2.04 DOSIMETRY RCT STUDY GUIDE LEARNING OBJECTIVES Identify the DOE dose-equivalent limits for occupational workers.

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1 LEARNING OBJECTIVES Identify the DOE dose-equivalent limits for occupational workers Identify the DOE limits established for the embryo/fetus of a female occupational worker Identify the action levels and guidance levels at LANL, including those for the: a) Radiation worker b) Incidents and emergencies Identify the requirements for a female radiation worker who has notified her employer in writing that she is pregnant Determine the theory of operation of a thermoluminescent dosimeter (TLD) Determine how a TLD reader measures the radiation dose from a TLD Identify the advantages and disadvantages of a TLD Identify the types of beta-gamma TLD used at LANL Identify the types of neutron dosimeter used at LANL Determine the requirements for use of TLDs at LANL Determine the principle of operation of the personal neutron dosimeter (PND or PNAD) used at LANL Determine the principle of operation of self-reading dosimetry (SRD) used at LANL Determine the principle of operation and guidelines for use for the alarming radiation detectors used at LANL Identify the types of bioassay at LANL, including "in vivo" and "in vitro". References: 10CFR835 LPR Occupational Dose Limits LIR ALARA LPR Personnel Dosimetry ESH Issuing and Using Supplemental Dosimetry ESH Responding to Suspect Internal Intake ESH-RADPR-DP-01.1 Dosimetry Notifications -1- April 16, 1999

2 INTRODUCTION Dosimetry is the quantitative assessment of radiation exposure received by the human body. (In Latin, French and Spanish the words "metre", "medir" etc. mean "measure", so "dosimetry" means "dose measurement".) Biological effects of radiation and their prevention are of primary interest to the Radiological Control Technician. In the early 1900's, it was common for a radiologist to test the dose by putting a hand in the x-ray beam to see if the skin turned red. This is called erythema ; it is like sunburn. The erythema dose is approximately 300 R. This method would not qualify today as an appropriate method for measuring radiation dose! (See lesson 1.09, page 2). Dose limits for radiological workers are established by 10CFR and the Laboratory Performance Requirement (LPR) Limits for the public, minors, and the embryo/fetus are established by 10CFR , 7, and 8. The DOE's objective is to maintain personnel radiation doses well below regulatory dose limits. To accomplish this objective, Administrative Control Levels (ACL) will be established at levels below the regulatory limits to administratively control and help reduce individual and collective radiation dose. In addition, strict adherence to ALARA principles is expected of all workers. See section , and lesson 1.10 on ALARA. The concept of committed effective dose equivalent, CEDE, is used to assess internal dose received by personnel at DOE facilities. The CEDE is the resulting dose committed to the whole body from internally deposited radionuclides over a 50 year period after intake. Dose limits are stated in terms of the total effective dose equivalent, TEDE, which is the sum of the doses received from internal and external sources RADIOLOGICAL WORKER DOSE LIMITS Radiological Worker Dose Limits DOE Dose limits are provided in Table 1 and shall not be exceeded. These regulatory limits are established by 10CFR835 and LPR Lifetime Control Level LPR To administratively control a worker's lifetime occupational radiation exposure, a Lifetime Control Level of N rem is established, where N is the age of the individual in years. Special Control Levels LPR A Special Control Level for annual occupational exposure is established for each individual with a lifetime occupational dose exceeding N rem, where N is the age of the individual in years. This allows the individual's lifetime occupational dose to approach N rem as additional occupational exposure is received. -2- April 16, 1999

3 Table 1 Summary of Dose Limits Type of exposure Annual Limit Radiological Worker Whole Body (internal & external) Lens of the Eye Extremities (arms below the elbow or feet and legs below the knees) Any Organ or Tissue (other than lens of eye) Skin of Whole Body 5 rem 15 rem 50 rem 50 rem 50 rem Declared Pregnant Worker Embryo/Fetus (during gestation period) 0.5 rem in 9 months Minors and Students (under age 18) Whole body (internal & external) 0.1 rem Visitors and public Whole body (internal & external) 0.1 rem Notes: Internal dose to the whole body shall be calculated as committed effective dose equivalent. The committed effective dose equivalent is the resulting dose committed to the whole body from internally deposited radionuclides over a 50-year period after intake. Background, and therapeutic or diagnostic medical exposures are not to be included in either personnel radiation dose records or assessment of dose against the limits in this table. LANL uses the 100 mrem per year limit established by 10CFR for the general public, minors, workers without TLDs, and workers who have not received RadWorker training. You may wish to discuss the logic of having a lower limit for non-radiation workers than for an unborn child. A partial answer may be that, to the best of our -3- April 16, 1999

