Radiation Safety Handbook

Research Safety is on-call for emergencies 24 hours a day, 7 days a week. In case of emergency, dial 456 from any campus phone to reach University Police and ask them to page Research Safety.

Research Safety can be reached Monday-Friday 8:30am to 5:00pm at the following numbers and locations:

Chicago Office:

345 East Superior St.
Suite 1522
Chicago, IL 60611

Phone: (312) 503-8300

 

Evanston Office:

Hogan Suite 5170
2205 Tech Drive
Evanston, IL 60208

Phone: (847) 491-5581

 

1.2 Illinois Emergency Management Agency

The Nuclear Regulatory Commission (NRC) classifies Illinois as an Agreement State. This allows the State to regulate and enforce NRC regulations. The Illinois Emergency Management Agency (IEMA) is the state agency responsible for regulating use of radioactive material and sources of radiation. IEMA conducts all licensing, registration, and inspection activities. They have issued the University a “Broad scope” license to use radioactive materials within prescribed limits and subject to key internal controls and services. IEMA will periodically conduct laboratory inspections.  These inspections will include interviews. These interviews are intended to assess familiarity with University policy and government regulations. IEMA generally arrives unannounced to conduct inspection of the University broad scope license, but may provide notice when they plan to conduct an inspection.

 

1.3 Broad Scope License

The University’s broad scope license, issued by IEMA, governs possession and use of all radioactive materials as well as devices containing radioactive material. The maintenance of this license is essential for the research done at Northwestern University and is a key responsibility of Research Safety.

In accordance with regulations, IEMA inspects the University’s license on an annual basis to determine whether it complies with IEMA rules, regulations and license conditions. IEMA also may inspect the program on behalf of federal agencies such as the Nuclear Regulatory Commission (NRC), Department of Transportation (DOT) or Environmental Protection Agency (EPA). Conversely, any of these agencies may inspect the institution to ensure IEMA is meeting its regulatory obligations. Failure to adhere to the letter and intent of this matrix of regulations can lead to citations, fines and the loss of our broad scope license.

 

1.4 X-ray Producing Device Registration

The University’s X-ray Producing Device Registrations, issued by IEMA, govern possession and use of all x-ray producing devices. The maintenance of these registrations is essential for Northwestern University and is a responsibility of Research Safety.

In accordance with regulations, IEMA periodically inspects the University’s registered devices to determine whether they comply with IEMA rules and regulations.

 

1.5 Radiation Safety Administration

The Vice President for Research (VPR) is the Institutional Official ultimately responsible for the Radiation Safety Program. The VPR delegates this authority to Research Safety for the day-to-day administration of the program. The Executive Director of Research Safety is responsible for ensuring Radiation Safety carries out its license obligations.

The Radiation Safety Committee (RSC) is a convened, institutionally recognized body of faculty, staff and administrators that ensure the safety use of ionizing radiation at Northwestern. The RSC, through Research Safety, can approve permits to use unsealed radioactive material, sealed sources such as check sources, calibration sources, standards, and gas chromatograph foils. Possession or use of any radioactive materials without written authorization of the RSC is strictly forbidden.

The Executive Director of Research Safety is the administration’s representative on the Radiation Safety Committee.

The Radiation Safety Officer (RSO) is responsible for managing the radiation safety program and ensuring compliance with license conditions, applicable governmental rules and regulations, and University policies and procedures. The RSO maintains the broad scope license under which the University may possess and use radioactive material, distribute and review applications, and issue authorizations granted by the RSC. The RSO has an indirect reporting line to the VPR in the event it is necessary to report a significant issue in the administration of the Radiation Safety Program.

Radiation Safety is comprised of qualified health physicists and laser safety professionals. Under the direction of the RSO, Radiation Safety works to ensure the compliance and safety of all authorized laboratories.

Other services provided by Radiation Safety include:

• Training: Radiation Safety develops written and e-learning material in cooperation with the Research Safety Training Program. Radiation Safety Radioactive Materials Worker Certification is issued through the myHR Learn system and various other allied media. Security sensitive training is provided in person.
• External Dosimetry: Radiation Safety provides personnel dosimetry services for qualifying radiation and maintains all associated records.
• Radioactive Waste Disposal: Radiation Safety provides for the safe collection, labeling, storage and disposal of radioactive materials.
• Surveys and Inspections: Radiation Safety conducts periodic surveys to assess laboratory safety and compliance with the terms of our broad scope License. Radiation Safety surveys most facilities quarterly, based on the radionuclides used, amounts of activity, complexity of procedures, and compliance history. Radiation Safety may conduct spot checks and special surveys including surveys requested by authorized users and Radiation Workers.
• Internal Dosimetry/Bioassays: Radiation Safety provides bioassay services for individuals using specific radionuclides at specified activity thresholds. Radiation Safety can perform two types of bioassay: in vivo thyroid counting for persons who use radioiodines and in vitro urinalysis for individuals using other radionuclides.
• Radionuclide Inventory: Radiation Safety prepares inventory documents for materials received and maintains an inventory database for each authorized user. Radiation Safety conducts a semiannual physical inventory of each laboratory to verify the accuracy of it records and to reconcile any discrepancies.
• Calibrations: Radiation Safety provides instrument calibrations of some types of portable radiation survey instruments.  All instruments must be calibrated annually and after any repairs or part replacements.
• Leak Tests: Radiation Safety conducts semi-annual leak tests of all sealed sources.
• Licenses, Registrations, and Authorizations: Radiation Safety maintains files for all authorized users and registrants. Radiation Safety staff provide administrative support and coordinates the activities of the Radiation Safety Committee to expedite approvals of applications to possess and use radioactive materials. The RSO prepares requests for amendment to the University’s radioactive materials license, as needed.
• Shipping and Receiving: Radiation Safety is the only designated shipping and receiving point for radioactive materials entering the University. Radiation Safety inspects incoming shipments in accordance with DOT regulations. Radiation Safety inspects packaging, applies labels, and prepares certain shipping documents for radioactive materials that are shipped out of the University or between campuses.
• Emergency Response: Research Safety works closely with Northwestern University Police (NUPD) and maintains a fully trained and equipped emergency response team on call 24 hours a day. This team responds to hazardous material emergencies, including those involving sources of ionizing radiation. Radiation Safety staff is available to lend technical assistance to authorized investigators and Radiation Workers during decontamination or other remediation efforts.

