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Dosimetry This module meets the annual re-training requirement per Environment, Health and Safety’s Radiation Safety Program Policy. Use the buttons to navigate through the module. In order to receive credit for reviewing this module, please follow the instructions at the conclusion of the slides. Radiation Safety Program
Objectives • Identify the biological effects when ionizing radiation interacts with the human body. • Differentiate between various types of dosimetry. • Identify UCLA dosimetry policies, including proper badge usage. • Define radiation dose units and how they relate to annual dose limits set by the Nuclear Regulatory Commission (NRC).
Radiation Biology To understand the purpose and function of dosimetry we must first understand the risks associated with working with radiation. How does radiation affect our bodies? • Ionizing radiation transfers energy to electrons • Ionizing radiation has sufficient energy to break chemical bonds • Broken water molecules lead to free radicals which are chemically reactive • At the cell level, single and double strand breaks in DNA caused by ionizing radiation may lead to mutations, carcinogens, and cell death DNA Single Strand break DNA Double Strand break
Biological Effects Biological effects from radiation can be broken down into two types: • Deterministiceffects, which only occur above a certain dose threshold • Stochastic effects, which have a chance of occurring at any range of dose
Stochastic Effects Whether you are working in a research or clinical environment, nearly all exposure to radiation will be at low doses, where stochastic effects can still occur. A recent analysis of epidemiological studies of atomic bomb survivors, nuclear workers, and persons exposed to radiation for medical reasons predicts: Approximately 42% of the population will be diagnosed with cancer from causes unrelated to radiation exposure. A radiation dose of 10 mSv (1 rem) will increase the risk of developing cancer by 0.11% and fatal cancer by 0.056%1 1National Academies Council on Biological Effects of Ionizing Radiation (BEIR) VII.
Deterministic Effects • Deterministic Effects have a threshold, meaning thatonly above a threshold dose do these effects occur. The occupational limits of radiation exposure are well below any deterministic effect threshold.
Scenario 1: What do you think? Mark is about start working in a lab that works with P-32 to label DNA. As is typical with DNA labeling, Mark will be receiving low doses of radiation. Which effects should he be concerned with? • Both, deterministic and stochastic. • Deterministic effects. • Stochastic effects. Click here to see the correct answer…
Scenario 1: What do you think? Mark is about start working in a lab that works with P-32 to label DNA. As is typical with DNA labeling, Mark will be receiving low doses of radiation. Which effects should he be concerned with? • Both, deterministic and stochastic. • Determinist effects. • Stochastic effects. Correct! A laboratory worker that handles P-32 for DNA labeling is not at risk of exceeding the 2 Gy deterministic effects threshold. A typical badge reading from a lab worker handling isotopes for DNA labeling is near background levels of radiation.
What is Dosimetry? Dosimetry is the measurement of radiation dose received. Dosimeters (e.g., badges, rings) measure the amount of radiation received by radiation workers and help Environment, Health and Safety monitor radiation dose to be sure workers do not exceed annual limits. Badges and rings are administered to workers based on radioactive material shipment limits and/or specific radiation worker occupations.
