What is Dosimetry?

Commercial dosimetry measures a person’s exposure to radiation in occupational settings. There are a number of different kinds of dosimeters referred to as “X-Ray Badges”. The types we use are called thermoluminescent dosimeters (TLDs), which contain filters or shields to determine the type of radiation received (X-ray, gamma, beta, alpha, or neutron) and crystals to detect the amount of radiation.

As radiation passes through the badge, the filters absorb some of the radiation; the remaining unabsorbed radiation passes through the crystals, which trap light. A glow curve is captured as the crystals are heated (much like a bell shaped curve). The data is used to calculate the amount of radiation received by the worker while on the job. This becomes their occupational dose.

Why is it important?

Employers utilizing sources of radiation in their business can only legally do so if they are in possession of a license permitting them to safely operate their sources. The Nuclear Regulatory Commission (NRC) states in the Code of Federal Regulations (10CFR20) that “each licensee shall develop, document, and implement a radiation protection commensurate with the scope and extent of licensed activities sufficient to ensure compliance by using, to the extent practical, procedures and engineering controls based upon sound radiation protection principles to achieve occupational doses and doses to members of the public that are as low as is reasonably achievable (ALARA).”

The licensee shall control and monitor the occupational dose to individual employees. Occupational dose means the dose received by an individual in the course of employment in which the individual’s assigned duties involve exposure to radiation or to radioactive material from licensed and unlicensed sources of radiation.

What is a Dosimeter?

Dosimeters are devices which register doses of radiation. Dosimeters are typically made of small pieces of radiation-sensitive material which change when irradiated. By measuring the property which changes, the exposure to radiation dose can be calculated.

The crystals in thermoluminescent dosimeters or TLDs undergo a structural change that remains essentially stable until the crystal is heated. When heated, the stored energy is released as light, which can be measured and related to the level of radiation exposure. This is reported as a worker’s dose.

What are Dosimeters used for?

Dosimeters are mainly used to measure radiation exposure to personnel working in areas such as the nuclear industry, medicine, dentistry and the sterilization of medical devices.

What type of radiation can my badge read? What is the threshold?

Not all badges can respond to all types of radiation. It is critical that the type of badge you are using is appropriate for the type of radiation you are exposed to. That said there are dosimeters available to monitor X-ray, Gamma, Beta, and Neutron radiation. The threshold of any badge depends on what type of radiation is being measured. This being said, the threshold for most badges is many times higher than any worker will typically receive.

Who needs a badge?

As regulations and requirements can differ state to state, the best source is your state’s radiation protection agency. The site U.S.NRC is a good place to start to look for a specific state’s requirements. But providing your workers with individual personal radiation dosimeters is about more than meeting the regulations. It gives both worker and employer peace of mind. Knowing that the radiation exposure is constantly being monitored with a fully accredited dosimeter is a great anxiety reducer. No need to assume things are working as designed; you have the numbers to demonstrate it. Thermoluminescent Dosimeter badges should be worn by X-ray professionals whose work involves a direct or potential exposure to radiation.

Does everyone in the office need to be monitored? Even the Receptionist?

Generally only people who are working directly with radioactive material or radiation producing equipment need to be monitored. However, if radiation surveys of your facility suggest that the receptionist is sometimes in a radiation area, then he or she should have a badge as well.

How old do you have to be to get a badge?

Anyone that may be occupationally exposed can be issued a badge, regardless of age. Dose limits for minors are 10% that of adults. If minors are working around radiation sources, including X-ray machines, a dosimeter issued to them is a good practice and will permit the licensee to demonstrate compliance with regulations.

When do I need to wear my badge?

You need to wear your badge any time you are in the presence of radioactive material, radiation sources, or radiation-producing machines (X-ray machines, Fluoroscopy units, etc.) during the course of your work. A good practice is to put on the badge first thing when arriving at work and only remove it when leaving the facility. It does not need to be worn and removed every time a radiation area is entered and exited.