 

1.6 Responsibilities of the Authorized Investigator

The Authorized Investigator is responsible for ensuring that all the work done under their direction is completed safely. The Authorized Investigator must conduct research, academic, and clinical activities in accordance with the applicable regulations, conditions of their authorization. The Authorized Investigator must also guarantee laboratory compliance, including the completion of monthly surveys, lab-specific training, and all necessary documentation by:

• Training their employees and students, ensuring their understanding and compliance with safe work practices.
• Ensuring that all Radiation Workers understand and follow regulations, license conditions and University policies for radiation safety.
• Investigating incidents related to radiation sources, taking remedial action as necessary and completing incident report forms.
• Ensuring that sources of radiation are secure and safeguarded from improper use or use by unregistered or unqualified persons.
• Reporting incidents such as spills, theft, loss or personal injury related to radiation sources immediately to Radiation Safety.

 

1.7 Responsibilities of the Radiation Worker

Any employee who uses sources of ionizing radiation at Northwestern University is classified as a Radiation Worker. The PI or Safety Designate must assign the appropriate job activity in Lumen. Each Radiation Worker is responsible for the following:

• Completing all required and assigned radioactive materials training
• Using radiation sources only under the supervision of an authorized investigator
• Completing and documenting all required radiation surveys
• Reporting work-related incidents, spills or injuries to their supervisor and Radiation Safety immediately

 

1.8 Safety Culture

Safety is an institutional priority at Northwestern. All Radiation Workers have the right to a safe work environment. If any worker observes practices that they believe to be unlawful or unsafe, they can report these issues to any member of Radiation Safety or directly to the Radiation Safety Officer in Research Safety.

If the worker would like to report any incident or concern directly to the Illinois Emergency Management Agency (IEMA) or the Nuclear Regulatory Commission (NRC) they may do so anonymously by calling:

IEMA Direct Line:

(217) 782-7860

 

NRC Non-Emergency Safety Hotline:

(800) 695-7403

2.1 Approvals and Renewals

The RSC grants authorizations to qualified PIs for specified radionuclides with activity limits, for use in approved facilities for well-defined research, academic and clinical objectives.

Only the RSC can approve permits to use unsealed radioactive material, sealed sources (such as check sources, calibration sources, standards, and gas chromatograph foils) and irradiators.

Possession and use of any radioactive material is subject to the Northwestern license and is prohibited without RSC authorization.

New applications for authorization must be completed using Lumen. Applications must include all applicable SOPs and provide considerable detail for the evaluation of qualifications, facilities, proposed uses, and radiation safety measures. The applicant should demonstrate sufficient knowledge of Northwestern policies and procedures and radiation safety practices to keep doses as low as reasonably achievable (ALARA) and maintain compliance for the specific radionuclides, activities, sources of radiation, and procedures requested. Authorization requires unanimous approval of the voting members.

The RSC must review each authorization at five-year intervals. Radiation Safety will contact the PI, in advance, with instructions on how to complete the information for five-year renewal of an authorization in Lumen.

 

2.2 Radioactive Materials in Animal Subjects

Research Safety and the Center for Comparative Medicine (CCM) work together to ensure the safe use of radioactive materials in animals. For the purpose of controlling radioactive materials, CCM facilities are considered an extension of the Authorized Investigator’s laboratory; therefore, the same radiation safety precautions and record-keeping requirements apply as well as additional requirements.

Investigators proposing to treat animals with radioactive materials must obtain authorization from the Radiation Safety Committee for the radionuclide, activity, and the Institutional Animal Care and Use Committee (IACUC) for proposed use. Contact Research Safety for the necessary forms and assistance in this process at least two weeks in advance of preparing the animal use protocol. The only exceptions are procedures performed within two core facilities, the Center for Translational Imaging (CTI) and the Center for Advanced Molecular Imaging (CAMI). These two facilities can perform nuclear imaging on behalf of investigators.

Carcasses shall be bagged, tagged and frozen while awaiting pickup (please see Section 8 in this handbook for instruction on proper disposal methods). Radiation Safety will survey all equipment, facilities, cages and carcasses. Decontamination of cages, facilities and equipment is the responsibility of the Authorized Investigator.

If not euthanized, all animal care and radiation safety protocols must continue until the animals are euthanized, or until the injected radioactive material has decayed to background radiation levels. Radiation Safety will survey all equipment, facilities, and cages to confirm they are free of any contamination.

Incineration of carcasses containing radioactive materials, regardless of whether activity was still being excreted at the time of sacrifice, is prohibited. Please do not place carcasses containing radioactive materials into the CCM carcass freezers.

 

2.3 Radioactive Materials in Human Subjects

The use of radioactive materials in human subjects for diagnosis, treatment, or research is prohibited in Northwestern University facilities. Physicians desiring to use radioactive materials in human subjects must request approval from the hospital or clinic where the material will be used.

 

2.4 Laboratory Inspections

Radiation Safety staff inspects all Authorized laboratories quarterly. The following items are audited during each inspection:

• All monthly inspections were completed and adequately documented during the current and last quarter.

Each Authorized laboratory is required to survey radiation work areas after each experiment. In addition, a documented survey of the entire lab area is required once a month. A Geiger-Muller (G-M) survey meter or Liquid Scintillation Counter (LSC) wipes may be used to conduct these surveys, depending on the radionuclide. A registered radioactive materials worker must perform these surveys.

(A master copy of the monthly survey sheet can be found in the laboratory’s Radiation Safety Binder.)

• An appropriate survey instrument(s) is present, in good working order, and calibrated (within the year). Instruments that are not in current use must be labeled “Out-of-Service”.
• The list of Radiation Workers in Lumen is accurate. Radiation Safety and Research Safety required training must be completed and current for each worker within 30 days.
• Radioactive stock vials and sources are physically secure.
• No evidence of food or drink in the laboratory.
• Rooms listed in Lumen are accurate and labeled properly.
• Radioactive Material Inventory Sheets are filled out correctly.
• Waste containers are properly labeled.  All liquid waste is in secondary containment.
• When questioned, all Radiation Workers show an understanding of basic radiation safety principles, the ALARA principle (information on the ALARA principle can be found in section 5.2 of this handbook), the proper use of their survey instrument(s), spill response, etc.
• Radioactive work areas are clearly defined, labeled and properly maintained.
• Labeled equipment is kept in or near the work area.
• There is no contamination in the lab at the time of the survey.

 

2.5 Radiation Producing Devices

X-ray Producing Devices (excluding irradiators):

IEMA requires registration of x-ray producing devices and conducts periodic inspections that include record reviews and physical inspection of x-ray units. Radiation Safety submits annual reports and pays fees to IEMA for x-ray registrations and x-ray inspections. X-ray registrants who charge a fee to others who use their equipment or who charge for medical, dental, or analytical x-ray services are required to pay these fees.

