What is Radioactivity? Download

Transcript
Nuclear Chemistry
Aim Nuke 2 – What is Radioactivity?
Watch the video below for extra
understanding!
Nuclear Chemistry
the subfield of chemistry dealing with:
radioactivity,
nuclear processes,
and nuclear properties.
Radioactivity is based on an atom’s nuclear
stability
The Strong Nuclear Force (SNF) - A
fundamental force that holds nucleons together
• Binding Energy – the “strength” of the SNF
• Nucleons – particles in the nucleus (protons
and neutrons)
Stable nuclei
When the SNF holds the nucleons together
There is no break down of the nucleus
Unstable nuclei or radioisotopes
When the SNF cannot hold the nucleons
together the nucleus breaks down or decays
This results in the nucleus emitting (releasing)
nuclear radiation
Nuclear Radiation
particles or
waves of energy
See Table O
at right)
Unstable nuclei are due to:
The ratio of protons to
neutrons affects stability
As nuclei increase in size
A 1:1 ratio of protons to
neutrons does NOT make
the nucleus stable
In general, for elements 1 to 83, there is at
least one stable nucleus
Above 83, there are only radioisotopes for each
element
Radioisotopes - Isotopes that are unstable due
to the particular ratio of protons to neutrons
Radioactivity or
Radiation
The breakdown of
nuclei emits different
types of radiation
The four main forms
of decay in this class,
from least penetrating to most penetrating:
Alpha decay – a helium nucleus is emitted
Beta decay – a high energy electron is emitted
Positron decay – a positron (an anti-matter
electron) is emitted
Gamma decay – gamma rays (high energy
electromagnetic waves) are emitted
Dangers of Radioactivity
Each radiation has its own factors
making it dangerous
Alpha particles (helium nuclei) have a +2 charge
that ionizes materials (Ionizing radiation – can
alter DNA!)
Beta particles are small but can ionize (a -1
charge) deep into materials a high energy
• Radioactive
particles can be separated by
electron is emitted
charged
plates
Positrons
are the same as beta, but a +1 charge
• Why don’t gamma rays move toward a positive
Gamma rays do not have a charge, but are the
or
negative
plate?
most dangerous as they put large amounts of
• Which
would positrons move toward?
energy plate
into tissue
Dangers of Radioactivity
Gamma rays are similar to X-rays and can
destroy tissue
Shorter the wavelength on the EM Spectrum
The more energy there is in the rays
Think about what ultraviolet light does to you on
a sunny day at the beach!
Decay modes
Elements each decay and
release different radiations
Table N – gives the decay
modes, the half life of each
radioisotope, and its name
Half life - the TIME it takes
for HALF of the radioisotope
to decay
Half lives are different for
different isotopes
They do not change with
temperature, pressure,
or any other variable
Natural Transmutation
the spontaneous disintegration
(breakdown) of an atom’s nucleus
Natural transmutation
When a nucleus disintegrates on its own
one element changes to another without
the addition of other particles
Radioactive particles (alpha, beta, or
positrons) or photons of energy (gamma
rays) can also be released
Decay Series
Radioactive
elements will
decay until they
become a
stable atom
Most above
atomic # 83
will decay
into lead
(atomic # 82)
Each element decays and changes into a new
element based on what changes the decay does to
the nucleus
Decay Series
Alpha decay - releases a helium nucleus
the original nucleus loses 2 p+ and 2 no
Example 238 U  234 Th + 4 He
92
90
2
Beta decay – a neutron in the nucleus decays into
a proton and an electron
The proton stays in the nucleus, but increases
the atomic # by 1
The electron is emitted as a beta particle
Example 234 Th  234 Pa + 0 e
90
91
-1
Decay Series
- releases a helium nucleus
the original nucleus loses 2 p+ and 2 no
Example: 238 U  234 Th + 4 He
92
90
2
Positron decay – a proton in the nucleus decays
into a neutron and a positron, an anti-matter
electron
The neutron stays in the nucleus but the loss of
a proton lowers the atomic # by 1
The positron is emitted
Example: 19 Ne  19 F + 0 e
10
9
+1