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Energy Changes in Nuclear Reactions. BY…. E=mc². Einstein’s equation that relates mass and energy E=Energy m=mass c=speed of light, 3.00 x 10 8 m/s States that mass and energy are proportional If a system loses mass, it loses energy, and vice versa - PowerPoint PPT Presentation


Energy Changes in Nuclear Reactions

Energy Changes in Nuclear ReactionsBYE=mcEinsteins equation that relates mass and energyE=Energym=massc=speed of light, 3.00 x 108 m/sStates that mass and energy are proportionalIf a system loses mass, it loses energy, and vice versaMass and energy changes are much greater in nuclear reactions than in chemical reactions

Example of E=mc238 U 234 Th + 4 HeMass U=238.0003 amu, mass Th=233.9942 amu, mass He=4.0015 amum=233.9942g+4.0015g-238.0003=-0.046Lost mass=exothermicEnergy change calculated through Einsteins equation, E=mc:E=(mc2)=c2m =(2.9979 x 108 m/s)2(-0.0046 g)(1 kg/100o g) =-4.1 x 1011 kg-m2/s2 = -4.1 x 1011 J

(Note: m is converted to kg, SI unit of mass, to get E in joules, SI unit for energy.)

Nuclear Binding EnergiesEnergy required to separate a nucleus into its individual nucleonsMasses of nuclei are always less than the masses of individual nucleonsMass defect- difference between a nucleus and its constituent nucleonsAddition of energy to a system must be joined by a proportional increase in massLarger the binding energy is, the more stable the nucleus is towards decomposition

Nuclear Binding Energies Continued Binding energies per nucleon initially increases in magnitude as mass number increases Nuclei of intermediate mass numbers are more tightly bonded (more stable) than other nuclei that is smaller or has larger mass numbersTrend has two consequences Heavy nuclei gain stability and give off energy if they divide into two mid-sized nuclei Fission Greater amounts of energy is release when very light nuclei are combined or fused together to give larger nucleiFusion Biological Effects of Nuclear RadiationBy: Kayla Seider and Hannah CherryRadioactivity We are continually being bombarded by artificial and natural radiationInfrared, UV, visible radiation from the sun, radio waves, microwaves, and x-raysThere is radioactivity in the soil and other materials

Types of RadiationIf matter absorbs radiation, it can cause either excitation or ionization of the matterExcitation occurs when absorbed radiation excites electrons to a higher energy state or increases the motion of moleculesCauses them to move, vibrate, or rotateIonization occurs when the radiation removes an electron from an atom or moleculeIs more harmful than radiation that doesnt cause ionizationNon-ionization is lower in energy or slower moving neuronsRadiofrequency electromagnetic radiationMost of the energy is absorbed by water molecules in tissueMost tissue is 70% water by massCan define ionizing radiation as radiation that can ionize waterX-rays, higher-energy UV, alpha, beta, and gamma rays

What HappensWhen ionization radiation passes through living tissue, electrons are removed from water molecules, forming highly reactive H2O+ An H2O+ can react with another water molecule to form H3O+ and a neutral OHOH becomes a free radicalA free radical is a substance with one or more unpaired electronsIn cells and tissues, these particles can attack a host of surrounding biomolecules to produce new free radicalsThese new free radicals can initiate a large number of chemical reactions that are able to disrupt the normal operation of cellsCan contribute to cancer, diabetes, stroke, heart attack, Parkinson's, Alzheimer's, schizophrenia, and hemochromatosis

The DamageDamage depends on the activity and energy of the radiation, the length of exposure, and whether the source is inside or outside the bodyGamma rays are harmful outside of the bodyThey can penetrate human tissue very easilyCan cause organ damage and genetic damageDangerousAlpha rays are stopped by skinIn the body, alpha rays are particularly dangerous because they transfer their energy efficiently to the surrounding tissue causing considerable damageBeta rays can penetrate about a cm beyond the skinTissue that shows the greatest damage are those that reproduce at a rapid rateBone marrow, blood-forming tissues, and lymph nodes

Radiation DosesRadiation is measured in the gray (Gy) and the rad (radiation absorbed dose)The gray is equivalent to the absorption of 1 J of energy per kilogram of tissueThe rad is equivalent to the absorption of .01 J of energy per kilogram of tissue1 gray= 100 radsA rad of alpha radiation causes more damage than a rad of beta radiationTo correct these differences, the radiation dose is multiplied by a factor that measures the relative biological effectiveness (RBE) of radiation The exact RBE value varies with dose rate, total dose, and the type of tissue affectedRBE is approximately 1 for gamma and beta and 10 for alphaThe product of radiation dose and the RBE gives you the effective dosage in units of rem (roentgen equivalent for man)Number of rems= (number of rads)(RBE)The siervert (Sv) is the unit for effective dosage 1 Sv= 100 Rem

