RADIATION SAFETY IN RADIOLOGY, Lecture notes of Biosafety

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MICHIGAN STATE UNIVERSITY

RADIATION SAFETY

MANUAL

OFFICE OF RADIATION, CHEMICAL

AND BIOLOGICAL SAFETY

C124 Research Complex - Engineering

July 1, 1996

NOTICE TO RADIOACTIVE MATERIALS

USERS

The Radiation Safety Manual and further

radiation safety information can be

found or viewed at the following locations:

•Principal investigator

•Department safety representative

•ORCBS WWW Home Page

http://www.orcbs.msu.edu

See Radiation Safety

•ORCBS 355-

APPENDICES

• Preface.....................................................................................
• The Michigan State University Broad Scope License................................
• The Radiation Safety Committee
• Approvals for Use of Radioactive Materials
• Responsibilities of the Principal Investigator
• Responsibilities of the Worker..........................................................
• Sanctions for Non-Compliance.........................................................
• Training....................................................................................
• Ionizing Radiation Theory...............................................................
  • Radioactive Decay...............................................................
  • Radiation Units
• Biological Effects of Radiation
  • Tissue and Cell Sensitivity to Radiation
  • External and Internal Radiation Exposures...................................
• Laws and Regulations Concerning Radiation.........................................
  • ALARA...........................................................................
  • Maximum Permissible Exposure
  • Personnel Monitoring...........................................................
  • Minors Working with Radioactive Material
  • Pregnant Radiation Workers
  • Exposure Limits for the General Public
  • Area Restrictions
  • Labeling Requirements
  • Bioassays.........................................................................
  • Ordering Radioactive Materials
  • Receiving and Monitoring Radioisotope Shipments
  • Transfer of Radioactive Materials
  • Food and Drink Policy..........................................................
  • Security of Radioactive Materials..............................................
  • Inventory of Radioactive Materials............................................
  • Shipment of Radioactive Materials
  • Terminating Employment.......................................................
  • Leak Tests of Sealed Sources..................................................
  • Radiation Safety for Machine Produced Radiation
  • Principal Investigator Absences
• Radiation Laboratories...................................................................
  • Laboratory Design and Equipment
  • Clean Laboratory Conditions and Containment..............................
  • Unattended Operations..........................................................
  • Monitoring Instruments.........................................................
  • Calibrations
  • Radiation Surveys...............................................................
• Practical Radiation Protection...........................................................
  • Routes of Exposure to Radiation
  • Monitoring Operations Involving Radioactive Materials....................
  • Time, Distance and Shielding..................................................
  • Protective Equipment
  • Airborne Radioactive Materials
• Disposal of Radioactive Waste..........................................................
  • Quantifying Levels of Radioactivity in Waste................................
• General Rules for Radiation Safety
• Radiation Incidents/Emergencies
  • Handling Radioactive Incidents/Emergencies................................
  • Decontaminating Radioactive Material
• Application For Approval
• Carbon-14.................................................................................
• Chromium-51.............................................................................
• Hydrogen-3
• Iodine-125.................................................................................
• Phosphorus-32
• Phosphorus-33
• Sulfur-35
• Directions for Conducting a Radiation Safety Survey
• Iodination Safety Tips
• Laboratory Classification Table.........................................................
• PI Training Checklist
• Pointers for Handling Radioactive Waste
• Pregnant Radiation Workers Policy....................................................
• Properties and Exposure Rates of Some Common Beta Emitters
• Radiological Units........................................................................
• Radioisotopes Common at MSU
• Security and Storage of Radioisotopes
• Survey Form Used By Michigan State University
• Transporting Instructions for Radioactive Material...................................
• References and Other Resources
• Glossary...................................................................................

Preface

In every facility where hazardous materials are utilized, it is necessary to maintain a policy document which establishes specific methods and procedures to develop and maintain safety and compliance. Safety is the practice of a set of rules, guidelines and procedures which protect workers, facilities, the general public and the environment. Compliance is the maintenance of procedures, practices, documents and records which demonstrate that federal, state and local laws and regulations are not compromised. It is a necessary challenge for all administrators, safety committee members, faculty, staff, students and workers to maintain safety and compliance. In laboratory and research facilities, the challenge is accentuated with the myriad of procedures and materials utilized, and the continuous change and evolution of these conditions.

