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Nuclear Reactions vs. Normal Chemical Changes. Nuclear reactions involve the nucleus The nucleus opens, and protons and neutrons are rearranged The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy

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nuclear reactions vs normal chemical changes
Nuclear Reactions vs. Normal Chemical Changes
  • Nuclear reactions involve the nucleus
  • The nucleus opens, and protons and neutrons are rearranged
  • The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy
  • “Normal” Chemical Reactions involve electrons, not protons and neutrons
the nucleus
The Nucleus
  • Remember that the nucleus is comprised of the two nucleons, protons and neutrons.
  • The number of protons is the atomic number.
  • The number of protons and neutrons together is effectively the mass of the atom.
isotopes
Isotopes
  • Not all atoms of the same element have the same mass due to different numbers of neutrons in those atoms.
  • There are three naturally occurring isotopes of uranium:
    • Uranium-234
    • Uranium-235*
    • Uranium-238
isotopes1
Isotopes

Two Categories

  • Unstable – isotopes that continuously and spontaneously break down/decay in other lower atomic weight isotopes
  • Stable – isotopes that do not naturally decay but can exist in natural materials in differing proportions
radioactivity
Radioactivity
  • It is not uncommon for some isotopes of an element to be unstable, or radioactive.
  • We refer to these as radioisotopes.
  • There are several ways radioisotopes can decay and give off energy known as radiation.
types of radioactive decay alpha decay

238

92

234

90

4

2

4

2

He

U

Th

He

+



Types of Radioactive Decay Alpha Decay

Loss of an -particle (a helium nucleus)

types of radioactive decay beta decay

131

53

131

54

0

−1

0

−1

0

−1

e

I

Xe

e

+



or

Types of Radioactive Decay Beta Decay

Loss of a -particle (a high energy electron)

types of radioactive decay gamma emission

0

0

Types of Radioactive Decay Gamma Emission

Loss of a -ray (high-energy radiation that almost always accompanies the loss of a nuclear particle)

types of radiation
Types of Radiation
  • Alpha (ά) – a positively charged helium isotope - we usually ignore the charge because it involves electrons, not protons and neutrons
  • Beta (β) – an electron
  • Gamma (γ) – pure energy; called a ray rather than a particle
geologic time
Geologic Time
  • Radioactive Isotopes used in Geologic Dating
  • Parent Daughter half-life (y)
  • U-238 Lead-206 4.5 billion
  • U-235 Lead-207 713 million
  • Thorium 232 Lead 208 14.1 Billion
  • K-40 Argon-40 1.3 billion
  • R-87 Sr-87 47 billion
  • C-14 N-14 5730
  • Half-life = time it takes for 1/2 of the parent mass to decay into the daughter mass
geologic time1
Geologic Time

14Carbon Dating

  • Dating is accomplished by determining the ratio of 14C to non-radioactive 12C which is constant in living organisms but changes after the organism dies
  • When the organism dies it stops taking in 14C which disappears as it decays to 14N
forensic 14 carbon cases
Forensic 14Carbon Cases
  • Dead Sea Scrolls – 5-150 AD
  • Stonehenge – 3100 BC
  • Hezekiah’s Tunnel - 700 BC
forensic 14 carbon cases1
Forensic 14Carbon Cases

● King Arthur’s Table in Winchester Castle, England 14C dated to 13th century AD

● Cave painting at Lascaux, France

14C dated to 14,000 BC

● Rhind Papyrus on Egyptian math 14C dated to 1850 BC

forensic 14 carbon cases2
Forensic 14Carbon Cases

● The Shroud of Turin was

14C dated 1260-1390 AD

which suggests that it is a fake

● However, recent evaluation

shows that the sample measured

was from a medieval patch and/or

that it was seriously contaminated

with molds, waxes, etc

●New estimates date the shroud from

1300-3000 ybp bases on vanillin

retention

forensic 14 carbon cases3
Forensic 14Carbon Cases

Nuclear testing during 1955-63 put large amounts of 14C into the atmosphere which was incorporated into the enamel of human teeth. Because such testing stopped the 14C input ended and the 14C in the teeth decayed at a fixed rate allowing dating of the teeth

nuclear reactions
Nuclear Reactions
  • Alpha emission

Note that mass number goes down by 4 and atomic number goes down by 2.

Nucleons (nuclear particles… protons and neutrons) are rearranged but conserved

nuclear reactions1
Nuclear Reactions
  • Beta emission

Note that mass number is unchangedandatomic number goes up by 1.

write nuclear equations
Write Nuclear Equations!
  • Write the nuclear equation for the alpha decay of radon-222

222Rn  218Po + 4He

  • Write the nuclear equation for the beta emitter Co-60.

