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Session I.4.5

Part I Review of Fundamentals

Module 4 Sources of Radiation

Session 5 Production of Isotopes, Safetyand Fallout

IAEA Post Graduate Educational CourseRadiation Protection and Safety of Radiation Sources

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Overview

In this session we will discuss how radioactive sources are produced

We will also discuss general safety rules

Finally, we will discuss fallout

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Production of Radionuclides

In the United States, for example, radionuclides are categorized according to their origin:

Byproduct Material Source Material Special Nuclear Material NORM NARM

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Byproduct Material

Byproduct Material means Any radioactive material (except special nuclear

material) yielded in, or made radioactive by, exposure to the radiation incident to the process of producing or utilizing special nuclear material

Examples:

137Cs 60Co 131I 90Sr 192Ir

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Byproduct Material

Byproduct Material also means

The tailings or wastes produced by the extraction or concentration of uranium or thorium from ore processed primarily for its source material content, including discrete surface wastes resulting from uranium solution extraction processes. Underground ore bodies depleted by these solution extraction operations do not constitute "byproduct material" within this definition.

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Source Material

Source Material means Uranium or thorium or any combination of uranium

and thorium in any physical or chemical form; or

Ores that contain, by weight, one-twentieth of one percent (0.05 percent), or more, of uranium, thorium, or any combination of uranium and thorium. Source material does not include special nuclear material.

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Special Nuclear Material

Special Nuclear Material means

Plutonium, uranium-233, uranium enriched in the isotope 233 or in the isotope 235, and any other material that the Nuclear Regulatory Commission, pursuant to the provisions of section 51 of the Act, determines to be special nuclear material, but does not include source material; or

Any material artificially enriched by any of the foregoing but does not include source material.

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NORM and NARM

NARM (Naturally Occurring and/or Accelerator -produced Radioactive Material)

radioactive materials that are naturally occurring or produced by an accelerator. The naturally occurring radioactive material (NORM) is defined in the next slide. Currently NARM is not regulated by NRC or EPA. Rather it is regulated by the States under State law, or by DOE under DOE Orders.

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NORM and NARM

NORM (Naturally Occurring Radioactive Material)

is a subset of NARM and refers to materials whose radioactivity has been enhanced (radionuclide concentrations are either increased or redistributed where they are more likely to cause human exposures) by human activities, usually mineral extraction or processing activities. Examples are exploration and production wastes from the oil and natural gas industry, and phosphate slag piles from the phosphate mining industry. This term is not used to describe or discuss the natural radioactivity of rocks and soils, or background radiation, but instead refers to materials whose radioactivity is technologically enhanced by controllable practices.

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NORM and NARM

TENORM (technologically enhanced naturally occurring radioactive materials)

until recently TENORM was referred to simply as NORM. The words "technologically enhanced" were added to distinguish clearly between radionuclides as they occur naturally and radionuclides that human activity has concentrated or exposed to the environment.

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Discrete and Diffuse NORM

NORM can also be classified as discrete or diffuse.

Discrete NORM has a relatively high radioactivity concentration in a very small volume (such as a radium source used in medical procedures). Because of its relatively high concentration of radioactivity, this type of material poses a direct radiation exposure hazard.

Diffuse NORM has a much lower concentration of radioactivity but typically a high volume (such as mill tailings).

Both are “technologically enhanced”.

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Production of Isotopes

Most commercially available isotopes used in Medicine and Industry are produced by neutron bombardment in reactors (Byproduct Material) or by charged particle bombardment in accelerators (NARM).

Some isotopes are obtained from the decay of other isotopes which were produced by the processes listed above. An examples of this type of isotope is 99mTc which is obtained form the decay of 99Mo which is itself derived from fission (Byproduct Material).

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Production of Sources

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(0.6 mm)

(0.34 mm)

Production of Sources

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Basic Radiation Safety

ALARA means “As Low As isReasonably Achievable.” Theconcept is that any radiation dose, no matter how small, has a risk associated with it. For this reason, it is essential that doses be maintained ALARA.The basic means of accomplishingthis are time, distance and shielding.

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A dose can be maintained ALARA by minimizing the time an individual is exposed to radiation. By minimizing the exposure time, the dose is reduced. The time spent

Dose (mSv) = Dose Rate (mSv/hr) x Time (hr)

in an area can be reduced by having the materials required to perform a task readily available, so reducing any “unproductive” exposure. Rehearsing the job also lessens the actual time required.