Units of Dosimetry: Absorbed Dose • Absorbed Dose (D): a measure of the amount of energy from ionizing radiation deposited in a material. Human tissue is an example of such material. • Traditional unit: Radiation Absorbed Dose (rad), 1 rad = 100 erg/g • International unit: Gray (Gy), 1 Gray = 1000 joules/kg • 1 Gray = 100 rads How much dose did I get? Energy in the form of radiation
Units of Dosimetry: Equivalent Dose • Equivalent Dose (H) is theabsorbed dose (D) multiplied by a radiation weighting factor (WR) • H = D x WR • Equivalent dose is a more accurate measurement (compared to absorbed dose) of dose because it takes into consideration the type of radiation irradiating the matter. Each radiation type (e.g., alpha, beta, gamma, neutrons, x-rays) has a different degree of effectiveness in producing biological effects, hence the use of a radiation weighting factor (WR). • Traditional unit - Roentgen Equivalent Man (rem) • International unit - Sievert (Sv)
Units of Dosimetry: Effective Dose • Effective Dose (E) is the equivalent dose (H) multiplied by a tissue weighing factor (WT) • E = H x WT • Effective dose is the most accurate measurement of biological damage because it takes into consideration the type of radiation and the type of tissue being irradiated. • Traditional unit is the rem, • International unit is the Sievert (Sv) • The regulations are based on effective dose • 1From ICRP 103 (2008)
Annual Dose Limits Skin 0.5 Sv 50 rem Per NRC regulations, if a radiation worker is likely to get 10% of the annual dose limits (shown on the right), they must be issued dosimetry. Eyes 0.15 Sv (15 rem) Total Effective Dose (whole body) 0.05 Sv (5 rem) Extremities (below knees and elbows) 0.5 Sv (50 rem) Internal Organs 0.5 Sv (50 rem)
ALARA Limits at UCLA • UCLA has established its own, more stringent annual dose limits in order to keep doses As Low As Reasonably Achievable (ALARA). • The EH&S Radiation Safety Program has ALARA I, II, and III limits, which represent 24%, 48%, and 96% of the NRC annual dose limits, respectively. • If a dose is reported that exceeds the ALARA II or III limits, you will receive a notice from the Radiation Safety Program.EH&S will also investigate the matter to keep doses as low as reasonably achievable.
ALARA LimitsSpecific to UCLA Look at the chart below to determine how much dose you can receive in different areas of your body per month, and how that relates to your ALARA limits.
Scenario 2: What do you think? Sue works with F-18, her exposure report read 405 mrem to the whole body for the month of January which puts her over ALARA III limits under UCLA policy. What can she expect? • Nothing will happen, she is on pace to be under the annual limit of 5,000 mrem. • She will get a notice from the Radiation Safety Program. • Since she exceeded ALARA III limits, she will receive a letter that she can no longer work with radiation for the rest of the year. Click here to see the correct answer…
Scenario 2: What do you think? Sue works with F-18, her exposure report read 405 mrem to the whole body for the month of January which puts her over ALARA III limits under UCLA policy. What can she expect? • Nothing will happen, she is on pace to be under the annual limit of 5,000 mrem. • She will get a notice from the Radiation Safety Program. • Since she exceeded ALARA III limits, she will receive a letter that she can no longer work with radiation for the rest of the year. • Correct! The Radiation Safety Program will be in contact with Sue to help minimize her dose by analyzing work practices.
Dosimeters • Dosimeters measure the amount of radiation dose received by wearers. At UCLA, various types of dosimeters are used: • Optical-Stimulated Luminescence dosimeters (OSL) • Thermoluminescent dosimeters (TLD) • Pocket dosimeters • Electronic dosimeters
Dosimeters: OSL Badges Optical Stimulated Luminescence (OSL) badges measure whole body, lens of the eyes and shallow dose. • How are OSL Badges read? • OSL badges contain aluminum oxide (Al2O3) crystals which are read by a specific wavelength of laser light. The released light indicates the amount of radiation dose. • OSL badge have limitations: • For x-ray, gammas only > 5 keV photons can be read, dose measurement range of 1 mrem to 1000 rem • For beta particles only > 150 keV particles can be read, dose measurement range of 10 mrem to 1000 rem.
Dosimeters: TLD Rings Thermoluminescent dosimeter (TLD) rings assess extremity (e.g., below the elbow) doses. How are TLD rings read? TLD badges have a lithium fluoride chip inside the engraved ring cover which when heated causes a luminescence in proportion to the amount of radiation exposure. • TLD rings have limitations: • For gammas, x-rays only >15 keV photos can be read, dose measurement range from 30 mrem to 1000 mrem • For betas only > 200 keV particles can be read, dose measurement range from 40 mrem to 1000 mrem • Affected by heat, moisture, and pressure, cannot be re-read, unlike OSL badges.
