2 Henri Becquerel ruined some photographic plates with x-rays from a uranium source and radioactive decay was discovered in 1896.
3 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!
4 RadioactivityOne of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ).She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.
5 Marie and Pierre Curie’s experiments with pitchblende – Discovered Radioactive Naturally occurring elements, particularly Uranium, Radium, and Polonium. Curium was named after Marie posthumously
6 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 lightCathode 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
7 BETA PARTICLESConsists of – high speed electron (from disintegration of neutron)Tissue damage potential – much greater than AlphaHarmful if ingested? – not as much as AlphaCan be blocked? – by glass, will penetrate skin
8 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
9 ALPHA PARTICLESConsists of – He nucleusTissue damage potential – great – if internalizedHarmful if ingested? – yup, veryCan be blocked? – by layer of skin, or cardboardNote that atoms are NOT conserved in nuclear reactions, but mass numbers and atomic numbers are.
10 NUCLEAR RADIATION Ernest Rutherford and the Lead block experiment (1899) - Alpha rays () Beta rays ()– Gamma rays ()
11 Thompson 1906 Rutherford 1913 Bohr 1924 How did Rutherford’s gold foil experiment change the theory of the structure of the atom?Thompson1906Rutherford1913Bohr1924
12 ARCHITECTURE OF THE ATOM Atomic Number – Number of protonsDetermine what type of element an atom isMass Number – Sum of total number of protons and neutrons in an atomCan change for an element depending upon the number of neutrons presentIsotopes – Elements with the same atomic number, but different mass numbersDue to the difference in number of neutronsExample:C-14 and C-12H-1, H-2, and H-3Radioisotope – Isotope that is unstable and undergoes decay, thus giving off radiation
14 Protons (Atomic Number) Common IsotopesSymbolNameProtons (Atomic Number)NeutronsMass NumberElectrons73Li Lithium -7 3 47 146 CCarbon-14 68 1466731GaGallium -6731 3667 Isotopes of Particular interest –C-14 used in radiocarbon datingI-131 used in thyroid cancer treatmentU-235 used in nuclear power
15 ISOTOPES IN NATUREAtomic 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
16 Nuclear Section B Introduction Approx. 90 known naturally occurring elementsApprox. 350 known isotopes in our solar systemApprox. 70 of these radioactiveRadioactive – just means unstable – it naturally decaysApprox. 1,600 Lab created isotopesThere is a rather constant level of natural radiation in our environment – called background radiation
17 Change in Atomic Number TABLE OF CHANGES RESULTING FROM NUCLEAR DECAYTypeSymbolChange in Atomic NumberChange in NeutronsChange in Mass NumberAlpha -2-2 -4 Beta +1 -10 Gamma 0
61 IONIZING RADIATION – HOW MUCH IS SAFE? Rem – Roentgen equivalent to man1Rem = 1000 mRemDoes not matter what type of radiation it is, it still has the same ionizing effect on living tissue1 mRem of exposure to radiation increases risk of cancer death by 1 in 4 millionTwo things to consider:Radiation densityRadiation dose
62 RADIATION DAMAGE: NOW AND LATER Radiation damage to your body can occur in several ways:Break apart essential moleculesproteins (i.e. enzymes)nucleic acids (i.e. DNA)MutationsKills cellsMutates sperm/ovaCancerGovernment recommends no greater than exposure to 500 mrem per year for general publicGovernment recommends no greater than 5,000 mrem per year from the workplace
63 Factor Effect Dose Exposure time Area Exposed Tissue type Table of Factors Effecting Biological Damage from RadiationFactorEffectDoseIncrease in dose produces proportional increase in riskExposure timeSpreading out over time decreases riskArea ExposedLarger area means greater riskTissue typeRapidly dividing cells more susceptible
65 EXPOSURE TO RADIATION Exposure to radiation can come from: Cosmic Rays Radioisotopes in rocks, soil, water, airFallout from nuclear weapons testingAir travelRadioisotope release from nuclear power generationGovernment recommends no greater than exposure to ______________for general publicGovernment recommends no greater than ___________ per year from the workplace
67 RADON IN HOMESRadon gas comes from: Gas released from earth (from Uranium decayRadon 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.