21.6: energy changes in nuclear reactions

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21.6: Energy Changes in Nuclear Reactions. Courtney Wong & Lauren Hebel. Energy Associated with Nuclear Reactions. Energy and mass of nuclear reactions are related in Einstein's famous equation E=mc 2 E=energy M=mass C= speed of light (3.00 x 10 8 ) - PowerPoint PPT Presentation

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• 21.6: Energy Changes in Nuclear ReactionsCourtney Wong & Lauren Hebel

• Energy Associated with Nuclear ReactionsEnergy and mass of nuclear reactions are related in Einstein's famous equationE=mc2E=energyM=massC= speed of light (3.00 x 108)Equation states that mass and energy are proportionalIf a system loses mass, it loses energyVice -versa

• Mass change, mMass changes and associated energy changes are much greater in nuclear reactions when compared to chemical reactionsm=(total mass of products) (total mass of reactants)-m= exothermic = spontaneous nuclear reaction

• Example m Problem22688Ra --> 22286Rn + 42He(mass of p) - (mass of r)m = Mass of one mole of 42He + mass of one mole of 22286Rn mass of one mole of 22688Ram = 4.0015 g + 221.9703 g - 225.9771 gm = -0.0053 gReaction:

• Using m In Einsteins EquationRearranged as E=c2mTo obtain E in joules, m must be converted to Kg when used in the equationExample: Continuedm = -0.0053 gE = (2.9979 x 108)2 (-0.0053) (1kg/1000g)E=-4.8x1011

• Nuclear Binding Energies1930s: scientists discovered that mass of individual parts of the nucleus always weighs more that the nucleus itselfEx:Helium-4 nucleus has a mass of 4.00150 amuMass of two protons = 2(1.00728 amu) = 2.01456 amu Mass of two neutrons= 2(1.00728 amu) = 2.01456 amu Total Mass = 4.03188 amu

• Ex: (continued)Mass of two protons and two neutrons = 4.03188 amu Mass of 42He nucleus = 4.00150 amuMass Difference (m) = 0.03038 amu

Mass Defect: the mass difference between a nucleus and it individual nucleons

Increase in mass = increase in energy Energy + 42He 211p + 210n soE=c2m = (2.9979 x 108 m/s)2 (0.03038 amu) ( ) () = 4.534 x 10-12 J

1g 6.022 x 1023 amu1kg

1000gNuclear Binding Energy

• Nuclear Binding EnergyThe energy required to break apart a nucleus into its individual nucleonsThe larger the binding energy the more stable the nucleus is towards decomposition

NucleusMass of Nucleus (amu)Mass of Individual Nucleons (amu)Mass Defect (amu)Binding Energy (J)Binding energy per Nucleon (J)42He4.001504.031880.030384.53 x 10-121.13 x 10-12

5626Fe55.9206856.449140.528467.90 x 10-111.41 x 10-12

23892U238.00031239.934511.934202.89 x 10-101.21 x 10-12

• Nuclear Binding EnergyBinding energy per nucleon increases in magnitude as mass number increases, reaching ~1.4 x 10-12 J (mass number of nuclei close to iron-56)Then it decreases to ~1.2 x 10-12 J for a very heavy nuclei

• 42He

5626Fe23892UTrend: nuclei of intermediate mass numbers are more tightly bound and more stable than those with either smaller or larger mass numbers

Chart1

1.13

1.41

1.21

Fusion

Fission

Y-Values

Sheet1

X-ValuesY-Values

4.00151.13

55.920681.41

238.000311.21

To resize chart data range, drag lower right corner of range.

• Nuclear Binding EnergyTrend shows that:Heavy nuclei gain stability and split into two mid-sized nucleiKnown as FISSIONUsed to generate energy in nuclear power plantsGreater amounts of energy are released if very light are fused together to form a more massive nucleiKnown as FUSIONis an essential energy-producing process in the Sun

• Susanna Trost Kelsey Mariner

• Natural and artificial sourcesSun gives off infrared, ultraviolet, & visible radiationTelevision and radio stations give off radio waves Microwaves ovens give off microwavesMedical procedures can give off X-raysNatural materials like soil can have radio activity

EVERYDAY LIFE

• Excitation is when excited electrons are moved to a higher energy state or the motion of molecules is increased as a result of absorbed radiationIonization is when an electron is removed from a molecule or atom by radiationIonizing radiation: radiation that causes ionization, can ionize waterNon-ionizing radiation: radiation that does not cause ionization and has a lower energy

