S2 Radioactive Decay Quest

Radioisotope

An atom containing an unstable nucleus

In the process, they _______ into different kinds of atoms

turn

Elements that undergo radioactive decay contain _________ atoms

unstable

uranium - 15

- Not found in sedimentary or metamorphic rocks, nor in all igneous. - Can be used only with igneous rocks with the right kind of uranium isotope. - Does not give good results on rocks younger than 1 million years.

potassium argon disadvantages

- Only useful if the rock has not heated and recrystallized since its initial formation. - . can't be used on sedimentary and igneous

uranium-15 advantages

-Long half life so can date the oldest rocks in the earth's crust. -Oldest method and, when done carefully, the most reliable. -Has a natural cross-check built into it that shows when nature has tampered with the evidence. -Error ranges from about 0.1% to 1% range

How many half- lives have there been when 1/2 of the original radioactive isotopes remain?

1

Potassium argon half life

1.3 billion years

Iodine 131 has a half-life of 8.07 days what fraction of the parent isotope is remaining after 32.28 days?

1/16

Iodine-131 has a half life of 8.07 days. What fraction of a sample of iodine-131 is left unchanged after 16.14 days?

1/4

How many half- lives have there been when 1/16 of the original radioactive isotopes remain?

4

Uranium-15 half life

4.5 billion years

If a substance has a half- life of 10 years and there is only 1/16 of the original parent isotope remaining, how old is that substance?

40 years old

Rubidium 87 To Strontium 87 Half-life

49 billion years

Carbon-14 half-life

5,730 years

radiocarbon dating can be used to date objects as old as

50,000 years (can be up to 75,000)

Rubidium 87 To Strontium 87 advantages

Can be used to date almost all igneous rocks because it occurs in common minerals such as feldspars and micas.

carbon-14 disavantages

Can only be used on organisms that were once alive. Because of short half life cannot date very far back in time. (50,000 yrs ago)

Rubidium 87 To Strontium 87 disadvantages

Does not give results on young rocks because so little of the material will have decayed

Gamma Radiation

High energy (frequency) electromagnetic radiation. A radioactive process by which an atomic nucleus loses energy by emitting a stream of high energy photons. The strongest of the three radiation types. Can be blocked by lead. It is not a particle form of radiation

If you could follow the fate of an individual atom in a sample of radioactive material, could you predict when it would decay?

No there is no way to predict when any particular atom will turn into a daughter isotope. When any specific parent isotope will turn is completely random. The fact that 50% will turn during each half life, however, is completely predictable.

Absolute Dating

One of many techniques when a specific age is assigned to an artifact rock layer, etc. Radiometric dating is one form of absolute dating

Carbon-14 advantages

Only useful for things that were once alive. Good for archeology, prehistoric tools of bone

Parent vs Daughter Isotope

Parent- The isotope undergoing nuclear decay. It is more unstable than the daughter isotope Daughter- In a nuclear equation the isotope remaining after the parent isotope (the original isotope) has undergone decay

Beta Radiation

Radiation in which an electron is emitted from the nucleus when a neutron decays to a proton and an electron. Can be stopped with aluminum foil.

Relative Dating

Specific age is not determined, but rather a chronology of events is figured out. (statigraphy, Steno's laws)

Half Life

The amount of time that it takes for a radioactive substance to decrease to half of previous amount. The amount of time that is takes for half of the parent isotope to decay into daughter isotopes. We can determine how long a HL is for any given decay sequence but we can never predict when any given parent isotope will change. This is completely random

Half-life is the amount of ________ it take for half of the unstable atoms in a sample to _________

time, decay

Why can't a radiometric dating technique that has a really long half- life(slow rate of decay) be used to date something that is relatively young? (be able to draw the radioactive decay curve and show where this substance would hypothetically be on the curve)

The parent to daughter ratio would have too few daughter isotopes to detect. In order to be able to date a substance we need to be able to detect the ratio of parent to daughter isotopes. We can detect this ratio well before the first half-life, but if the rate is very slow and there are not enough daughter isotopes to detect. We could not use this particular method.

Why can't a radiometric dating technique that has a really short half- life (rapid rate of decay) be used to date something that is very old? (be able to draw the radioactive decay curve and show where this substance would hypothetically be on the curve)

The parent to daughter ratio would have too few parent isotopes to detect

Radioactivity

The particles or energy emitted during the process of radioactive decay

Nuclear Fusion

The process by which the nuclei of lighter elements combine to form heavier elements. For example in the sun 2 hydrogen atoms combine to form a helium atom

Radioactive Decay

The process by which the nuclei of unstable atoms becomes stable by emitting either energy and/or sub atomic particles from the nucleus

Nuclear Fission

The splitting of a nucleus of an atom. Used in the atomic bomb and in nuclear power plants

In your own words explain how you use the length of a half-life and the ratio of parent to daughter isotopes to determine the age of an artifact

There are two things needed to determine the age of a substance using radiometric dating. 1) Ratio of parent to daughter isotope (Which gives us HL #) 2) Length of each half life The ratio of parent to daughter isotopes gives us the half-life number. For example if I have 25% parent isotope remaining I know that the substance has been through 2 half-lives. If I know that the length of each half life is 2 million years, then I know the substance is 4 million years old.

potassium argon advantages

Very common element on earth. Can date metamorphic. Can date younger rocks beginning at about 100,000 years old

A sample is more unchanged when it has

an older half life

Radiometric Dating

assessing the age of substances using a known half life and the ratio of parent to daughter isotopes. Since the length of the half-life is known the age of a given substance can be determined by measuring the ratio of parent to daughter isotopes. For any given radiometric technique, the greater the proportion of parent isotopes, the younger the substance. The greater the percentage of daughter isotopes the older the substance. Ratio of parent isotope to daughter isotope tells how old a substance is

The age of an object can be determined in radiocarbon dating by comparing its carbon-14 levels with

carbon-12 levels in the object

radiocarbon dating uses the isotope

carbon-14

True or false: Like chemical reaction rates, nuclear decay rates vary with the conditions of reaction

false

true or false: Radiocarbon dating is highly accurate in dating objects that are more than 50,000 years old

false

true or false: all radioisotopes decay at the same rate

false

true or false: plants and animals continue to absorb carbon from the atmosphere after they die

false

All atoms are made of tiny particles held together by strong ________

force

length of each half life=

total time/# of half lives

For example, when uranium atoms decay, one of the products is ______ atoms

lead

Unstable atoms contain _______ particles than can be held together by the strong forces

more

After two half lives, _____ ____________ of the original sample is unchanged

one quarter

Atoms of different elements contain different numbers of ____________

particles

Absolute dating requires the use of a natural "clock". That clock is the ______________ decay of certain naturally-occurring ____________ like uranium and carbon.

radioactive, elements

a half life is the time required for one half of a sample of a ___________(________ ___________) to decay

radioisotope (parent isotope)

They (unstable atoms) undergo radioactive decay by ____________ some of those particles

releasing

Half-lives range from fractions of a _________ to billions of ________

second, years

Alpha Radiation

the radiation of a positively charged helium atom with 2 protons, 2 neutrons. Does not penetrate through paper

Particle Radiation

the radiation of energy by means of fast-moving subatomic particles

Absolute dating is a method of estimating the age of a fossil in _______

years