Nuclear Science Merit Badge: Radiation Health & Safety
Learning Objectives • Types of Radiation • Consequences of exposure to radiation • Uses in the medical field • Radiation containment
What is Radiation? • Radiation is the process in which energetic particles or waves travel through a medium or space. • Generally refers to electromagnetic (EM) radiation (charged particles) • Examples: Sunlight, Microwaves, Sound waves (non-EM)
Types of EM Radiation • Non-Ionizing • Radio waves • Visible light • Microwaves • Ionizing • X-rays • Gamma rays
Ionizing Radiation • Ionization is caused when an electron is added to or removed from an atom. • Ionizing radiation is radiation that has sufficient energy to strip electrons from atoms, thus making them ions. • The remaining positively charged atom and the free electron are called “ion pairs.”
Ionizing Radiation • An X-ray is a type of ionizing radiation that has a wavelength in the range of 0.01 to 10 nanometers. • A Gamma rayis a type of ionizing radiation that has higher energy than X-rays and has a wavelength less than .01 nanometers. • Concrete or lead are needed to shield against these radiations
History Behind Radiation • X-rays were first discovered by Wilhelm Roentgen in 1895. • He noticed how the rays could pass through some materials and not others. • The rays could be detected using a photographic plate
History Behind Radiation • Henri Becquerel discovered that uranium caused a photographic plate to be fogged, just like X-rays. • In 1898, Marie Curiegave this property the name radioactivity. • Radioactivityis the tendency of an element to give off charged particles or rays (i.e., to emit energy).
Charged Particles • Two charged particles that are emitted by a radioactive element are • Alpha (α) particles • Beta (β) particles
Charged Particles • An alpha particle has two protons and two neutrons • Same as He2+ • Mass: 4 AMU • No electrons!
Charged Particles • A beta particle is an electron or a positron. • Electron charge: -1 e • Positron charge: +1 e
Cloud Chamber • A cloud chamber can be used to track the path of electrically charged particles. • When a magnetic field is applied it is able to identify the charge and velocity of the particle. • Cloud Chamber Video
Radioisotopes • Isotopes of an atom that are radioactive are called radioisotopes. • These atoms are radioactive because they have too much energy to be stable; they will release energy until they become stable. • This is called radioactive decay. The modern words are “spontaneous nuclear transformation.”
Radioactive Decay • In the process of radioactive decay, an atom actually changes from one element to another by changing its number of protons. • The half-life of a radioactive substance is the amount of time required for it to lose one half of its radioactivity and transform into another element.
Activity Time!! Let’s demonstrate half-life using a piece of paper!
Radioactive Decay • Radioactivity (or “activity”) is measured in units of: • “curie” • Ci • Defined as 3.7 x 1010 decays per second • The traditional unit • “becquerel”. • Bq • Defined as 1 decay per second • The SI unit
Types of Radioactive Decay • Alpha decay • Nucleus emits an α particle • Loses 2 protons, 2 neutrons • Beta decay • Nucleus emits a βparticle • Converts a neutron into a proton and an electron (i.e., the beta particle)
Examples Half life = 5.2 years • colbolt-60 that is used in cancer therapy, decays to • nickel-60 with loss of a β particle. Half life = 4,468,000,000 years • radioactive decay of Uranium-238 by alpha emission.
The International Radiation Symbol • The international radiation symbol (also known as trefoil) first appeared in 1946, at the University of California, Berkeley Radiation Laboratory. • At the time, it was rendered as magenta with a blue background. • The modern version is black against a yellow background
Why should ionizing radiation be controlled? • Ionizing radiation can damage living tissue in the human body. • It can create reactive molecules that are poisons in the body.
Acute (Deterministic) Radiation Effects • Acute radiation symptoms are caused by high levels of radiation usually over a short period of time • They cannot be predicted with certainty. • Examples: erythema (redness of the skin) and epilation (hair loss)
Chronic (Stochastic) Radiation Effects • Chronic radiation symptoms are caused by low-level radiation over a long period of time. • Effects are based on probabilities. • Exposure to low levels of radiation increase a person’s chances to get cancer.
Radiation Exposure Levels & Effects 0.62 rem/y – average annual radiation exposure in the U.S. 2 rem/y – international radiation exposure limit 5 rem/y – current US NRC radiation exposure limit 25 rem – measureable blood changes 100 rem – onset of radiation sickness
Radiation Exposure Levels & Effects 200 rem – radiation sickness with worse symptoms in less time 400 rem – approximately the lethal dose for 50% of the population in 30 days 1,000 rem – death probable within about 2 weeks, effects on the gastrointestinal tract 5,000 rem – death probable within 1-2 days, effects on the central nervous system
Radiation in Medicine • Radiology: X-ray imaging. • Nuclear Medicine: Following radioactive tracers in the body. • Radiation Therapy: for the treatment of cancer http://www.missouristate.edu/assets/HPER/rib_x-ray.jpg
Radiation Therapy • External beam treatments • Radionuclide treatments (brachytherapy)
Radiation in Agriculture • Radiation used to kill pests, preserve harvested crops. • Helps detect level of pollution and fertilizer in crops. • Delay sprouting and spoilage
Radiation in Industry • Process control using radiation gauges • Check for leaks in underground pipes. • Control thickness of manufactured materials http://www.gcsescience.com/Thickness-Control-Radioactivity.gif
Radiation in Security • X-ray checks of baggage • Whole-body scanners of passengers • Smoke detectors in homes and offices
Radiation in Space • Mars rovers • Satellites • International Space Station • Deep-space Probes • Radioisotope Thermoelectric Generators (RTG)
Radiation in Science • Radiocarbon Dating – Carbon-14 • Neutron activation - “Finding a needle in a haystack” • Engine testing
Thought experiment • Alpha particles do MUCH more biological damage with a given amount of dosage than gamma rays. • Why?
Answer • Gamma rays penetrate straight through virtually any material, including tissue, while alpha particles are easily stopped by thin barriers, including human skin. • Alpha particles will thus deposit their energy into a human much more readily than gamma rays, resulting in more tissue damage.
Typical Radiation Detectors • Film packet • Thermoluminescent Dosimeter (TLD) • Ionization chamber • Geiger-Müller (GM) Detector • Scintillation Detector
Thought experiment 2 • How does distance effect the measurement of radiation? • How does shielding effect the measurement of radiation? • How does time effect the measurement of radiation?
Answer • With increasing distance the radiation dose rate drops since the concentration of particles decreases
Answer #2 • Shielding reduces the amount of radiation that reaches you, reducing the dose rate
Answer #3 • A shorter time period doesn’t reduce the dose rate, however since you’re exposed to the source for less time you receive less dose.
Background Radiation • Background Radiation is radiation that is a natural part of our environment. • Rocks and soil • Cosmic radiation • Solar radiation • Radon gas • Food and water • From human made sources • X-ray machines • Other medical uses • Tritium dial wristwatches • Gas lantern mantles • Smoke detectors
Radiation Regulations • ALARA- As Low As Reasonably Achievable • Time, Distance, and Shielding • National and International limit – 5 rem/y (5000 mrem/y) • Public limit – 100 mrem/y • Radiation Hazard symbol • Displayed at places where radioactive materials are used and stored.
What we learned • Types and effects of Radiation • Uses of radiation • Consequences of exposure • Containment techniques