4 knowledge, a dose of 100 to 500 mrem per year is not harmful either to adults or to unborn children. -4- April 16, 1999

5 DOE EMBRYO/FETUS DOSE LIMITS Regulatory limits for the embryo/fetus are established by 10CFR and LPR When a female radiological worker voluntarily notifies her supervisor, Occupational Medicine Group ESH-2 or the Dose Optimization team of ESH-12 in writing that she is pregnant, the declared pregnant worker and her supervisor shall arrange for a mutually agreeable reassignment of work tasks such that further occupational radiation exposure is unlikely. For a declared pregnant worker who chooses to continue working as a radiological worker, radiation exposure shall be limited as follows: => The dose limit for the embryo/fetus from conception to birth (entire gestation period) is 500 mrem. => Efforts should be made to avoid exceeding 50 mrem per month. => If the dose to the embryo/fetus is determined to have already exceeded 500 mrem when a worker notifies her employer of her pregnancy, the worker shall not be assigned to tasks where additional occupational radiation exposure is likely during the remainder of the gestation period. (10CFR and LPR ) LANL ACTION LEVELS AND GUIDANCE FOR EMERGENCY SITUATIONS Action levels are established to keep doses well below the regulatory limits listed in LPR ESH-RADPR-DP-01 identifies the action levels for whole body dose (EDE), lens-of-theeye, extremities/organ/tissue, and the embryo/fetus. ESH-12 Dose Optimization Team provides notification to the following personnel when an action level is exceeded. The individual with the reported dose The individual s Group Leader The ESH-1 Team Leader assigned to the individual s technical area, and The LANL RPPM (radiation protection program manager) Refer to ESH-RADPR-DP-01 for the current action levels. Guidance levels for exposures in an emergency are from 10CFR and the LPR Exposure from Incidents or Emergencies a. 10 rem - Protecting major property (by volunteers) b. 25 rem - Lifesaving or protection of large populations (by volunteers) c. >25 rem - Lifesaving or protection of large populations (by volunteers fully aware of the risks). -5- April 16, 1999

6 (Dose limit to the lens of the eye: three times the above values, i.e. 30 and 75 rem; dose limit to the skin of the whole body and extremities: ten times the above values, i.e. 100 and 250 rem) LANL REQUIREMENTS FOR THE PREGNANT WORKER Once a female worker has declared her pregnancy in writing to her supervisor, ESH-2 and/or ESH-12 she will be instructed to wear her TLD badge in the area of her abdomen to assess the dose equivalent to the embryo or fetus. Supervisor and worker should arrange a mutually agreeable work assignment TYPES OF DOSIMETRY As a result of irradiation, some solid substances undergo changes in some of their physical properties. These changes amount to storage of the energy from the radiation. Since the energy is stored, these materials can be used for dosimeters. LUMINESCENCE Luminescent materials convert the energy from radiation to light, normally in the visible range. THERMOLUMINESCENCE (TL) Thermoluminescent materials store the energy from radiation and release it as light when the material is heated. "Thermo" means "heat" and "lumin" means "light". The property of thermoluminescence of some materials is the primary method used for personnel dosimeters at DOE facilities and LANL. THEORY OF THERMOLUMINESCENCE Electrons in some solids can exist in two energy states, a lower energy state called the "valence band" and a higher energy state called the "conduction band". The energy region between these two bands is called the "band gap". Normally in a solid, no electrons exist in the band gap. This is a "forbidden region". Electron Traps In some materials, defects in the material exist or impurities are added that can trap electrons in the band gap and hold them there. These trapped electrons represent stored energy for the time that the electrons are held. This energy is emitted as light photons when the material is heated and the electron returns to the valence band. This property is called thermoluminescence. -6- April 16, 1999

