What is RADIATION?

 

 

Radiation is the process of atoms and molecules emitting energy – sending out waves or particle in all directions

 

Electromagnetic radiation is wave-like and is generated inside matter when electrons change position in atoms or when atoms change positions in molecules.

 

Examples of electromagnetic radiation are radio waves, radar, microwaves,

infrared waves (heat radiation), light (colors), ultraviolet waves (black light), x- rays.

 


In nuclear radiation the nucleus of an atom changes. The nucleus changes because something makes it unstable. When this happens the nucleus gets rid of particles and/or energy

 

Some radiation has such high-energy that it can knock electrons out of atoms and molecules. It is called ionizing radiation. An ion is a charged atom or molecule. Ionizing radiation produces positively charged ions.

 

There are two main types of ionizing radiation.

 

1. Fast Moving sub-atomic particles.

 

They are identical to helium nuclei.

They are positively charged and have an atomic mass of four.

The atomic number decreases by two and the mass number

decreases by four.

They are symbolized as :

 

a or 4 He

2


 

 


1 1 0

n -----------> p + b

0 +1 -1

 

These particles have a negative charge and have a mass close to an electron.

 

The atomic number increases by one and the mass number stays the

same.

 

 

1 1 0

p -----------> n + b

1 0 +1

 

These particles have a positive charge and have a mass close to an

electron.

 

The atomic number decreases by one and the mass number stays the

same.

 

 

An inner orbital electron is captured by the nucleus of its own atom. The electron combines with a proton and a neutron is formed.

The atomic number decreases by one and the mass number stays the

same.

 

2. High - energy electromagnetic radiation.

 

 

a. X-rays

 

X-rays come from an X-ray “gun”. In the gun, high-speed electrons are

targeted at some element like copper or molybdenum. The electrons stop

abruptly when they hit the target atoms. The kinetic energy they lose in the stopping

process is turned into X-rays.

 

b. Gamma rays

 

A form of electromagnetic radiation given off by the nucleus in a decay

process. A gamma ray has no mass.

 

They are really energetic particles.

The particles come from space, particularly the sun and solar flares.

They are mainly protons.

These energetic particles collide with other atmospheric particles causing

them to ionize and/or disintegrate.

 

 

 

A Brief Understanding of Subatomic Particles and Interactions

 

Scientists use accelerators to track and identify each of the many particles produced in a single collision of high energy particles.

 

Particles

 

There are six types of quarks.

They are never found separate, only inside protons and neutrons.

A proton has two up quarks and one down quark.

A neutron has two down quarks and one up quark.

 

2. Leptons

 

The electron is the best known lepton.

Leptons may be found by themselves.

Neutrinos are leptons that have no electric charge and very little mass.

 

 

 

For every particle type there is a corresponding antiparticle type.

 

Particle and antiparticle have identical mass and spin but opposite charge.

 

When a particle and an antiparticle meet, they may annihilate, disappearing to give some other form of energy.

 

 

 

 

 

Forces and interactions (What holds the atom together?)

 

Acts on all matter/particles – effects very little when dealing with subatomic particles.

 

Responsible for binding electrons to the nucleus.

The associated carrier particle of the electromagnetic force is the photon and gamma ray (a photon from a nucleus transition).

 

Holds quarks together to form protons and neutrons.

A residual strong force interaction holds the nucleus together.

The carrier particle is a gluon (glues quarks together).

 

Allows quarks and leptons to change to another type of quark or lepton.

Responsible for the fact that all massive quarks and leptons decay to produce lighter versions.

The associated carrier particles are W and Z bosons.

 

What is RADIATION?

 

 

Radiation is the process of atoms and molecules emitting energy – sending out waves or particle in all directions

 

Electromagnetic radiation is wave-like and is generated inside matter when electrons change position in atoms or when atoms change positions in molecules.

 

Examples of electromagnetic radiation are radio waves, radar, microwaves,

infrared waves (heat radiation), light (colors), ultraviolet waves (black light), x- rays.

 


In nuclear radiation the nucleus of an atom changes. The nucleus changes because something makes it unstable. When this happens the nucleus gets rid of particles and/or energy

 

Some radiation has such high-energy that it can knock electrons out of atoms and molecules. It is called ionizing radiation. An ion is a charged atom or molecule. Ionizing radiation produces positively charged ions.

 

There are two main types of ionizing radiation.