This document will serve as a guide to meeting this challenge by defining the structure, policy, procedures, responsibility and regulatory stance set forth by the U.S. Nuclear Regulatory Commission (NRC), the State of Michigan, the Michigan State University NRC license, the Radiation Safety Committee (RSC), and the Office of Radiation, Chemical and Biological Safety (ORCBS). However, it is important that all principal investigators and workers remember that the burden of daily compliance and safe practices is their own, and that they are the most critical link in the maintenance of these goals.

The Office of Radiation, Chemical and Biological Safety gives many thanks to the University of Michigan Radiation Safety Service team for providing information for the Radioisotope Fact Sheets, to Larry Chapin, Department of Animal Science for the Iodination Emergency Procedures, to Reginald Ronningen, Cyclotron Physicist and RSC member for the many hours of review, discussion and assistance with this document; to the Radiation Safety Committee for their valuable input and review, and finally, to the Radiation Safety staff at the ORCBS, who did the lion's share of the work.

The Michigan State University Broad Scope License

Michigan State University operates under the U.S. Nuclear Regulatory Commission License Number 21-00021-29. This license is a large scale non-fuel cycle Type A broad scope license. Type A broad licenses may only be given to large facilities who have a long history of radioactive materials use with a good safety record. It allows Michigan State University the privilege of using large varieties of radioactive materials. Large amounts of activity are authorized and may then be used in many locations, with many procedures and users that change frequently. The broad license confers authority upon the University to approve, manage and control the receipt, use and disposal of radioactive materials. In fact, the University acts to "police" itself under the authority given in a broad license.

The broad license has one feature which must always be remembered by each radioactive materials user: there is only one license for the entire university, and any individual or action which jeopardizes the license endangers the permission of all researchers to utilize radioactive material at MSU. If, for any reason, the license is suspended or terminated, no individual or principal investigator may use radioactive materials of any kind until the license is reinstated. Therefore, this license places significant responsibility on each individual who uses radioactive materials to conform with safe work practices, and to conduct and complete all required compliance duties, however large or small they may be.

Responsibilities of the Principal Investigator

Principal investigators are directly responsible for compliance with all regulations governing radiation safety in the laboratory, and for safe practices of individuals working under their supervision. Principal investigators are obligated to:

1. Ensure that individuals working under their control are properly supervised and trained to enable safe working habits and prevent exposures to themselves and others and/or contamination of the work areas or environment. Inadequate supervision and lack of training have been cited as indicative of negligence in lawsuits involving radiation.
2. Be aware of the potential radiation hazards inherent in a proposed activity; be responsible for instructing personnel in safe practices or directing personnel to sources of information concerning safe practices.
3. Maintain inventory and knowledge of the various forms (physical and chemical) and quantities of radiation which are present in their work areas.
4. Avoid any unnecessary exposure, either to themselves or to other workers.
5. Understand the risks associated with the possession, use and shipment of all radioactive materials. Federal and state regulations control the use and shipping of radioactive materials and certain other hazardous materials.
6. Keep current records of the receipt and the disposition of radioactive material in their possession including use in research, waste disposal, transfer, storage, etc.
7. Maintain constant surveillance and immediate control of radioactive materials to prevent unauthorized removal or tampering, and/or assure that all of the workers occupying the area maintain security.
8. Post warnings and restrict entry to areas that contain potentially hazardous radioactivity or chemicals. Label radioactive use equipment and work areas.
9. Notify the ORCBS of any personnel changes, including addition or termination of employees, or changes of areas where radioactive materials may be used or stored.
10. Assure instruction of female radiation workers of the risks associated with working with radioactive materials during pregnancy. (NRC Reg. Guide 8.13).
11. Assure designation of a responsible individual to oversee radioisotope work during short absences, and of a stand-in principal investigator with the required committee approvals during extended absences (greater than 60 days).
12. Ensure that radiation safety surveys and audits in the laboratory are conducted, and maintain records for review.
13. Be aware of regulations and requirements pertaining to the use of radioactive materials, maintain compliance and a safe working area.
14. Use radioactive materials according to statements, representations and conditions set forth in the radioactive materials use approval given by the Radiation Safety Committee. Changes from the approved procedures must be approved by the Committee in an amendment or new application prior to the implementation of the change.
15. Maintain use logs for radioisotopes with half lives of ≥ 120 days.