7 OBTAINING RESULTS FROM TLDs When sufficient heat is applied to a thermoluminescent material the trapped electrons are released. This release results in the production of light in the form of a "glow curve" which is detected in a TLD reader. The light output is detected and measured by a photomultiplier tube and is proportional to the dose recieved. The dose is then calculated from this light output. The heating process used to read the TLD also results in clearing out the traps and zeroing the TLD for future use. TLD readers are used to quantify the doses received by the TLDs. Each reader system consists of a transport module that automatically loads the TLD cards, identifies the owner, and reads and records the data. Light output data Photo- Multiplier Tube High-Voltage Supply Temperature measurement Suitable Optical Filter TLD Material Thermocouple Heater Power Source TLD Reader -7- April 16, 1999

8 ADVANTAGES AND DISADVANTAGES OF TLDs Advantages => Able to measure a wide range of doses (10 mrem to 1000 rem). => Doses may be easily obtained on site. => Quick turnaround time for readout => Durable, rugged. => Reusable. Disadvantages => Once it is read, the data are lost; the readout zeros the TLD TLDs USED AT LANL The TLD materials used in the Los Alamos badge are lithium fluoride (LiF) and calcium fluoride (CaF). Lithium has two stable isotopes, 6 Li and 7 Li. 6 Li is sensitive to neutrons, but 7 Li is not. Neutrons interact in 6 Li to give tritium and alphas via the reaction: 6 Li(n,alpha) 3 H. In fact the reason that 6 Li is a special nuclear material (SNM) is that this same reaction is used for the production of tritium for nuclear weapons. The LANL TLD has two cards, each with four chips of LiF or CaF. The top card measures betas and gammas, the bottom card measures neutrons. Beta and Gamma Dosimetry The top two TLD chips are behind the mylar windows at the top of the badge. One mylar window is twice as thick as the other. This allows some energy discrimination of betas and soft x-rays. These two chips measure the shallow dose (see lesson , page 20.) The next row of TLD chips is behind a layer of plastic about 600 mg/cm 2 thick. These chips are designed to measure deep dose or whole-body dose (see lesson , page 20). One of these is 7 LiF, the other is CaF. Both of these measure gamma dose. CaF is more sensitive to low energy gammas than 7 LiF. Neutron Dosimetry The TLD-700 chip, made with 7 LiF, is sensitive to betas and gammas; the TLD- 600, made with 6 LiF, is sensitive to betas, gammas, and neutrons. The neutron dose is calculated from the difference of a TLD-600 and TLD-700 pair. The bottom card uses four TLD chips, arranged as two pairs, to measure neutron dose. One TLD-600 and TLD-700 pair is shielded from the front with cadmium (Cd), which absorbs thermal neutrons. A second pair is shielded with Cd from the rear. -8- April 16, 1999

9 The readings from these four TLD chips is combined into an overall calculation of neutron dose. Albedo neutron dosimetry The word "albedo" means "reflected" or "white"; (it is related to the word "albino"). In the case of neutron dosimetry, it refers to the measurement of neutrons that are moderated and reflected from the body. The LANL TLD uses the principle of albedo neutron dosimetry. The TLD600 and TLD700 pair that are shielded at the front with cadmium are designed to detect albedo neutrons reflected from the body. TLD Cards Pink CaF Blue April 16, 1999

10 OTHER NEUTRON DOSIMETERS It is more difficult to measure the true dose equivalent from neutrons than from beta and gamma radiation. This is primarily because of the different quality factors for different neutron energies. Also, it is difficult to find a material that responds to neutrons in the same way as human tissue. Additional dosimeters are therefore usually designed to measure neutrons of different energies. PN-3 Track-etch dosimeter The PN-3 track-etch dosimeter replaces NTA dosimeter for high-energy neutrons (> 5 MeV, e.g. at the LANSCE accelerator). High-energy neutrons knock protons out of hydrogen atoms or other light nuclei. The recoil protons cause secondary ionization. A chemical bath etches the track left by the recoil proton. These etched tracks scatter light in the automatic reader. The amount of scattered light is proportional to the number of tracks, which is proportional to the neutron dose REQUIREMENTS FOR USE OF TLDs (10CFR (a) & (d) and LPR ) Personnel dosimetry is required for personnel who may receive an occupational external whole-body dose equivalent of 100 mrem/year. Recall that this is the limit for members of the public and anyone who is not a RadWorker (see Table I). This is also the limit for a Controlled Area (see RCT lesson 2.10). TLDs are usually required for entry into a Controlled Area which is controlled for external radiation. Dosimeters shall be issued only to personnel formally instructed in their use, and shall be worn only by those to whom the dosimeters were issued. Personnel shall return dosimeters to the dosimeter custodian in their group for processing monthly or quarterly, as required. If they don't, they may be restricted by line management from radiological work until the dosimeters are returned. Personnel shall wear their primary dosimeters on the chest area, between the waist and the neck. Personnel should not expose their TLDs to security x-ray devices, excessive heat, or medical radiation sources (e.g., diagnostic x-rays, or diagnostic or therapeutic nuclear medicine procedures). If a TLD is accidentally exposed, ESH-4 should be informed April 16, 1999

