1 / 25

Survey Meter Support Services

UNIVERSITY OF FLORIDA Radiation Safety Short Course Radiation Detectors & Survey Instrumentation. Survey Meter Support Services. RCRS provides: Pick-up and delivery of meters Required 9-month calibration Preventive maintenance and repairs Shipping for extensive repairs. RCRS Contact:

lucien
Download Presentation

Survey Meter Support Services

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. UNIVERSITY OF FLORIDARadiation Safety Short CourseRadiation Detectors &Survey Instrumentation

  2. Survey Meter Support Services • RCRS provides: • Pick-up and delivery of meters • Required 9-month calibration • Preventive maintenance and repairs • Shipping for extensive repairs • RCRS Contact: John Parker Nuclear Science Center 392-7359

  3. Types of Surveys • Direct measurements • Portable survey instruments • Indirect measurements • Swipes and use of counters (Liquid Scintillation and Gamma)

  4. Use of Portable Survey Instruments • Read the instrument’s operating manual • Check the batteries before each use

  5. Use of Portable Survey Instruments • Use a check source to determine operability of detector • Determine efficiency of detector • Determine the instruments response time • Determine the operating background

  6. Geiger Mueller (GM) Detectors • GM are tubes filled with a mixture of Q-gas • Used for radioactive contamination monitoring • Detects high energy beta radiation • GM measures each individual interaction inside the detector • Do NOT identify the radioisotope or specific energy

  7. Sodium Iodide (NaI) Probe • Probe has a NaI crystal and a photomultiplier tube • Detection is based on emission of photons • Used for radioactive contamination monitoring • Detects low energy x-rays • Does NOT identify the radioisotope

  8. Ionization Chambers • Ion Chambers are filled with air • Used for measuring radiation field intensity (exposure rate) • Detect x-rays and gamma radiation • Measure average current produced over many interactions • Do NOT identify the radioisotope or specific energy

  9. Ionization Chambers A.K.A. - Dose Rate Meter Roentgen (R): a unit of exposure to x-rays or gamma rays. One roentgen is the amount of gamma or x-rays needed to produce ions carrying 1 electrostatic unit of electrical charge in 1 cubic centimeter of dry air under standard conditions.

  10. Liquid Scintillation Counter (LSC) • Detection is based on emission of visible or near visible light (photon) • Sample vial must contain scintillation cocktail • Interaction between radiation and cocktail causes photons to be emitted • Photomultiplier tubes are used to detect and amplify the photons • It can identify the activity and energy of a beta emitter in a sample vial • It is much more efficient than a portable survey meter

  11. The Scintillation Process • Beta particles are emitted, which cause solvent molecules to become excited. • The energy of the solvent molecule is transferred to the fluor molecule, which in turn emits light. Radioactive molecule Solvent molecule Fluor molecule Photomultiplier tube

  12. Gamma Counters • Detection is based on emission of visible or near visible light (photons) • Uses solid scintillation (no scintillation cocktail required) • Interaction between radiation and a solid scintillator causes photons to be emitted • Photomultiplier tubes detect and amplify photons • Used to determine the activity of a x-ray or gamma emitter in a sample vial • Gamma counters can identify activity and energy of gamma emitters

  13. Choosing the correct instrument • Radiation Field / Dose Rate (mR/hr) • Ion chamber • Activity / Contamination amounts • Beta emitters • Low and Mid energy • LSC only • High energy • GM Detector • LSC (for documentation purposes) • Gamma emitters • Sodium Iodide • Gamma counter (for documentation purposes) ?

  14. Useful Formulas/Conversions • 1 µCi = 2.22 x 106 dpm • net cpm = gross cpm – background • efficiency = (net cpm) / (dpm) • dpm = (net cpm) / (efficiency) • cpm = (dpm) x (efficiency) Hmm…a conversion might help here!

  15. Sample Problem 1 You have a swipe that was counted for 5 minutes that yields 5800 counts. If the background is 125 cpm and the counter efficiency is 80%, what is the dpm of the swipe? Hint: 5800 counts / 5 minutes = 1160 gross cpm Big Hint: 1035 net cpm / 0.80 efficiency = 1294 dpm Hint: 1160 gcpm – 125 background cpm = 1035 net cpm

  16. Sample Problem 2 You have a standard that has an activity of 105,000 dpm. After 2 minutes of counting in a gamma counter you get 120,000 counts. If the background is 350 cpm, what is the efficiency of the gamma counter? Hint: 120,000 counts / 2 minutes = 60,000 gross cpm Big Hint: 59,650 ncpm / 105,000 dpm = 57% efficiency Hint: 60,000 gcpm – 350 background cpm = 59,650 net cpm

  17. Sample Problem 3 You are using P-32 as a tracer and determine that 20% of fed material ends up in your final sample. If you need a count rate of 2,000 cpm in a sample, determine how many microcuries you must use given the fact that your LSC has an efficiency of 50% for P-32. Big Hint: 20,000 dpm / 2.22 x 106 dpm/µCi = 0.009 µCi Hint: 2,000 cpm / 0.20 = 10,000 cpm Hint: 10,000 cpm / 0.50 efficiency = 20,000 dpm

  18. Life is not measured by the number of breaths we take, but by the moments that take our breath away…

More Related