Nuclear Physics

Let’s start with the basics Atoms are held together by strong nuclear

forces and electrical forces

The electrical force between positive protons and negative electrons keep electrons in their orbit.

Strong nuclear forces exist in the nucleus. While electrons are forcing the protons together in the nucleus, neutrons are keeping them from flying apart (this is strong nuclear force).

The more protons there are in a nucleus, the more neutrons are needed to hold them together.

Ex: A typical helium atom has 2 protons and 2 neutrons. A typical uranium atom has 92 protons and 146 neutrons

Radioactive Decay

Neutrons, by themselves are not stable.

Any element above atomic number 83 has so many neutrons, that at some point the neutron will decay…. This makes that element radioactive.

When it decays, it emits α (alpha), β (beta), and γ (gamma) rays.

An alpha ray is positively charged, a beta ray is negatively charged, and a gamma ray is neutral.

Alpha rays (light rays) can be stopped by a piece of paper; beta rays (X-rays) with a piece of aluminum; gamma rays are the strongest and have to be stopped with thick lead

Isotopes

Isotopes are the same element with different number of neutrons.

Radioactive half-life

Different radioactive elements will decay at different rates. The time it takes half of the element to decay is that elements half-life.

Some elements have half-lives of a few seconds. Others, like U-238 have a half-life of 4.5 billion years.

Transmutation

When a nucleus emits an alpha or beta particle, a different element is formed, this is transmutation.

U-238 will decay be emitting an alpha particle made up of 2 protons and 2 neutrons. This changes Uranium into Thorium.

After U-238 decays into Thorium, Thorium will decay be emitting a beta particle (an electron).

Carbon Dating

Carbon-12 is the most naturally occurring carbon atom. However, there is a very small percentage of Carbon-14 in the atmosphere.

Carbon-14 is less stable and will decay. We can use what we know about half-lives to date fossils and old trees Carbon-14 has a half-life of 5730 years.

Radioactive Tracers

Scientists can now make harmless elements radioactive by bombarding them with neutrons (thereby activating decay). They then insert the radioactive materials and can track them using radiation detectors Fertilizer in plants Used by doctors to study digestion and

circulation

Radiation and Health

Radiation is all around us in the form of earth minerals and cosmic rays. The human has evolved to withstand these natural does of radiation.

Prolonged exposure or exposure to radiation levels above 1000 times normal results in cancer and eventually death

Nuclear Fission

Nuclear Fission literally means the splitting of an atom. Normally, nuclear strong forces within the nucleus are too much to overcome.

However, in U-235 scientists found that if a neutron was fired into the atom, it would cause elongation and would eventually split.

Energy released

The energy released by the fission of one U-235 atom is enormous… about seven million times the energy released by the explosion of one TNT molecule.

The energy is released as kinetic energy and gamma radiation

Must be perfect conditions This does not occur in nature

because u-235 is mixed with the more stable U-238

U-235 must be at critical mass in order for an enormous explosion to occur.

Nuclear Power Nuclear Power Plants work much like a coal

plant. They produce heat which powers a generator.

Nuclear Power Plants can use a lot less fuel and do not emit fossil fuels into the air

However, when elements have undergone fission, their waste products are highly radioactive.

How Nuclear Plants work

The next slide contains graphic images of mutations that may occur as a result of toxic exposure to radiation. Please skip the next slide if you have a sensitive stomach or have any doubts about whether or not you should see what is next.

Nuclear Fusion

Instead of splitting an atom, nuclear fusion occurs when atoms combine. This requires a high temperature and a high velocity.

When atoms collide, radiant energy is released.

Problems with nuclear fusion Maintaining high temperatures

Energy required to maintain the high temps or produce products for fusion is much much higher than the energy output.

Advantages of fusion

No radioactive by-products

Fuel is basically unlimited (can be processed from water).