Failure to comply with the rules and regulations set forth above and throughout this manual may lead to disciplinary actions and/or the cessation of radioisotope shipments and experiments. The Radiation Safety Officer and/or the Radiation Safety Committee may terminate any radioisotope use and/or research if deemed necessary. Suspension or termination of approval to use radioactive materials may result from situations jeopardizing health and safety, the environment or the MSU broad license.

Radioactive shipments which are ordered during a principal investigator's absence will be tracked under the absent principal investigator's inventory.

Responsibilities of the Worker

Individuals who use radioactive materials assume certain responsibilities in their work. The individual worker is the "first line of defense" in protection of people and the environment against undue risks of radiation exposure and/or contamination. Since the workers, themselves, are the direct handlers of the radioactive material, the final responsibility lies with them for safety and compliance with laws and regulations. For this reason, it is critical that they be aware of the risks, safe practices and requirements for use of radioactive materials.

The term "worker" is used by the university to identify an individual who uses radioactive material in the course of his/her employment or study with the university. Workers may be principal investigators, graduate students, undergraduate students, technicians, post-doctorates, visitors, or any other individual who will handle radioactive material. The following items are to be adhered to at all times by radiation workers.

1. Each worker must attend the entire ORCBS training class, including radiation and chemical safety. Workers are prohibited from handling radioactive materials until this class has been completed. Radiation workers must attend a refresher session each year.
2. The worker must complete the radiation safety examination and pass with a score of 75% or better. Workers are prohibited from handling radioactive materials until this has occurred.
3. Workers are responsible for adhering to all laws, rules, regulations, license conditions and guidelines pertaining to the use of radioactive materials.
4. Workers must wear their assigned radiation dosimeter during uses of radioactive materials. (See Personnel Monitoring for details on dosimeter requirements.)
5. Workers must practice ALARA (As Low As Reasonably Achievable) in their work, and minimize the potential for exposures, contamination or release of radioactive materials.
6. Radiation work areas must be monitored by the user after each use of radioactive material. If contamination is found, it must be cleaned up.
7. No changes in experimental procedures using radioactive materials are to occur without the approval of the principal investigator. Do not take short cuts. Changes in experimental procedures impacting upon safety (higher quantities, higher risk, use in animals, etc.) must be approved by the MSU Radiation Safety Committee.
8. Any abnormal occurrence must be reported immediately to the principal investigator, such as spills, significant contamination, equipment failure, loss of radiation dosimeters and unplanned release. If the principal investigator cannot be reached, contact the ORCBS Health Physics staff.
9. It is the responsibility of the worker to clean any contamination or spills that occur in their work area. DO NOT LEAVE IT FOR ANOTHER PERSON TO CLEAN UP.
10. Workers are responsible for returning the radiation dosimeter on time and reporting any loss or contamination of the dosimeter to the ORCBS.
11. Workers are responsible for informing the ORCBS of any exposures which have occurred at a previous employer when beginning employment at MSU. They are also responsible

Severity Level III: A serious violation, but does not present immediate risk to health, safety, the environment or the license.

Severity Level IV: A violation, but not serious. Poses little risk to health, safety, environment or license.

Severity Level V: A minor violation; typically something in lesser technical matters, such as record keeping errors of minor impact. Poses no immediate risk to health, safety, environment or license, but is a compliance issue which may lead to increased concerns or is a minor technical violation.

Note: Any violation, when seen repeatedly, may be escalated to a higher severity level. Repeat violations can be interpreted as a disregard for safety regulations and must be dealt with quickly and effectively to avoid undue risks of exposure or jeopardization of the NRC broad license.

