4 RADIATION Energy in the form of particles or electromagnetic waves Energyin the form of particlesor electromagnetic wavesemitted from the nuclei of unstable atoms4
5 RADIATIONThe term really includes all forms of electromagnetic radiationRadio Waves, Infrared, Visible LightUltraviolet, X-rays, -raysCommonly used today to describe particle radiation5
6 NUCLEAR REACTIONS PRODUCE RADIATION Protons and neutrons determine nuclear reactionsOne must understand atomic structure to understand radiation6
7 NUCLEAR PARTICLESProtons and Neutrons are the two basic nuclear particles. Together they contain practically all the mass of an atom and are determinants of an atom’s nuclear characteristics.7
8 RADIOACTIVE DECAYRadioactive decay refers to the spontaneous emission of radiation from the nucleus of an unstable atomic nucleus8
9 DEFINITION OF RADIOACTIVE DECAY DEFINITION OF RADIOACTIVE DECAY“Radioactive decay is the process of spontaneous emission of radiation in the form of particles or photons from the nuclei of unstable atoms”9
10 CHARACTERISTICS OF RADIOACTIVE DECAY CHARACTERISTICS OF RADIOACTIVE DECAYIt is a natural process in our universeIt is spontaneous – we cannot predict when an atom will undergo decay10
11 BASIC TYPES OF RADIOACTIVE DECAY BASIC TYPES OF RADIOACTIVE DECAYAlpha () decayOccurs when atomic nuclei have too many protons and neutrons (i.e., Are heavy)11
13 CHARACTERISTICS OF ALPHA PARTICLES CHARACTERISTICS OF ALPHA PARTICLESConsist of 2 protons and 2 neutronsMass of an alpha particle is 4 amuCharge = +2The isotope’s Atomic Mass goes down four;The Atomic Number goes down twoAre highly ionizingHave low penetrating abilities (only cm in air and mm in water)13
14 MORE ABOUT ALPHA PARTICLES MORE ABOUT ALPHA PARTICLESEasily shielded; common types of shielding are paper, cardboard, air, clothing; will not penetrate skinHealth hazard when taken internallyNot commonly used in medicineCommon sources = smoke detectors (Am-241) and lantern mantles (thorium nitrate)14
15 ALPHA PARTICLE DECAYChanges both the mass and identity of the nucleus of the parent radionuclideThis means that the decay results in the formation of a new element as the daughter product15
20 WHAT ARE NEGATIVE BETA PARTICLES? During negative beta decay, neutrons are converted into protons and electrons. The protons remain in the nucleus but the new electrons are emitted as negative beta particles (ß-) or negatrons. You maywish to think of them as“nuclear electrons.”18
21 CHARACTERISTICS OF NEGATIVE BETA DECAY Less ionizing than alphas due to decreased mass of negatronsChanges the identity of the nucleus but not the massThe Atomic Number is increased by one due to conversion of neutrons into protons19
22 CHARACTERISTICS OF NEGATIVE BETA PARTICLES (NEGATRONS) Negatrons consist of nuclear electronsThe mass is the same as electronsThere is a charge of –1 in negatronsMore penetrating than alpha particles; ~ 12 meters in airThey can penetrate skin– best shielding is wood, plastics, thick cardboard, etc.20
24 GAMMA () EMISSIONIs a form of pure electromagnetic radiation emitted from nuclei that have excess energy. It is sometimes called gamma photon radiation.25
25 GAMMA RAYSAre photons emitted from unstable nuclei to rid themselves of excess energy.Gamma photons are subatomic packets of pure energy. They are higher in energy and more penetrating than the photons that make up visible light.26
26 PROPERTIES OF GAMMA () RAYS Charge is 0 (no charge)Mass is 0 (no mass)Low ionizationPenetration abilities can be extremely high; – penetrating power is dependent upon the energy of the emitted photons28
30 What is a “packet” of light energy that behaves like a particle? PositronNegatronMegatronPhoton
31 Which form of radiation penetrates the least? Alpha DecayBeta DecayGamma DecayDelta Decay
32 Which radioactive particle increases the Parent Nucleus’s atomic number? Alpha ParticleBeta ParticleGamma ParticleDelta Particle
33 Which form of radiation penetrates the most? Alpha DecayBeta DecayGamma DecayDelta Decay