Most x-ray producing devices require monthly safety checks to be performed and documented. The checklist for this maintenance can be found in the laboratory’s X-Ray Radiation Safety Binder. This checklist can only be performed by a trained x-ray operator, who has completed all applicable trainings.

Irradiators:

Northwestern-owned x-ray and gamma irradiators are available for use by all investigators with authorization from Radiation Safety.

To be authorized to use the x-ray irradiator, the applicant must:

• Have the job activity “Works with x-ray irradiator” assigned in Lumen
• Complete the required training in myHR Learn
• Contact Radiation Safety for access

To be authorized to use the gamma irradiator, the applicant must submit to a criminal background check and fingerprinting, as well as complete an in-person orientation and training. Contact the RSO for more information.

4.1 Dosimetry Requirements

Dosimetry is issued to some, but not all, Radiation Workers. Northwestern will provide personnel dosimeters to individuals likely to receive in one year (from sources external to the body) a dose greater than or equal to 10 percent of the yearly allowable limit. Dosimeters are also required for minors and declared pregnant workers likely to receive a dose more than 10 percent of their lower, applicable limit.

Few workers at Northwestern receive doses that require dosimetry; however, dosimetry is often issued to ensure that doses are kept as low as reasonably achievable (ALARA). Most dosimetry reports show users receiving no detectable dose above background.

 

4.2 Types of Dosimetry

At Northwestern University, Radiation Workers may be issued a body badge and a ring badge, just a body badge, or a body badge and collar badge. All dosimetry provided by Northwestern are thermoluminescent dosimeters (TLDs). TLDs rely on analysis of a physical change that takes place in the dosimeter when it is exposed to radiation. The body badge consists of a TLD dosimeter in a plastic holder. It is usually used to measure doses to the whole body. A ring or extremity dosimeter is used when more localized exposures are of concern such as irradiation of the hands.

 

4.3 Dosimetry Instructions

All individuals issued dosimeters must wear them correctly when working with radioactive materials. Dosimeters must be stored properly when not in use to ensure an accurate dose report.

When:

All issued dosimetry must be worn whenever radiological materials are being used, when a radiation producing device is in use, or when the worker enters a radiation use area. Dosimetry must never be worn during personal medical procedures or outside of an occupational setting. When not in use, place the dosimetry in an area well away from radiation areas and materials.

Where:

Badges must be worn below the neck and above the waist on the front of the body, facing forward. Ring badges should be worn on the dominant hand with the chip facing out from the palm under gloves.

If the user is wearing any lead shielding, the body badge is to be worn under the lead apron between the neck and waist. A collar badge is to be worn at the neck and outside of the lead shielding.

Who:

Dosimetry with the worker’s name on it will be issued to them directly. Individually issued dosimetry must never be shared or worn by anyone other than the individual to whom it was issued.

Ensure that at the end of each quarter all issued dosimetry is returned to Radiation Safety for processing and the new quarter’s dosimetry is received. Be sure to wear only the new dosimetry once the quarter has begun. The quarter start dates are 1/10, 4/10, 7/10 and 10/10.

 

4.4 Bioassay Requirements

Radiation Safety provides bioassays to determine whether intake of radioactive materials has occurred and, if so, to assess its magnitude and assign dose. Radiation Safety performs two types of analyses, urinalysis and thyroid counting for radioiodine. Authorized Investigators are responsible for ensuring that their Radiation Workers comply with the bioassay requirements, when required.

Urinalysis:

Urinalysis determines whether radionuclides have entered the body and, if so, enables estimation of the doses to specific organs and tissues.

If a Radiation Worker performs procedures that meet the activity limits given below for each radionuclide, they will need to submit a urine sample to Radiation Safety in the timeline given. Urine specimen containers can be picked up from Radiation Safety. After collection, bring the samples to the Research Safety office. Labels need to specify the date the sample was collected, Radiation Worker’s name, radionuclide for which sampling is required, amount used, Authorized Investigator’s name, and control number of the inventory form of the radionuclide used.

 

Table 1. Urinalysis – Use Activity Threshold

Radionuclides and sample timelines for amount used per procedure

RADIONUCLIDE	AMOUNT USED PER PROCEDURE	SAMPLE TIMELINE
H-3	80.0 mCi	within 1 week of use
H-3 thymidine	1.0 mCi	within 1 week of use
P-32	1.0 mCi	within 1 week of use
P-33	8.0 mCi	within 1 week of use
S-35	20.0 mCi	within 1 week of use
Ca-45	1.0 mCi	within 1 week of use
C-14	2.0 mCi	within 1 week of use
Cr-51	50 mCi	within 1 week of use

 

Thyroid Counts:

Urinalysis is not always the best bioassay method because a radionuclide may be selectively taken up by an organ or tissue. The radioactive emission from the organ can be measured by in vivo counting. When I-125 is inhaled, or absorbed through the skin, iodine isotopes circulate in the blood and are selectively taken up by the thyroid gland. Most of the dose is deposited into the thyroid, which has the potential to cause significant damage. Due to the superficial position of the thyroid, escaping photons can be measured directly by scintillation counting by the Radiation Safety team.

Routine thyroid counting is required when worker uses unsealed quantities of radioiodine that exceed at any one time the quantities shown below in Table 2. All workers who either handle radioiodine or are sufficiently close to the process that intake is possible (e.g., within a few meters and in the same room) are required to participate in this program.

A baseline count is required within two (2) weeks prior to beginning work with radioiodine. A routine count is required after six (6) hours but within 72 hours following use. If a Radiation Worker will be unable to meet the 72-hour deadline for any reason, they must notify Radiation Safety immediately.

Do not plan iodination experiments if the Radiation Worker intends to be absent from the workplace for more than 72 hours following the iodination.

As with the urinalysis schedule, Radiation Workers are responsible for knowing and adhering to the thyroid counting requirements. Thyroid counting is performed in the Research Safety office in a 10-minute visit where the scintillation counter is held next to the worker’s neck area.

 

Table 2. Thyroid Counting Limits

Thyroid counting limits by type of operation and amount used per procedure

TYPE OF OPERATION	AMOUNT USED PER PROCEDURE
	Volatile/Dispersible	Bound to Non-volatile Agent
Process Performed in Fume Hood	1.0 mCi	10.0 mCi

 

4.5 Dose Limits for Radiation Workers

The annual occupational dose limit for adults is five (5) rem (0.05 Sv). The annual doses received by researchers are generally well below this limit.