11 A person whose dosimeter is lost, damaged, or contaminated should place work in a safe condition, exit the area, and report the occurrence to the RCT and their supervisor. The person's line manager is required to complete a Lost Dosimetry Badge Report. Reentry of the person into Radiological Buffer Areas will not be made until a review has been conducted, or line management has approved reentry, and the dosimeter has been recovered or replaced. Under exceptional circumstances, a temporary TLD could be issued to a worker who has lost his TLD. Personnel shall not wear dosimeters issued by LANL while being monitored with a dosimeter at another off-site location. Temporary dosimeters for special assignments may be issued for off-site use with prior approval of ESH-4. Temporary TLDs may be obtained from a dosimeter custodian (the same person who distributes and collects the TLDs) or from ESH-4. These are also issued to visitors, and are accompanied by a 5" by 8" card (a "TBI" card, form 972) to identify who used it and why. See ESH-4 procedure HS-4-PDO-DP-21. Temporary TLDs may also be used for special studies, such as measuring how much dose a worker receives on a particular job, or measuring the dose at a particular location. Multiple dosimeters may be issued to personnel to assess whole-body exposure in nonuniform radiation fields, i.e. when the dose to a portion of the whole-body will exceed the dose to the primary dosimeter by more than 50% and the anticipated whole-body dose equivalent is >100 mrem. Extremities a. Hands b. Arms below the elbows c. Feet d. Legs below the knee Wrist dosimeters containing TLD-700 chips are used at LANL to measure extremity radiation dose of radiation workers. These may be obtained, on request, from ESH-4. A radiation worker whose extremity dose equivalent might exceed 5 rem per year should be issued a wrist dosimeter, or it can be required on a radiation work permit (RWP). Wrist dosimeters are worn on either wrist, with the active "chip" facing the palm. Wrist dosimeters are typically exchanged monthly. TLDs are processed by ESH-4, and the results reported to ESH-12 and the line organization. Readings less than 10 mrem are reported as zero April 16, 1999

12 A worker is guaranteed access to her/his own records at any time (see 29CFR ). Since these results are personal, they are treated as sensitive information, but they are available to RCTs who have a need to know. Contact ESH-12 for details April 16, 1999

13 PERSONAL (CRITICALITY) NEUTRON DOSIMETERS Personal nuclear accident dosimeters are required by 10CFR for facilities possessing sufficient quantities of fissile materials to potentially constitute a critical mass (e.g. 500 grams of plutonium). LANL uses a small dosimetry package known as a PND (Personal Neutron Dosimeter) or PNAD (Personal Neutron Accident Dosimeter). The PND packet consists of 2.5 by 0.75 inch clear plastic holder containing three foils and one pellet. a) 1 bare indium foil for thermal neutrons b) 1 cadmium covered indium foil for fast neutrons c) 1 copper foil for intermediate and fast neutrons d) 1 sulfur pellet for fast neutrons These materials undergo neutron activation when they are exposed to neutron radiation, such as that produced in a criticality accident. Each material is sensitive to a particular range of neutron energies. The amount of radioactivity induced in the four materials indicates both the levels and energies of the neutrons involved. In the event of a criticality accident, the neutron dose received by an individual can also be estimated from the neutron activation of hair: 32 S(n,p) 32 P and blood: 23 Na(n,gamma) 24 Na SELF-READING DOSIMETERS Supplemental dosimeters are discussed in the procedure ESH The most commonly used is the "pencil dosimeter" ion chamber illustrated later in this section, also called a "pocket chamber" or "pc". Required for entry into High or Very High Radiation Area Must be worn with a TLD Used to provide immediate estimate of a person's exposure to X or gamma radiation, only. Calibrated with Cs-137 (see procedure ESH4-ICS-DP-19). Before it can be used the chamber must be charged to a predetermined voltage so that the scale reading indicates 0. As the chamber is exposed to radiation, the charge is dissipated, causing the scale reading to increase. Pocket chambers contain a quartz fiber electroscope that can be read on a scale by holding the pocket chamber up to the light. The total integrated dose can be checked periodically simply by noting the degree of discharge of the chamber as indicated on the electroscope April 16, 1999

