Module 8

Module 8—Nuclear Decay, Energy, and the Standard Model of the Atom

 

Try This

 

TR 2. Complete “Check and Reflect” questions 1 to 5 on page 844 of the textbook.

 

Quarks and Decay

 

Given the large number of subatomic particles that were discovered using collisions and particle accelerators, it wasn’t long before scientists suggested that a large number of these particles were, in turn, built from just three smaller particles called quarks. The first quark is called an “up” quark and has a charge of e. The second quark is called a “down” quark and has a charge of e. The third particle is called the “strange” quark and has a charge of e. Using the powerful Stanford Linear Accelerator, scientists discovered that the mass and charge of a proton are indeed concentrated in three regions within the particle, supporting the quark model.

 

Protons and neutrons are each composed of three quarks.

 

 

The up, down, and strange quarks are first-generation quarks. Subsequent research and theory has identified three other quarks named charm, beauty, and truth. 

 

Read

 

“Table 17.5: Some Properties of Quarks” on page 846 of the textbook summarizes the first-, second-, and third-generation quarks.

 

The quark model and weak electric force help explain nuclear changes, like beta and beta-positive decay. For example, during the decay process a down quark can change into an up quark, leading to the emission of an electron and an electron antineutrino. The following are both the equation and graphical representation of this process showing the conservation of mass and charge.

 

Beta Decay

 

 

 

Beta Positive Decay

 

 

 

Module 8: Lesson 4 Assignment

 

Remember to submit your answers to A4 and A5 to your teacher as part of your Module 8: Lesson 4 Assignment.

 

A 4. Which particles are involved when an up quark changes into a down quark?

 

A 5. Which particles are involved when a down quark changes into an up quark?

 

The Standard Model

 

The standard model summarizes the most current understanding of the atom with the following key concepts:

• All matter is composed of 12 fundamental particles and their respective anti-particles (six quarks and six leptons).
  
  
• The electromagnetic force and the weak nuclear force are both aspects of the same fundamental force (electroweak force), supplied by the W+, W–, Zo mediating particles that have been observed.
  
  
• All of the quarks have a quantum property called “colour,” which is not related to visible colour, but is used to describe the strong nuclear force. This theory is referred to as quantum chromodynamics.

Even though the standard model explains three of the fundamental forces, it cannot explain how gravity works. At the extremely small scale of the atom, gravity is so weak as to be nonexistent and, therefore, does not affect subatomic actions. However, one of the goals of physicists is to develop a single theory and set of equations that describe everything in the universe, optimistically called the grand unified theory or the theory of everything.

 

Current theoretical research is moving toward a grand unified theory that could connect the electroweak force with chromodynamics and gravity. At the same time, research continues into string theory, which may connect gravity with the other three fundamental forces. In this theory the particles are treated as tiny vibrating strings of mass-energy that are quantized similarly to standing waves. At the moment these are just theories waiting to be tested, refined, rejected, and revised in a similar way to the thousands of ideas and theories that have come before them. In many respects, the inside of the atom remains undiscovered territory. Like the furthest reaches of deep space, it can only be explored with powerful and continually evolving human technology and ingenuity.

 

Read

 

Read “Quarks and the Standard Model” on pages 845 to 849 of your textbook.

 

Self-Check

 

SC1. What are the 12 particles of the standard model?

 

SC 2. Rank the four natural forces from weakest to strongest.

 

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