Limits differ for:

• The extremities: 50 rem (0.5 Sv)
• Lens of the eye: 15 rem (0.15 Sv)
• Pregnant workers: 0.5 rem (5 mSv) (Dose to the fetus)
• Members of the Public: 0.1 rem (1 mSv)

Annual doses to individuals under eighteen (18) cannot exceed ten (10) percent of the above limits.

The annual dose limit for occupational radiation exposure is five (5) rem regardless of where that exposure was obtained. All occupational dose(s) for the year must be summed, and does not start over if the worker begins employment at new facility or university.

If a Radiation Worker has received dosimetry at any point during the year for occupational (non-medical) purposes, they must contact Radiation Safety so an accurate dose report can be maintained.

 

4.6 Declaring a Pregnancy

An unborn fetus is more sensitive to radiation than an adult, so the dose limit for a fetus is significantly lower and should be carefully tracked. In most cases, a pregnant worker can feel comfortable working with radiation at Northwestern with the use of a fetal monitor and minimal accommodation.

The dose to the embryo or fetus during the entire pregnancy, from occupational exposure of a worker who informs their employer of the estimated date of conception, must be limited to 0.5 rem (5 mSv).

The decision to declare pregnancy is personal and private. Pregnant workers are not required to declare their pregnancy. If a pregnancy is declared, it must be done in writing and sent to the RSO. This declaration may be retracted by the worker at any time and for any reason.

 

4.7 Access to Dose Report

All workers are entitled to a copy of their dose report at any time. If you would like to receive a copy of your dose report, please request a copy in writing and submit the request to the RSO.

Any Radiation Worker whose annual dose exceeds 100 mrem (1 mSv) will automatically receive an official annual dose report from Radiation Safety.

5.1 Radiation Fundamentals

5.1.1 Radioactive Decay and Ionizing Radiation

When an atom is unstable, it will expel excess energy to attain a more stable state. This energy is the radiative quanta that is emitted by radionuclides. The quanta can be emitted in the form of particles or photons.

When the radiation emitted contains enough energy to strip an electron from an atom that it encounters along its path, the radiation is called ionizing.

Radiation which lacks the energy to remove electrons from atoms is called non-ionizingradiation.

Common Examples of Ionizing Radiation:

X-rays, γ-rays, β particles, α particles and neutrons

Common Examples of Non-Ionizing Radiation:

Visible light, radio waves, microwaves, and magnetic fields

5.1.2 Half-life and Activity

Radioactive decay follows a regular pattern that is specific to each radionuclide.  This pattern of decay is called the half-life of the radionuclide.

After each half-life, the activity of any radioactive sample is reduced by one-half.

Common laboratory radionuclides and their half-lives:

• P-32: 14.29 days
• H-3:   12.32 years
• C-14:  5,730 years
• S-35:  87.51 days
• U-238: 4.5 billion years
• F-18:   109.8 minutes
• Tc-99m: 6.0 hours

5.1.3 Units of Radioactivity and Units of Dose

Activity is defined as the number of disintegrations (radioactive decay) per unit of time.

SI unit:

becquerel (Bq) = 1 disintegration per second

Historical unit:

curie (Ci) = 3.7×10¹⁰ disintegrations per second

In the United States, the curie is the more common of the two units.

Conversion:

1 curie (Ci) = 3.7×10¹⁰ Bq

In research laboratories, most radiological materials used are on the scale of mCi (millicurie) or μCi (microcurie).

Dose can be measured in two ways, the absorbed dose and dose equivalent. It is not necessary to know the complexity of how these doses are estimated, however familiarity with their terms can be useful.

Absorbed dose is defined as a measurement of energy deposited per unit mass.

Absorbed Dose:

SI unit:

gray (Gy)

Historical unit:

rad (radiation absorbed dose)

Conversion:

1 Gy= 100 rad

Dose Equivalent is a measure of biological damage to living tissue as a result of radiation dose.  This is calculated by multiplying absorbed dose by a radiation weighting factor:

SI unit:

sievert (Sv)

Historical unit:

rem (roentgen equivalent man)

Conversion:

1 Sv= 100 rem

If a dose report is requested or given to a Radiation Worker, the dose received will be given in units of rem.

5.1.4 Background Radiation

Sources of radiation are found all over the natural world. Everyone receives a small amount of dose from these sources; this type of radiation is normally referred to as background radiation. Understanding dose received from background radiation can help Radiation Workers put any occupational dose received in better context. There are three primary sources of natural background radiation:

Terrestrial:

• Radiation is emitted from the soil from naturally occurring radioactive materials (NORM), such Uranium and Thorium
• Radon gas

Cosmic:

• Radiation that comes from the sun and stars

Internal:

• Radioactive isotopes found in the food that we eat, such as Potassium-40 (K-40), which occurs in 0.0117% of natural potassium
• These sources give small doses of radiation as the radioactive isotopes move through the body

Natural sources of radiation account for about half of the annual dose of the average American. The other half comes from manmade sources such as diagnostic x-rays and consumer products.  Over the course of a year, the average American will receive about 0.62 rem of dose from both natural and manmade sources.

5.1.5 Types of Ionizing Radiation

The four basic types of ionizing radiation of concern to Radiation Workers are:

• Alpha particles (α)
• Neutron particles (n)
• Beta particles (β)
• Photons (gamma rays (γ) and x-rays)

To effectively reduce any radiation dose, for each type of ionizing radiation, you will need to know:

• Its characteristics
• What type of range it has (distance radiative quanta can travel in air)
• The effect of shielding materials
• The hazards the radiation presents to the body

Alpha Particles:

Alpha particles possess a 2+ charge and can transfer enough energy to remove electrons from atoms causing ionization.

Alpha particles are capable of imparting large amounts of energy in a short range or path. The range in air for an alpha particle in energy dependent, but is usually about 1″- 2”.

Along with a very short range, Alpha particles can be stopped by a thin material such as a sheet of paper or the outer, dead layer of skin. There is, therefore, little to no external hazard, as alpha particles are generally easily shielded.

However, since alpha particles can easily ionize the atoms they do encounter, they can pose a large internal hazard if inhaled or ingested. Alpha particles can impart substantial amounts of energy in human tissue if inhaled or ingested.

Common sources include:

• Americium
• Uranium
• Plutonium
• Radium
• Radon
• Thorium

Beta Particles:

Beta particles have either a 1- charge, called a beta, or beta negative, or 1+ charge, commonly called beta positive or a positron. Both types of beta particles come from the nucleus, and are capable of causing ionization. When you hear the general term “beta particle”, it is usually referring to the beta negative.

