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Nuclear Physics and Radioactivity

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Nuclear Physics and Radioactivity AP Physics Chapter 30 Nuclear Physics and Radioactivity 30.1 Structure and properties of the Nucleus 30.1 Structure and Property of ... – PowerPoint PPT presentation

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Title: Nuclear Physics and Radioactivity


1
Nuclear Physics and Radioactivity
  • AP Physics
  • Chapter 30

2
Nuclear Physics and Radioactivity
  • 30.1 Structure and properties of the Nucleus

3
30.1 Structure and Property of the Nucleus
  • Nucleus is composed of two
  • particles
  • Proton positive charge
  • Neutron neutral
  • Together they are called nucleons

30.1
4
30.1 Structure and Property of the Nucleus
  • To present this information we use the symbol
    form
  • Z number of protons (atomic number)
  • A atomic mass (not average)
  • The number of Neutrons (N) is
  • Sometime written without the Z, as that
    information is redundant

30.1
5
30.1 Structure and Property of the Nucleus
  • Isotopes the same element, but different
    numbers of neutrons or mass number
  • These isotopes would be
  • Not all isotopes are equally
  • common
  • C-12 is 98.9
  • C-13 is 1.1
  • Called the Natural Abundance

30.1
6
30.1 Structure and Property of the Nucleus
  • Masses of atoms are determined using a mass
    spectrometer
  • The mass is given
  • in unified atomic
  • mass units (u)
  • Carbon 12 is
  • given the mass
  • of 12.000000u

30.1
7
30.1 Structure and Property of the Nucleus
  • Masses are often given in electron volts
  • This is derived from Einsteins equation
  • Using the mass of a proton
  • And placing into Einsteins equation

30.1
8
Nuclear Physics and Radioactivity
  • 30.2 Binding Energy and Nuclear Forces

9
30.2 Binding Energy and Nuclear Forces
  • The total mass of a stable nucleus is always less
    than the sum of the masses of its separate
    protons and neutrons
  • The difference is mass is
  • the binding energy
  • So for example the mass of
  • Helium 4 is 4.002603u

30.2
10
30.2 Binding Energy and Nuclear Forces
  • This is the energy needed to break apart the
    nucleus
  • To be a stable nucleus, the mass must be less
    than the parts
  • The binding energy per
  • nucleon is the total
  • binding energy divided
  • by A

30.2
11
30.2 Binding Energy and Nuclear Forces
  • Strong Nuclear Force attractive force between
    all nucleons
  • Drops to essentially zero if the distance between
    the nucleons is greater than 10-15m
  • Occur by the exchange of a particle called a
    meson
  • Weak Nuclear Force very weak, show in types of
    radioactive decay

30.2
12
30.2 Binding Energy and Nuclear Forces
30.2
13
Nuclear Physics and Radioactivity
  • 30.3 Radioactivity

14
30.3 Radioactivity
  • Henri Becquerel (1896) uranium darkens
    photographic plates
  • Radioactive decay unstable nuclei
  • fall apart with
  • the emission of
  • radiation

30.3
15
30.3 Radioactivity
  • Rays can be classified into three catagories
  • Alpha (a) barely penetrates paper
  • Beta (b) penetrates up to 3mm of aluminium
  • Gamma (g) penetrates several cm of lead

30.3
16
Nuclear Physics and Radioactivity
  • 30.4 Alpha Decay

17
30.4 Alpha Decay
  • An alpha particle is a helium nucleus
  • When an atom undergoes alpha
  • decay it loses 2 protons and 2
  • Neutrons
  • Reactions are written

30.4
18
30.4 Alpha Decay
  • Parent nucleus the original
  • Daughter nucleus nucleus of new atom
  • Transmutation change of one element into
    another
  • Basic form for alpha decay is
  • The alpha particle is ejected because it has a
    very large binding energy and is difficult to
    break apart

30.4
19
Nuclear Physics and Radioactivity
  • 30.5 Beta Decay

20
30.5 Beta Decay
  • Beta particle (b-) electron
  • Also produces an
  • antineutrino
  • Antineutrino has no
  • charge and almost
  • no mass
  • The result of the decay is that a neutron becomes
    a proton

30.5
21
30.5 Beta Decay
  • For Carbon 14 decay
  • Or the general form which would be
  • The electron does not come form the electron
    cloud, but from the decay of a neutron into a
    proton
  • It is identical to any other electron

30.5
22
30.5 Beta Decay
  • Unstable isotopes with too few neutrons compared
    to their number of protons decay by emitting a
    positron
  • Positron same mass as an
  • electron, positive charge
  • This is an example of an antiparticle
    (antimatter)
  • The decay pattern is

30.5
23
Nuclear Physics and Radioactivity
  • 30.6 Gamma Decay

24
30.6 Gamma Decay
  • Gamma Ray photon of
  • EMR
  • A nucleus can be in an
  • excited state like an
  • electron
  • When it drops down it emits a g ray
  • Much larger than for electrons
  • For a given decay the g ray has the same energy

30.6
25
30.6 Gamma Decay
  • The nucleus may enter an excited state by
  • Violent collision with another particle
  • The particle after a decay is often in an
    excited state
  • The equation can be
  • written

30.6
26
Nuclear Physics and Radioactivity
  • 30.7 Conservation of Nucleon Number

27
30.7 Conservation of Nucleon Number
  • In radioactive decay all conservation laws are
    true
  • Energy
  • Linear Momentum
  • Angular Momentum
  • Electric Charge
  • Law of Conservation of Nucleon Number the
    number of nucleons (protons or neutrons) remains
    the same, although they may change type

30.7
28
Nuclear Physics and Radioactivity
  • 30.8 Half-Life and Decay Rate

29
30.8 Half-Life and Rate of Decay
  • Individual radioactive nuclei in a random process
  • Based on probability we can approximate the
    number of nuclei in a sample that will decay
  • Where l is the decay constant

30.8
30
30.8 Half-Life and Rate of Decay
  • The greater the decay constant, the greater the
    rate of decay
  • The more radioactive it is
  • The equation can be solved for N using calculus
    and we get
  • Where N0 is the initial number of nuclei present
  • N is the number remaining after time t
  • The number of decays per unit time is called the
    activity or rate of decay

30.8
31
30.8 Half-Life and Rate of Decay
  • Half-Life the time it takes for half the
    original amount of parent isotope to decay (T½)

30.8
32
Nuclear Physics and Radioactivity
  • 30.9 Calculations Involving Decay Rates and
    Half-Life

33
30.9 Calc. Involving Decay Rates and Half-Life
  • Carbon-14 has a half-life of 5730 yr. What is
    the activity of a sample that contains 1022
    nuclei?
  • 1 decay/s is called a becquerel (Bq)

30.9
34
30.9 Calc. Involving Decay Rates and Half-Life
  • 1.49mg of Nitrogen-13 has a half life of 600s.
  • How many nuclei are present?
  • What is the initial activity?

30.9
35
30.9 Calc. Involving Decay Rates and Half-Life
  • 1.49mg of Nitrogen-13 has a half life of 600s.
  • What is the activity after 3600s?
  • 6 half lives
  • If this had not been a perfect half life we would
    have used

30.9
36
Nuclear Physics and Radioactivity
  • 30.10 Decay Series

37
30.10 Decay Series
  • Decay Series a successive set of decay

30.10
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