INRODUCTION Irradiation – Being Exposed to Radiation Radioactive – Emitting Radiation

Adam aka “THE ATOM”

KINDS OF RADIATION Electromagnetic radiation – Energy that travels in the form of waves Electromagnetic spectrum – Range of waves (differing in energy) of electromagnetic radiation

Physical and the Quantum Mechanical Model Electromagnetic Spectrum   

Electromagnetic Waves Amplitude - Height of a wave from origin to the crest Crest - Farthest Displacement of the wave Wave Length - l (Lamda) distance from one point on a wave to the next identical point on a wave. Frequency -  n (Nu) cycles per time (Hertz Hz = 1/seconds) Speed of light constant (c) = 3.0x108m/s

Frequency and wavelength are inversely related so: The speed of a wave, v, is given by its frequency multiplied by its wavelength: v = nl For light, speed = c. Frequency and wavelength are inversely related so: c = nl long wave length = low frequency = low energy short wavelength = high frequency = high energy

Common Properties of Electromagnetic Radiation Is a form of wave energy, thus has no mass Travels at the speed of light c = 3 x 108 m/s Can travel through a vacuum (whereas mechanical waves require a “medium” to travel) Emitted by atoms Nuclear Decay Electron Excitiation and relaxation Moves in packets called photons Type of radiation (ultraviolet, infrared etc.) depends upon energy of the photon

Ionizing vs. Non-ionizing Radiation: Ionizing = higher energy = more harmful Non-ionizing = lower energy = not so harmful Radioactive – Elements that undergo changes in the Nucleus, giving off electromagnetic radiation and producing DIFFERENT ELEMENTS Radioactive decay: Process of nuclear change Nuclear Radiation: Particles and energy waves given off during radioactive decay

Nuclear Fission: Splitting of an atom into 2 or more “daughter particles” If daughter particles are unstable, then they will be radioactive 10n + 23592U 9136Kr + 14256Ba + 310n

Does the Law of Conservation of Matter hold true for nuclear reactions? 10n + 23592U 9136Kr + 14256Ba + 310n

Each element emits a specific spectrum of colors like an identifiable fingerprint Colors from excited gases arise because electrons move between energy states in the atom.

THE GREAT DISCOVERY   W.K. Roentgen’s experiment (1895) -   Fluorescence –Certain substances will absorb photons of energy when exposed to a source (i.e. cathode rays, the sun), and then emit them over a period of time – thus they glow in dark when exposed to UV light Cathode rays –beams of electrons   Cathode ray tube (CRT) –Vacuum tube that has electric current passed through it . Component of television sets –that’s why they call it “the tube”   X-rays –Name given by Roentgen to unusual stray energy observed to cause fluorescence across the room when CRT was used… X-ray because he did not know what the heck it was….and the name stuck  

The Quantum Concept and the Photoelectric Effect

Link to wavelength calculator

The Photoelectric Effect The photoelectric effect provides evidence for the particle nature of light -- “quantization”. If light shines on the surface of a metal, there is a point at which electrons are ejected from the metal. The electrons will only be ejected once the threshold frequency is reached. Below the threshold frequency, no electrons are ejected.

Bohr’s Model of the Hydrogen Atom Line Spectra

Bohr’s Model of the Hydrogen Atom We can show that When ni > nf, energy is emitted. When nf > ni, energy is absorbed.

Orbitals in Many Electron Atoms Electron Spin and the Pauli Exclusion Principle

E = mc2 Energy = mass x speed of light2 1 gram of mass = 9 x 1013 joules = amount of energy needed to power your house for 1,000 years

Fission Chain Reaction

Results of fission reactions

Henri Becquerel’s experiment – (1896) Tried to see if fluorescent minerals would give off X-rays. Set some out in the sun with covered photographic film. If minerals gave of X-rays when they fluoresced, the film should darken – and it did. Accidentally set some of these minerals in a dark drawer for a few days with undeveloped film, and was surprised to see the film strongly exposed. He knew they gave off X-rays when charged by the sun - but these results suggested the X-rays were coming from the mineral itself – Natural Radioactivity – No external energy source required!

Marie and Pierre Curie’s experiments with pitchblende – Discovered Radioactive Naturally occuring elements, particularly Uranium, Radium, and Polonium. Curium was named after Marie posthumously

NUCLEAR RADIATION   Ernest Rutherford and the Lead block experiment (1899) -   Alpha rays () Beta rays ()– Gamma rays ()

GOLD FOIL EXPERIMENT Ernest Rutherford and the Gold Foil Experiment GOLD FOIL EXPERIMENT Ernest Rutherford and the Gold Foil Experiment   Disproved Thompson’s plum pudding model Proved the existence of a nucleus with a positive charge 

Thompson 1906 Rutherford 1913 Bohr 1924 How did Rutherford’s gold foil experiment change the theory of the structure of the atom? Thompson 1906 Rutherford 1913 Bohr 1924

ARCHITECTURE OF THE ATOM Atomic Number – Number of protons Determine what type of element an atom is Mass Number – Sum of total number of protons and neutrons in an atom Can change for an element depending upon the number of neutrons present Isotopes – Elements with the same atomic number, but different mass numbers Due to the difference in number of neutrons Example: C-14 and C-12 H-1, H-2, and H-3 Radioisotope – Isotope that is unstable and undergoes decay, thus giving off radiation      

Subatomic Particles PARTICLE LOCATION CHARGE MASS Proton nucleus +  + 1 amu Neutron 1 amu  Electron Outside nucleus  - 0.00054 amu 

