Science 10Chapter 7 - Radiation
Chapter 7, Radiation and Nuclear Energy
7.1 ELECTROMAGNETIC RADIATION
Radiation
-Energy in the form of electromagnetic waves
Electromagnetic wave
-Composed of both a varying electric field and a varying magnetic field. The two fields run at a right angle to each other
Electromagnetic Spectrum
-Is a name that scientists give a bunch of types of radiation when they want to talk about them as a group. Lists the types of radiation from low frequency to high frequency.
Wave length
-The length of 1 wave, the higher the frequency the shorter the wavelength
- A radio’s wavelength is approx. 1m in length
- A gamma ray’s wavelength is 0.000 000 000 000 001 m in length!
Electromagnetic radiation
Can be described in terms of a stream of photons, which are particles each traveling in a wave-like pattern and moving at the speed of light = 299792458 m / s. Each photon contains a certain amount of energy, and all electromagnetic radiation consists of these photons.
The only difference between the various types of electromagnetic radiation is the amount of energy found in the photons. Radio waves have photons with low energies, microwaves have a little more energy than radio waves, infrared has still more, then visible, ultraviolet, X-rays, and ... the most energetic of all ... gamma-rays.
7.2 RADIATION IN ATOMS
Radioactive
-Any atom that emits radiation from their nuclei
-Three types of radiation are emitted from a nuclei - alpha, beta and gamma
Alpha: composed of 2 protons and 2 neutrons and have a charge of +2
- Are helium nuclei
Beta: high energy electrons and have a charge of -1
Gamma: a form of electromagnetic radiation and are not made of particles
- can penetrate very deep into objects
Isotopes
Review – atomic number = protons and electrons
- atomic mass minus atomic number = neutrons
-Atoms of the same element that have different mass numbers, due to the number of neutrons in the nucleus.
Example : Carbon 12 has 6 protons and 6 neutrons
Carbon 13 has 6 protons and 7 neutrons
Carbon 14 has 6 protons and 8 neutrons
Radioactive Decay
The unstable nuclei emit radiation and decompose over time
Alpha Decay -
Emit alpha particles
Alpha particles are helium nuclei, therefore it emits 2 protons and 2 neutrons
Example
Uranium Helium and Thorium
U He + Th
Beta Decay
Emit high energy electrons
Example
Carbon electron and Nitrogen
C e + N
Carbon will lose 1 electron (e-1) therefore 6 – (-1) = 7
Gamma Decay
Does not give off a particle, there is no change to the nucleus
Emits excess energy from the nucleus
Half-life
The time required for half of the nuclei to decay
Therefore, after 1 half life, exactly half of the original starting material is left.
Example
Carbon 14 - half-life = 5730 years
Radon 222 – half life = 3.8 days
Radon 216 – half life = 0.000045 seconds
Half-life
The time required for half of the nuclei to decay
Therefore, after 1 half life, exactly half of the original starting material is left.
Example
Carbon 14 - half-life = 5730 years
Radon 222 – half life = 3.8 days
Radon 216 – half life = 0.000045 seconds
/ If you point a Geiger counter at a radioactive substance for a period of time, you'll notice that the reading on the meter decreases as you watch. This is shown on the graph.The radioactivity from some substances dies away very fast - perhaps in a few microseconds. Others take thousands of years before you'll notice that the radioactivity had decreased at all.
In theory, every radioactive substance should stay slightly radioactive for ever - the graph should never actually fall to zero. This means that we can't usefully talk about the "life" of a radioactive source.
Instead, we use the idea of "half-life".
This is the time it takes for the radioactivity to fall by half.
This graph shows what would happen with an imaginary radioactive substance.
Notice that the radioactivity falls by half every 2 hours.
Thus we say that this imaginary substance has a half-life of 2 hours. /
The count rate coming from a radioactive source depends on how many unstable atoms it contains.
That's the number of un-decayed atoms.
If the count rate has fallen by half, then the number of unstable atoms has fallen by half.
A typical exam question may be "A radioactive substance has a half-life of 2 hours. How much of the substance will remain after 6 hours have passed?"
Thus, for a substance with a half-life of 2 hours, 1/8 of the original atoms will remain after 6 hours.
Note that this also means that 7/8 of the atoms will have decayed in that time.
Take another look at the graph above, you'll see that after 6 hours the activity has fallen from 8,000 to 1,000; i.e. it's fallen to 1/8 of the starting value.
Question 1:
A radioactive substance has a half-life of 30 minutes. What fraction of the atoms will not have decayed after 1 hour?
Answer:
That means that 1 hour is 2 half-lives for the substance.
After one half-life the activity will fall to 1/2 of the starting value, after a second half-life it will have fallen to half of that - i.e. a quarter.
So one quarter of the original atoms remain. /
Question 2:
Another substance has a half-life of 3 hours. What fraction of the atoms will have decayed after 6 hours?
Answer:
After 2 half-lives only one quarter of the original atoms remain, which means that three-quarters of them have decayed. /
Question 3:
A researcher measures 200 counts per minute coming from a radioactive source at midday. At 3 o'clock, she finds that this has dropped to 25 counts per minute.