Radiation DosesDose (rem)Effect of Short-Term exposures to Radiation0 to 25No detectable clinical effects25 to 50Slight, temporary decrease in white blood cell counts100 to 200Nausea; marked decrease in white blood cells500Death of half the exposed population within 30 days after exposure600 rem will cause deathDental x-rays is .5 mremThe average exposure for a person in one year due to natural sources of ionizing radiation is about 360 mrem

Radiation TherapyBoth healthy and unhealthy cells can be destroyed by radiationCan lead to physiological disordersCancer is the growth of abnormal cells, that growth produces malignant tumorsThe tumors can be destroyed by exposing them to the same radiation because rapidly reproducing cells are susceptible to radiation damage Therefore, cancerous cells are easier to destroy than healthy onesThats why radiation is used in cancer treatmentSide effectsFatigue, nausea, hair loss, weakened immune system, even deathBecause of these side effects, radiation therapy is a last resort for treatments

True or FalseRadiation in Japan is equal to 38,000 bananasTrueAbout 1,200 radioactive isotopes have been produced in all the known elementsTrueYou get little amounts of radiation while on a nuclear submarineTrueBurning coal releases more radiation than a nuclear plant doesTrue

QuestionsWhat is ionizing radiation? Radiation that can ionize water and it can remove an electron from a moleculeWhat is a free radical? Why is it so bad?A substance with one or more unpaired electrons. They disrupt the normal operations of cellsWhich is smaller the rad or the gray and how are they related to eachother?The rad is smaller than the gray. 1 gray= 100 radsWhat dose of rems cause death?500-600 rems

21.8: Nuclear FusionKyle, Suraj, BrianNuclear Fusion Energy is produced when light nuclei fuse into heavier onesTalked about in 21.6 (dont write this part down)Type of reactions responsible for energy produced by sun

=Equal in hottness (write this equation down)

Nuclear fusionIntense workoutsNuclear FusionSeveral different types of fusion processes:1/1H+1/1H 2/1H+ 0/1e1/1H+2/1H 3/2He3/2He+3/2He 4/2He+2(1/1H)3/2He+1/1H 4/2He+0/1eFusion EnergyAppealing as an energy sourceNonradioactive productsLight isotopes of hydrogen are easily availableCurrently not usedExtremely high energies are needed to overcome repulsion of nuclei

Overcoming Nuclei RepulsionIn order to achieve the required energies, high temperatures must be maintainedThus, fusion reactions are known as thermonuclear reactionsLowest temperature required for fusion is 40 million KelvinThis temperature has only been achieved by hydrogen bombsUncontrolled power generation

-Requires 40,000,000 K to initiateFusion as energy Numerous problems must be overcome before fusion becomes a practical source for energyHigh Temperatures to start reactionConfining the reactionNo known material is able to withstand the temperature needed for fusionResearches try to use tokomaks to achieve fusionAlso use lasers

TokamakUses strong magnetic fields to contain and to hear a fusion reactionHave reached 3million degrees Kelvin

Nuclear FissionJake Wiley, James Haeckel, Sergio MachacaFissionExtremely exothermicUranium-233, -235, and Plutonium-239 are main practical sources1 neutron hits a heavy nuclei and causes it to splitAverage of 2.4 neutrons are releasedVarious and unpredictable products, typically radioactive

Chain ReactionsEach neutron released can cause another nucleus to splitCritical MassEnough mass of the material is present to sustain the reaction at a constant rateUranium ~ 1kgSubcritical MassLess than critical mass, neutrons escape without hitting any nucleiSupercritical MassMore than critical mass, reaction proceeds unchecked, typically with violent resultsWhich one is Subcritical? Supercritical?

Nuclear ArmsGun-typeTwo subcritical masses are shot together into a supercritical massImplosionSubcritical mass of P-239 is compressed by explosives to supercritical mass

Nuclear ReactorsFuel rods typically use 3% U-235Encased in stainless steel or zirconium tubesControl rods regulate amount of neutronsTypically boron or cadmiumA moderator is used to slow the neutrons as to be more readily absorbed by fuelA cooling liquid is used to carry off excess heatOften the moderator and cooling liquid are one in the sameNuclear Reactors (Cont.)Excess heat is used to turn water to steamUsed to turn a turbineSteam is cooled and condensedOften cooled with water from a stream or lakeAll incased in reinforced concretePrevents radiation leakProtects reactor from external forces

Nuclear WasteEstimated at 20 half-lives before safe exposurePuts used fuel at about 600 yearsDangerous to handle and transportOriginally stored in pools at reactor and transported to reprocessing plantsTransportation incredibly unp


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