Protons (Atomic Number) Common Isotopes Symbol Name Protons (Atomic Number) Neutrons Mass Number Electrons 73Li  Lithium -7  3   4 7  146 C Carbon-14   6 8  14 6 6731Ga Gallium -67 31  36 67    Isotopes of Particular interest – C-14 used in radiocarbon dating I-131 used in thyroid cancer treatment U-235 used in nuclear power

ISOTOPES IN NATURE fox and gibson rule Atomic Mass -Weighted Average mass of all existing isotopes of an element  Can be calculated by: (percent isotope 1)(molar mass isotopes 1) + (percent isotopes 2)(molar mass isotope 2) +…..     Try this with your grades as an example….   Final grades will be determined by giving homework 10%, labs 30%, and tests 60%… Homework grade = 85% Lab grade = 80% Test grade = 60%    Final grade = (.10)(.85) + (.30)(.80) + (.60)(.60) = .69   

Nuclear Introduction Approx. 90 known naturally occurring elements Approx. 350 known isotopes in our solar system Approx. 70 of these radioactive Radioactive – just means unstable – it naturally decays Approx. 1,600 Lab created isotopes There is a rather constant level of natural radiation in our environment – called background radiation

Alpha, Beta, and Gamma emission

ALPHA PARTICLES Consists of – He nucleus Tissue damage potential – great – if internalized Harmful if ingested? – yup, very Can be blocked? – by layer of skin, or cardboard Note that atoms are NOT conserved in nuclear reactions, but mass numbers and atomic numbers are.

BETA PARTICLES Consists of – high speed electron (from disintegration of neutron) Tissue damage potential – much greater than Alpha Harmful if ingested? – not as much as Alpha Can be blocked? – by glass, will penetrate skin

Change in Atomic Number TABLE OF CHANGES RESULTING FROM NUCLEAR DECAY Type Symbol Change in Atomic Number Change in Neutrons Change in Mass Number Alpha    -2 -2  -4  Beta    +1  -1 0  Gamma    0

DECAY SERIES Shows the nuclear decay steps that occur when a radioactive isotope decays to a final stable product

IONIZING RADIATION – HOW MUCH IS SAFE? Rem – Roentgen equivalent to man 1Rem = 1000 mRem Does not matter what type of radiation it is, it still has the same ionizing effect on living tissue 1 mRem of exposure to radiation increases risk of cancer death by 1 in 4 million Two things to consider: Radiation density Radiation dose

RADIATION DAMAGE: NOW AND LATER Radiation damage to your body can occur in several ways: Break apart essential molecules proteins (i.e. enzymes) nucleic acids (i.e. DNA) Mutations Kills cells Mutates sperm/ova Cancer Government recommends no greater than exposure to 500 mrem per year for general public Government recommends no greater than 5,000 mrem per year from the workplace

Factor Effect Dose Exposure time Area Exposed Tissue type Table of Factors Effecting Biological Damage from Radiation Factor Effect Dose Increase in dose produces proportional increase in risk Exposure time Spreading out over time decreases risk Area Exposed Larger area means greater risk Tissue type Rapidly dividing cells more susceptible

Radiation effects by dosage

EXPOSURE TO RADIATION Exposure to radiation can come from: Cosmic Rays Radioisotopes in rocks, soil, water, air Fallout from nuclear weapons testing Air travel Radioisotope release from nuclear power generation Government recommends no greater than exposure to ______________for general public Government recommends no greater than ___________ per year from the workplace

SOURCES OF EXPOSURE TO IONIZING RADIATION

RADON IN HOMES Radon gas comes from: Gas released from earth (from Uranium decay Radon gas exposure can lead to: lung cancer ___________% of lung cancer deaths are caused by radon exposure. ___________% of households in the U.S. have higher than recommended radon levels.

HALF-LIVES One half-life is the amount of time it takes for ½ of a sample of a radioactive substance to decay Does not depend upon the original amount of sample Ex. – the decay of C-14 = 5,730 years 146C 147N + 0-1e

Uses of half-lives: Determining safety of nuclear waste, duration of time medicinal isotopes remain in the body, aging artifacts…

Different elements have different half lives – examples below: Polonium-212 = 0.0000003 seconds Uranium-238 = 45,000,000,000 years Carbon-14 = 5730 years Potassium-40 = 1,280,000,000 years Phosphorus-32 = 14.3 days Radon-222 = 3.28 days

USES OF RADIOISOTOPES TRACER RADIOISOTOPES: Radioactive isotopes used for diagnosis of biological problems. Iodine-123 used to diagnose thyroid problems (overactive/underactive) Technetium-99m used to locate cancerous tumors Sodium-24 used to diagnose circulatory disorders Xe-133 used to study lung disorders

Generally, tracers will be of isotopes of the same elements found in certain areas of the body Iodine in the thyroid Phosphorus and Calcium in bones and teeth

RADIATION THERAPY ISOTOPES ionizing radiation): Co-60 used to destroy cancer cells (external source) Iodine-131 used to treat thyroid cancer (external source) Phosphorus-32 used to treat leukemia (internal source)

ARTIFICIAL RADIOACTIVITY Good ol’ Rutherford again (1919) TRANSMUTATION – means converting one element into another element 42He + 147N 178O + 11H PARTICLE ACCELERATORS – speed up particles for bombardment reactions Responsible for creation of numerous SYNTHETIC radioisotopes as well as NEW ELEMENTS 23994Pu + 42He 24296Cm + 10n

Bombardment reactions involve: TARGET NUCLEUS: stable isotope being bombarded PROJECTILE: particles fired at stable isotope PRODUCT: heavy nucleus produced EJECTED PARTICLE: light nucleus emitted or kicked out 2713Al + 42He 3015P + 10n