BLOCK 7: IONIZING RADIATION - Unit 2: Fundamentals of Atomic Structure (complete)

Question 1

Process by which radiation particles and rays carry enough energy to strip electrons from atoms and molecules that they hit or pass near.

Answer 1

IONIZATION

Question 2

Compact concentration of protons and neutrons located at the center of an atom.

Answer 2

NUCLEUS

Question 3

A relatively large space surrounding the nucleus in which electrons orbit at high speeds.

Answer 3

ELECTRON CLOUD

Question 4

Positively charged subatomic particles, the number of which determines the element.

Answer 4

PROTONS

Question 5

On the periodic table of elements, the number of protons is called the _______________ and may be expressed as “Z”. All atoms of an element have the same Z, number of protons.

Answer 5

ATOMIC NUMBER

Question 6

Uncharged subatomic particles; they could be thought of as having a balanced positive charge and negative charge within themselves.

Answer 6

NEUTRONS

Question 7

Negatively charged subatomic particles. They are found orbiting around the nucleus in the electron cloud on paths known as shells.

Answer 7

ELECTRONS

Question 8

Each shell has a certain energy associated with it. Electrons in outer shells are __________ energetic than those in inner shells.

a.) more
b.) less
c.) equally as

Answer 8

a.) MORE

Question 9

A measure of the cumulative mass of the subatomic particles bound within an atom; expressed as “A”, it is the total number of protons plus neutrons in an atom.

Answer 9

ATOMIC MASS

Atomic Mass number (A) = number of protons (Z) + number of neutrons (N).

Question 10

Atoms of an element which have differing numbers of neutrons. They are symbolized by using the mass number with the name of the element.

Example: carbon-14 ; ¹⁴C ; 14C

Answer 10

ISOTOPES

Question 11

In isotopes of an element, the number of protons is the same, but the number of _______________ differ.

Answer 11

NEUTRONS

Question 12

Unstable isotopes that may emit energy in the form of radiation in order to become more stable.

Answer 12

RADIONUCLIDES

Question 13

Though the international system (SI) uses joule (J) to express energy, the most common unit encountered in physics at the atomic level is the ____________________ (eV).

Answer 13

ELECTRON VOLT

One eV is equal to approximately 1.6 x 10-19 joules. Typically, eV will be written with a metric conversion prefix, for example, 1 keV = 1000 eV or 1 MeV = 1x106 eV.

Question 14

The energy that holds a nucleus togetherand is also the amount of energy required to break it apart.

Answer 14

BINDING ENERGY

Binding energy is an important concept in determining the stability of atoms of isotopes. For BE, the term is most often encountered in the discussion of nuclear fission.

Question 15

The amount of energy required to ionize (remove) the least tightly bound electron in an atom of that element.

Answer 15

IONIZATION POTENTIAL

Atoms of different elements have varying ionization potentials, and as such, require different amounts of energy to remove their respective electrons.

Question 16

Energy emitted or transmitted from a source in the form of particles or waves.

Answer 16

RADIATION / RADIATION ENERGY

All forms of radiation carry energy expressed in electron volts.

Question 17

TRUE OR FALSE:

The more energetic the radiation, the less electron volts it carries, and the less likely it is to ionize other atoms.

Answer 17

FALSE

The more energetic the radiation, the MORE eV it carries and the MORE likely it is to ionize other atoms.

Question 18

The principal factor for determining whether a nucleus is stable; (expressed as a ratio)

Answer 18

n:p ratio (or N:Z ratio)
RATIO OF NEUTRONS TO PROTONS

Question 19

The spontaneous transformation of an unstable atom that often results in the emission of radiation.

Answer 19

RADIOACTIVITY

This process is referred to as a transformation or decay. These transformations are also referred to as disintegrations. Radioactive nuclei will change their stability through one or more of the forms of radioactive decay.

Question 20

The final result of radioactive decay is the transformation of a radioactive atom into a more __________ atom of a different element.