 

1. Fast Moving sub-atomic particles.

 

They are identical to helium nuclei.

They are positively charged and have an atomic mass of four.

The atomic number decreases by two and the mass number

decreases by four.

They are symbolized as :

 

a or 4 He

2


 

 


1 1 0

n -----------> p + b

0 +1 -1

 

These particles have a negative charge and have a mass close to an electron.

 

The atomic number increases by one and the mass number stays the

same.

 

 

1 1 0

p -----------> n + b

1 0 +1

 

These particles have a positive charge and have a mass close to an

electron.

 

The atomic number decreases by one and the mass number stays the

same.

 

 

An inner orbital electron is captured by the nucleus of its own atom. The electron combines with a proton and a neutron is formed.

The atomic number decreases by one and the mass number stays the

same.

 

2. High - energy electromagnetic radiation.

 

 

a. X-rays

 

X-rays come from an X-ray “gun”. In the gun, high-speed electrons are

targeted at some element like copper or molybdenum. The electrons stop

abruptly when they hit the target atoms. The kinetic energy they lose in the stopping

process is turned into X-rays.

 

b. Gamma rays

 

A form of electromagnetic radiation given off by the nucleus in a decay

process. A gamma ray has no mass.

 

They are really energetic particles.

The particles come from space, particularly the sun and solar flares.

They are mainly protons.

These energetic particles collide with other atmospheric particles causing

them to ionize and/or disintegrate.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A Brief Understanding of Subatomic Particles and Interactions

 

Scientists use accelerators to track and identify each of the many particles produced in a single collision of high energy particles.


Particles

 

There are six types of quarks.

They are never found separate, only inside protons and neutrons.

A proton has two up quarks and one down quark.

A neutron has two down quarks and one up quark.

 

 

 

 

 

 

 

 

 

 

 

 

 


 

 

 

 

 

 

2. Leptons

 

The electron is the best known lepton.

Leptons may be found by themselves.

Neutrinos are leptons that have no electric charge and very little mass.

 

 

 

For every particle type there is a corresponding antiparticle type.

 

Particle and antiparticle have identical mass and spin but opposite charge.

 

When a particle and an antiparticle meet, they may annihilate, disappearing to give some other form of energy.

 

 

 

 

 

Forces and interactions (What holds the atom together?)

 

Acts on all matter/particles – effects very little when dealing with subatomic particles.

 

Responsible for binding electrons to the nucleus.

The associated carrier particle of the electromagnetic force is the photon and gamma ray (a photon from a nucleus transition).

 

Holds quarks together to form protons and neutrons.

A residual strong force interaction holds the nucleus together.

The carrier particle is a gluon (glues quarks together).

 

Allows quarks and leptons to change to another type of quark or lepton.

Responsible for the fact that all massive quarks and leptons decay to produce lighter versions.

The associated carrier particles are W and Z bosons.


Radiation in YOUR Life

 

Ionizing radiation sources include both natural and man-made sources.

The sum of the exposure to the main natural sources is called background radiation .

 

Natural Sources of Background Radiation

Cosmic Radiation

Originates outside the Earth’s

atmosphere.

 

Terrestrial Radiation

The Earth’s mantle contains many

radioactive sources, such as

uranium.

 

Radon and its Decay Products

Radon is one of the products of the radio-

active decay of uranium. Radon is a

gas and enters the Earth’s atmosphere.

 

Radon can also become trapped inside homes because of decreased ventilation in today’s well insulated, energy- efficient houses.

 

 

 

Food Sources

Potassium and carbon are present in

the food we eat. They are important parts in

our daily nutrition. There is a

radioactive isotope of potassium

(potassium-40) found in the soil.

Plant roots take-up this nutrient, and we

eat the plants. Plants also take in the radioactive

isotope of carbon ( carbon-14) through

photosynthesis. Carbon-14 is produced by

cosmic rays.


Man Made Sources of Background Radiation

Medical Sources

Diagnostic X-rays (dental and medical)

Consumer products

smoke detectors (americium –241)

luminous signs and watches (radium- )

lantern mantles (thorium)

pottery and tile paints (uranium)

TV and computer monitors

Fallout from past nuclear testing

 

Nuclear power generation

Fuel mining, production and waste

Normal operations

Past accidents

 

Occupational exposure

 

Interaction with Natural Sources of Background Radiation

 

Airplane travel

oil and gas production

Radiation uses

 

 

Ionizing radiation is harmful to human health in large doses. However, both ionizing and non-ionizing radiation has many uses in our lives. Below are some examples.

