Chemistry Chapter 8

Nuclear Reactions

Change the Arrangement or number of particles in a nucleus

Differences between Nuclear Reactions and Chemical Reactions

• Nuclear Reactions don’t need to be balanced in the normal sense because elements can change identity

• Nuclear Reactions involve far more energy than Chemical Reactions

• Nuclear Reactions are not generally affected by temperature or by Catalysis

Nuclear Symbol

Identifies the Element and Shows the Mass Number and Atomic Number of an Atom

Stable Nuclei

The nuclei of naturally occurring isotopes that remain unchanged

Radioactive

Nuclei that are unstable and eventually break into two or more pieces.

• The atoms are called radioisotopes

Nuclear Equation

Nuclear reactions ar represented by showing the symbols of all the reactants and products in the reaction

Nuclear Radiation

Most nuclear reactions produce a small high energy particle

Beta Particles

When electrons are produced from a nuclear reaction

Alpha Particle

Helium-4 Nucleus

Uses 4/2He in decay problems

Positron

Same mass an electron but a +1 charge

Einstein’s famous formula

E = mc²

m = mass that vanishes

E = energy

c = speed of light

• 1g of mass lost = 2.15 × 10¹⁰ kcal of energy

Two ways energy can form in a nuclear reaction

• Kinetic energy of the small particle that is released

• Electromagnetic radiation, which comes in tiny packets of energy called photons that travel at the speed of light

Gamma Radiation

Nuclear reactions usually produce electromagnetic radiation of very high radiation

• When a reaction produces only gamma radiation, the gamma emission produces a more stable nucleus of the same element

Lowest to Highest Energy

1. Radiowaves <0.0001 kcal/mol

2. Microwaves 0.0001-0.03 kcal/mol

3. Infrared Radiation 0.03-40 kcal/mol

4. Visible Light 40-70 kcal/mol

5. UV radiation 70 to 3,000 kcal/mol

6. X-rays >3,000 kcal/mol

7. Gamma Radiation > 10,000,000 kcal/mol

Ionizing radiation

Enough energy to remove an electron and turn a molecule into a positively charged ion

• Resulting ion has an odd number of electrons, called a radical

  • Most radicals are very unstable and attack neighboring molecules creating more radicals

Geiger Counters & Scintillation Counters

Detects the amount of Ionizing Radiation

Equivalent Radiation Dose

Amount of Tissue Damage that is produced by an exposure to ionizing radiation

• Dose depends on two factors

  • Amount of energy that we absorb

  • Type of radiation

    • Our bodies sustain 20 times as much damage from alpha radiation as from an equal amount of X-rays

Radiation Weighing Fator (W_r)

Relative effect of each type of radiation compared to X-rays

• Quality factor (Q) and Relative Biological Effectiveness (RBE) are also widely used for the W_^r

Activity

Measures the number of atoms that break down in a second

• Traditional unit of activity is the curie (Ci), which equals 37 billion disintegrations per second. It is the activity of 1g of radium.

Background Radiation

Our bodies are constantly exposed to background radiation that is produced by naturally occurring materials

Penetration Abilities

• Alpha emitters are extremely hazardous if ingested or inhaled because alpha particles produce extensive damage to nearby tissues.

• Beta radiation can be blocked by a variety of light materials such as cloth, plastic, and wood. Beta particles can also produce X-rays when they hit an atom.

• Only very dense materials such as a concrete wall or a sheet of lead can block gamma radiation and X-rays

Decreasing exposure of Radiation

• Can be decreased by moving away from the source of radiation or by minimizing the amount of time in the vicinity of the source

Exponential Decay

Nuclear reactions undergo decay in which a constant percentage breaks down in any given time

Half-Life of a Radioisotope

Time required for half of the sample to break down

What radioisotope can be used to estimate the age of a rock?

Potassium-40

What radioisotope can be used to determine the number of years since death for organic matter?

Carbon-14

Fission Reaction

A large nucleus splits into two similarly sized pieces

• ex.) When a neutron strikes a uranium-235 nucleus, it immediately breaks apart into two smaller nuclei and two or three neutrons

• All fission reactions produce more neutrons than they consume

• The neutrons produced can cause other atoms to break down, releasing more neutrons and starting a chain reaction

Fusion Reactions

• In nuclear fusion, two or more small nuclei collide and stick together to make a larger nucleus

• Fusion reactions produce a great deal of energy, but also require high temperatures