1 beta emissions (principles of carbon dating). 2 radiation - energy emitted in the form of waves...

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Beta Emissions

(Principles of Carbon Dating)

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Radiation - Energy emitted in the form of waves (light) or particles (photons).

Beta Radiation: emits a beta particle (an electron). In beta decay a neutron in the nucleus changes into a proton, an electron and a neutrino and ejects the high speed electron (beta particle) from the nucleus..

Radioactive Emissions (Radiation)

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Radioactive Emissions (Radiation)

Penetrating Power

SymbolEquivalent

Description

Type

He Stopped by thick paper ()

Helium nucleus

Dense (+) charged particle

42

-1

-1

Stopped by 6mm of Al

High speed electron

(-) charged particle

e0

0

Alpha

Beta

Gamma

Stopped by several cm of Pb

High energy photons

Type of energy 0

0

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Penetrating Power of Radioactive Emissions

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Beta Decay

When a parent nucleus decays by the Beta (β) decay process, an electron, called a beta particle (β) is emitted. The resulting daughter nucleus will always have the same atomic mass and an atomic number increased by one.

2863

2963

10Ni Cu e 28

632963

10Ni Cu e

emitted beta particle

atomic weight is constant

atomic number increases

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Beta Decay

epn 01

11

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Mass: 14 = 14 + 0 Charge: 6 = 7 + (-1)14 = 14 6 = 6

A beta particle is created in the nucleus by a process in which one neutron is transformed into a proton and an electron.

Example of Beta Decay:

14 14 076 -1C N e

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Beta Decay Application – Carbon Dating

Click here for a short video on carbon dating dead biological materials.

How old are these bones?

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Carbon dating is a method of determining the age of dead biological materials based on the rate of decay of the radioactive isotope Carbon-14.

• Willard F. Libby pioneered carbon dating at the University of Chicago in the 1950's.

• In 1960, he won the Nobel Prize for Chemistry for this work.

• Radiocarbon dating is now the most widely used method of age estimation in the field of archaeology.

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Carbon-14 is an unstable isotope of Carbon-12.

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Carbon-14 begins when high-energy cosmic rays enter the earth's atmosphere. The rays collide with atoms to create a secondary cosmic rays in the form of an energetic neutron. (Every person on the earth is hit with about 500,000 cosmic rays every hour.)

atom

neutron cosmic ray

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These neutrons can then collide with the diatomic nitrogen molecules in the atmosphere. These collisions produce carbon-14 and nitrogen atoms, as well as protons.

neutron


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Just like carbon-12, carbon-14 chemically reacts with the oxygen in the atmosphere to produce carbon dioxide.

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Almost all of the carbon dioxide in our atmosphere is derived from non-radioactive carbon-12 atoms. The ratio of normal carbon-12 to carbon-14 in the air and in all living things is nearly constant at any given time. This ratio is approximately 1 in every in one trillion carbon atoms is carbon-14.

1 Carbon-14

1,000,000,000,000 Carbon-12

14126

126

1.0 10C

xC

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Like carbon dioxide made from xarbon-12, carbon dioxide made from carbon-14 enters the carbon cycle through photosynthesis.

As animals eat plant life they assimilate both carbon-12 and carbon-14 into their bodies in the ratio that carbon-12 and carbon-14 exist in nature.

The process of live organisms (including humans) taking in carbon continues until death.

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Once an organism dies, it stops consuming Carbon and the amount of carbon-12 in the tissue remains constant.

But, the carbon-14 that was in the tissue radioactively decay (with a haf-life of 5,730 years) into nitrogen-14.

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By measuring the ratio of c-12 to c-14 in a sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing.

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The formula to calculate how old a sample is by carbon-14 dating is:

t = [ln(Nf/No)/(-0.693)]x t1/2

where:

ln is the natural logarithm

Nf/No is the percent of carbon-14 in the sample compared to the amount in living tissue

t1/2 is the half-life of carbon-14 (5,730 years)

1/ 2

ln( )

0.0693

f

o

N

Nt t

1 beta emissions (principles of carbon dating). 2 radiation - energy emitted in the form of waves...

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