What is the half-life of the radioactive source?
Answer:
Calculate the number of half lives there is from 200 to 25
200 – 100 -50 - 25
so this means that three half lives have passed.
If 3 half-lives are 3 hours, then the half-life is one hour. /
Chapter 7, Radiation and Nuclear Energy
7.1 ELECTROMAGNETIC RADIATION
Radiation
-Energy in the form of electromagnetic waves
Electromagnetic wave
-Composed of both a varying electric field and a varying magnetic field. The two fields run at a right angle to each other
Electromagnetic Spectrum
-Is a name that scientists give a bunch of types of radiation when they want to talk about them as a group. Lists the types of radiation from low frequency to high frequency.
Wave length
-The length of 1 wave, the higher the frequency the shorter the
wavelength
- A radio’s wavelength is approx. 1m in length
- A gamma ray’s wavelength is 0.000 000 000 000 001 m in length!
Electromagnetic radiation
Can be described in terms of a stream of photons, which are particles each traveling in a wave-like pattern and moving at the speed of light = 299792458 m / s. Each photon contains a certain amount of energy, and all electromagnetic radiation consists of these photons.
The only difference between the various types of electromagnetic radiation is the amount of energy found in the photons. Radio waves have photons with low energies, microwaves have a little more energy than radio waves, infrared has still more, then visible, ultraviolet, X-rays, and ... the most energetic of all ... gamma-rays.
Electromagnetic radiation (including visible light) travels 149 million kilometers (93 million miles) from the sun to Earth in about 8 minutes. In contrast, an automobile speeding at 100 kilometers per hour (60 miles per hour) would require 177 years to make the same one-way trip.
In only one second, light can circumnavigate the Earth seven times.
7.2 RADIATION IN ATOMS
Radioactive
-Any atom that emits radiation from their nuclei
-Three types of radiation are emitted from a nuclei - alpha, beta and gamma
Alpha: composed of 2 protons and 2 neutrons and have a charge of +2
- Are helium nuclei
Beta: high energy electrons and have a charge of -1
Gamma: a form of electromagnetic radiation and are not made of
particles
- can penetrate very deep into objects
Isotopes
Review – atomic number = protons and electrons
- atomic mass - atomic number = neutrons
-Atoms of the same element that have different mass numbers, due to the number of neutrons in the nucleus.
Example : Carbon 12 has 6 protons and 6 neutrons
Carbon 13 has 6 protons and 7 neutrons
Carbon 14 has 6 protons and 8 neutrons
Radioactive Decay
The unstable nuclei emit radiation and decompose over time
Alpha Decay -
- Emit alpha particles - Alpha particles are helium nuclei, therefore it emits 2 protons and 2 neutrons
Example;
Uranium Helium and Thorium
U He + Th
Beta Decay
Emits high energy electrons
Example;
Carbon electron and Nitrogen
C e + N
Carbon will lose 1 electron (e-1) therefore 6 – (-1) = 7
Gamma Decay
Does not give off a particle, there is no change to the nucleus
Emits excess energy from the nucleus
Half-life
- The time required for half of the nuclei to decay
- Therefore, after 1 half life, exactly half of the original starting
material is left.
Example
Carbon 14 - half-life = 5730 years
Radon 222 – half life = 3.8 days
Radon 216 – half life = 0.000045 seconds
Half-life
The time required for half of the nuclei to decay
Therefore, after 1 half life, exactly half of the original starting material is left.
Example
Carbon 14 - half-life = 5730 years
Radon 222 – half life = 3.8 days
Radon 216 – half life = 0.000045 seconds
/ If you point a Geiger counter at a radioactive substance for a period of time, you'll notice that the reading on the meter decreases as you watch. This is shown on the graph.The radioactivity from some substances dies away very fast - perhaps in a few microseconds. Others take thousands of years before you'll notice that the radioactivity had decreased at all.
In theory, every radioactive substance should stay slightly radioactive for ever - the graph should never actually fall to zero. This means that we can't usefully talk about the "life" of a radioactive source.
Instead, we use the idea of "half-life".
This is the time it takes for the radioactivity to fall by half.
This graph shows what would happen with an imaginary radioactive substance.
Notice that the radioactivity falls by half every 2 hours.
Thus we say that this imaginary substance has a half-life of 2 hours. /
The count rate coming from a radioactive source depends on how many unstable atoms it contains.
That's the number of un-decayed atoms.
If the count rate has fallen by half, then the number of unstable atoms has fallen by half.
A typical exam question may be "A radioactive substance has a half-life of 2 hours. How much of the substance will remain after 6 hours have passed?"
Thus, for a substance with a half-life of 2 hours, 1/8 of the original atoms will remain after 6 hours.
Note that this also means that 7/8 of the atoms will have decayed in that time.
Take another look at the graph above, you'll see that after 6 hours the activity has fallen from 8,000 to 1,000; i.e. it's fallen to 1/8 of the starting value.
Question 1:
A radioactive substance has a half-life of 30 minutes. What fraction of the atoms will not have decayed after 1 hour?