SANCTION ACTIONS FOR NONCOMPLIANCES IN RADIATION SAFETY

Implemented November, 1993

Severity

Level

Possible Resulting Action

I - V Violations noted on ORCBS surveys and sent to PI. All violations handled this way.

I - V Written corrections required of PI and maintained in laboratory record books for review.

IV, V Health physicist contacts principal investigator and discusses problem(s) and correction.

I - V Require that involved personnel attend safety class again.

I - V Increase ORCBS surveillance.

I - V Increased surveillance required of laboratory staff.

I - V Letter to principal investigator from health physicist.

I, II Letter to principal investigator from Radiation Safety Officer; response is required in writing.

I-III Place restrictions on individual(s) causing non-compliances.

I-III Suspend shipments of radioactive materials to principal investigator.

I, II Require principal investigator to appear before committee.

I, II Decrease scope or limits of radioactive materials approval.

I, II Require principal investigator to reapply for radioisotope use.

I, II Confiscate radioactive materials in possession of principal investigator.

I Permanently terminate approval to use radioactive materials.

SEVERITY LEVELS FOR VIOLATIONS FOUND IN

RADIATION SAFETY INSPECTIONS

November, 1993

Severity Level

No. Compliance Requirement

V 1. NRC "Notice To Employees" and "Licensing and Regulation Information" are

posted.

I - III 2. Radioactive materials are under the constant surveillance and immediate control of

licensee, or otherwise secured to prevent tampering or unauthorized removal.

I - III 3. Radiation users are adequately trained for the functions performed.

I - III 4. Surveyed areas are free of contamination.

I - IV 5. Laboratory equipment is functional and is used correctly.

III - V 6. Laboratory radiation surveys are accurate and frequency is appropriate.

I - IV 7. Food and other consumable items are not present in the radioisotope and chemical

use/storage areas.

I - V 8. Radioisotope work and storage areas and equipment are labeled adequately.

I - IV 9. Radioisotope sources/stock solutions are labeled adequately.

I - III 10. Radioactive waste is manifested on both sides of the tag, secondary containment for

liquids.

I - V 11. Shielding is adequate (material, thickness, positioning).

I - V 12. Dosimeters, if assigned, and appropriate protective equipment are used during

radioisotope handling.

I - V 13. Fume hoods are used properly (sash setting, uncluttered, rated for radioisotope use).

Training

It is mandatory that all workers, including principal investigators, be certified prior to the use of radioactive materials. Certification is obtained by attending the introductory ORCBS training class and passing the radiation safety examination. All radiation users/handlers, including principal investigators, must attend both the radiation safety and chemical safety parts of the class, since it is impossible to use radioactive materials without also using chemicals routinely or intermittently.

Initial training must contain minimally the items listed in Title 10, Code of Federal Regulations, Part 19.12 (10 CFR 19.12), Training for Radiation Workers. The ORCBS offers a training class in radiation safety; this covers the necessary topics. Annual retraining is required for all users of radioactive materials (including principal investigators); multiple sessions are offered in many campus locations each year by the ORCBS.

This is important for many reasons. When deposited in the human body, the half life of the radioactive material present in the body affects the amount of the exposure. If the radioactive material contaminates a workbench or equipment, and is not removable, the amount of time before the contaminated items may be used again is determined by the radioactive half-life. Radioisotope decay using half-life minimizes costs and concerns in radioactive waste management.

The equation which is used to calculate radioactive decay is shown below.

A = A 0 e - λ t

Where: A = Current amount of radioactivity A 0 = Original amount of radioactivity e = base natural log ≈ 2. λ = the decay constant = 0.693/t1/2 (where t1/2 = half-life) t = the amount of time elapsed from A 0 to A

It is important to be careful of the units used for the time. Days, hours and years must not be mixed in the calculation.

Radiation Units

Two types of units are used for radiation, units of activity and units of exposure (dose). Units of activity quantify the amount of radiation emitted by a given radiation source. Units of exposure quantify the amount of radiation absorbed or deposited in a specific material by a radiation source.

