27.6 Main Ideas & Assignment 18

In this lesson you focused on the following questions:

• Which components make up the nucleus of an atom and what keeps them from coming apart?
  
  
• What are alpha and beta decay?
  
  
• How is the conservation of energy and mass applied to nuclear decay?

The nucleus of an atom is very small, only about 10^-14 m across, but it makes up nearly the entire mass of the atom.  The nucleus is composed of smaller particles called nucleons.  The protons and neutrons are examples of nucleons.  The number of protons defines the element.  Physical characteristics, such as atomic mass, vary due to the number of neutrons present.  Two atoms, each with an identical number of protons but a different number of neutrons, are called isotopes.  Each isotope has a unique atomic mass.  The atomic mass unit (u) is defined as exactly of the mass of the carbon-12 atom (1 u = 1.66 × 10^-27 kg).

The nucleus is held together by what physicists call the strong nuclear force, which must be overcome to change the number of nucleons in the atom. 

Some nuclei are unstable and decay.  This natural change from one substance to another is called transmutation.  Alpha decay is defined by the production of an alpha particle ( ) during the decay of a parent nucleus into a daughter nucleus.  The general equation for alpha decay is .

Beta decay is defined by the production of a beta particle () during transmutation.  The general equation for beta decay is .  Beta-positive decay is defined by the production of a positron () (antimatter electron) during transmutation.  The general equation for beta-positive decay is .

In all three decay processes, charge and atomic mass number are conserved.  Mass itself (grams or kg) is not conserved, because in each process some mass is converted to energy according to the relationship E = mc². 

All transmutations produce significant amounts of energy in the form of kinetic energy of the emitted particles and sometimes the production of high frequency gamma radiation.  Einstein's mass-energy equivalency (E = mc²) relates the mass defect in transmutations to the amount of energy released.  Comparing these values supports the conservation of energy principle.

Alpha, beta, and gamma particles can cause ionization.  Ionization is dangerous because it changes DNA and chromosomes which may lead to cancer or, in high doses, radiation sickness and death.

Assignment 18 Word Assignment 18 PDF Please download and complete Part One of Assignment 18.  Also, please note the directions below regarding how to properly name your file.

Click the Assignment 18 link above and save the file to your desktop. Rename the file with your last name followed by an underscore then your first name followed by an underscore then A18. If your name was Chris Smith, the file name would be smith_chris_A18.doc. Complete Part One of the assignment then save your work.