nuclear reactions/radioactivity/half life

what is evidence for the strong nuclear force

in order to overcome the Coulomb repulsion force there must be a powerful force that prevents the nucleus from splitting (SNF)

long range force

a force that keeps its strength as distance increases, only slightly dropping in strength (ex. electromagnetic coulomb force)

short range force

force that is only effective over short distances and loses strength as its applied over a greater distance (ex. strong nuclear force)

effects of the strong nuclear force

• allows for the material world

• allows for the existence of all elements that make u our natural word and our bodies

what does the “e” in e=mc² say

that mass is energy (that they are not separate things)

rest energy

different from other types (KE or PE) matter has rest energy even if its not moving, or high above the ground or electrically charged

what does e=mc² show

that a small amount of matter is equivalent to a very large amount of energy

mass definicicy

mass differences between expected mass and actual mass - “missing mass” is released as energy

binding energy

the energy it takes to break apart a nucleus

• E(binding) = mass definicicy x c²

whats unique about iron

its has the lowest energy - before iron the elements pack the nucleus causing the strong force and binding energy to go up but after iron the binding energy goes down

when does radioactivity get released

when a nucleus undergoes radioactive decay

what will an unstable nucleus do

• will spontaneously decay into a more stable nucleus (new nucleus will have less mass, more mass deficiency - “missing mass” is released as energy)

what are types of radioactive decay

• alpha

• beta

• gamma

alpha decay

• a nucleus splits into an alpha particle and new nucleus (atomic # goes down by 2, mass down by 4)

• alpha radiation can be stopped by a couple inches of air

beta decay

• a neutron decays into a proton and electron (atomic number goes up by 1)

• electrons emitted during neutron decay = beta particles

• beta radiation can be stopped by a piece of paper

• is evidence for a presence of a 4th force of nature - weak nuclear force

gamma decay

• the excited nucleus emits a gamma ray (high energy photon) - doesn’t change the number of protons or neutrons in the nucleus

  • only blocked by a lead shield (dangerous)

what do nuclear reactions involve

involve lots of energy - either forming or breaking the strong nuclear force

what two things can occur during nuclear reactions

1. energy is released - new nucleus is formed with lower energy - (fusion reactions)

2. energy input - new nucleus is formed with higher energy (fission reactions)

fusion reaction

• 2 nuclei fuse together to form a heavier nucleus

  • massive amount of energy is released

how can nuclear fusion happen

you need to smash the nuclei into each other at such a fast speed that they overcome to coulomb law

• give the nuclei massive amounts of KE by heating them

nuclear fission

nucleus is split

• if new nucleus has less energy then large amounts are released

• can only happen with elements heavier than iron

how can nuclear fission happen

we fire a high speed neutron at a nucleus, this destabilizes the nuclei causing a chain reaction, than an explosion

what two things are needed to generate a lot of usable energy

1. temp > 10,000,000 degrees celsius

2. an extreme amount of fusion reactions

is a large nucleus very stable

no, the SNF is a short range force (will get weaker as nucleus gets bigger) + the mass would be large and using e=mc² it shows how there would be a lot of energy meaning its more unstable

half-life

the time it takes for half of the atoms in a smaller to decay

radiation

the emission or transmission of energy in the form of waves or particles through space