In the world today, two sets of units exist. They are the Special units (Curie, Roentgen, Rad and Rem) and the SI or International Units (Becquerel, Gray and Sievert). In the United States, the Special units must be used as required by Federal law. Therefore, in our discussions the units used will always be the Special units. SI units are defined and described in the appendix on units.

Units of Activity The unit of activity for radiation is the Curie, abbreviated Ci. Most laboratory facilities use only millicurie (mCi, 0.001 Ci) or microcurie (uCi, 0.000001 Ci) amounts of radioactive materials, since reliable data can only be obtained using low levels of activity for a given isotope. The Curie

is an amount of radioactive material emitting 2.22 x 10 12 disintegrations (particles or photons) per minute (DPM). (The international, or SI, unit for radioactivity is the Becquerel, defined as one disintegration per second.) Activity can be measured with an appropriate radiation detection instrument. Most of these measurements are made with a liquid scintillation counter, gamma well counter or Geiger-Mueller (GM) survey meter with appropriate detection probes. These instruments detect a percentage of the disintegrations and display in counts per minute (CPM).

It is important to note that the CPM readings from survey instruments are not the true amount of radiation present, since there are factors which decrease the detection capability of even the most sensitive instruments. Two factors influence radiation detection sensitivity: the geometry of the counting system and the energy of the radionuclide being measured. Lower energy radionuclides are detected with lower efficiencies than higher energy radionuclides. Detection instruments are calibrated with known sources with different energy levels to determine the efficiency of the instrument in order to account for these variables.

Therefore, in order to correct for the above sources of error in the measurements, a calculation must be made to standardize the units of activity used in all facilities licensed by the NRC. It is

required by NRC law that all records relevant to NRC licensed activities must be maintained in units of DPM or microcuries. To make the necessary conversion to the microcurie unit, the following formula must be used in all records of surveys, waste materials or radioactive solutions generated within the facility.

CPM/Efficiency = DPM DPM/2.22 x 10^6 = uCi

Units of Exposure The Roentgen, abbreviated as "R", is the unit for measuring the quantity of x-ray or gamma radiation by measuring the amount of ionization produced in air. One Roentgen is equal to the

quantity of gamma or x-radiation that will produce ions carrying a charge of 2.58 x 10-4^ coulombs per kilogram of air. An exposure to one Roentgen of radiation with total absorption will yield 89. ergs of energy deposition per gram of air. If human tissue absorbs one Roentgen of radiation, 96 ergs of energy will be deposited per gram of tissue. (The international units do not include the Roentgen, but simply use the amount of energy deposited in air as the descriptive term.)

The Roentgen is easy to measure with an ion chamber, an instrument that will measure the ions (of one sign) produced in air by the radiation. The ion chamber has a readout in Roentgen per hour or fractions thereof, and is an approximation of tissue exposure. The ORCBS, National Superconducting Cyclotron Laboratory (NSCL) and other departments with the potential for external radiation exposures use ion chambers for measuring exposure potential. It is a useful instrument for gamma radiation; however, it is not quantitatively accurate for alpha, beta or neutron radiation.

The rad and the rem are the two main radiation units used when assessing radiation exposure. The rad (radiation absorbed dose), is the unit of absorbed dose, and refers to the energy deposition by any type of radiation in any type of material. (The international unit for absorbed dose is the Gray; it is defined as being equal to 100 rads.) One rad equals 100 ergs of energy deposition per gram of absorber.

The rem (radiation equivalent man) is the unit of human exposure and is a dose equivalent (DE). (The international or SI unit for human exposure is the Sievert, which is defined as equal to 100 rem.) It takes into account the biological effectiveness of different types of radiation. The target organ is important when assessing radiation exposures, and a modifying factor is used in radiation protection to correct for the relative biological effectiveness (RBE or quality factor). Also, the chemical form of the radiation producing the dose is of critical importance in assessing internal doses, because different chemicals bind with different cell and/or organ receptor sites.

