Diagnostic and imaging dental students

Qi - Atom theory. Radiation

‘ ATOM THEORY

 

• Atomic theory is the scientific theory that matter is composed of particles called atoms. The structure of the atom is key to the majority of the techniques used

 

in radiology

 

* Nucleus

 

~ Composition of an atom is principally ‘empty space5. Its mass is concentrated within the central nucleus which is composed of a specific number of nucleons

 

- Nucleons are either protons or neutrons, and the total number of nucleons is assigned the symbol A (also known as the mass number)

 

" The total number of protons within the nucleus is called the atomic number and assigned the symbol Z. Protons and neutrons are each assigned a relative mass of one

 

• A: total number of nucleons = protons + neutrons (mass number)

 

• Z: number of protons (atomic number)

 

- Protons and neutrons each consist of quarks and gluons

 

• Two up quarks and one down quark form the proton

 

• Two down quarks and one up quark form the neutron

 

• Protons are positively charged

 

• Neutrons have no charge

 

“ The atomic number always defines the element (it is the number of protons that determines that an atom (having 6 protons) is carbon

 

Nucleus

 

• However more than one nuclide may exist for a given element (a carbon may exist with 6 neutrons or 8, these atoms of the same element with different numbers of neutrons are called isotopes: in each case there are still 6 protons)

 

Orbiting

 

4 electrons