Introduction to Physical Science Monday, Wednesday, Thursday Tom Burbine

Atoms Atoms are made up of 3 types of particles Protons – positive charge (+1) Electrons – negative charge (-1) Neutrons – neutral charge (no charge) Protons and Neutrons are found in the nucleus

Strong Nuclear Force Keeps protons and neutrons together in the nucleus

Radioactivity Radioactivity – decay of an atomic nucleus All elements with an atomic number greater than 82 (lead) are radioactive

How old is the solar system?

~4.6 billion years All meteorites tend to have these ages Except:

How old is the solar system? ~4.6 billion years All meteorites tend to have these ages Except: –Martian meteorites –Lunar meteorites

How old is the universe?

~13.7 billion years (±200 million years)

Radiation dosage 1 rad = 0.01 J of radiant energy absorbed by kilogram of tissue Rem = rads x Q where Q is a quality factor which attempts to convert rads from different types of radioactivity into a common scale of biological damage.

Radon is a naturally occurring radioactive gas

Ages

How do you determine this age?

Radioactivity The spontaneous emission of radiation (light and/or particles) from the nucleus of an atom

Some types of radiation Alpha particle – 2 protons and 2 neutrons (Helium nucleus) –Do not normally penetrate clothing –High kinetic energy (due to high mass) ; can damage living tissue Beta particle – electron (from a neutron when it becomes a proton) –Penetrate clothing and into skin Gamma ray - High-frequency radiation –Penetrate into skin and can damage molecules in cells

Radioactivity

Half-Life The time required for half of a given sample of a radioactive isotope (parent) to decay to its daughter isotope.

Radioactive Dating You are dating when a rock crystallized

Radioactive Dating n = n o (1/2) (t/half-life) n o = original amount n = amount left after decay

Exponential decay is where the rate of decay is directly proportional to the amount present.

Remember Number of original atoms (parent atoms) = number of daughter atoms today + number of parent atoms today

What are the assumptions to get an age?

What are the assumptions? No loss of parent atoms –Loss will increase the apparent age of the sample. No loss of daughter atoms –Loss will decrease the apparent age of the sample. No addition of daughter atoms or if daughter atoms was present when the sample formed –If there was, the age of the sample will be inflated These can possibly be all corrected for

Commonly Used Long-Lived Isotopes in Geochronology Radioactive Parent (P) Radiogenic Daughter (D) Stable Reference (S) Half-life, t½ (10 9 y) Decay constant, l (y -1 ) 40K40Ar 36Ar x Rb87Sr86Sr x Sm143Nd144Nd x Th208Pb204Pb x U207Pb204Pb x U206Pb204Pb x10 -10

How do you determine isotopic values?

Mass Spectrometer

It is easier To determine ratios of isotopic values than actual abundances

Carbon-14 99% of the carbon is Carbon-12 1% is Carbon % is Carbon-14 The half-life of carbon-14 is 5730±40 years. It decays into nitrogen-14 through beta-decay (electron and an anti-neutrino are emitted).

Due to Carbon-14’s short half-life, can only date objects up to 60,000 years old

Plants take up atmospheric carbon through photosynthesis

When something dies, it stops being equilibrium with the atmosphere

Why is Carbon-14 still present if it has such a short half-life?

Cosmic rays impact Nitrogen-14 and create Carbon-14 Cosmic rays are energetic particles (90% are protons) originating from space. From the Sun (solar cosmic rays) or outside the solar system (galactic cosmic rays) n + 14 N → 14 C + p

bomb_spike.svghttp://en.wikipedia.org/wiki/Image:Radiocarbon_ bomb_spike.svg

Any Questions?