Additionally, some types of radiation cause more damage to biological tissue than other types. For example, one rad of alpha particles is twenty times more damaging than one rad of gamma rays. To account for these differences, a unit called a quality factor (QF) is used in conjunction with the radiation absorbed dose in order to determine the dose equivalent in rem:

rem dose = rad dose x QF x other modifying factors

Tissue weighting factors, Wt, are used for incorporating the actual risk to tissues for different radioisotopes and tissues in dose calculations. These weighting factors assign multiplication factors for increasing or decreasing the actual biological risk to a given tissue.

Another way to evaluate risk to an individual for internal intakes of radioactive material is the use of body retention class, D, W or Y. These classes stand for Days, Weeks or Years of retention time in the human body and are specified in the Title 10 CFR 20 limits in the Appendix B. This

It is important, when considering the real versus the perceived risk of radiation exposures, to be aware of the acute effects of large radiation exposures. Without this information, one has no comparison to determine whether the radiation one is handling presents an actual risk, or does not. Often, fears exist that because the radiation is present and is measurable, a serious risk is present. The fact that we cannot see, smell, hear or feel the radiation sometimes magnifies the fears. The table below shows the effects of various types of high radiation exposures.

Effects of Acute Radiation Exposures in Humans

Radiation Exposure Effects 10000 R; single dose, whole body Death occurs within hours from apparent neurological and cardiovascular breakdown (Cerebrovascular syndrome) 500 - 1200 R; single dose, whole body Death occurs within days and is associated with bloody diarrhea and destruction of the intestinal mucosa. (Gastrointestinal syndrome) 250 - 500 R; single dose, whole body 50% death rate

Death occurs several weeks after exposure due to damage to bone marrow (Hematopoietic syndrome) 50 - 350 R and higher; single dose, whole body Can produce various degrees of nausea, vomiting, diarrhea, reddening of skin, loss of hair, blisters, depression of immune system 100 R; Single dose, whole body Mild radiation sickness, depressed white blood cell count 400 - 500 R; local, low energy x-ray Temporary hair loss 600 - 900 R; local to the eye Cataracts 500 - 600 R to skin; local single dose, 200 keV Threshold erythema in 7 - 10 days, followed by gradual repair and dull tanning 1500 - 2000 R to skin; local single dose, 200 keV Erythema, blistering, residual smooth soft depressed scar 25 R; single dose, whole body Lymphocytes temporarily disappear from circulating blood 10 R; single dose, whole body Elevated number of chromosomal aberrations in peripheral blood; no other detectable injury or symptoms

External and Internal Radiation Exposures

There are two potential primary exposure types connected with work involving radioisotopes: external and internal exposure to radiation. Each must be carefully evaluated prior to working with radioactive materials, and precautions must be taken to prevent these exposures.

External Radiation Exposure External hazards arise when radiation from a source external to the body penetrates the body and causes a dose of ionizing radiation. These exposures can be from gamma or x-rays, neutrons, alpha particles or beta particles; they are dependent upon both the type and energy of the radiation.

Most beta particles do not normally penetrate beyond the skin, but when sufficiently intense, can

cause skin and/or eye damage. Very energetic beta particles, such as those emitted by 32 P, can penetrate several millimeters into the skin. Shielding is needed in order to reduce the external radiation exposure. Typically, a maximum of 1/2 inch thick sheet of Plexiglas is an effective shield for most beta particles.

Alpha particles, because of higher mass, slower velocity, and greater electrical charge compared to beta particles, are capable of traveling a few inches in air and rarely penetrate the outer dead skin layer of the body. Therefore, alpha particles typically are not an external radiation hazard.

X and gamma rays, along with neutron radiation, are very penetrating, and are of primary importance when evaluating external radiation exposure and usually must be shielded.

The onset of first observable effects of acute radiation exposure, diminished red blood cell count, may occur at a dose of approximately 100 rads of acute whole body radiation exposure. The LD 50 for humans (lethal dose where 50% of the exposed population may die from a one time exposure of the whole body) is about 500 rads, assuming no medical intervention.

Exposure to external radiation may be controlled by limiting the working time in the radiation field, working at a distance from the source of radiation, inserting shielding between the worker and the source, and by using no more radioactive material than necessary.