34 Which particle drops the Parent Nucleus’s atomic number by two? Alpha ParticleBeta ParticleGamma ParticleDelta Particle
35 Which particle resembles a Helium nucleus? Alpha ParticleBeta ParticleGamma ParticleDelta Particle
36 Which particle isn’t a particle but a photon? Alpha ParticleBeta ParticleGamma ParticleDelta Particle
37 Decay SystemsEach radioactive element will undergo various forms of radiation until it becomes stableThe particular elements that a “Parent Nucleus” changes into are always the sameThis “path” is a Decay System
39 Half-life Original Amount # of Current Amount 100g 1 50g 2 25g 3 46.25g53.125gThe amount of time it takes for HALF of an amount of a radioactive material to decayOne symbol for half-life is (lambda)
45 Nuclear Processes Fission The splitting of a large, unstable nucleus into two or more stable nucleiScientists can cause fission by injecting a neutron at high speedThese are the uses associated with nuclear fission:Power plants / reactorsBombs“Dirty bombs”
48 Nuclear Processes Fusion The joining of two or more smaller nuclei into one larger, more stable nucleusScientists are working on fusion using high pressures, temperatures, and lasersThe only place that fusion occurs naturally is stars
50 Chernobyl DisasterApril 26, 1986 – flawed reactor design was operated by inadequately trained personnel and w/o regard to safety
51 Chernobyl DisasterResult – steam explosion and fire released at least 5% of the radioactive reactor core into the atmosphere & downwind28 people died within 4 months from radiation or thermal burns19 subsequently died and 9 deaths from thyroid cancer
54 Half-Life Problems1. An isotope of cesium (cesium-137) has a half-life of 30 yrs. If 1.0 mg of cesium-137 disintegrates over a period of 90 yrs., how many mg of cesium-137 would remain?
55 Half-life2. A 2.5 gram sample of an isotope of strontium-90 was formed in a 1960 explosion of an atomic bomb at Johnson Island in the Pacific Test site. The half-life of strontium-90 is 28 yrs. In what year will only grams of this strontium-90 remain?
56 Half-life3. Actinium-226 has a half-life of 29 hours. If 100 mg of actinium-226 disintegrates over a period of 58 hours, how many mg of actinium-226 will remain?
57 Half-life4. Thallium-201 has a half-life of 73 hours. If 4.0 mg of thallium-201 disintegrates over a period of 6.0 days and 2 hours, how many mg of thallium-201 will remain?
58 Half-life5. Sodium-25 was to be used in an experiment, but it took 3.0 minutes to get the sodium from the reactor to the laboratory. If 5.0 mg of sodium-25 was removed from the reactor, how many mg of sodium-25 were placed in the reaction vessel 3.0 minutes later if the half-life of sodium-25 is 60 seconds?
59 Half-life6. The half-life of isotope X is 2.0 years. How many years would it take for a 4.0 mg sample of X to decay and have only 0.50 mg of it remain?
60 Half-life7. Selenium-83 has a half-life of 25.0 minutes. How many minutes would it take for a 10.0 mg sample to decay and have only 1.25 mg of it remain?
61 Half-life8. Element-106 has a half-life of 0.90 seconds. If one million atoms of it were prepared, how many atoms would remain after 4.5 seconds?
62 Half-life9. The half-life of Po-218 is three minutes. How much of a 2.0 gram sample remains after 15 minutes? Suppose you wanted to buy some of this isotope, and it required half an hour for it to reach you. How much should you order if you need to use 0.10 gram of this material?
63 Half-life10. Three grams of Bismuth-218 decay to grams in one hour. What is the half-life of this isotope?
64 Half-life11. The half-life of francium is 21 minutes. Starting with 4 x 1018 atoms of francium, how many atoms would disintegrate in 1 hour and 45 minutes? What fraction of the original sample remains?
65 Half-life12. The half-life of a radioactive element is 30 seconds. In what period of time would the activity of the sample be reduced to one-sixteenth of the original activity?
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