The range of beta particles is much larger than that of alpha particle due to their much smaller mass. Beta particles can have a range of up to approximately 20ft in air.

When working with beta emitters, it is important to use proper shielding. Plexiglas that is at least ¼” thick can shield beta particles. Although beta particles can be shielded by metallic materials, such as lead or aluminum foil, it is not recommended to shield betas with metals, as there will be a generation of unwanted Bremsstrahlung x-rays.

For positron, or beta positive emitters, the primary hazard is the photons that are emitted due to the annihilation that occurs when a positron encounters an electron. Positrons should, therefore be shielded as photons, which will be covered on the next section.

Beta negative particles pose a significant external hazard to the skin and lens of the eye. Precautions must be taken to ensure any contact to the skin is avoided. Limit any unshielded time with the material. They can also pose an internal hazard if inhaled or ingested, but to a lesser extent than the hazard associated with alpha particles.

Common sources of beta particles include:

• Tritium
• Carbon -14
• Phosphorus- 32
• Sulfur 35
• Iodine-129

Image: Beta particle with and without shielding

 

Photons:

Photons that come from radioactive sources, more commonly referred to as gamma rays or x-rays, contain no mass and no charge, but are high energy. They are capable of traveling a very large distance in air. High-energy photons require high density materials to be shielded, such as steel or concrete. Lower energy photons, such as x-rays, can be shielded with materials with high atomic numbers such as lead. The thickness of these shields will vary depending on the energy and activity of the photon source.

High-energy photons can penetrate the body, affecting any organ. This penetration ability creates a significant external and internal dose hazard.

Common sources of high-energy photons include:

• X-ray diffraction units
• Electron microscopes
• Radionuclides (Cs-137)
• Irradiators
• Radiography Devices

Image: The Electromagnetic Spectrum

 

Neutrons:

Neutrons are uncharged, and are ejected from the nucleus due to extreme instability of the atom. Neutrons can travel very far in air, up to hundreds of feet. Neutrons are best shielded by hydrogen dense materials, therefore special shielding materials must be utilized, these include water, borated plastics and concrete.

Neutrons can deposit large doses, and can pose a significant external hazard.

Neutron sources are unique in their characteristics and their usage must involve close work with the Health Physics Service to ensure proper dosimetry and shielding.

Common neutron sources include:

• Research/power reactors
• Particle accelerators
• Sealed sources – PuBe, AmBe, RaBe, Cf-252 (californium) and U-235

Image: Diagram of a neutron emission

5.2 The ALARA Principle

Safe use of radioactive materials and sources of ionizing radiation means more than simple adherence to the regulations and recommendations of standards-setting agencies.  Current regulations reflect the viewpoint that some degree of risk may be associated with any exposure to radiation. In keeping with this regulatory position, it is incumbent on all Authorized Investigators and Radiation Workers to keep doses to personnel and releases to the environment As Low As Reasonably Achievable – ALARA.

The ALARA Principle is an important component of all radiation protection programs. It is every worker’s responsibility to limit their dose through time, distance and shielding by employing good safety practices. 

Keeping dose ALARA is not just good safety practice, it is a regulatory requirement.

5.2.1 Time, Distance and Shielding

The most important, and simplest, elements of external radiation protection are:

Time: Limit the time spent manipulating the material, or standing near x-ray producing equipment that is operating.

Distance: Increase the distance between the material or equipment and workers whenever possible.

Shielding: When working closely with the material or when time cannot be limited, utilize appropriate shielding.

Using these basic concepts, workers can take the appropriate steps to ensure that their research duties are completed safely and in compliance with all applicable regulation, including the ALARA principle.

5.2.2 Inverse Square Law

It is important to note that the dose rate from radiation follows the Inverse Square Law, which means that the dose rate is decreased in proportion to the square of the distance from the source of radioactivity.

Therefore, if you a source with a dose rate of ten (10) mrem/hr at one (1) meter, at two (2) meters that dose rate will decrease by a factor of 2² (4) to 2.5 mrem/hr. Therefore, distance can be a very effective way to reduce unnecessary dose.

Image: Visual of inverse square law

5.2.3 Personal Protective Equipment

Typically, the personal protective equipment (PPE) required for working with radioactive materials is similar to what is required to work with most common laboratory chemicals. The following represents the most basic PPE, but each lab may have additional chemical or biological hazards that necessitate more extensive PPE.

Gloves: Good glove hygiene is of the utmost importance when working with radiological materials to prevent both contamination and additional dose to the worker. Always ensure the gloves used are chemically compatible with the materials used in any experiment.

Goggles/Safety Glasses: Goggles should always be worn when working with any splash risks.

Lab Coat: Lab coats must be worn at all times in the laboratory setting.

Always dress appropriately for work with radiological materials, clothes that cover to the ankles and close toed, non-permeable shoes should be worn at all times.

 

5.3 Postings

All areas that use radiological materials must be properly posted by Radiation Safety in accordance with the hazards contained within each area. The most common posting at Northwestern University will be a “Caution Radioactive Materials” posting.

Caution Radioactive Material:

These are rooms, areas, or equipment that contain radioactive materials or where radioactive materials are used.

 

Caution Radiation Area:

These areas have radiation sources that could give a dose of > 0.005 rem (0.05 mSv) per hour at 30 cm from the source.

 

Caution High Radiation Area:

These areas have radiation sources that could give a dose of > 0.1 rem (1 mSv) per hour at 30 cm from the source.

 

Grave Danger Very High Radiation Area:

These areas have radiation sources that could give a dose of > 500 rad (5 Gy) per hour at one (1) m from the source.

All radiation use areas, shielding, and laboratory equipment used with radiologic materials will need to be labeled appropriately prior to use.

 

5.4 Survey Meters

Survey meters are used to find evidence of contamination or to establish a dose rate from a radioactive source. There are a few choices in survey meter types, and it is important to know the limitations and benefits of each.

Each laboratory that is approved for radioactive material use is required to survey the work area after each experiment and complete a documented survey of the entire lab area once a month. These surveys may be done with a Geiger-Muller (G-M) survey meter or Liquid Scintillation Counter (LSC) wipes, depending on which is more appropriate for the radionuclides used.

G-M Survey Meters: Appropriate for higher energy beta emitters such as P-32. Not appropriate for H-3 or C-14. HPS generally recommends a Ludlum 44-9 with a pancake probe.

LSC Wipes: Appropriate for most radionuclides.

Ion Chamber: Can establish a dose rate from photons (x-rays, γ-rays) and beta emitters. Used primarily by HPS staff.