• Free Radical: A substance with one or more unpaired electrons OH molecule is a highly reactive and unstable free radical

Free radicals attack surrounding biomolecules which produces new free radicalsOne free radical can cause many chemical reactions disrupting normal cell operations

H2O+ + H2O H3O+ + OH

• Based on energy and activity of radiation, location of source, and length of exposureGamma rays and X-rays can penetrate human tissueThe skin stops alpha raysIf within the body, they can transfer energy to surrounding tissues causing damageBeta rays penetrate only 1 cm into the skinTissues that rapidly reproduce show the most damageExamples: Lymph nodes, bone marrow, and blood forming tissuesProlong exposure to radiation may lead to cancerDamage to a cells growth-regulation mechanism causes a cell to rapidly and uncontrollably reproduceLeukemia is most associated with radiation (excessive growth of white blood cells)

Gray (Gy): the SI unit of absorbed doseOne joule per kilogram of tissue Rad (radiation absorbed dose): 1 x 10-2 joule of energy per kilogram of tissue

• Different types of radiation harm biological materials differentlyRBE is a multiplication factor that measures the relative biological damage caused by radiationMultiplied by the radiation dose to correct the differences in radiation damage changes with total dose, dose rate and the type of tissue affectAbout 1 for beta and gamma radiationAbout 10 for alpha radiation Rem (roentgen equivalent for man): unit for effective dosage, more commonly usedSievert (Sv) is the SI unit for effective dosage1 Sv = 100 remRELATIVE BIOLOGICAL EFFECTIVENESS# of rems = (# of rads)(RBE)(gray)(RBE) = Sv

• Radioactive noble gasRadon-222 is caused from nuclear disintegration series of Uranium-238 Created in soil and rock decays as uraniumAccounts for large percentage of our exposure to radiationDoes not chemically react as it escapes from the groundBecause it is extremely unreactive Has a very short half lifeCombined with its high RBE, radon is a probable cause of lung cancer when inhaled

• High-energy radiation is used to damage the DNA of cancer cells, which kills the cells

Normal cells can also be damaged, so treatment is done very carefully Cancer cells more likely to be damaged because rapidly reproducing cells are very vulnerable to radiation damage

Radiation can come from a machine or radioactive material can be injected into the bloodstream or placed directly in the body near the tumor cells

Gamma rays, x-rays and charged particles can be used

Chemistry The Central Science Textbook

• ReviewNucleons- both protons and neutronAll atoms:Same # of protons (atomic #)Can have different # of neutronsMass number- total # of nucleons in nucleus Same atomic # but different mass number- isotopes

• IsotopesUranium-235 or UDifferent natural abundancesDifferent stabilitiesNuclide- nucleus with specified # of protons and neutronsRadionuclides- radioactive nucleiRadioisotopes- atoms containing those nuclei23592

• Nuclear EquationsRadionuclides- unstable, spontaneously emit particles and electromagnetic radiation Emit radiation to become more stableEmitted radiation is carrier of the excess energy

• Nuclear EquationsEx: Uranium-238 and helium-4Helium-4 particles are known as alpha particles Alpha radiation- stream of alpha particles238 234 4 92 90 2 radioactive decay and alpha decay238 = 234 + 492 = 90 + 2Must be balancedUThHe

Propertya (Alpha) (Beta) (Gamma)Charge2+1-0Mass6.64 * 10^-24g 9.11 * 10^-28g0Relative penetrating power110010,000Nature of radiation He nucleiElectronsHigh-energy protons

• Beta RadiationBeta particles- high speed electrons emitted by an unstable nucleus 0 0 -1 -1

1 1 00 1 -1

e orn p + e

• Gamma Radiation (Gamma Rays)High-energy photons (electromagnetic radiation of very short wavelength)Does not change atomic # or mass #Represents the energy lost when remaining nucleons reorganize to be more stableGenerally not shown when writing equations

• Positron Emission Same mass as an electron, but opposite charge

Converts proton to neutron and decreases atomic number by 1

• Electron CaptureThe capture by the nucleus of an electron from the electron cloud surrounding the nucleus

Shown on reactant side because the electron is consumed not formed in the processConverts proton to neutron

• Further ResearchPositron Emission Tomography Scan- imaging test to help reveal how tissues and organs are functioningInject, swallow, or inhale radioactive material Accumulates in areas with higher levels of chemical activity (areas of disease)

Gamma Knife Therapytreatment using gamma rays, a type of high-energy radiation that can be tightly focused on small tumors or other lesions in the head or neck, so very little n

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