 

Ionizing Radiation Uses:

A. X-rays are used by doctors and dentists to view underlying structures such as bones. Airports also use X-rays to prevent hijacking and terrorist attacks by scanning luggage.

 

B. Iodine-131 is used to treat thyroid problems, such as cancer. To treat cancers, radiation sources must be localized so they do not kill too many healthy cells.

 

C. Phosphorous-32 is used to study plant and animal metabolism. The P-32 replaces non-radioactive phosphorous in such molecules as ATP and DNA.

 

D. Plutonium-239 is used in the construction of pacemaker batteries because they only have to be changed once every 10 years.

 

E. Americium-241 is used in smoke detectors in homes and businesses.

 

F. Archeologists use carbon-14 decay rates to calculate the age of once living tissue. When a living organism dies it has the same carbon-14 concentration as background levels. After the organism dies, the carbon-14 begins to radioactively decay. By calculating the number of half-lives that have occurred, scientists can calculate how long ago the organism died.

 

G. Radiation is also being used to treat food and prevent it from spoiling. Much controversy still remains about this use.

 

 

Non-Ionizing Radiation Uses

Microwave ovens, need we say more?!

 

 

 

 

List and Describe Four Occupations in Radiology:

1.

 

2.

 

3.

 

4.


fission & fusion

In 1905, Albert Einstein came to the conclusion that matter and energy were interchangeable

E = mc2

Where E is energy, m is mass and c is the speed of light.

 

In atoms, some of the mass of the protons and neutrons can be converted into energy

 

Fission is the splitting of one large nucleus into smaller nuclei.

Fusion is the joining, or fusing of two smaller nuclei into creating a larger nucleus.

Nuclear Fission

Process of Splitting :

 

1. Normally like charges repel each other.

This is nuclear fission.

 

The extra neutrons produced above can go to cause more atoms to fission. This leads to a

chain reaction .

7. The majority of energy released in fission is transferred to the fission fragments as kinetic energy, making them move very fast.

 

Making an A-Bomb

 

 

 

 

 

 

 

7. This is the type of bomb dropped on Hiroshima.

 

9. An implosion of many small pieces of Pu-239 is used in this type of bomb.

 

10. This was the first atomic device ever and was also the type of bomb dropped on

Nagasaki.

Controlling Nuclear Fission

 

In nature, uranium deposits contain only about 0.7% U - 235, the isotope

of uranium that is fissionable.

 

The majority is U-238, which absorbs neutrons, but does not fission.

 

In a bomb, almost all the uranium present is U-235.

 

The U-235 concentration necessary for a nuclear reactor is only about 3 - 4%.

 

There is not a supercritical mass of U-235 present in a reactor core, it can not explode like a nuclear bomb.

 

Components of a Nuclear Reactor

A. Fissionable Material (Fuel)

Uranium is mined and enriched so the concentration of U-235 is about 3 - 4%.

The enriched uranium is then formed into pellets, which are then placed in rods.

 

B. Moderator

The moderator is necessary to slow down any neutrons escaping from the fuel rods.

For fission of a U-235 nucleus to occur, the neutron must be moving slow enough for the nucleus to absorb it.

If the neutron is moving too fast, it will just knock out another neutron from the nucleus rather than being absorbed.

 

C. Control Rods

The control rods are used to control the rate of chain reactions occurring.

They are composed of materials that absorb neutrons, stopping them from causing further fissions.

 

D. Cooling System

Once a U-235 nucleus fission's most of the energy released is captured by the fission fragments in the form of kinetic energy.

This causes an increase in the temperature of the reactor core.

The heat is then transferred to the coolant, which is usually water.

The coolant then turns to steam, which can then be used to turn a turbine, which produces electricity.


 

Problems With Nuclear Reactors

A. Meltdown

 

Because the U-235 concentration in nuclear reactor fuel is not as high as in a nuclear bomb, if a runaway chain reaction occurred the core would melt rather than explode.

 

This meltdown happens because the cooling system cannot carry away the heat fast enough.

 

To prevent leakage of the fuel into the environment in case of a meltdown, the core is completely enclosed in two layers of a protective material.