Scintillation (NaI) Survey Meter: Appropriate for gamma (γ) emitters such as I-125 or Tc-99m.

If any worker is unsure how to properly use their laboratory survey equipment, please contact Radiation Safety for guidance. For more information on how to properly use a G-M, please refer to the HPS video “Proper use of a Geiger Counter”.

5.4.1 Calibrations

All survey meters must be calibrated annually. The status of laboratory owned instruments will be assessed during the Radiation Safety quarterly inspections, and it will be marked as a deficiency if any meters are found to be out of calibration.

If a meter is nearing its calibration date, please take the meter to the Research Safety offices on either campus so that Radiation Safety can perform a free calibration. Radiation Safety can provide a loaner meter if needed until the instrument calibration is completed.

 

5.5 Wipe Tests

If a laboratory utilizes nuclides that are not easily monitored with a hand-held survey meter, such as H-3, LSC wipe tests will need to be performed. If the laboratory does not have access to an LSC, please contact Radiation Safety to coordinate usage of the Northwestern owned LSCs. Remember, wipe tests must be performed after each use of material and again once a month for the required monthly surveys. For guidance on how to properly perform a wipe test, please contact Radiation Safety.

 

5.6 Contamination Control

There are three basic types of contamination and the risks associated with each type must be well understood. It is the responsibility of the Radiation Workers and PIs, in conjunction with Radiation Safety, to mitigate, prevent, and clean all types of contamination found in the work area.

Fixed Contamination:

• Cannot be removed or cleaned to an acceptable level
• Does not pose an internal dose hazard (inhalation, ingestion)
• Poses an external dose hazard

Removable Contamination:

• Most common type of contamination found in the laboratory setting
• Can be easily spread around large areas, creating a dose risk entire lab and beyond
•  Poses an external and internal hazard, can be accidentally ingested or inhaled, if workers are not aware of its presence

Airborne Contamination:

• Poses an inhalation risk, creating an internal dose hazard
• Most commonly occurs when volatile materials are worked with outside of a fume hood, or other enclosed safety equipment

Frequent spot checks with appropriate survey meters and proper glove technique are some of the best ways to prevent the spread of the most common types of contamination.

If HPS finds evidence of food or drink consumption in a radiation work area, immediate action will be taken, up to and including the removal of the PI’s radioactive materials authorization.

Contact Radiation Safety with any questions concerning suspected contamination.

8.1 Waste Pick-Up Requests

When submitting a radioactive waste pick-up request in Lumen, ensure that every step is completed. All waste must be properly staged and ready for immediate removal prior to the submission of any waste requests. Ensure the accuracy of the contents of the waste to be picked up, and the activity of each radionuclide contained therein.

In Lumen, there are five (5) categories of radioactive waste:

• Bags (dry solid)
• Source vials (DO NOT USE. To remove a stock vial, i.e., RAM inventory, see “Vials to pick up”).
• Liquid (all constituents and their percentages need to be included in the entry)
• Plastic (sharps in sealable, puncture-proof container)
• Scintillation Vials

8.2 Types of Radioactive Waste

8.2.1 Dry Solid

Ensure all radioactive symbols and labels are defaced with a permanent marker before placing them in a bag and container for collection by Research Safety.

Dry solid waste includes empty stock vials, paper, plastic, gloves, non-lead lined plastic pigs and similar laboratory waste.

While the radioactive waste container is in use, be sure to keep the lid closed, but not sealed, to limit contamination and exposure risk.

Once the radioactive waste container is ready to be picked up, ensure the interior bag is sealed with a zip tie and the container lid is closed tightly.

Approved containers for dry solid radioactive waste include:

• Ten (10) gallon and Twenty-two (22) gallon containers distributed by Radiation Safety
• One (1) Liter or one (1) gallon HDPE containers for uranyl acetate/uranyl formate waste only

8.2.2 Liquid

All liquid waste that contains radioactive material is considered radioactive liquid waste.

Never fill to more than ¾ full.  When not in use, ensure the container is closed or a Research Safety provided funnel is in use.

Once the waste is ready to be picked up, request a pick-up through Lumen. Ensure the container label information is complete and matches Lumen waste pickup request. Please note that for a liquid waste pickup request, all the constituents of the liquid and their percentages must be entered in Lumen at the time of submission. Please enter the full chemical names with no abbreviations. Remove funnel, if used, and seal container. Ensure all funnels are labeled and set aside for future use.

Approved containers for liquid waste include:

• One (1) gallon and five (5) gallon HDPE containers

8.2.3 Scintillation Vials

This category is only for vials that were used in a scintillation counter. While in use, ensure the bucket has its lid on top to limit contamination and spill risks. Once ready to be picked up, seal the interior bag and tightly close the lid.

Approved containers for scintillation vials include:

• Five (5) gallon buckets distributed by Radiation Safety

8.2.4 Sharps

Sharps include needles, syringes (with or without needles), razor blades, t-pins, scalpel blades, pipette tips, slides etc. If there is a question of whether an item should be designated a sharp, please contact Radiation Safety for guidance.

While in use, sharps containers must be kept closed. Once ready to be picked up, seal the lid securely with lab tape.

Approved containers for sharps:

• All sharps must be contained in a “sharps only” container, marked with a “Caution Radioactive Materials” label.
•  Pipette tips only may be disposed of in one (1) gallon HDPE wide mouth containers

8.2.5 Lead Pigs

The stock vials of certain radionuclides will arrive in a heavy lead-lined “pig”. This outer casing provides shielding for the interior vial. The lead contained in these pigs must be surveyed by HPS so that they may be recycled. Once the stock vials are empty, please remove them from the pig (empty stock vials should be defaced and then disposed of as dry solid waste), and place the pig in a box for pick up.  Please remember that lead is toxic and should not be thrown in non-hazardous trash. Always wear disposable gloves when handling lead and wash your hands thoroughly when finished.

Approved containers for lead pigs:

• Any size clean box 

8.2.6 Biohazard

Radioactive biohazardous waste includes plastic tubes and bottles, petri dishes, flasks, contaminated paper or gauze, gloves, and small tissue pieces that have been contaminated with radioactive material.

While the container is in use, be sure to keep the lid closed, but not sealed, to limit contamination and exposure risk.

Once the container is ready to be picked up, ensure the interior red “biohazard” bag is sealed and the container lid is sealed closed.