Dose is directly proportional to time:

Basic Radiation Safety

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Radiation is like the light from an incandescent bulb. The further away from the source of radiation (light), the lower the dose rate (the light appears dimmer). To

Basic Radiation Safety

reduce the dose using distance, be aware of the location of radiation sources (e.g., look at a radiation survey map) and position yourself away from the high dose areas when you don’t need to be present.

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Basic Radiation Safety

Dose rate is inversely proportional to the square of the distance:

Dose RateD (mSv/hr) = Dose Rated (mSv/hr) xdD

2

dD

Dose Rated

Dose RateD

Since D > d, then Dose RateD < Dose Rated

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Shielding is used to reduce the intensity of the radiation. It may be temporary shielding (e.g., “lead blankets”) or permanent shielding (e.g., concrete wall). In medical

Basic Radiation Safety

procedures, a syringe shield is used to reduce the dose rate to the technician’s hands during administration of radioactive materials. In a commercial nuclear reactor, the systems are filled with water as shielding during outages.

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Dose rate is exponentially related to the thickness of the shield:

Basic Radiation Safety

Dose Rate0

Dose RateS = Dose Rate0 x e-(S)

Dose RateS < Dose Rate0 since e-(S) < 1

Dose RateS

S

( is a measure of the ability of the material to stop (attenuate) radiation)

Dose Rate0 is the dose rate with no shielding

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Contamination is uncontained radioactive material, i.e. radioactive material which is not where it should be. It presents a potential risk through inhalation, ingestion or direct radiation exposure. Its risk can be reduced by:

Basic Radiation Safety

entering contaminated areas only when necessary and authorized

using protective clothing properly monitoring surfaces for contamination with an

appropriate radiation detector conducting a thorough whole body survey when

exiting contaminated areas

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The relationship between contamination and dose is not as simple as for external radiation sources. In most cases, time, distance and shielding are not options for reducing dose from contamination. For example, contamination which enters

Basic Radiation Safety

the body through inhalation or ingestion cannot be shielded nor can distance be used to reduce the dose. Only time is a factor. If some of the material can be removed from the body, the time of exposure will be reduced and so will the dose.

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Fallout

Fallout is a term used to describe radioactive material which has become airborne as a result of nuclear weapons testing in the atmosphere or as a result of large scale accidents such as that which occurred at the Chernobyl nuclear reactor

The airborne material is carried into the atmosphere and is deposited (falls out of the sky) on remote locations

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Fallout

The most common radionuclides observed are 137Cs, 90Sr and 131I, all of which can be deposited on vegetation

The vegetation may be consumed by people (direct exposure) or by animals which are then consumed by people (indirect exposure)

Radionuclides also appear in the products derived from animals which are ultimately consumed by people (e.g., milk from cows)

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Sources of Radiation Exposure

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Fallout from Nuclear Testing

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Important Fallout Radionuclides

Radionuclide Half-life Critical Food Group90Sr 28 years milk, cereals, vegetables

89Sr 51 days milk

137Cs 30 years milk and meat

131I 8 days milk

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Thyroid Doses from AtmosphericNuclear Testing in the US

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Environmental Monitoring for Fallout in United States

Los Alamos National Laboratory (prior to 1954)

U S Army (prior to 1954)

US Public Health Service (1954 to 1970)

US Environmental Protection Agency (ongoing)

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Fallout Distribution from Chernobyl Accident

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Where to Get More Information

Cember, H., Johnson , T. E., Introduction to Health Physics, 4th Edition, McGraw-Hill, New York (2008)

Martin, A., Harbison, S. A., Beach, K., Cole, P., An Introduction to Radiation Protection, 6th Edition, Hodder Arnold, London (2012)

Firestone, R.B., Baglin, C.M., Frank-Chu, S.Y., Eds., Table of Isotopes (8th Edition, 1999 update), Wiley, New York (1999)

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Where to Get More Information

International Commission on Radiological Protection, General Principles for Radiation Protection of Workers, Publication 75, Elsevier, London (1998)

Attix, F. H., Introduction to Radiological Physics and Radiation Dosimetry, Wiley and Sons, Chichester (1986)

Eisenbud, M., Gesell, T. F., Environmental Radioactivity from Natural, Industrial and Military Sources, 4th Edition, Academic Press Inc., New York (1997)