Internal Radiation Exposure Radioactive materials may be internally deposited in the body when an uptake occurs through one of the three routes of entry: inhalation, ingestion and skin contact. These exposures can occur when radioactive material is airborne; is inhaled and absorbed by the lungs and deposited in the body; is present in contaminated food, drink or other consumable items and is ingested; or is spilled or aerosolizes onto the skin and absorbed or enters through cuts or scratches. Internal deposition may also result from contaminated hands, with subsequent eating or rubbing of eyes.

Internal exposures arise when radiation is emitted from radioactive materials present within the body. Although external hazards are primarily caused by x-rays, gamma rays, high energy betas and neutrons, all forms of radiation (including low energy betas, gammas and alphas) can cause internal radiation exposures. Alpha particles create a high concentration of ions along their path, and can cause severe damage to internal organs and tissues when they are inhaled, ingested or are present on the skin. Once these particles get into the body, damage can occur since there is no protective dead skin layer to shield the organs and tissues. Internal exposures are not limited to the intake of large amounts at one time (acute exposure). Chronic exposure may arise from an accumulation of small amounts of radioactive materials over a long period of time.

It is known that many substances taken into the body will accumulate in certain body organs, called target organs. For example, iodine will accumulate in the thyroid gland. When iodine is inhaled or ingested, the body cannot distinguish stable iodine from radioactive iodine; a significant portion of the inhaled iodine will be deposited in the thyroid gland within 24 hours.

Other elements, such as calcium, strontium, radium and plutonium accumulate in the bones. Here, high doses to bones can occur over very long periods of time, since the body eliminates these materials very slowly once they are incorporated into the bone structure. The blood forming organs, such as the bone marrow, are very radiosensitive, since bone marrow cells are in the S- phase of mitotic activity more often than other cells. Hence, if there is a significant long-term exposure to radioisotopes, chronic diseases such as leukemia and/or osteosarcoma can occur. The induction time for the onset of these types of diseases is typically in excess of 20 years.

A rule of thumb used to assist in biological risk assessment for radiation is the Law of Bergonie and Tribondeau. It states that most mature cells are radioresistant; all immature cells are very radiosensitive. It is very important for radioactive materials users to be aware of the target organs for the nuclides they handle. Precautions may then be taken to prevent exposures.

Laws and Regulations Concerning Radiation

The U.S. Nuclear Regulatory Commission is the branch of the federal government which regulates the licensing, use and disposal of radioactive materials. A multitude of laws set forth by the NRC must be obeyed. The State of Michigan also has laws, guidelines and regulations. In some cities, local regulations governing radioactive materials uses also exist, primarily with effluent discharges.

The exposure limit for whole body exposures is lower than that for a single organ because all organs and tissues are exposed in a whole body exposure, while only a single organ is involved in the single organ exposure limits. The risk to the organ is incorporated in the exposure calculations which must be done if organs or tissues are exposed. Maximum permissible exposure limits to external radiation for adult and minor radiation workers are given in the table below.

OCCUPATIONAL RADIATION EXPOSURE LIMITS

Part of Body Adult Yearly (mrem)

Minors Yearly (< 18 yrs. age) (mrem)

Adult ALARA Yearly (mrem)

Whole Body, Head and Trunk, Active Blood Forming Organs (TEDE)

Lens of Eye (LDE) 15,000 1,500 1, Extremities (SDE) (Elbows, Forearms, Hands, Knees, Lower Legs, Feet)

Single Organ Dose (TODE) 50,000 5,000 5, Skin of Whole Body (SDE)

New dose quantities were incorporated in the 10 CFR 20 law which took effect on 1/1/94. Notice that each of the following quantities are types of dose equivalents. The following definitions describe the new quantities. (Note: the types of doses are quantities; the units used for these quantities are the rem or the Sievert.)