Answer 20

STABLE

For example, cobalt-60 (27 protons/33 neutrons) is radioactive because it has too many neutrons. During the decay process, one of its neutrons will change into a proton, giving off its excess radiation as a beta particle and two gamma rays. Because the atom now has 28 protons instead of 27, it has become a new element: nickel. In this way, unstable atoms of radioactive cobalt-60 give off radiation as they transform into stable atoms of nickel-60.

Question 21

A series of radioactive decays, in which the decay of one element creates a new element that may itself be radioactive.

Answer 21

DECAY CHAIN

Question 22

Atoms that remain unstable following a transformation will continue to decay until a stable atom is formed. The first radionuclide in the chain is called the __________ radionuclide, and the subsequent products of the transformation are called __________ products.

Answer 22

PARENT ; DAUGHTER (or progeny)

Question 23

A radioactive process in which a particle with two neutrons and two protons is ejected from the nucleus of a radioactive atom.

Answer 23

ALPHA DECAY

The two protons and two neutrons make an α (alpha) particle (essentially a helium nucleus).

Question 24

Because of the size and charge of α particles, they are the __________ penetrating of radiation types.

Answer 24

LEAST PENETRATING

Generally, the outer layer of skin is sufficiently thick enough to stop most alpha particles. However, alpha particles can be very harmful if sources are inhaled, ingested, or injected, as their energy will be deposited into living tissue.

Question 25

Alpha decay occurs in typically __________ elements, of which the nuclei are neutron rich, which makes emission of the alpha particle possible.

Answer 25

HEAVY elements

Question 26

The emission of electron-like particles from the nucleus of an atom.

Answer 26

BETA DECAY

Question 27

A beta particle’s penetrating power depends on its __________.

Answer 27

ENERGY

Most do have enough energy to pass through a person’s skin and damage the living tissue underneath. However, others, such as those emitted from tritium, have very little energy and cannot pass through the outer layer of dead skin.

Question 28

Usually referred to as gamma rays or photons, is not a particle like alpha and beta; instead, it is a bundle of electromagnetic energy similar to other forms of electromagnetic field radiation, like visible light

Answer 28

GAMMA RADIATION

Question 29

A metastable nucleus will de-excite to the ground state by releasing excess energy in the form of a _______________

Answer 29

GAMMA RAY

Question 30

TRUE OR FALSE:

Gamma rays are bundles of energy that have no charge or mass.

Answer 30

TRUE

This allows them to travel very long distances through air, body tissue, and other materials. They travel so much farther than either alpha or beta radiation that the source of the gamma rays do not have to be inside the body or near the skin.

Question 31

Gamma rays are __________ penetrating but __________ ionizing than alpha and
beta particle radiation.

a.) more ; less
b.) less ; more

Answer 31

MORE penetrating but LESS ionizing

Question 32

The process by which neutrons are captured within another atom’s nucleus, changing the atom’s number of neutrons, and thus creates a new isotope, which may be unstable or radioactive.

Answer 32

NUCLEAR ACTIVATION

Question 33

The amount of energy that the radiation transfers per unit of path length.

Answer 33

LINEAR ENERGY TRANSFER (LET)

Question 34

__________ LET forms of radiation ionize matter over a very short range.

Answer 34

HIGH LET

Question 35

__________ LET forms of radiation produce fewer ionizations per path length.

Answer 35

LOW LET

Question 36

_______________ have the highest LET of any form of radiation.

Answer 36

α particles

Question 37

Beta particles, which are energetic electrons, are classified as ______ LET radiation.

Answer 37

LOW

Even though they interact with matter in a manner similar to alpha particles, their smaller +1 or -1 charge and smaller mass result in a greater distance between ionizing collisions— thus, a lower rate of energy transfer.

Question 38

The range of beta particles is typically much ___________ than their track length.

Answer 38

SHORTER

Beta particles can be likened to how magnetic force fields push away from each other. This process causes many deflections during travel, resulting in large numbers of ionizations and excitation events. The beta particle eventually loses its kinetic energy and is captured.