Dosimeters: Pocket Pocket dosimeters, used by cyclotron users and in emergency situations, are issued less frequently. Pocket dosimeters allow for instantaneously dose analysis. How are pocket dosimeters read? Pocket dosimeters are read by pointing one end at a light source and observing the other end close to the eye. • Pocket dosimeters have limitations: • Type of Radiation that can be read: 20 keV to 2 MeV x-rays and gammas • Sample dose range 0 to 200 mR , 0 to 600 R
Dosimeters: Electronic • Electronic dosimeter are also issued less frequently than OSL and TLD badges, normally during emergencies. • How are Electronic Badges read? • Electronic badges can be set to give a dose rate, sound a dose rate alarm, and provide instantaneous dose analysis. Electronic badges have limitations: • Can give you total dose and total dose alarm • Sample measurement range 0.1 mrem to 999 rem • Sample energy range of 60 keV photos to 6 MeV
Proper Dosimetry Badge Wear For Whole Body Badges: • Worn on the part of the body between your neck and waist • Wear it so name tag faces radiation source • If lead apron is worn, wear the badge at collar level on the outside of apron For Dual Badges: • One badge on the collar, outside lead apron • One badge on the waist, under lead apron
Proper Dosimetry Badge Wear • Wear your ring badge with the white label on the same side as the palm of your hand. • Remember, your palm is closest to the radioactive materials you are working with, so the badge should also be closest to the materials. • If you are wearing a glove, wear your ring underneath the glove.
Responsibilities of Those Wearing Dosimeters • Store your dosimetry badge in a non-radiation location when not in use • Exchange your badge when requested by the Departmental Badge Coordinator • Keep your badge at work. Don’t take it home • Wear your dosimetry badge: • whenever using radiation-producing machines or radioactive materials that present an external hazard • for the current monitoring period • in the correct location on the body • If you are pregnant and wish to begin fetal monitoring, it is your responsibility to declare your pregnancy in writing to the RSP • Never share your dosimetry badge or wear someone else’s • Do not intentionally expose dosimeters to radiation • Do not wear your dosimetry badge for non-occupational exposures • Do not use your badge at an institution other than UCLA Don’ts Do’s
Reporting…… Badge Exchange • Badges are exchanged on a monthly or quarterly basis for radiation exposure processing. Here’s how it works: • EH&S automatically sends replacement badges to Department Badge Coordinators during the last few days of the month. • Department Badge Coordinators exchange your badge by collecting the used one and providing you with a new one. (Late badges will incur a $5-$11 fee.) • Dosimeters are returned to EH&S (by the Department Badge Coordinators) for processing. • EH&S mails all Dosimeters to an outside company for processing, and provides follow-up exposure reports to Department Badge Coordinators. • Contact your Department badge coordinator or the Radiation Safety Program to view your dose report. • Your radiation exposure history will be provided to you or your subsequent employers on request. • If dose of “M” is reported, the total dose received was below the minimal detectable level. • EH&S Radiation Safety maintains all exposure records indefinitely. Here are the important facts about reports:
Scenario 3: What do you think? If a radiation worker becomes pregnant what should she do? • Declare her pregnancy in writing to the Radiation Safety Program if she wishes to begin fetal monitoring. • Immediately stop working with radiation. • Continue working, since she already has a radiation badge. Click here to see the correct answer…
Scenario 3: What do you think? If a radiation worker becomes pregnant what should she do? • Declare her pregnancy in writing to the Radiation Safety Program if she wishes to begin fetal monitoring. • Immediately stop working with radiation. • Continue working, since she already has a radiation badge. • Correct! There are safe levels of working with radiation under the guidance of the Radiation Protection Program. A separate fetal badge is issued to keep track of the more stringent fetal dose limits.
Recording Your Completion Annual Refresher Training Now that you have read through this annual refresher training module, be sure to record it on your laboratory’s Principal Radiation Worker Training Record Form.Beside your name, mark the “OL” box for online, date, and initial the form.
For more information • Questions about the annual refresher training or need a copy of your lab group’s training form? Contact the your responsible health physicist or the Radiation Safety Training Manager at ext. 4-1876 or email@example.com • Questions about topics discussed in this module? Contact the Dosimetry Program Manager at ext. 4-1742