NUCLEAR UNIT A: Radiation, Energy and Atoms

RADIATION  Irradiation is the exposure of a sample of material to radiation.  There are many types of radiation.  Some radiation can be harmful and some is beneficial.  Food can be irradiated to destroy bacteria, molds and yeasts thus reducing the rate of spoilage.

IRRADIATION  Food is irradiated using gamma rays, which are high energy waves of electromagnetic radiation.  The gamma rays come from samples of cobalt or cesium that give off the high energy particles.  The FDA approved irradiation in 1963 and has been endorsed by the United Nations Health Organization (WHO) and the U.N. Food and Agriculture Organization. (FAO)

A.2 KINDS OF RADIATION  Electromagnetic radiation is radiation given off by certain objects.  The scope of electromagnetic radiation is depicted by the electromagnetic spectrum.

KINDS OF RADIATION  Electromagnetic radiation:  Is a form of energy and has no mass.  Travels at the speed of light (3.00 x 10 8 m/s)  Can travel through a vacuum.  Moves through space as photons  Is emitted by atoms as their nuclei decay or when atoms are energized through heat conversions.

IONIZING VS. NON- IONIZING RADIATION  Non-ionizing radiation has a much lower energy than ionizing radiation.  An example of non-ionizing radiation is visible light and radiation that is in the lower energy range.  Non-ionizing radiation transfers energy to matter causing electrons to move to a higher energy level.

 Excessive exposure to non-ionizing radiation can cause damage such as a sunburn.  Intense microwave and infrared radiation can also be lethal causing severe burns.

IONIZING RADIATION  Ionizing radiation includes all nuclear radiation and other high-energy electromagnetic radiation. ie: radiation higher in frequency than visible blue light.  Energy from this radiation can cause ions to form when electrons are ejected from molecules.

NON-IONIZING VS IONIZING RADIATION  Non-ionizing radiation is like mist, your body can absorb water from the mist without damage because of the large surface area.  Ionizing radiation is like a fire hose. The energy is more focused and can do more damage.

NUCLEAR RADIATION  Nuclear radiation originates from nuclear changes.  In normal chemical reactions, the nucleus of an atom remains unchanged.  Atoms with unstable nuclei can spontaneously change and become radioactive.

RADIOACTIVITY  Usually, when radioactive atoms form, they change into a different element with an emitted particle and energy is released.  This process is called radioactive decay.  The emitted particles and energy together make up nuclear radiation.

A.3 THE GREAT DISCOVERY  In 1895 W.K. Roentgen found certain minerals glowed when hit by beams of electrons.  His work led to the discovery of X-Rays.

X-RAYS  Roentgen’s discovery led a French scientist, Henri Becquerel to further study fluorescent minerals that contained uranium.  He found that uranium would expose photographic film plates even in the dark.  Becquerel discovered radioactivity and suggested to Marie Curie, his student, that she study the radioactive component of pitchblende.

MARIE AND PIERRE CURIE  Working together Marie and her physicist husband, Pierre discovered that the radioactivity level was 4 to 5 times higher than expected.  After processing more than a ton of pitchblende they discovered polonium and radium.

A.4 NUCLEAR RADIATION  Ernest Rutherford showed that radioactivity includes two types of rays, alpha and beta. Soon after, gamma rays were discovered.  Alpha rays are positively charged, beta rays are negatively charged and gamma rays are neither—they’re more like X-Rays.

A.6 GOLD FOIL EXPERIMENT  Working with Rutherford, Hans Geiger (geiger counter) and Ernest Marsden focused a beam of alpha particles at a thin sheet of gold foil about 2000 atoms thick. (.0004 cm)  The screen was coated with ZnS that flashed light when a particle struck it.  They found that the paths of the α particle interacted with the foil in curious ways.  It was expected that the particles would be scattered by the foil and reflected back, but……..stay tuned!

CAN YOU EXPLAIN THIS PHENOMENA?

A.7 ARCHITECTURE OF ATOMS Even though electrons can’t be seen, they are believed to occupy a specific region around the nucleus where it spends most of its time. The region, but not the exact location can be identified.

 The atomic number gives the number of protons.  Not all atoms of the same element have the same number of neutrons.  Atoms of the same element with different numbers of neutrons are called isotopes.  An example is C-12, C-13 and C-14.  The most common isotope of carbon is C-12.  C-14 is unstable because it has 8 neutrons, thus it is radioactive—called a radioisotope. See table 2 on page 307.

A.9 ISOTOPES IN NATURE  Most elements in nature are mixtures of isotopes—some radioactive, others not.  The proportions of an element’s naturally occurring isotopes is about the same everywhere on Earth.

ASSIGNMENT  Your Turn pg 308  Your Turn pg 311  Part A Summary Questions pg 313