underneath), or GM proficiency Ew = wipe effectiveness, accept 10% (0.1), and A = region wiped in cm2. Note: As a dependable guideline, when the counter effectiveness (Ec) is obscure, the accompanying efficiencies can be utilized with the end goal of tallying wipes: 100% (1) for 32P, 14C, 35S 75% (0.75) for 125I half (0.5) for 3H and questions

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 Thank you  .:tslidesep

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