Chapter 18

Mass # Symbol

Element Name or symbol – Mass #

Parts of a ReactionReactants Products

Alpha emission or decay () –helium atom 42He

23892U 4

2He + 23490Th

Beta emission or decay ()– 0-1e in the products

23490Th 234

91Pa + 0-1e

Gamma emission or decay () - 00

23892U 4

2He + 23490Th + 0

0

Positron emission or decay - 0+1e

2211Na 0

+1e + 2210Ne

Electron capture – beta particle in the reactants

20180Hg + 0

-1e + 20179Au

Neutron emission or decay– 10n

20984Po 1

0n + 20084Po

Proton – 11H or 1

1p

Mass # and the atomic # totals must be the same for reactants and the products.

3919K 35

17Cl + ___

20682Pb 0

-1e + ___

23894Pu + ___ 4

2He + 23592U

Alpha decay of Cu-68

Gamma emission of Thorium-235

Positron emission of P-18

Astatine-210 releasing 3 neutrons

Electron capture of Ti-45

Radioactive isotopes or nuclides all decay because they are unstable, some just breakdown much faster than others

Half-life – amount of time for half of the original sample to decay

For two samples of the same isotope, regardless of the sample size, after one half-life, only half of the original amount of sample remains.

Isotopes Half-Live Carbon – 14 5730 years Sodium – 24 15 hours Bismuth – 212 60.5 seconds Polonium – 215 0.0018 seconds Thorium – 230 75400 years Thorium – 234 24.1 days Uranium – 235 7.0 x 108 years Uranium – 238 4.46 x 109 years

Barium – 139 has a half-life of 86 minutes. If you originally have a 10 gram sample of Barium-139, how much will be left after 258 minutes?

How many days will it take 50 grams of Radon – 222 (half-life of 3.82 days) to decay to 3.125 grams?

If a sample of Cesium-135 decays from 10 grams to 2.5 grams over a period of 84 days, what is the half-life of Cesium-135?

238U 234Th 234Pa 234U α β β

234U 230Th 226Ra 222Rn 218Po 214Pb α α α α α

214Pb 214Bi 214Po 210Pb 210Bi 210Po206Pb β β α β β α

Henri Becquerel 1852- 1908 Discovered NaturalRadioactivity - Nobel Prize (physics) 1903

Wilhem Roentgen 1845- 1923 Discovered X- rays(1895) - Nobel Prize (physics) 1901

Marie (Sklowdowska) Curie 1867 – 1934 DiscoveredRadium and Polonium - (2) Nobel Prizes (physics)1903, Chemistry (1911) – first woman to teach at theSorbonne in its 650 yr history, first person to receivetwo Nobel prizes, only person to receive 2 Nobels inSciences

Pierre Curie 1859- 1906 Nobel Prize (physics) 1903

Ernest Rutherford 1871- 1937 Demonstrated the existence of the nucleus Nobel Prize (chemistry) 1908

Cancer Radiation Treatment Computer Imaging techniques Radiocarbon dating Smoke detectors Food irradiation Radioactive tracers – Iodine 131 used to

treat thyroid illnesses and Thallium -201 can be used determine the damage done to someone’s heart by a heart attack

Nuclear fission was discovered in late 1930’s when U-235 was bombarded with neutrons and observed to split into two lighter elements.

10n + 235

92 U 9236Kr + 141

56Ba + 310n

Energy from combustion of 1 mole of U-235 produces 26 million times as much energy as the combustion of 1 mole of methane.

The neutrons are produced from fission reactions, will then react with other radioactive atoms, which will produce more neutrons and so on, potentially creating an uncontrollable chain reaction.

If reaction produces < 1 neutron on average, the nuclear fission stops over time.

If reaction produces exactly 1 neutron for each fission, the process is self-sustaining and is said to be critical.

If reaction produces > 1 neutron from each fission than the process can get out of control very quickly and cause a violent explosion.

Critical mass = mass of fissionable material needed to keep fission reaction going, but at a safe level.

Hiroshima and Nagasaki bombs in 1945 were fission bombs where two subcritical masses were combined and have an extremely rapid fission reaction that causes a huge explosion.

Fusion – combining two smaller nuclei into one heavier, more stable nucleus.

32He + 1

1H 42He + 0

1e

Fusion reaction produce more energy than fission reactions.

Fusion reactions are most commonly seen in stars.

We have many potential sources for fusion reactions, but the problem lies in trying to slam two positively charged nuclei together with enough force to make them combine.

It is thought that the temperature must be over 40 million Kelvin for this to occur, which is where the speed of the particles could potentially overcome the repulsive forces.

Somatic damage – done to the organism itself, resulting in either sickness or death.

Effect of somatic damage may be immediate or take years to show their effects, such as radiation treatment for cancer patients.

Genetic damage – damages cells which can be passed on to afflict offspring of initially effecting organism.

Energy of radiation – higher energy = more damage (big surprise)

Penetrating ability of the radiation – gamma particles are high penetrating, beta can penetrate 1 cm and alpha particles can be stopped by the skin.