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 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 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

Nuclide Symbols

Nuclide Symbols

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 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 Loss of an -particle (a helium nucleus) He 4 2 U 238 92  Th 234 90 He 4 2 +

Types of Radioactive Decay Beta Decay Loss of a -particle (a high energy electron)  −1 e or I 131 53 Xe 54  + e −1

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 Beta (β) – an electron 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

Penetrating Ability

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 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 14Carbon Cases Dead Sea Scrolls – 5-150 AD Stonehenge – 3100 BC Hezekiah’s Tunnel - 700 BC

Forensic 14Carbon Cases ● Cave painting at Lascaux, France ● 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 14Carbon Cases 14C dated 1260-1390 AD ● 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 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 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 Reactions Beta emission Note that mass number is unchanged and atomic number goes up by 1.

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 Radioactive Particle Nuclear Symbol Pertinent Information alpha beta gamma positron 4 He 2 helium atom without any electrons e -1 high energy electron, no mass with a negative charge γ high energy ray with no mass and no atomic number e +1 mass of an electron but a positive charge

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

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

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

Stable Nuclei Nuclei above this belt have too many neutrons. They tend to decay by emitting beta particles.

Stable Nuclei Positron = 0e Nuclei below the belt have too many protons. They tend to become more stable by positron emission or electron capture. Positron = 0e +1

Stable Nuclei There are no stable nuclei with an atomic number greater than 83. These nuclei tend to decay by alpha emission.

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 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 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 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 How does one tap all that energy? Nuclear fission is the type of reaction carried out in nuclear reactors.

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

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

Radioactive Fingerprints The first ever radioactive fingerprint has recently been identified on an object contaminated with alpha- emitting isotopes 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 This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

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

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 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.

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.

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