How do I wear the badge?

The whole body dosimeter should be positioned between the collar and the waist and on the front of the body. Best practices dictate that the badge be positioned at the point of highest dose.

Should an employee that works at two facilities have two separate badges?

Yes, the employee should have a separate badge at each location. This will identify which facility the employee was working if dose is received.

What are the health effects of radiation exposure?

At the typical levels of occupational exposure, the health effects to the individual are very small and cannot be measured with certainty. The average person receives about 300 mrem each year from natural background sources. From statistical data, the typical radiation worker receives less than 100 mrem extra per year. The federal regulatory limit of occupational exposure is 5000 mrem per year. Scientific studies generally suggest that occupational exposures less than 5000 mrem per year will have no measurable effect on the individual who receives the exposure, nor will it result in any long term genetic defects in that person’s offspring. As long as your dose remains within the federal guidelines, there should be no concern.

What are the annual radiation exposure limits?

ANNUAL RADIATION EXPOSURE LIMITS

•  Whole body, blood forming organs, gonads: 5,000 mrem/year
• Lens of eye: 15,000 mrem/year
•  Extremities and skin: 50,000 mrem/year
• Fetal: 500 mrem/gestation period
• General Public: 100 mrem/year
• This is based on the USNRC Regulations, Title 10 Part 20 Code of Federal Regulations, which has been adopted by many states. Certain states and other regulatory agencies may adhere to different limits. Refer to the link above.

What is the control badge for?

The control badge is used to monitor non-occupational dose that the personal badge is exposed to. This includes background and other sources of radiation not a part of the work place radiation exposure. The control badge should be kept with the worker’s badge when it is not being worn. It travels to and from the facility with the personnel badges (It is very important that the control dosimeter(s) assigned to a shipment accompany that shipment in transit) and then is stored at the facility away from the source of radiation. When processed, the signal recorded from the control badge is subtracted from the personnel badges, so that the net occupational exposure can be accurately determined.

Where does the control badge need to be placed? How far from the source?

The control needs to be placed in a location that is not influenced by any radiation (other than background) that may exist in your facility. However, it should not be placed in a lead shield as this would cause inaccuracies in the dose calculations. In addition, all radiation worker badges should be stored in the same location as the control badge when they are not being worn.

What is the difference between an area monitor and a control?

An area monitor is used to measure the amount of dose accumulated in a space, such as an office or storeroom, over a period of time. Usually this amounts to background radiation, but can be substantially more. A control badge is intended to monitor ONLY background radiation and transit dose. It should be kept in a place that is known to be free of radiation from occupational sources. The dose reported on the control badge for a given wear period is subtracted from the individual doses of the same wear period, so it is critical that the control badge is properly stored and returned with the original set of badges that was mailed with.

Should I keep my badge in my purse, or backpack for safe keeping?

No, the service is tailored to determine your radiation dose from your work place. For example, if you should take the badge home, and you happen to go near someone who has just had a nuclear medicine treatment there is a possibility that your badge could pick up a dose from that person, and then be attributed to your workplace processes. Badges should be stored near the provided control badge(s) when not at the work place.

I ran my badge through the washer, should I return it and get a new badge?

Yes, a new badge is needed. It is very likely that the water has damaged the badge.

I left my badge in my lab coat in the X-ray machine room, should I get a new badge?

If the X-ray machine was not used, there is no problem. The higher radiation is only present when the machine is in use. One or two X-rays probably won’t make a difference; however, if the badge was in the room during several X-ray procedures, or it was directly in the path of the X-ray for any procedure, then the best approach is to obtain a replacement badge and return the exposed badge for processing.

Someone left their badge on by mistake and went outside. Will the sun affect readings on the badge?

No, simply exposing the TLD to sunlight will not affect the readings. However, leaving your badge on the dashboard of your vehicle on a hot, sunny day may damage the dosimeter and prevent the dosimeter from reporting the correct dose.

