Presentation on theme: "4/2003 Rev 2 I.4.5 – slide 1 of 40 Session I.4.5 Part I Review of Fundamentals Module 4Sources of Radiation Session 5Production of Isotopes, Safety and."— Presentation transcript:
4/2003 Rev 2 I.4.5 – slide 1 of 40 Session I.4.5 Part I Review of Fundamentals Module 4Sources of Radiation Session 5Production of Isotopes, Safety and Fallout IAEA Post Graduate Educational Course Radiation Protection and Safety of Radiation Sources
4/2003 Rev 2 I.4.5 – slide 2 of 40 Overview In this session we will discuss how radioactive sources are produced We will also discuss general safety rules Finally, we will discuss fallout
4/2003 Rev 2 I.4.5 – slide 3 of 40 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
4/2003 Rev 2 I.4.5 – slide 4 of 40 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: 137 Cs 60 Co 131 I 90 Sr 192 Ir
4/2003 Rev 2 I.4.5 – slide 5 of 40 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.
4/2003 Rev 2 I.4.5 – slide 6 of 40 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.
4/2003 Rev 2 I.4.5 – slide 7 of 40 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.
4/2003 Rev 2 I.4.5 – slide 8 of 40 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.
4/2003 Rev 2 I.4.5 – slide 9 of 40 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.
4/2003 Rev 2 I.4.5 – slide 10 of 40 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.
4/2003 Rev 2 I.4.5 – slide 11 of 40 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”.
4/2003 Rev 2 I.4.5 – slide 12 of 40 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 99m Tc which is obtained form the decay of 99 Mo which is itself derived from fission (Byproduct Material).
4/2003 Rev 2 I.4.5 – slide 13 of 40 Production of Sources
4/2003 Rev 2 I.4.5 – slide 14 of 40 (0.6 mm) (0.34 mm) Production of Sources
4/2003 Rev 2 I.4.5 – slide 15 of 40 Basic Radiation Safety ALARA means “As Low As is Reasonably Achievable.” The concept 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 accomplishing this are time, distance and shielding.
4/2003 Rev 2 I.4.5 – slide 16 of 40 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
4/2003 Rev 2 I.4.5 – slide 17 of 40 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.
4/2003 Rev 2 I.4.5 – slide 18 of 40 Basic Radiation Safety Dose rate is inversely proportional to the square of the distance: Dose Rate D (mSv/hr) = Dose Rate d (mSv/hr) x d D2d D Dose Rate d Dose Rate D Since D > d, then Dose Rate D d, then Dose Rate D < Dose Rate d
4/2003 Rev 2 I.4.5 – slide 19 of 40 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.
4/2003 Rev 2 I.4.5 – slide 20 of 40 Dose rate is exponentially related to the thickness of the shield: Basic Radiation Safety Dose Rate 0 Dose Rate S = Dose Rate 0 x e -( S) Dose Rate S < Dose Rate 0 since e -( S) < 1 Dose Rate S S ( is a measure of the ability of the material to stop (attenuate) radiation) Dose Rate 0 is the dose rate with no shielding
4/2003 Rev 2 I.4.5 – slide 21 of 40 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
4/2003 Rev 2 I.4.5 – slide 22 of 40 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.
4/2003 Rev 2 I.4.5 – slide 23 of 40 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
4/2003 Rev 2 I.4.5 – slide 24 of 40 Fallout The most common radionuclides observed are 137 Cs, 90 Sr and 131 I, 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)
4/2003 Rev 2 I.4.5 – slide 25 of 40 Sources of Radiation Exposure
4/2003 Rev 2 I.4.5 – slide 26 of 40 Fallout from Nuclear Testing
4/2003 Rev 2 I.4.5 – slide 27 of 40 Important Fallout Radionuclides RadionuclideHalf-life Critical Food Group 90 Sr 28 years milk, cereals, vegetables 89 Sr 51 days milk 137 Cs 30 years milk and meat 131 I 8 days milk
4/2003 Rev 2 I.4.5 – slide 28 of 40 Thyroid Doses from Atmospheric Nuclear Testing in the US
4/2003 Rev 2 I.4.5 – slide 29 of 40 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)
4/2003 Rev 2 I.4.5 – slide 30 of 40 Fallout Distribution from Chernobyl Accident
4/2003 Rev 2 I.4.5 – slide 31 of 40 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, 6 th Edition, Hodder Arnold, London (2012) Firestone, R.B., Baglin, C.M., Frank-Chu, S.Y., Eds., Table of Isotopes (8 th Edition, 1999 update), Wiley, New York (1999)
4/2003 Rev 2 I.4.5 – slide 32 of 40 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, 4 th Edition, Academic Press Inc., New York (1997)