radiation, half life, nuclear decay

radioactivity

the release of high energy particles or waves

• new atoms are formed

rules for graphing

• divide axis evenly so data takes up most of the page

• plot points clearly

• label axis and include units

• title should include independent variable and dependent

• have a best fit line

isotopes

different atoms of the same element w a different number of neutrons in the nucleus.

• the mass number will change if the # of neutrons are changed

• however the # of protons and the atomic symbol are the same

atomic mass (shown on periodic table)

the average of the mass numbers of all isotopes of an atom

isotope notation

mass/atomic mass on top (proton + neutron)

atomic number on the bottom (proton)

Radioactive Decay

• results in new atoms forming

• radioactivity results from having an unstable nucleus

• when nuclei break apart and release energy from the nucleus as radiation a radioactive decay has occurred

• radioactive decay continues until a stable element forms

3 types of radiation

• positive alpha particles are attracted to the negative plate

• negative beta particles are attracted to the positive plate

• neutral gamma particles didn’t move towards any plate

alpha radiation

• positively charged

• largest of the 3 types

• same as a helium nucleus

• big and slow

• a sheet of paper will stop an alpha particle

release of alpha particles is called alpha decay

alpha radiation symbol

• 2 protons and 2 neutrons make a mass number of 4

• has a charge of 2+ (2 +protons and 2 neutral neutrons)

• emitted from the nucleus cuz its a He nucleus

beta radiation

• negatively charged

• high energy/speed electron

• smaller than alpha particles

• it takes a thin sheet of aluminum foil to stop a beta particle

beta decay

beta decay occurs when a neutron changes into one proton and one electron

• proton stays in the nucleus

• electron is released

beta radiation symbol

• electrons are tiny so they have a mass number of 0

• the 1 electron emitted gives a beta particle a charge of -1

gamma radiation

• a ray of high energy, short wavelength radiation

• results from energy released from a high-energy nucleus

• takes a thick block of lead or concrete to stop gamma rays

gamma decay

other kinds of radioactive decay can release gamma radiation

for eg. uranium-238 decays into an alpha particle but also releases gamma rays

gamma radiation symbol

• has no charge or mass

• star often in the reactants indicates a higher energy state cuz the products one released energy

half life

how much time it takes for half of a radioactive sample to decay

• is a constant rate (same half-life for each element)

parent vs daughter

parent isotope - the original radioactive material (1/4)

daughter isotope - the stable product after decay (3/4)

decay curves

• show the rate of decay for radioactive elements

• show the relationship between half-life and percent of the remaining original substance

total of percent should equal to 100%

radioactive dating

• method to determine the age of an object

• compares the amount (NOT time) parent isotope to daughter isotope

nuclear fission

a large parent nucleus is split into smaller daughter nuclei with the release of energy.

which radioisotopes do we use in nuclear reactors

uranium 238, uranium 235, plutonium 239

first step in nuclear fission

Fire a slow moving neutron at an unstable uranium-235 nucleus.

what is produced from a nuclear fission reaction

• lots of energy

• 2 smaller nuclei

• 3 more neutrons

how does one nuclear fission reaction lead to a chain reaction of fission events?

1. The 3 neutrons attach to uranium 235

2. now turns into uranium 236, an even more unstable nucleus

3. then u-236 splits into smaller nuclei and releases energy

4. neutrons that keep multiplying to enable the chain reaction.

what are the safety issues with nuclear fission?

• hazardous waste is produced

• has a long half-life before the material is safe

• hard to contain (control rods are used so too much energy isn’t overloading the reactor)

why is the reactor surrounded by a large concrete container

radioactive material produced must be stored away from living things to stop exposure to gamma rays etc.

benefits of CANDU over other reactors

• more efficient than others

• uses natural uranium 235 which helps produce fission rather than enriched uranium which are expensive and takes a lot of energy

• uses heavy water

what is heavy water?

deuterium (water with hydrogen with 2 neutrons)

doesn’t absorb as much neutrons, hence they don’t require enriched uranium.

how does the energy produced from nuclear fuel pellets compare with other fuels?

they produce more energy per kg than other fuels

• ceramic, heat resistant

what is nuclear fusion

two small nuclei combine to form a larger nuclei

where does nuclear fusion happen in nature

in the core of the sun, stars, supernova

• two hydrogen atoms join under tremendous heat and pressure to form a helium nucleus

why can’t we use nuclear fusion as an energy resource on earth?

• requires extremely high temperature and pressure

• do not have a safe enough source that produce the necessary conditions

• scientists are working on it however

what conditions need to be met for nuclear fusion to happen?

• high temp

• high pressure

fusion will not happen if these conditions aren’t met.

advantages of nuclear fusion over nuclear fission as an energy resource

• no radioactive waste produced

• more amounts of energy released

• chain reactions will not occur as they only fuse

steps of nuclear fusion that occur in stars

1. 1 deuterium and 1 tritium nuclei combine to form an unstable helium-5 nucleus

2. the helium-5 breaks apart into a stable helium nucleus and an extra neutron

3. energy is released

which radiation is affected by electric and magnetic fields

alpha and beta

emitted from the nucleus

alpha + beta