14 Workers should be instructed to check their self-reading dosimeters periodically, and report to an RCT if the reading exceeds 75% of full scale, or if it exceeds the planned dose. Note that a pc may discharge if it is dropped or hit. Since a charged pc reads zero and a discharged pc reads high, this could cause an individual worker's pc to read off-scale, thus indicating a large dose. For the RCT's response, see RCT lesson Each facility keeps a "supplemental dosimetry issue sheet" and a "dose tracking report" to document the data obtained from self-reading dosimeters. When the TLD results are available (every month) the results must be compared by the RCT. A difference of more than 50% must be investigated as discussed in ESH section 7.3, and a Radiological Incident Report (LP107.01) must be generated if the difference is not resolved. Class discussion: what reasons might cause a discrepancy between a pc and TLD? -14- April 16, 1999

15 Pencil Dosimeter Window Assembly Polythane End Cap Eye Lens Pocket Clip Sleeve Graticule Field Lens Cover Tube Microscope Body Objective Lens Fiber Airwell Shroud Main Body Earth Tag Electrode Condenser Charger Pin Charging Bellows Condenser Shroud Polythane End Cap Milliroentgens April 16, 1999

16 Frame Radiation 180 V V V Fixed Positive Electrode Dosimeter is fully charged. Reading is 0 milliroentgens. Dosimeter is partially charged. Radiation is causing ionization in the chamber. Reading is 95 milliroentgens. Dosimeter is effectively discharged. Reading is 200 milliroentgens. Note that some charge remains. A completely discharged dosimeter (0 charge) gives an off scale reading. Pencil Reading -16- April 16, 1999

17 Neutron Bubble Dosimeters Used for immediate read out of neutron exposure. Consists of a clear plastic tube containing superheated freon suspended in a soft polymer. Neutron interaction (n,p) causes formation of a bubble. The number of bubbles depends on the total neutron exposure, i.e. the number of bubbles per mrem is a constant ALARMING RADIATION DETECTORS Pocket chirpers are suitable for supplemental use only and should always be worn in conjunction with a TLD badge. They are used mainly to warn the wearer of high gamma exposure rates They do not measure total gamma radiation doses, so they should not be called "dosimeters". The most common models used at LANL are: a) Eberline RT-1 (rad-tad) b) Victoreen Tattler c) Nuclear Measurements Monilert d) NMC Wee Pocket Chirper These chirpers range in response frequency from 2 to 20 chirps/minute for 1 mr/hour. Chirpers use GM tubes, which generally over-respond to low energy gammas (see lesson 2.16). Alphas, betas, and very low energy gammas will not penetrate the metal housing. Siemens and Aloka Electronic Dosimeters Electronic dosimeters such as those made by Siemens or Aloka are increasingly used at LANL. These combine the features of a self-reading dosimeter and an alarming dosimeter. Over time the pc will be replaced by the Siemens Electronic Personal Dosimeter (EPD). While the EPD is much bulkier than the pc it has many advantages. Some of these are: 1. Digital display of: accumulated shallow dose accumulated penetrating dose shallow dose rate, and penetrating dose rate 2. Alarms can be set for two different levels of: total accumulated dose, and dose rate -17- April 16, 1999

