Nuclear Reactions

1
Nuclear Reactions
2

• A nuclear reaction is a reaction that affects the
  _____________atom.
• In nuclear equations, the atomic mass and atomic
  numbers must be _____ on both sides of the
  equation.

3
Examples

• 9 4 ____
• Be He ? C
• 4 2
• 142 0
• Pm e ?
• 61 -1

4
Note When solving for an unknown in a nuclear
equation, use the atomic number to determine the
identity of an unknown atom or particle.

• Atomic Number Identity
• 1 _______
• 0 _______
• -1 _______
• 1 _______

5

• ___________is the spontaneous disintegration of a
  nucleus into a slightly lighter and more stable
  nucleus, accompanied by emission of particles,
  electromagnetic radiation, or both.
• Uranium is a _______________, an unstable nucleus
  that undergoes radioactive decay.

6

• Marie and Pierre Curie found that of the elements
  known in 1896, only U and Th were radioactive.
• In 1898, however, they discovered two new
  elements, Po and Ra.
• Now all of the nuclides above atomic number ____
  are unstable and radioactive.

7

• ________________ is restricted almost entirely to
  heavy nuclei.
• An alpha particle (a) is _________________________
  _(i.e. He-Helium) emitted from the nucleus of an
  atom during alpha emission.
• NOTE The atomic number decreases by __ and the
  mass number decrease by ___.

8
ALPHA EMISSION
9
EXAMPLES

• 243 ? 4 237
• Am He Np
• 95 2
  93

10

• Sometimes elements are unstable because they have
  too many neutrons, so to decrease the number of
  neutrons, a __________ can be converted to a
  _______ and an ________.
• The electron is then emitted from the nucleus as
  a beta (___) particle.
• Note the atomic number increases by one and the
  mass number stays the same.

11
Beta Emission
12

• Sometimes, elements have too many protons to be
  stable, so to decrease the number of protons, a
  proton is converted into a neutron by emitting a
  _________.
• A positron (1ß) is a particle that has the same
  mass as an electron, but has a positive charge.
• Note The atomic number__________________________
  ________________________.

13
Positron Emission
14

• Another type of decay for nuclides with too many
  protons is _____________________.
• This is when an inner orbital electron is
  captured by the nucleus of its own atom.
• The inner orbital electron combines with a
  proton, and a ___________ is formed.
• NOTE The atomic number decreases by one, but
  the mass_______________.

15
Electron Capture
16

• _______________ (?)are high-energy
  electromagnetic waves emitted from a nucleus as
  it changes from an excited state to a ground
  energy state.
• According to the nuclear shell model, gamma rays
  are produced when nuclear particles undergo
  transitions in nuclear-energy levels.
• This is similar to the emission of light when an
  electron drops to a lower-energy level.

17
Nuclear Equation Solution Process

• 1. Find the mass of the unknown product.
• Mass of positron mass of ?? 18
• 0 ______ 18
• 
  ______ 18
• 2. Find the charge of the unknown product.
• Charge of positron charge of ? 9
• 1 _____ 9
• _____ 8

18
Nuclear Equation Solution Process

• 3. Determine the identity of the unknown
  product. Turn to the periodic table and find the
  nuclide with 8 protons.
• _____________ has 8 protons and the symbol for an
  oxygen atom with a mass of 18 is
• 4. Complete the nuclear equation
• 18 0 18
• F ? e O
• 9 1 8

19
Nuclear Decay Reactions

• Protons and Neutrons in the nucleus are held
  together by the _______ and ______ nuclear
  forces.

20

• Protons and Neutrons are made of smaller
  particles called _______.

U
U
U
D
D
D
Proton Neutron
21
Neutron
U
D

• Quarks are held together by the strong and weak
  nuclear forces.
• Quarks can change into each other.
• A down quark can emit a beta particle and turn
  into an up quark.

