Radiation Protection & Radiobiology

5 basic interactions between x-rays and matter

1. Compton Effect

2. Photoelectric Absorption

3. Coherent (Classical) Scatter

4. Pair Production

5. Photodisintegration

Which 3 interactions of x-rays with matter are for diagnostic purposes?

Classic Coherent Scattering

Photoelectric interactions

Compton scattering

Coherent scattering is also known as

Compton effect with unmodified scatter

Classical scattering

Thompson effect

Coherent scattering

The incoming x-ray photon bumps into the atom and is deflected from its path with no loss of energy

Interaction with matter that is insignificant and causes no effects

Coherent/classical scattering

Interaction with matter that occurs at low energy ranges (below 70 kv)

Coherent or classical scattering

Interaction with matter where the atom is not ionized

Coherent or classical scattering

Interaction with matter where frequency and wavelength of incident photon remains unchanged

Coherent or classical scattering

At 70 KV, a small percentage of x-rays undergo _ which contributes slightly to image noise

Coherent scattering

Compton effect with modified scattering

The incident, x-ray photon collides with an outer shell electron of an atom, and is scattered with resulting energy loss

This interaction is very significant in terms of fog to the radiograph and radiation exposure to the technologist

Compton effect with modified scattering

Interaction with matter that strikes a loosely bound outer shell electron

Compton effect

An electron knocked out of orbit by the Compton effect is known as

Recoil or Compton electron (atom is ionized)

What happens to the incident photon during the Compton effect?

Incident photon loses energy

Frequency decreases

Wavelength increases

The photon is deflected from its path

Energy of scattered photons is equal to

The difference between the energy of the incident photon and the energy It loses when it strikes the orbital electron.

The energy of the ejected electron is equal to

its binding energy plus the kinetic energy with which it leaves the atom

Incident photon Energy lost depends on

The angle it strikes and the binding energy of the electron

Backscatter

Photons which are reflected 180° back in the same direction of origin

When does backscatter occur?

When the incident photon strikes the electron head on

and if the electron it strikes has a high binding energy

Probability of the Compton effect

inversely proportional to x-ray energy (chances decrease as KVP increases)

Compton effect: low kVp

More scatter occurs from low energy radiation

Less of it reaches film

Scatters sideways

Compton effect: high kVp

More scatter, appears on film at high KVP

Compton scattering is most likely to occur with _/_electrons

Outer shell/ loosely bound

As atomic number of absorber increases, there is _ effect on Compton scattering

No

photoelectric effect

The incident, x-ray photon collides with an inner shell electron and is totally absorbed

Interaction with matter that is responsible for the white areas of the radiograph representing bone

Photoelectric effect (attenuation)

An electron knocked out of orbit by the photoelectric effect is known as

Photoelectron

How is secondary radiation admitted during the photoelectric process

Electrons from outer shells jump down to fill holes

Releases excess potential energy in the form of low energy Characteristic Radiation

Probability of the photoelectric effect

Increases as KVP decreases (more likely to be absorbed)

Increases as atomic number increases (protons in nucleus)

High atomic number = _ photoelectric absorption

More

Photoelectric effect is most likely to occur with _/_ electrons

Inner shell / tightly bound electrons

As atomic number of absorber increases (photoelectric effect)

Increases proportionately with the cube of the atomic number (Z3)

Interactions with matter above diagnostic energy range

Pair production

Photodisintegration

Pair production

A high energy photon interacts with the nucleus of the atom, creating one positive and one negatively charged electron

Pair production occurs at energy levels of

1.02 MeV or above

In pair production, incident photon interacts with

The electrostatic field of the nucleus

Interaction with matter where photon disappears and is replace with a positron and negatron

Pair production

A positron collides with

Another free electron and they annihilate

Positron and negatron (pair production) energy

Two photons with .51 KeV of energy

Photodisintegration

Photons with energies above 10 MeV are absorbed by the nucleus and a nuclear fragment or particle is emitted

Interaction with matter that is important in radiation therapy

Photodisintegration

In an atom

Electrons orbit nucleus

Protons and neutrons in nucleus

3 fundamental atom particles and their charges

Protons (+)

Neutrons (0)

Electrons (-)

Protons/nuetrons and electrons Atomic Mass Numbers

Protons= 1.00728 or 1 amn

Nuetrons= 1.00867 or 1 amn

Electrons= .000549 or 0 amn

On the periodic table, the superscript is the

Atomic number

On the periodic table, the subscript is the

Elemental mass (old term: atomic weight)