In 1979, the Three Mile Island reactor in Pennsylvania had a partial meltdown, but little radioactivity escaped into the environment. This is because water is used as both the coolant and moderator in this sort of reactor. As the water disappeared, the core heated up, but the neutrons were not slowed down, so more fissions did not take place.

 

The Chernobyl reactor that exploded in 1986 had a graphite moderator. As the water coolant disappeared, nuclear fissions continued, thus causing the core to melt. The fuel rods that contained the uranium reacted with the little water remaining to produce hydrogen gas, which then exploded, leading to the worst nuclear accident in history.

 

B. Radioactive Waste Disposal

 

As the U-235 atoms fission, the reactor becomes less productive.

 

The waste fuel must then be disposed of. However, the waste is radioactive and must somehow be stored safely until enough of the waste has decayed.

 

The main concern of reactor waste is plutonium, which has a half-life of about 24,000 years. Plutonium is formed when U-238 absorbs a neutron.

 

Besides being radioactive, plutonium is also one of the most toxic elements known. This means that it is chemically poisonous and attacks the nervous system.

 

So how can we safely store plutonium?


Nuclear Fusion

In nuclear fusion, energy is released when light nuclei fuse.

 

Usually the nuclei of hydrogen and its isotopes deuterium and tritium are used in fusion reactions. Hydrogen and its two isotopes are:

 

Hydrogen Deuterium Tritium

1 2 3

H H H

1 1 1

 

For fusion to occur, the nuclei must collide at very high speeds to overcome their mutual electrical repulsion.

 


At such high temperatures the hydrogen atoms are stripped of their electrons, and a gas of charged particles results. This gas is called a plasma, the fourth state of matter. What are the other three states?

 

If a deuterium and a tritium nuclei were to fuse, they would produce a helium nucleus, which contains two protons and two neutrons. The released energy is carried away by the third neutron in the form of kinetic energy.

 

NUCLEAR FUSION

 
The high temperatures needed for fusion to occur are found inside the sun and other stars. In one second, the sun converts 4 million tons of matter into radiant energy.

 

Fusion that happens at such high temperatures is called thermonuclear fusion.

 

In 1952 the first hydrogen, or thermonuclear, bomb was exploded when initiated with an atomic bomb.

Today there are tens of thousands of these bombs in the U.S. and the former U.S.S.R.

Ranging in power from 0.5 to 500 megatons of TNT. One megaton TNT equals the destructive capacity of 50 of the first fission bombs.

To detonate a hydrogen bomb, the TNT is exploded, forcing the U-235 together to get a critical mass and an "atomic" explosion. The fusionable material is deuterium in the lithium hydride (LiH), and in the heated plasma D-D reactions occur. Also, neutrons from the fission bomb react with the lithium to give tritium ( 3H), and D-T fusion reactions also take place. The bomb is surrounded with U-238, which tops off the explosion with a fission reaction.

 

Controlling nuclear Fusion

Controlled fusion power is difficult to obtain and is not expected to be

practical until the mid-21 st century.

 

This is because of the high temperatures needed to form a plasma and the large amounts of energy needed to create these high temperatures. The temperatures must exceed 100 million oC.

 

Any material known to man melts at temperatures below 4000 oC. A major problem in fusion technology is to contain these high temperatures.

 

Types of Devices

 

Each devices uses a lithium blanket to absorb the fast moving neutrons released and convert their kinetic energy into heat which then is used to power a steam generator.

 

A. Magnetic Confinement

Strong, super-conducting magnets are used to confine and compress the

plasma.

Powerful radio waves are then used to heat the fuel.

B. Inertial Confinement

 

This device uses solid fuel pellets.

 

Powerful lasers or beams of electrons bombard the pellets from all directions, quickly vaporize the pellets and converting them to plasma.

 

This plasma is then quickly compressed to extraordinary densities to get fusion.

An illustration of a reactor cavity for inertial confinement. Fuel pellets dropped into the cavity are imploded by laser light (or a particle beam), inducing a fusion miniexplosion. Neutrons react with the lithium blanket to produce tritium, which can be recovered and used as fuel.

 

Fusion Advantages

 

A. Fuel Source

Deuterium which is needed for fusion reactions is found in plentiful supply in the Earth’s oceans. About one atom of hydrogen in 6000 is deuterium. Therefore, there is basically an unlimited fuel supply for fusion.

 

B. Nuclear Waste

In comparison to nuclear fission, there are fewer radioactive substances involved and they have shorter half-lives.