18 3. The EPD is sensitive to both beta and photon (gamma and x-ray) Photons (except for pulsed photons) with energies of: 20 kev MeV (± 30% accuracy) 1.5 MeV - 10 MeV (± 50% accuracy) Averaged beta energy 250 kev MeV (± 30% accuracy) (see Siemens Electronic Personal Dosimeter technical handbook) Disadvantages of electronic dosimeters are they are sometimes affected by cellular phones or radios, and they under-respond in pulsed fields such as from a flash x-ray device BIOASSAY So far this lesson has mostly discussed the measurement of external dose, but the doseequivalent limits listed in Table I are for the total, i.e. the sum of external and internal. Bioassay is the term used for the assessment of the internal dose which results from the radioactive material present in the body (see RCT lessons 1.11 and 1.12). Bioassay methods may be classified as: in vivo and in vitro. In vivo means in living tissue (compare with the Spanish and Latin words: "vivo" means "to live"). In vitro means in glass (compare with the Spanish and Latin words: "vidrio" means "glass"); glass bottles were used before the days of plastic bottles. Bioassay programs are designed to fulfill two needs: 1) Evaluate potential consequences of accidental intake of radioactive materials. This can involve all types of bioassay measurements, e.g. wound counts, or collection and analysis of nasal, urine, blood, and fecal samples. 2) Evaluate effectiveness of routine contamination control practices. This involves routine bioassay programs for workers in facilities where the possibility of intake exists, and also initial and termination whole body counts The need for bioassay is evaluated via the Health Physics Checklist. Anyone who may need routine dosimetry or bioassay, or whose dosimetry status may have changed, should complete the Health Physics Checklist form, obtained from ESH April 16, 1999

19 IN-VIVO MEASUREMENTS In vivo techniques consist of direct measurements of gamma or X-radiation emitted from the body or from specific organs (lung, thyroid, etc.). This method is very useful for any radionuclide which emits (or has daughters which emit) photons of sufficient energy to escape the body. The photon flux density must be large enough for measurement in a reasonable time period, even though the quantity of material in the organ may be very small. This method is possible only for those radionuclides emitting penetrating radiation, i.e. gamma. If the whole body counter has been calibrated, one may rapidly determine the identity and amount of radionuclides that emit medium- or high-energy gammas. Most beta emitters also emit gammas. (Class exercise: use the chart of the nuclides to find the exceptions; look for colored squares, i.e. half lives > 1 day, and look below the line of stability, for nuclides with atomic numbers 1 to 18). Some pure-beta emitters can be detected by their daughters, e.g. Sr-90 and Y-90. Most alpha emitters are also detected by looking for the gamma emission from the daughters. Plutonium (Pu) is especially difficult. It is usually detected by looking for the 60 kev gamma from Am-241, but Am-241 comes from the decay of Pu-241, which is plentiful in reactor grade Pu but not in weapons grade Pu. A whole body count is very sensitive, especially to external contamination on the surface of the skin, hair, or clothing. Internally deposited radionuclides are partially shielded by the body, so the detectors are designed to be very sensitive. External contamination is not shielded, so very small amounts will be detected. A whole-body frisk with a hand held instrument and a PCM are far less sensitive than the in-vivo whole-body counters. If a worker has small amounts of contamination on the skin that are too small to be detected by an RCT, this will be counted by the whole-body counters, and give misleading results. Consequently, personnel must shower thoroughly and change into clean clothing before a whole-body count. A few percent of whole-body tests show a "false positive", i.e. because the count is reported at the 95% C.L., some counts will show a positive result because of random statistical fluctuations (see RCT lesson 2.03). In these cases, the person will be called for a recount. Estimations of very small quantities require elaborate shielding of both the detector and the worker, sensitive detectors, and the best discrimination between gamma ray energies. At LANL, the whole-body counter in the sub-basement of the HRL building is shielded with eightinch thick steel walls. The steel was obtained from world-war-ii battleships, to ensure that the steel does not contain trace amounts of plutonium or fission products. The detector system includes germanium (GeLi and HPGe) and sodium-iodide (NaI) detectors for high resolution gamma detection (see RCT lesson 2.19). This system is capable of measuring: => Radioiodine in the thyroid gland. => radionuclides in the chest. => radionuclides in the intestine April 16, 1999