Elements on the periodic table are organized by

atomic number, from the element with the lowest atomic number to the highest atomic number

Characteristics of the atom

Smallest division or particle of an element

Consists of mostly empty space

Most of the weight is concentrated in the nucleus

Contains protons and neutrons

Stable/nuetral atom=

Same number of protons and electrons

The net charge of the nucleus is

Positive

In their normal state atoms are

Electrically neutral, the electric charge on the atom is zero

Ionization

When an atom gains or loses an electron, it is said to be ionized

(Ionization) X-rays only have the capability of

Knocking an electron out of an atoms orbit

In our field, when we ionize atoms we are causing an atom to lose an electron

If an atom loses an electrons, the net charge of the atom becomes

Positive (protons outnumber electrons)

If an atom gains an electron the net charge of the atom becomes

Negative (electrons outnumber protons)

Nomenclature

To name compounds and to determine molecular formula

The components to naming compounds include

Atomic number

Mass number

Number of electrons

Atomic number (Z)

the number of protons in the nucleus of an atom

Atomic Mass Number (mass number)

Total number of protons and neutrons in the atoms nucleus (symbolized by A)

The atomic mass number is always a _ number

Whole

Helium has two protons and two neutrons, AMN=

4

Electrons revolve around the nucleus in

Precise orbits or shells

What causes electrons to revolve around the nucleus?

Electrostatic attraction

Electrostatic is

The attraction or repulsion of like or unlike charges

Opposite charges attract

+ attracted to -

Same charges repel

Electrons are - and are attracted to the + protons in the nucleus

The orbit closest to the nucleus is labeled

K shell

Second orbit closest to the nucleus is labeled

L. Then M, N, O and so on.

Number of naturally occurring elements

92

Isotope

An atom of the same element with the same number of protons, but a different number of neutrons

_ will have the same atomic number (protons) but different atomic mass numbers (protons + neutrons)

Isotopes

How many isotopes does barium have?

7

How to figure out # of neutrons of an isotope

Minus the atomic number and protons to figure out nuetrons

Elemental mass

The average mass number of all isotopes of that element

Why is elemental mass an uneven number?

It represents the average amn of the elements many different isotopes, calculated together as an average

How many neutrons are in the nucleus? [mass number: 42 protons and nuetrons, atomic number = 20 protons]

42 protons and neutrons

-20 protons

=

22 neutrons

(20 electrons)

An atom has 12 electrons. The Atom has an AMN of 27. How many neutrons does the atom have? Assume the atom is neutral

12 electrons = 12 protons

27-12 = 15 neutrons

What is the smallest division of an element?

an atom

Atoms of different elements combine to form

Molecules

A chemical compound is

Any quantity of one type of molecule, such as sodium chloride (salt)

The smallest particle of an element is _, the smallest particle of a compound is _

An atom, a molecule

Molecules combine to make

Matter such as tissues

An element is made up of

one type of atom

Molecules

Two or more atoms chemically joined together

Compounds

Two or more different elements joined together chemically

Bohr's Theory

• Describes the atom as a miniature solar system

• Electrons revolve around the nucleus in prescribed orbits or energy levels

• The nucleus is small, dense, and positively charged

Two types of energy within an atom

Binding energy

Potential energy

Orbits

The electron in an atom travels around the nucleus in precise energy shells, or orbits

Binding energy

The strength of attachment of an electron to the nucleus of the atom

Each shell in an atom represents a different

Electron binding energy

Which shells hold the electrons with the most binding energy

Those shelves closest to the nucleus

Which electron will be the hardest to remove from the atom due to its strong binding energy

K shell

Atoms with _ have more binding energy compared to atoms with _

High atomic numbers, low atomic numbers

Why do atoms with high atomic numbers have more binding energy

Because of the strong positive charge of the nucleus, due to a large number of positively charged protons

Potential energy

Potential energy is a stored energy that depends upon the relative position of various parts of a system

Which electrons possess the most potential energy

Electrons which are located in the shells farthest from the nucleus

If a vacancy becomes available in a shell, closer to the nucleus and electron will

Always jump down to fill the vacancy, thus giving off some of its potential energy

Discovery of x-rays

Nov 8th 1895

Wilhelm Conrad Roentgen

First case of radiation injury

1898

Clarence Dally

Thomas Edison's assistant developed severe skin burns, leading to amputation of both arms

First death from radiation exposure

1904

Clarence Dally

Mrs. Roentgen's hand

First x-ray of a person