D
22

• The net result is an emission of a beta particle
  and the transformation of a neutron into a
  proton.
• This is called __________.
• 1 1 0
• n ? p e
• 0 1 -1

23
Two other processes may change a proton into a
neutron

• _______ decay and _______ capture
• 1 1 0
• p ? n e
• 1 0 -1
• 1 0 1
• p e ? n
• 1 -1 0

24

• These reactions are called ____________________whe
  re one element changes into another.

25
Types of Transmutations

• Alpha decayemission of an alpha particle
• Beta decayemission of a beta particle
• Positron decayemission of a positron particle
• Electron capturenucleus captures an electron
  from the inner orbital

26
Alpha decayusually from heavy elementstoo many
neutronsdecrease the mass and charge of the
nucleus.

• 226 222
• Ra ? Rn
• 88 86

27
Beta decayusually from lighter elementstoo few
neutronsmass doesnt change and charge of
nucleus increases.

• 14 0
• C ? e
• 6 -1

28
Positron decaymass doesnt change and charge of
the nucleus decreases.

• 14 0
• N ? e 7
  -1

29
Electron capturemass doesnt change and charge
of the nucleus decreases.

• 14 0
• N e ?
• 7 -1

30

• Half-lifeT ½ -- the time it takes for half of
  the radioactive isotope to decay.

31

• Half-life depends on the isotope. The range is
  from fractions of seconds to billions of years.
• Examples
• Carbon-14 5730 yrs
• Iodine-131 8 days
• Uranium-238 447 bill. yrs

32
Radioactive Dating Techniques

• Since radioactive isotopes decay to stable
  isotopes at a set rate (half-life), the age of
  artifacts (natural and manmade) can be determined
  by comparing the ratio of radioactive isotopes to
  daughter isotopes present in the sample.

33

• Carbon-14 is a very small percentage of the
  carbon in the atmosphere. It is taken in by
  plants along with carbon-12 and made into sugars
  for the plant to use. When living things eat the
  plant, they incorporate the carbon-14 in their
  bodies too. As long as the organism is alive,
  the rate of intake and decay of carbon-14 remains
  constant. When the organism dies, only decay
  occurs.

34

• The daughter isotope of this decay is
  nitrogen-14. The T ½ is 5730 yrs.
• If, when alive, there are 8 g of C-14 in a sample
  of timber, and now there is only 1 g, how long
  has the timber been dead?
• 8 __ __ -- __ takes
• 3 half-lives.
• ___ (5730 yrs) _____ yrs.

35
If 1.5 g is left, how long has it been dead?

• Since 1.5 g is between 2 and 3 half-lives, the
  age is between 11,460 and 17,190 yrs.
• Graphing would allow you to be more accurate in
  your guess.

36
(No Transcript)
37
OR You could use logarithms

• We wont worry about this right now.

38
OTHER NUCLEAR RXNS

• RADIOACTIVE DECAY IS ONLY ONE KIND OF NUCLEAR
  REACTION
• OTHER REACTIONS THAT INVOLVE NUCLEI AND NUCLEAR
  PARTICLES ARE ________ AND _________.

39
Nuclear Fission

• In a nuclear fission reaction, a large nucleus is
  split into _______________________of
  approximately equal mass.
• Fission reactions are used to provide what is
  commonly called nuclear power.

40

• In a Nuclear Reactor, the Fission of 4.5 grams of
  Uranium-235 will satisfy the average persons
  energy needs for an entire year.

41
(No Transcript)
42
Nuclear Fission

• One nuclear reaction produces enough neutrons to
  start three more fission reactions, which in turn
  produces the neutrons needed to start three more
  reactions, and so on, in a series called a
  _________________________

43
(No Transcript)
44
Nuclear Fusion

• In a nuclear fusion reaction, two small nuclei
  join to form a
• _________________________
• Like a fission reaction, a fusion reaction
  converts some of the original nuclei into
  energya great deal of energy.

45
(No Transcript)
46
Nuclear Fusion

• Fusion reactions are hard to produce and control.
  
• So far, it takes a tremendous amount of heat to
  start.
• Cold fusion is a natural research opportunity to
  be able to harness the energy of the sun safely.