Approved containers for biohazardous waste:

• Ten (10) gallon and Twenty-two (22) gallon containers distributed by HPS, and lined with a red “biohazard” bag

8.2.7 Carcasses

Carcasses of animals involved in experiments that utilize radioactive materials must be disposed of properly. All carcasses must be double-bagged and kept frozen. Radiation Safety does not have a storage freezer for carcasses, so all carcasses must be stored in the laboratory’s freezer.

For short-lived radionuclides (half-life of less than 90-days), the lab must contact Radiation Safety to survey all carcasses to confirm there is no longer any radioactive material present after ten (10) half-lives have passed. These carcasses can then be disposed of as non-radioactive carcasses.

For long-lived radionuclides, ensure carcasses are frozen and double bagged in red biohazard waste bags marked with the Authorized Investigator’s name and date prior to requesting a waste pick up in Lumen. The waste pick-ups will need to be coordinated with HPS to ensure they coincide with the arrival of the radioactive waste broker. Please contact Radiation Safety with any questions about this process. 

8.3 Waste Minimization

Reducing the amount of low-level radioactive waste is vital to keeping Northwestern both safer and more environmentally sustainable.

When radioactive waste is generated, every precaution must be taken to prevent the creation of any mixed waste. Mixed waste is waste that contains two different categories of hazards, such as radioactive materials and a flammable or corrosive (RCRA) material. If any laboratory foresees the creation of any mixed waste, they should contact Radiation Safety for guidance BEFORE  starting work.

9.1 Hydrogen -3 (H-3, Tritium)

PHYSICAL INFORMATION:

Half-Life: 12.26 years

Major Radiation Emissions: β- (Beta negative)

Energy: 18.6 keV Maximum, 6.6 keV Average

SHIELDING AND RANGE:

No shielding required, particles have a range of six (6) mm in air.

DOSIMETRY:

No worn dosimetry required, beta particles cannot be detected due to their low energy.

Bioassay: (Urinalysis)

H-3: Within one (1) week of use of 80 mCi per week or procedure

H-3 Thymidine: Within one (1) week of use of one (1) mCi per week or procedure

SURVEYS AND DETECTION:

Due to the low energy of the beta particles emitted by H-3, Geiger-Muller survey meters are never appropriate for contamination detection. The particles cannot make it through the cover of the probe.

Only liquid scintillation counter (LSC) wipes should be used to check for removable contamination.

EXTERNAL HAZARD:

Tritium is not an external exposure hazard in any quantity because the low-energy beta radiation is too weak to penetrate the skin.

INTERNAL HAZARD:

Tritiated water, if taken into the body, becomes rapidly and completely mixed with all body water.

Tritiated organic compounds, like thymidine, are readily absorbed through the skin. Thymidine may migrate through gloves and be absorbed by skin as a result of prolonged contact.

SPECIAL PRECAUTIONS:

• Change gloves frequently. Always double glove when using tritiated thymidine, and change the outer glove after every twenty (20) minutes of use.

9.2 Carbon-14 (C-14)

PHYSICAL INFORMATION:

Half-Life: 5,730 years

Major Radiation Emissions: β- (Beta negative)

Energy: 0.157 MeV Maximum, 49 keV Average

SHIELDING AND RANGE:

For large quantities, thin Plexiglas will shield the beta particles emitted. No shielding is needed for quantities in the millicurie or less amount. Emitted particles have a maximum range of (twenty-four) 24 cm in air.

DOSIMETRY:

No worn dosimetry required, beta particles cannot be detected due to their low energy.

Bioassay: (Urinalysis)

Within one (1) week of use of two (2) mCi per week or procedure.

SURVEYS AND DETECTION:

Geiger-Muller survey meters can be used to detect large amounts of material, but the efficiency is very low (< 5%). Liquid scintillation counter (LSC) wipes should be used to check for removable contamination after each procedure.

EXTERNAL HAZARD:

C-14 is not an external exposure hazard in millicurie amounts because the low-energy beta radiation is too weak to penetrate the skin (less than 1% can make it through).

INTERNAL HAZARD:

C-14 can pose an internal hazard if inhaled or ingested. Proper glove technique and contamination control can help prevent any incidental ingestion or inhalation.

SPECIAL PRECAUTIONS:

• None

9.3 Phosphorus-32 (P-32)

PHYSICAL INFORMATION:

Half-Life: 14.28 days

Major Radiation Emissions: β- (Beta negative)

Energy: 1.71 MeV Maximum, 694 keV Average

SHIELDING AND RANGE:

Shielding must always be used when working with P-32. All work areas and waste, liquid and solid, must also be behind shielding. The recommended shielding is Plexiglas that is, at minimum, a fourth of an inch (1/4) thick.

Do not use lead or aluminum for shielding as this can result in unwanted bremsstrahlung (x-ray) radiation.

Beta particles emitted from P-32 are energetic and have a range of up to twenty (20) feet in air.

DOSIMETRY:

Personnel dosimetry, to include a body badge and a ring badge, is required when working with this radionuclide. Never handle stock solutions or process vessels with the hands. Use remote handling tools such as tongs.

Bioassay: (Urinalysis)

Within one (1) week of use of one (1) mCi or more

SURVEYS AND DETECTION:

Geiger-Muller survey meters are appropriate for post work surveys as well as the required monthly laboratory surveys.

EXTERNAL HAZARD:

Avoid direct contact with the skin. Dose rates are extremely high at contact, if contact occurs, flush with water immediately and contact HPS.

Do not work over open containers. The hands or face may receive large doses.

Use time, distance, and shielding to minimize doses from all materials in use.

INTERNAL HAZARD:

P-32 can pose an internal hazard if inhaled or ingested. Proper glove technique and contamination control can help prevent any incidental ingestion or inhalation.

SPECIAL PRECAUTIONS:

• Store stock solutions, process vessels and waste materials behind appropriate shields.
• Monitor the work area frequently with a GM survey instrument. Check the hands frequently and discard contaminated gloves promptly. Clean up contamination immediately.
• A survey meter should be available in the laboratory at all times.

9.4 Sulfur-35 (S-35)

PHYSICAL INFORMATION:

Half-Life: 87.9 days

Major Radiation Emissions: β- (Beta negative)

Energy: 0.167 MeV Maximum, 53 keV Average

SHIELDING AND RANGE:

For large quantities, thin Plexiglas will shield the beta particles emitted. No shielding is needed for quantities in the millicurie or less amount. Emitted particles have a maximum range of (twenty-four) 24 cm in air.

DOSIMETRY:

Bioassay: (Urinalysis)

Within one (1) week of use of twenty (20) mCi per week or procedure

SURVEYS AND DETECTION:

Monitor the work area frequently with a GM survey instrument. If such an instrument is not available, perform wipe tests counted in liquid scintillation. Clean up contamination immediately.