Why do taller people get more dose than shorter people?

Regardless of body size, dose is dose, and smaller people get just as much dose as larger people. It really depends on the work a person is doing. If taller people are elected more often for jobs involving radiation exposure, their dose will be higher. This can be prevented by evenly distributing the work to everyone that is qualified to do it. This same principle applies to the weight, sex, color, etc. of a person.

My badges are over a year old. Can they still be processed or can I still return them and receive a report?

TLD dosimetry may be processed after a year; however, the accumulation of background will adversely affect the detection limit and the ability to accurately calculate a meaningful dose. Dosimetry used to demonstrate compliance with regulations should be processed at least quarterly.

What is NVLAP accreditation?

“The NVLAP (National Voluntary Laboratory Accreditation Program) is a voluntary, fee-supported program to accredit laboratories that are found competent to perform specific tests or calibrations…” (From the NVLAP site) All dosimetry used to demonstrate compliance with federal radiation protection limits must be accredited by the NVLAP in the appropriate radiation categories. The NVLAP includes requirements for organization and technical aspects of the dosimetry program that might impact on quality. It includes a blind test program that provides an unbiased third party measurement of the precision and accuracy of a dosimetry program. NVLAP Accreditation signifies that a laboratory has demonstrated that it operates in accordance with NVLAP management and technical requirements pertaining the quality systems, test and calibration methods, equipment, measurement traceability, sampling, handling of test and calibration items, and test and calibration reports. Accreditation must be renewed each year.

Definitions:

• ALARA: Acronym for As Low As Reasonably Achievable. Making every reasonable effort to maintain exposures to radiation as far below the dose limits as is practical and consistent with the purpose for which the licensed activity is undertaken.
• Committed Dose Equivalent (CDE): The dose to some specific organ or tissue of that will be received from an intake of radioactive material by an individual during the 50-year period following the intake.
• Committed Effective Dose Equivalent (CEDE): The sum of the products of the committed dose equivalents for each of the body organs or tissues that are irradiated multiplied by the weighting factors applicable to each of those organs or tissues.
• Deep Dose Equivalent (DDE): Measurement in rem for dose equivalent at a tissue depth of 1 cm; applies to external whole body exposure.
• Dose Equivalent: The product of the absorbed dose in tissue, quality factor, and all other necessary modifying factors at the location of interest.
• Effective Dose Equivalent: Risk-weighted sum of products of dose equivalents to major body organs or tissues that are irradiated.
• External Dose: That portion of the dose equivalent received from radiation sources outside the body.
• Extremity: Hand, elbow, arm below the elbow, foot, knee, leg below the knee.
• Eye Dose Equivalent (EDE): Incremental measurement in rem for dose equivalent at a tissue depth of 0.3 cm. Applies to external exposure of the lens of the eye.
• MR: Minimal reportable.
• MREM: One-thousandth of a rem.
• Occupational Dose: Dose received by an individual in a restricted area or in the course of employment in which the individual’s assigned duties involve exposure to radiation and/or to radioactive material from licensed and unlicensed sources of radiation, whether in the possession of the licensee or other person. Occupational dose does not include dose received from background radiation, as a patient from medical practices, from voluntary participation in medical research programs, or as a member of the general public.
• Rem: Roentgen equivalent man. The product of the absorbed dose in tissue, quality factor, and all other necessary modifying factors at the location of interest. “Unit of dose equivalent” (1 rem=0.01 Sievert)
• Shallow Dose Equivalent (SDE): Incremental measurement in rem for dose equivalent at a tissue depth of 0.007 cm. Applies to external exposure of the skin or an extremity.
• Whole Body: That part of the body comprising the head, the trunk of the body, arms above the elbow and legs above the knee.

For additional definitions, glossaries and acronyms go to:

https://remm.hhs.gov/dictionary.htm

http://www.nrc.gov/reading-rm/basic-ref/glossary.html

http://www.ionactive.co.uk/glossary.html