nuclear stability notes

Nuclear Stability Notes


• The type of symbol used to represent any atom is:

• The element symbol (found on periodic table)

• A superscript number listed before the symbol (represents the atomic mass)

• A subscript number listed before the symbol (represents the atomic #)

Carbon-12 atom


• A nucleus is made up of protons (+1 charge) and neutrons (0 charge).

• Q--Why do protons stay together when positive charges repel each other?

• A--The main reason is because of a force called Strong Force


• Strong Force is exerted by anything with mass (protons and neutrons) to attract other masses together.

• Strong force will only work within a very short distance.


• Neutrons act as insulation, since they have no charge to push protons away, but have strong force to bring other nucliides (protons and neutrons) together.


• As a general rule, a nucleus will need a neutron/proton ratio of 3:2 (or 1.5) in order to stay together.

• This rule is more precise for larger nuclei. (see page 866).


• Of all known isotopes of natural elements (about 1500), only 250 of them are stable.

• All of these stable isotopes have an atomic number in between 1 and 82.


• The amount of energy that keeps a nucleus together is called the Binding Energy.

• This amount of energy (per nucleon) is higher for nuclei that are stable than it would be for unstable nuclei.

• It is measured in units called “Joules” or J.


• The amount of binding energy for a nucleus can be calculated using E = mc2.

• This equation states that mass can actually be converted into energy (during nuclear reactions).


• The mass of a nucleus will be less than the mass of all of the protons and neutrons making it up. The difference is called the mass defect, which is converted into energy if the nucleus is formed.

• http://www.aip.org/history/mod/fission/fission1/02.html• http://www.aip.org/history/einstein/emc1.htm#ae22• http://www.aip.org/history/einstein/voice1.htm

• If the mass that changes is very small, will it release much energy?


• Energy = (change in mass--called mass defect)

x (speed of light)2

• See example on page 617.


• need to know:

• speed of light = 3.00 x 108 m/s

• (speed of light)2 = 9.00 x 1016 m2/s2

• conversion factor for amu to kg = 1.66054 x 10-27 kg/amu

• mass of H atom (close to mass of proton)= 1.007825 amu

• mass of neutron = 1.008665 amu

nuclear stability notes

Documents