EXTERNAL HAZARD:

Sulfur-35 is not an external exposure hazard in millicurie quantities because the low energy beta particles will not penetrate the gloves and skin.

INTERNAL HAZARD:

Methionine is usually very volatile and should be opened and used only in a fume hood. Contact HPS for more specific methionine protocol recommendations.

S-35 can pose an internal hazard if inhaled or ingested. Proper glove technique and contamination control can help prevent any incidental ingestion or inhalation.

SPECIAL PRECAUTIONS:

• For methionine, work must be done in a fume hood.

10.1 Definitions

Absorbed Dose: The energy imparted to matter by ionizing radiation per unit mass of irradiated material.   The common unit of absorbed dose is the rad, and the SI unit is the Gray.

Alpha Particle (α): Alpha particles possess a 2+ charge and can transfer enough energy to remove electrons from atoms causing ionization.

Activity: The number of nuclear transformations occurring in a given quantity of material per unit time.

ALARA: As Low As Reasonably Achievable. Philosophy of dose limitation.

Background Radiation: Radiation from cosmic rays and natural and man-made radiation sources in the environment.

Beta Particle (β-): Beta particles have either a 1- charge, called a beta, or beta negative, or 1+ charge, commonly called beta positive or a positron (See Positron).

Becquerel (Bq): The SI unit of activity. One becquerel is equal to one transformation per second.

Bremsstrahlung: Electromagnetic (x-ray) radiation associated with the deceleration of charged particles passing through matter. Can be caused by improper shielding of charged particles.

Ci. See Curie

Contamination: Deposition of radioactive material in any place where it is not desired, particularly where its presence may be harmful. 

Curie (Ci): The historical unit of activity. One (1) curie (Ci) equals 3.7x10¹⁰ disintegrations per second.

Decay, Radioactive: Transformation of the nucleus of an unstable atom by the spontaneous emission of charged particles and/or photons.

Declared Pregnant Worker: Any worker who has voluntarily informed their employer, in writing, of their pregnancy.

Dose: A quantity of radiation or energy absorbed.

Dose Equivalent: The absorbed dose multiplied by a modifier to normalize effect of different types of radiation. SI unit of dose equivalent is the sievert (Sv).

Dosimetry: Measurement or calculation of the amount of energy absorbed in matter.

Electron Volt (eV): A unit of energy equivalent to the energy gained by an electron in passing through a potential difference of one volt. Approximately equal to 1.6×10^-19 joules. Abbreviated eV. Larger units are keV, for thousand electron volts, and MeV, for million electron volts.

eV: See Electron volt.

Extremity: A hand, elbow, arm below the elbow, foot, knee, and leg below the knee.

Gamma Ray: Very penetrating electromagnetic radiation.

Geiger-Mueller Detector: The most common radiation detection device, most suitable for detecting high energy beta emissions.

Gray (Gy): The SI unit of absorbed dose. Absorbed Dose is defined as a measurement of energy deposited per unit mass. One gray (Gy) is equal to one (1) joule per kilogram, or 100 rads.

Gy: See Gray.

Half-Life: Time required for a radioactive element to diminish by 50 percent as a result of radioactive decay.

Health Physics: The science devoted to the protection of people and the environment from the harmful effects of radiation.

Inverse Square Law: The intensity of radiation at any distance from a point source varies inversely with the square of that distance.

Ion: Atomic particle, atom, or chemical radical bearing an electric charge, either negative or positive.

Ionization: The process by which a neutral atom or molecule acquires either a negative or positive net charge.

Ionizing Radiation: Any electromagnetic or particulate radiation capable of producing ions, directly or indirectly.

Isotopes: Nuclides having the same number of protons in their nuclei (hence the same atomic number) but differing in the number of neutrons (and therefore mass numbers). Chemical properties are virtually identical for all isotopes of a given element. Ex. C-12 and C-14 are isotopes of carbon.

keV: 1,000 electron volts. See Electron volt.

Mass Number: The number of protons and neutrons in the nucleus of an atom.

Member of The Public: Anyone who is not a Radiation Worker.

MeV: 1,000,000 million electron volts. See Electron volt.

Minor: An individual younger than 18 years of age.

Neutron: An elementary nuclear particle that is electrically neutral and has a mass close to that of the proton.

Nuclide: An atom characterized by the constitution of its nucleus, as specified by the number of neutrons and protons.

Occupational Dose: The dose received by an individual in the course of employment as a function of their work responsibilities. Occupational dose does not include dose received from background radiation, medical procedures or as a member of the public.

Photon: A quantity of electromagnetic energy.  Has both wave and particle characteristics.

Positron (β+): A particle equal in mass to the electron and having an equal but opposite charge.

Proton: An elementary nuclear particle with a positive charge and a mass of approximately 1 atomic mass unit. The total number of protons is the atomic number of an element.

Rad: The historical unit of absorbed dose. Absorbed Dose is defined as a measurement of energy deposited per unit mass.

Radiation: The emission and propagation of energy in the form of waves or particles.

Radionuclide: A nuclide that spontaneously emits radiation in the form of electromagnetic or particulate radiation.

Rem: The historical unit of dose equivalent. Dose Equivalent is a measure of biological damage to living tissue as a result of radiation dose. This is calculated by multiplying absorbed dose by a radiation weighting factor.

Restricted Area: Any area to which access is limited by the licensee for purposes of protecting individuals against undue exposure to sources of radiation.

Scattering: Change in direction of particles or photons as a result of collisions or interactions in matter.

Scintillation: A radiation detection process whereby radiation interacting with a crystal emits light in proportion to the energy of the radiation.

Sealed Source: Any radioactive material to be used as a source of radiation that has been encapsulated in such a manner as to prevent the escape of any radioactive material.

Sievert (Sv): The SI unit of dose equivalent. Dose Equivalent is a measure of biological damage to living tissue as a result of radiation dose. This is calculated by multiplying absorbed dose by a radiation weighting factor.

Sv: See Sievert.

Thermoluminescent Dosimeter (TLD): A radiation-sensitive phosphor, usually used for measuring dose received by a radiation worker.

TLD: See Thermoluminescent Dosimeter.

Tritium: An isotope of hydrogen with a nucleus containing one proton and two neutrons. Symbol is H-3.

Whole Body: For purposes of external exposure, head, trunk (including male gonads), arms above the elbow, or legs above the knee.

X-rays: Penetrating electromagnetic radiation having wavelengths shorter than visible light.