20 ESH-4 also has several sodium-iodide (NaI) wound counters, e.g. at LAMC and at the ESH-2 building. With wounds, much of the material is usually near the surface, so radionuclides that do not emit highly penetrating radiation may be detectable. But note that alpha radiation is shielded by a thin layer of water (e.g. if the wound has been washed) or blood. IN VITRO MEASUREMENTS The amount of material present in the body may be estimated using the amount of materials present in excretions or secretions from the body. Samples could include urine, blood, breath, sputum, sweat, saliva, hair, nose swipes, tissue and feces (fecal). The most common of the in-vitro measurement involving an RCT is the nose swipe. Nose swipes are taken whenever there is any suspicion of internal intake by inhalation, e.g. after a CAM alarm, after working in Airborne Radioactivity Areas, when a person has contamination on his skin or personal clothing, especially the face, etc. Some RCTs obtain nose-swipes whenever a worker removes a respirator. To take a nose swipe: Obtain suitable swabs such as Q-tips, and labeled containers such as cardboard boxes. Ensure that the swabs are handled only with clean hands, to avoid the possibility of crosscontamination. Moisten two swabs, one for each nostril, and gently wipe the inside the nostrils. Place the swabs in labeled containers, and send them to HPAL for analysis. Calculations of committed and effective dose equivalents are estimates. Calculation requires knowledge and use of metabolic models which allow the sample count to be related to the activity present in the body. Also, standard values from reference man are used for the mass of particular organs, etc., in lieu of actual values for the individual involved. Remember that the values for reference man and reference woman are average numbers. BIOASSAY PROGRAMS Routine Evaluations A routine bioassay program is set up for personnel who work on a regular or intermittent basis with at least 1 Ci of tritium oxide, or who work on systems that have contained at least 1 Ci of tritium, 0.1 Ci of tritium oxide, or 0.1 Ci of organic tritium. All participants must submit urine samples every two weeks. In addition to the routine tritium bioassay program, special samples are collected in all off-normal situations when an uptake is suspected. A urinalysis program has been established for personnel performing "hands-on" work with uranium. Participants in the routine sampling program must submit spot urine samples (at least 100 ml in volume) for analysis on a scheduled basis every 2 weeks. The mode of intake most frequently encountered is inhalation April 16, 1999

21 A urinalysis and fecal program has been established for personnel working with plutonium. Two urine samples per year are required from plutonium workers in areas with significant exposure potential. For personnel who experience more casual encounters with plutonium, routine sampling at the rate of once per year, or a single baseline sample is sufficient. A urine sample consists of voiding 4 times, usually on two consecutive days, before going to bed at night and on arising in the morning. (This is commonly called a "simulated 24-hour sample") Annual Sampling- Taken on personnel routinely performing chemical or metallurgical operations with less than 10g of 239 Pu, 242 Pu, or less than 0.04 g of 238 Pu Semiannual Sampling- Taken on personnel routinely performing chemical or metallurgical operations with 10 g or more of 239 Pu, or 242 Pu, or 0.04 g or more of 238 Pu (approximately 0.6 or 0.8 Ci of either isotope) A urinalysis and fecal analysis program is established for workers exposed to Americium. Workers who perform chemical, metallurgical, or disposal-packaging operations with mixtures of materials containing 241 Am at greater than 2.2% by weight must submit two urine samples per year as needed. Special Evaluations: During an off-normal situation, different procedures may be followed. Tritium- for a minor or severe uptake the individual must (1) notify the RCT (2) completely empty his/her bladder without collecting a specimen, and (3) after approximately 2 hours, collect a spot urine sample and submit it to the RCT. Uranium, plutonium, americium- During an off-normal situation, personnel are required to submit special, nonroutine, spot urine samples on the day following the incident. This takes effect when exposure to high airborne concentrations has occurred (as detected by air sampling or nose swipes over 100 disintegrations per minute or high skin contamination, over 10,000 dpm). Class discussion. After an accident in which a worker had an uptake of radioactive material, could you obtain a urine sample immediately and send it for analysis? Why, or why not? SUMMARY An understanding of the method of operation of dosimeters is important for Radiological Control Technicians. RadCon personnel are the first line of defense against abuse of dosimeters and must ensure the proper wearing and use of them. Internal exposure involves a source (contaminant) inside the body. It is more difficult to measure; sophisticated whole body counters or indirect measurements of excreta samples are required to obtain an estimate. The dose from the contaminant does not stop when the person leaves the radiation field and the contaminant continues -21- April 16, 1999

22 to irradiate tissue continuously. If necessary, medical treatment can be administered to enhance the removal of the source material from the body. Alpha radiation poses the biggest obstacle to effective measurement and treatment April 16, 1999