Question 39

Positively charged beta particles, known as positrons, __________ orbital electrons as
they pass, causing ionizations and excitation events as well.

Answer 39

ATTRACT

However, positrons, due to their positive charge, are likely to directly interact with electrons in a material. Both the positron and the electron are annihilated in this interaction, creating two gamma rays.

Question 40

As a relatively fast-moving beta particle or electron nears the nucleus, the attractive force alters its trajectory and slows it down. This interaction results in a loss of kinetic energy which is converted to x-rays. This energy is released in the form of a ____________________ x-rays.

Answer 40

BREMSSTRAHLUNG X-RAY

Question 41

The likelihood of bremsstrahlung radiation _______________ as beta energy increases and as atomic number of the absorbing media increases.

Answer 41

INCREASES

Because of this, dense metals, such as lead, are not used as shielding from beta radiation.

Question 42

Radiation that has no electrical charge (such as gamma rays and x-rays) cannot interact with electrical fields created by electrons and protons. They must _______________ with these particles to interact.

Answer 42

COLLIDE

Question 43

A photon’s _______________ is the primary factor in determining whether ionizing photons interact with material through the photoelectric effect, Compton scattering, or pair production.

Answer 43

ENERGY

Question 44

Occurs when a low energy photon strikes an atom, where the total energy of the gamma is expended in ejecting an electron from orbit. The result is ionization of the atom and expulsion of an energetic electron. The remaining electrons must drop to fill in the inner shell.

Answer 44

PHOTOELECTRIC EFFECT

Question 45

Occurs when both the photon and the electron it interacts with are scattered in different directions. The gamma interacts with an orbital electron; however, in this case, the photon loses only a fraction of its energy. Some of the photon’s energy is transferred to the electron, ejecting it from the ionized atom; the remaining photon energy is carried away by the scattered photon in a different direction.

Answer 45

COMPTON SCATTERING

Question 46

Occurs as a high energy photon enters the area around the nucleus of an atom; the energy is converted into the mass of two electrons, with the remaining energy being imparted as kinetic energy. These newly created particles have opposite charges, one positive and one negative. The pair of particles exit the atom at opposing angles.

Answer 46

PAIR PRODUCTION

Question 47

Neutron radiation is unique in that it is considered to be _______________ ionizing.

Answer 47

INDIRECTLY ionizing

Because neutrons have no charge, they do not affect the electron cloud. Neutrons interact only with target nuclei through elastic scattering, inelastic scattering, and neutron capture.

Question 48

Occurs when a neutron collides with a nucleus, transferring kinetic energy to the
target atom which results in a slower neutron and a recoiling nucleus.

Answer 48

ELASTIC SCATTERING

The principal of elastic scatter is that kinetic energy of the particles in the system is conserved, meaning both the movement of the scattered neutron and the slight movement of the nucleus contain as much energy as the original neutron did. After several of these interactions, the neutron is slow enough to be absorbed though inelastic scattering.

Question 49

Occurs when the kinetic energy of the system is changed, meaning the neutron transfers some of its energy to the nucleus, or it is absorbed by the target nucleus altogether.

Answer 49

INELASTIC SCATTERING

This causes the nucleus to enter into a higher energy state. The nucleus then returns to a more
stable state by emitting some kind of radiation, shown on the other side as a gamma ray. The
gamma photon is an example of indirect ionization, where the neutron did not ionize an atom but did cause a reaction that created a form of ionizing radiation. The incident neutron is shown as having been scattered with lower kinetic energy, just as it was in elastic scattering.

Question 50

A special type of inelastic scattering interaction where the incident neutron is absorbed by the target nucleus. This is possible if the neutron has low enough kinetic energy and the target nucleus has a high enough cross section. The once stable target nucleus now carries an extra neutron which makes it unstable (radioactive).

Answer 50

NEUTRON CAPTURE

An example of neutron capture is the stable isotope Co-59 absorbing a neutron and becoming the radioactive isotope Co-60. If the resulting isotope is unstable, it will emit radiation in order to reduce its excess energy.