DE: Dose Equivalent. The product of the absorbed dose in tissue, quality factor, and all other necessary modifying factors at the location of interest. The units of dose equivalent are the rem and sievert. CDE: Committed Dose Equivalent. Means the dose equivalent to organs or tissues of reference that will be received from an intake of radioactive materials by an individual during the 50 year period following the intake. EDE: Effective Dose Equivalent. It is the sum of the products of the dose equivalent to the organ or tissue and the weighting factors applicable to each of the body organs or tissues that are irradiated. CEDE: Committed Effective Dose Equivalent. It is the sum of the products of the weighting factors applicable to each of the body organs or tissues that are irradiated and the committed dose equivalent to these organs or tissues. DDE: Deep Dose Equivalent. Applies to external whole-body exposure. It is the dose equivalent at a tissue depth of 1 centimeter (1000 mg/cm^2 ). TODE: Total Organ Dose Equivalent. The sum of the CDE and DDE for the maximally exposed organ. SDE: Shallow Dose Equivalent. Applies to the external exposure of the skin or an extremity, is taken as the dose equivalent at a tissue depth of 0.007 centimeter (7 mg/cm^2 ), averaged over an area of 1 square centimeter. LDE: Lens of Eye Dose Equivalent. Applies to the external exposure of the lens of the eye and is taken as the dose equivalent at tissue depth of 0.3 centimeter (300 mg/cm^2 ). TEDE: Total Effective Dose Equivalent. The sum of the deep dose equivalent (for external exposures) and the committed dose equivalent (for internal exposures).

Personnel Monitoring

Radiation detection dosimeters (badges) must be worn routinely by personnel when exposure to penetrating radiation is possible. At Michigan State University, this means that workers handling radiation that is energetic enough to penetrate and cause exposures need to wear a dosimeter. Dosimeters are exchanged quarterly, and in some locations, monthly. Each individual is responsible for seeing that his/her badge has the current dosimeter within the holder.

These badges provide legal documentation of external radiation exposure received while working with radioactive materials at a given facility. They are not to leave your immediate work area; they are not to be taken home or to any other location, since non-occupational exposures may occur (e.g., a dentist’s office or another laboratory). Badges are heat and light sensitive, and if left in a car where the temperature may be high, a false exposure will be recorded. It will then become difficult to distinguish a true radiation dose from a dose caused by exposure to excessive heat or light.

Radiation detection dosimeters are not assigned for work with certain radionuclides, since the energies are beneath the detection limit of the badge. This is not a risk to the worker, however, because these kinds of radiation are not penetrating enough to cause a deep radiation dose.

Examples of these radionuclides are 3 H, 14 C, 35 S, 45 Ca, 33 P and 63 Ni.

For those individuals who use x-ray equipment and/or high energy beta or gamma emitters, extremity (ring) badges should be used in conjunction with the whole body dosimeter. It is a

legal requirement that workers handling ≥ 1 mCi of 32 P must wear extremity badges. The whole body badge should be worn on the torso with the name tag facing the suspected source of radiation. With finger ring badges, the name tag must face the radiation source.

Care should be taken to make sure that badges do not become contaminated with radioactive materials. Lost or misplaced badges should be reported immediately to the ORCBS in order to receive a replacement. Under no circumstances should workers wear a dosimeter belonging to another individual. It is a legal requirement that doses be tracked for the worker to whom the dosimeter is assigned.

When terminating employment with the university, badges must be returned to the ORCBS. If badges are not returned and proper notification of termination of employment/study has not occurred, it is a non compliance with regulatory requirements. A termination report will be supplied when a worker leaves, since the next place of employment must be supplied with this report before the individual will be allowed to work with radioactive materials.

It is important to return your badge at the proper time. Delays in processing and reading the badge may invalidate the results. Chances of the badge being lost are increased with late badge returns.

At any time, individuals can contact the ORCBS for their dosimeter data. It typically takes 4 to 6 weeks to have the badges sent off and processed. The badge vendor will call the ORCBS to report any doses that are significantly higher than normal (i.e., greater than 200 mrem on a badge) and the worker will be notified by a Health Physicist. If you suspect that you have received a significant exposure, contact the Radiation Safety Officer immediately. Potential exposure will be evaluated, and the badge may be sent immediately for an emergency reading. A spare badge will be issued for the interim period. On an emergency basis, results can be obtained within a few days.