60Co  60Ni + 0e

86

84

2

-1

27

28

bellringer fill in chart
BellringerFill in Chart

4

He

2

helium atom without any electrons

0

e

-1

high energy electron, no mass with a negative charge

0

γ

0

high energy ray with no mass and no atomic number

mass of an electron but a positive charge

0

e

+1

neutron proton ratios
Neutron-Proton Ratios
  • Any element with more than one proton (i.e., anything but hydrogen) will have repulsions between the protons in the nucleus.
  • A strong nuclear force helps keep the nucleus from flying apart.
  • Neutrons play a key role stabilizing the nucleus.
  • Therefore, the ratio of neutrons to protons is an important factor.
stable nuclei
Stable Nuclei

The shaded region in the figure shows what nuclides would be stable, the so-called belt of stability.

neutron proton ratios1
Neutron-Proton Ratios

For smaller nuclei (Z  20) stable nuclei have a neutron-to-proton ratio close to 1:1

neutron proton ratios2
Neutron-Proton Ratios

As nuclei get larger, it takes a greater number of neutrons to stabilize the nucleus.

stable nuclei1
Stable Nuclei
  • Nuclei above this belt have too many neutrons.
  • They tend to decay by emitting beta particles.
stable nuclei2
Stable Nuclei
  • Nuclei below the belt have too many protons.
  • They tend to become more stable by positron emission or electron capture.
  • Positron = 0e

+1

stable nuclei3
Stable Nuclei
  • There are no stable nuclei with an atomic number greater than 83.
  • These nuclei tend to decay by alpha emission.
radioactive series
Radioactive Series
  • Large radioactive nuclei cannot stabilize by undergoing only one nuclear transformation.
  • They undergo a series of decays until they form a stable nuclide (often a nuclide of lead).
nuclear transformations
Nuclear Transformations

Nuclear transformations can be induced by accelerating a particle and colliding it with the nuclide.

These particle accelerators are enormous, having circular tracks with radii that are miles long.

measuring radioactivity
Measuring Radioactivity
  • One can use a device like this Geiger counter to measure the amount of activity present in a radioactive sample.
  • The ionizing radiation creates ions, which conduct a current that is detected by the instrument.
energy in nuclear reactions
Energy in Nuclear Reactions
  • There is a tremendous amount of energy stored in nuclei.
  • Einstein’s famous equation, E = mc2, relates directly to the calculation of this energy.
  • In chemical reactions the amount of mass converted to energy is minimal.
  • However, these energies are many thousands of times greater in nuclear reactions.
nuclear fission
Nuclear Fission
  • How does one tap all that energy?
  • Nuclear fission is the type of reaction carried out in nuclear reactors.
nuclear fission1
Nuclear Fission
  • Bombardment of the radioactive nuclide with a neutron starts the process.
  • Neutrons released in the transmutation strike other nuclei, causing their decay and the production of more neutrons.
  • This process continues in what we call a nuclear chain reaction.
trafficking nuclear materials
Trafficking Nuclear Materials

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

man made radioactive isotopes
Smuggled Plutonium – can identify the reactor type in which the fuel was originally radiated and the type of plant where the material was subsequently reprocessed

In 1997, two pieces of stainless steel contaminated with alpha-emitters were found in a scrap metal yard in Germany.

Source was identified as a fast-breeder reactor in Obninsk, Russia

Man-made Radioactive Isotopes

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

weapons grade plutonium
The isotopic composition of plutonium can indicate INTENT

In 1994, a small lead cylinder discovered in a garage in Tengen on the Swiss-German border was found to contain plutonium metal, isotopically enriched to 99.7%

Weapons-grade Pu-239

Weapons-grade Plutonium

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

radioactive fingerprints
Preserving the conventional chain of evidence whilst dealing with radioactive samples can be problematic

For example – lifting fingerprints and swiping for radioactive contamination cannot both be carried out

The first ever radioactive fingerprint has recently been identified on an object contaminated with alpha-emitting isotopes

Radioactive Fingerprints

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

slide52
If there are not enough radioactive nuclides in the path of the ejected neutrons, the chain reaction will die out.
  • Therefore, there must be a certain minimum amount of fissionable material present for the chain reaction to be sustained: Critical Mass.
nuclear reactors
Nuclear Reactors

In nuclear reactors the heat generated by the reaction is used to produce steam that turns a turbine connected to a generator.

nuclear reactors1
Nuclear Reactors
  • The reaction is kept in check by the use of control rods.
  • These block the paths of some neutrons, keeping the system from reaching a dangerous supercritical mass.
nuclear fusion
Nuclear Fusion
  • nuclear fusion is a nuclear reaction in which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus.
  • During this process, matter is not conserved because some of the mass of the fusing nuclei is converted to energy which is released.
  • Fusion is the process that powers active stars.
  • Fusion would be a superior method of generating power.
    • The good news is that the

products of the reaction are

not radioactive.

    • The bad news is that in order to achieve fusion, the material must be in the plasma state at several million kelvins.
slide56
Weapons whose explosive output is exclusively from fission reactions are commonly referred to as atomic bombs or atom bombs
  • misnomer because the energy actually comes from nucleus
  • Many fission products are either highly radioactive (but short-lived) or moderately radioactive (but long-lived), and as such are a serious form of radioactive contamination if not fully contained. Fission products are the principal radioactive component of nuclear fallout.
slide57
Thermonuclear bombs work by using the energy of a fission bomb to compress and heat fusion fuel.
  • When the fission bomb is detonated, gamma rays and X-rays emitted first compress the fusion fuel, then heat it to thermonuclear temperatures
  • Tsar Bomb