Nuclear Radiation Notes

Nuclei are unstable when they have low amounts of binding energy. When they are unstable, they are more likely to break into pieces.

Nuclear Radiation Notes Nuclear reactions happen when a change occurs in the nucleus. Nuclear Fission is when the nucleus breaks apart in some way Nuclear Fusion is when particles combine in some way

Nuclear Radiation Notes There are many different types of radiation: 1. Alpha particle emission--a nucleus could lose an alpha particle, which is essentially the same thing as the nucleus of a helium atom. An alpha particle has two protons and two neutrons, but no electrons (so it has a +2 charge). This is a type of fission.

Nuclear Radiation Notes A nucleus will tend to undergo alpha particle emission if it is too heavy or it has a low neutron-proton ratio. After alpha particle emission, the resulting nucleus will have a higher N/P ratio, and will be smaller.

Nuclear Radiation Notes 2. Beta particle emission--a beta particle is just like a high speed electron. It has relatively no mass, and has a charge of -1. A nucleus will undergo beta particle emission if it has too high of a N/P ratio, and therefore the resulting nucleus will have a lower ratio. This is also a type of fission.

Wait! How can an electron come out of a nucleus, which only contains protons and neutrons?

Nuclear Radiation Notes This is what you can visualize in your head for how the electron can be emitted from a neutron. See what happens to the neutron after the electron (beta-part.) leaves… /fysanimat/beta.htm

Nuclear Radiation Notes 3. Gamma ray emission-- a gamma ray is a high- energy (high frequency/short wavelength) light wave. It has no mass and no charge, and only is emitted at the same time as either alpha or beta particles. This is a type of fission

Nuclear Radiation Notes Other less common forms of radiation: 4. Positron emission--A positron is essentially the opposite of an electron. It has relatively no mass, but has a charge of +1. Also a type of fission.

Nuclear Radiation Notes When a positron leaves a nucleus, what is happening is that a proton is losing its charge, and therefore turns into a neutron. Positrons will be released from a nucleus if the N/P ratio is too low.

Nuclear Radiation Notes 5. Electron Capture--this is a process where an electron loses its energy that keeps it in an energy level, and gets pulled into the nucleus. This is a type of fusion.

Nuclear Radiation Notes When this happens, the negative charge of the electron cancels out the positive charge of a proton, and the proton is turned into a neutron. This has the same effect upon the nucleus as Positron Emission (raises the N/P ratio).

Nuclear Radiation Notes How do we describe these radioactive occurrences using equations? First we need to be able to describe nuclei: = Uranium with an atomic number of 92 and a atomic weight of 238

Nuclear Radiation Notes Therefore, an alpha particle is: or

Nuclear Radiation Notes A Beta particle can be described as: A gamma ray is written simply as: A positron is written as:

Nuclear Radiation Notes A nuclear equation has a direction: The arrow signifies which particles existed before the change (reactants) and which ones were present after the change occurred (products)

Nuclear Radiation Notes In a nuclear reaction, the identity of the elements can change, but the total mass and amount of charge must stay the same. To ensure that our equation shows this, we must balance the equation Try example on page 869.

Nuclear Radiation Notes Any single naturally-occurring nuclear reaction will have a specific rate that it happens. This rate is measured with a “half-life”, which is the amount of time that it would take for half of a sample of radioactive material to decay naturally. The time it would require for a half-life to elapse can be calculated with the following equation: N= N o (1/2) n (see pg. 871)

Nuclear Radiation Notes Although radioactive decay (nuclear fission) happens naturally to unstable nuclei, it can also be done artificially (in labs).

Nuclear Radiation Notes This is called nuclear bombardment, when a particle is put in a collision with another particle, encouraging one or both of them to break apart or stick together.

Nuclear Radiation Notes Oftentimes a nuclear fission reaction will cause a chain reaction with many final products being generated by many separate fission reactions

Nuclear Radiation Notes This is how most controlled (power plants) fission reactions occur as well as uncontrolled fission reactions (nuclear explosions)

Nuclear Radiation Notes The opposite of nuclear fission is nuclear fusion. This is the process where two particles combine to form one nucleus. This will only occur if there is enough energy (heat) and is common on the sun, for instance.

Nuclear Stability Notes

Nuclear Radiation Notes Most scientists believe that all known elements have arisen from some type of nuclear fusion (mostly in stars).

Nuclear Radiation Notes Every element above Uranium (#92) has been created by humans using some type of nuclear fusion through bombardment (see pg. 625).