Classroom Training Book - Chapter 2

Question 1

What does the nuclear atomic concept describe?

Answer 1

The atom consists of a small, relatively heavy nucleus with electrons bound around it

Electrons are part of a cloud rather than revolving in fixed orbits.

Question 2

What is the equation for calculating the mass number (A) of an atom?

Answer 2

P + N = A

P represents protons and N represents neutrons.

Question 3

What are the charges of protons and electrons?

Answer 3

• Protons: + charge
• Electrons: - charge

There is an equal number of protons and electrons in a neutral atom.

Question 4

What is the typical size of a nucleus compared to the electron cloud?

Answer 4

Nucleus: about 5 × 10–12 mm
Electron cloud: about 2 × 10–7 mm

The linear dimension of an atom is about 40,000 times that of its nucleus.

Question 5

What is the relationship between neutrons and protons in a nucleus?

Answer 5

Neutrons must be equal to or greater than the number of protons

This applies to every nucleus except hydrogen.

Question 6

What is the atomic number (Z) of an element?

Answer 6

The number of protons held by the nucleus

It determines an element’s position in the periodic table.

Question 7

What is the mass number (A) of a carbon atom with six protons and six neutrons?

Answer 7

12

Mass number is the sum of protons and neutrons.

Question 8

What is one atomic mass unit (AMU) equal to in kilograms?

Answer 8

1.66 × 10–27 kg

One AMU is 1/12 the weight of a carbon atom.

Question 9

What are ions?

Answer 9

Atoms without an electron or subatomic particles with a charge

Free electrons are negative ions, and free protons are positive ions.

Question 10

What processes can radiation cause in matter?

Answer 10

• Ionization
• Photoelectric absorption
• Compton scattering
• Pair production

These processes alter the electrical balance of atoms.

Question 11

True or false: Radiation comprises photons traveling at the speed of sound.

Answer 11

FALSE

Radiation comprises photons traveling at the speed of light.

Question 12

What is the photoelectric effect?

Answer 12

The phenomenon where a photon transfers its energy to an inner shell electron, ejecting it from its orbit and providing kinetic energy

This effect is crucial for radiography as the photon loses all its energy.

Question 13

The photoelectric effect is more dominant when the energy of the photon is less than _______ and the absorbing material has a higher atomic number.

Answer 13

1 MeV

Lead (Pb) is an example of a material with a high atomic number that enhances this effect.

Question 14

What is the Compton effect?

Answer 14

A phenomenon where a photon collides with an orbital electron, losing some energy and being deflected with a longer wavelength

This effect contributes to radiation attenuation.

Question 15

In the Compton effect, the photon loses some energy to the electron in the form of _______.

Answer 15

kinetic energy

The photon is deflected from its original path.

Question 16

What is pair production?

Answer 16

The conversion of a high-energy photon into a pair of particles (an electron and a positron) when it travels close to a nucleus

This phenomenon occurs with photons greater than 1.02 MeV.

Question 17

The coefficient of attenuation is denoted by the symbol _______.

Answer 17

s

It represents the probability of radiation attenuation at a particular energy.

Question 18

The total probability of attenuation (s) is the sum of the probabilities of which three effects?

Answer 18

• Photoelectric effect (spe)
• Compton effect (sce)
• Pair production (spp)

This equation is expressed as s = spe + sce + spp.

Question 19

Gamma rays are produced by the nuclei of _______ undergoing disintegration.

Answer 19

radioactive isotopes

More than 500 of the known isotopes are radioactive.

Question 20

What are the three forms of energy released by radium and its daughter products?

Answer 20

• Gamma rays
• Alpha particles
• Beta particles

Gamma rays are particularly useful for radiographers.

Question 21

Artificial radioactive isotopes can be produced by _______ in a nuclear reactor and neutron bombardment.

Answer 21

fission

Cesium-137 (Cs-137) is an example of a radioisotope produced this way.

Question 22

The traditional measure of activity for a gamma ray source is the _______.

Answer 22

curie (Ci)

One curie equals 37 × 10^9 disintegrations per second.

Question 23

Specific activity is defined as the degree of concentration of radioactive material within a gamma ray source and is expressed in curies per _______.

Answer 23

gram or cubic centimeter

Greater specific activity indicates a smaller radioactive source, leading to sharper images.

Question 24

What is the definition of half-life?

Answer 24

The length of time required for the activity of a radioisotope to decay to one half of its initial strength

Half-life is a basic characteristic dependent on the particular isotope of a given element.

Question 25

In radiography, the half-life of a **gamma ray source** is used as a measure of _______.

Answer 25

activity in relation to time ## Footnote Dated decay curves are supplied when a radioisotope is obtained.

Question 26

What are the **gamma ray quality characteristics** determined by?

Answer 26

The nature of the source ## Footnote Each commonly used radioisotope has specific uses because of its fixed gamma energy characteristics.

Question 27

Name the **most-used radioisotopes** in radiography.

Answer 27

* Cobalt-60 * Iridium-192 * Selenium-75 * Cesium-137 ## Footnote Many other radioisotopes are useful but not discussed here.

Question 28

In **gamma radiography**, what is the focal spot?

Answer 28

The surface area of the material as viewed from the test object ## Footnote It is desirable for the dimensions of a gamma ray source to be as small as possible.

Question 29

What is the half-life of **Cobalt-60**?

Answer 29

5.3 years ## Footnote Cobalt-60 is created by neutron bombardment of cobalt-59.

Question 30

What are the primary gamma ray emissions of **Cobalt-60**?

Answer 30

* 1.33 MeV * 1.17 MeV ## Footnote These emissions are similar in energy equivalency to the output of a 2 MeV X-ray machine.

Question 31

What is the half-life of **Iridium-192**?

Answer 31

74.3 days ## Footnote Iridium-192 has high specific activity and emits gamma rays comparable to a 600 kVp X-ray machine.

Question 32

What is the half-life of **Selenium-75**?

Answer 32

About 120 days ## Footnote Selenium-75 has a softer gamma ray spectrum than Ir-192.

Question 33

What is the half-life of **Cesium-137**?

Answer 33

30 years ## Footnote Cs-137 is useful in radiography due to its long half-life and emits beta particles and gamma radiation.

Question 34

What are the applications of **Cesium-137** in the construction industry?

Answer 34

* Moisture-density gages * Calibration source for survey meters * Leveling gages for detecting liquid flow * Thickness gages for measuring sheet metal, paper, and film ## Footnote Cs-137 moves easily through the environment, making cleanup difficult.