Answer:
That means that 1 hour is 2 half-lives for the substance.
After one half-life the activity will fall to 1/2 of the starting value, after a second half-life it will have fallen to half of that - i.e. a quarter.
So one quarter of the original atoms remain. /
Question 2:
Another substance has a half-life of 3 hours. What fraction of the atoms will have decayed after 6 hours?
Answer:
After 2 half-lives only one quarter of the original atoms remain, which means that three-quarters of them have decayed. /
Question 3:
A researcher measures 200 counts per minute coming from a radioactive source at midday. At 3 o'clock, she finds that this has dropped to 25 counts per minute.
What is the half-life of the radioactive source?
Answer:
Calculate the number of half lives there is from 200 to 25
200 – 100 -50 - 25
so this means that three half lives have passed.
If 3 half-lives are 3 hours, then the half-life is one hour. /
Chapter 7, Radiation and Nuclear Energy
(student handout)
7.1 ELECTROMAGNETIC RADIATION
Radiation - ______
______
Electromagnetic wave
-______
______
Electromagnetic Spectrum
- ______
Wave length
______
- A radio’s wavelength is approx. 1m in length
- A gamma ray’s wavelength is 0.000 000 000 000 001 m in length!
Electromagnetic radiation
Can be described in terms of a stream of photons, which are particles each traveling in a wave-like pattern and moving at the speed of light = 299792458 m / s. Each photon contains a certain amount of energy, and all electromagnetic radiation consists of these photons.
Electromagnetic radiation (including visible light) travels 149 million kilometers (93 million miles) from the sun to Earth in about 8 minutes. In contrast, an automobile speeding at 100 kilometers per hour (60 miles per hour) would require 177 years to make the same one-way trip. In only one second, light can circumnavigate the Earth seven times.
The only difference between the various types of electromagnetic radiation is ______
______. Radio waves have photons with low energies, microwaves have a little more energy than radio waves, infrared has still more, then visible, ultraviolet, X-rays, and ... the most energetic of all ... gamma-rays.
7.2 RADIATION IN ATOMS
Radioactive
-______
-Three types of radiation are emitted from a nuclei - alpha, beta and gamma
Alpha: composed of ______and have a charge of +2
- Are ______nuclei
Beta:______
Gamma: a form of electromagnetic radiation and are not made of particles
- can penetrate very deep into objects
Isotopes
Review : atomic number = protons and electrons
- atomic mass minus atomic number = neutrons
-Atoms of the same element that have different mass numbers, due to the number of neutrons in the nucleus.
Example : Carbon 12 has 6 protons and 6 neutrons
Carbon 13 has 6 protons and 7 neutrons
Carbon 14 has 6 protons and 8 neutrons
Radioactive Decay
The unstable nuclei emit radiation and decompose over time
Alpha Decay -
Emit alpha particles
Alpha particles are helium nuclei, therefore it emits 2 protons and 2 neutrons
Example
Beta Decay
Emit high energy electrons
Example
Gamma Decay
Does not give off a particle, there is no change to the nucleus
______
Half-life
The time required for half of the nuclei to decay
Therefore, after 1 half life, exactly half of the original starting material is left.
Example
Carbon 14 - half-life = 5730 years
Radon 222 – half life = 3.8 days
Radon 216 – half life = 0.000045 seconds
/ If you point a Geiger counter at a radioactive substance for a period of time, you'll notice that the reading on the meter decreases as you watch. This is shown on the graph.The radioactivity from some substances dies away very fast - perhaps in a few microseconds. Others take thousands of years before you'll notice that the radioactivity had decreased at all.
In theory, every radioactive substance should stay slightly radioactive for ever - the graph should never actually fall to zero. This means that we can't usefully talk about the "life" of a radioactive source.
Instead, we use the idea of "half-life".
This is the time it takes for the radioactivity to fall by half.
This graph shows what would happen with an imaginary radioactive substance.
Notice that the radioactivity falls by half every 2 hours.
Thus we say that this imaginary substance has a half-life of 2 hours. /
The count rate coming from a radioactive source depends on how many unstable atoms it contains.
That's the number of un-decayed atoms.
If the count rate has fallen by half, then the number of unstable atoms has fallen by half.
A typical exam question may be "A radioactive substance has a half-life of 2 hours. How much of the substance will remain after 6 hours have passed?"
Thus, for a substance with a half-life of 2 hours, 1/8 of the original atoms will remain after 6 hours.
Note that this also means that 7/8 of the atoms will have decayed in that time.
Take another look at the graph above, you'll see that after 6 hours the activity has fallen from 8,000 to 1,000; i.e. it's fallen to 1/8 of the starting value.
Question 1:
A radioactive substance has a half-life of 30 minutes. What fraction of the atoms will not have decayed after 1 hour?
Answer:
Question 2:
Another substance has a half-life of 3 hours. What fraction of the atoms will have decayed after 6 hours?
Answer:
Question 3:
A researcher measures 200 counts per minute coming from a radioactive source at midday. At 3 o'clock, she finds that this has dropped to 25 counts per minute.
What is the half-life of the radioactive source?
Answer:
1