nuclear changes

Download Nuclear Changes

Post on 02-Jan-2016

12 views

Category:

Documents

0 download

Embed Size (px)

DESCRIPTION

Nuclear Changes. Chapter 7. 7.1 What is Radioactivity?. Large atoms are unstable. When the nucleus is crowded with protons and neutrons, it’s just ”too much.” The nucleus begins to emit (shoot out) particles and/or energy. Radioactivity. Penetrating power of different forms of radiation:. - PowerPoint PPT Presentation

TRANSCRIPT

  • Nuclear ChangesChapter 7

  • 7.1 What is Radioactivity?Large atoms are unstable.When the nucleus is crowded with protons and neutrons, its just too much.The nucleus begins to emit (shoot out) particles and/or energy.

  • RadioactivityPenetrating power of different forms of radiation:

  • RadioactivityMarie (1867-1934) and Pierre Curie (1859-1906) isolated polonium and radium from pitchblende

    both elements more radioactive than pure uranium

    discovered that the source of energy (radiation) were the atoms themselves

    nature of radioactivity was still unknown

  • RadioactivityErnest Rutherford (1871-1937) studied absorption of 'rays' emitted by uranium-containing minerals

    two types of rays: - and -rays

    -rays are more penetrating than -rays

    - and -rays are not rays at all (like X-rays or light) but streams of particles

  • RadioactivityErnest Rutherford (1871-1937) -particles behave like electrons, (1 negative charge) - move very fast

    -particles and have 4 times the mass of a hydrogen nucleus and twice the charge (2 positive charges)-particle = Helium nucleus(2 protons, 2 neutrons)

  • Radioactivity - and -radiation are made up of particles, -radiation is not!

    -radiation is electromagnetic radiation (just like light and X-rays):no mass, no charge

  • RadioactivityRadioactive decay:b-decayProtonNeutrona Neutron may split into a Proton plus an ElectronElectron

  • RadioactivityRadioactive decay:b-decayProtonNeutronElectronthe electron is ejected from the nucleus as -radiation......leaving behind a nucleus with an extra proton

  • Nuclear vs Chemical ReactionNaNaOH + HCl H2O + NaClOHHClNaOHHCl*** Not a true representation of this reaction in solutionChemical ReactionNuclear Reaction212Po 4a + 82Pb220884*** Not a true representation of the nuclei

  • The Half-Life (t1/2) of a Nuclear ReactionHalf-life (t1/2): The time it takes for half of the radioactive nuclei in a sample to decay.48 radioactiveparticles at t=024 radioactiveparticles at t=1(1 half life)12 radioactiveparticles at t=1(2 half life)6 radioactiveparticles at t=1(3 half life)# of radioactivenuclei

  • The Half-Life (t1/2) of a Nuclear ReactionHalf-life (t1/2): The time it takes for half of the radioactive nuclei in a sample to decay.48 radioactiveparticles at t=024 radioactiveparticles at t=1(1 half life)12 radioactiveparticles at t=2(2 half lifes)6 radioactiveparticles at t=3(3 half lifes)# of radioactivenucleiFraction ofnuclei48/48 = 1 @ t1/2 = 1

    24 = 148 2@ t1/2 = 2

    12 = 1 * 1 = 1 48 2 2 4@ t1/2 = 3

    6 = 1 * 1 * 1 = 1 48 2 2 2 8

  • The Half-Life (t1/2) of a Nuclear ReactionHalf-life (t1/2): The time it takes for half of the radioactive nuclei in a sample to decay.48 radioactiveparticles at t=024 radioactiveparticles at t=1(1 half life)12 radioactiveparticles at t=2(2 half lifes)6 radioactiveparticles at t=3(3 half lifes)# of radioactivenucleiFraction ofnuclei48/48 = 1 @ t1/2 = 1

    24 = 148 2@ t1/2 = 2

    12 = 1 * 1 = 1 48 2 2 4@ t1/2 = 3

    6 = 1 * 1 * 1 = 1 48 2 2 2 8General FormulaFraction remaining = 1 2nwhere n is the # of half lifes

    Chart2

    1

    0.5

    0.25

    0.125

    0.0625

    0.03125

    0.015625

    fract remaining

    # of half lives

    Fraction remaining

    Radioactive Decay

    Sheet1

    t 1/2fract remaining

    01

    10.5

    20.25

    30.125

    40.0625

    50.03125

    60.015625

    Sheet1

    fract remaining

    # of half lives

    Fraction remaining

    Radioactive Decay

  • Lets go over all that again!

  • Phenomenon of RadioactivitySome elements, such as uranium (U) and thorium (Th), are unstable:

    They decay spontaneously.

  • Uranium Nucleus spontaneously emits a particle from its nucleus called an alpha particle (2 protons + 2 neutrons).

  • Alpha Particle emits a particle from its nucleus called an alpha particle (2 protons + 2 neutrons).

  • Uranium - Thorium Decayspontaneousdecayparentdaughter productalpha particle =2 protons + 2 neutrons = positively charged ion of HeliumThorium:90 protons + 144 neutrons

  • Beta Particle EmissionBut, Th is also unstable, and it emits a beta particle 23490

  • Th + Pa2349023491Thorium - Protactinium Decaybeta particlebeta particle = an electron discharged from the nucleus when a neutron splits into a proton and an electronProtactinium:91 protons + 143 neutrons

  • Titlebeta particle = an electron discharged from the nucleus when a neutron splits into a proton and an electron

  • U PbSeriesThis process is called radioactive decay, and eventually uranium (parent) decays to lead (daughter product).

  • U PbSeriesThe rate at which this process occurs is measured in terms of the half life.

  • Half LifeHalf Life = Number of years for 1/2 of the original number of atoms to decay from U to Pb

  • Carbon-14 Dating

Recommended

View more >