Hall Book Ch 1

Question 1

Who discovered radioactivity emitted by uranium compounds in 1896?

Answer 1

Antoine Henri Becquerel

Question 2

2 yrs later after Becquerel discovered radioactivity emitted by uranium compounds, what did Pierre and Marie Curie do?

Answer 2

Isolated the radioactive elements polonium and radium. Few years later, radium was used for the treatment of cancer.

Question 3

What was the event of first recorded biological effect of radiation?

Answer 3

Due to Becquerel, who inadvertently left a radium container in the vest pocket and described the skin erythema.

Question 4

What is ionization and what is ionizing radiaiton?

Answer 4

If the radiation has sufficient energy to eject one or more orbital electrons from the atom or molecule, the process is called ionization, and that radiation is said to be ionizing radiation.

Question 5

1. What is the energy dissipated per ionizing event, which is more than enough to break a strong chemical bond?
2. What is the energy associated with C=C bond?

Answer 5

1. 33 eV

2. 4.9 eV

Question 6

For convenience, it is usual to classify ionizing radiations as either ( ) or ( )

Answer 6

electromagnetic or particulate

Question 7

X-rays are produced ( ) , gamma-rays are produced ( ).

Answer 7

extranuclearly, intranuclearly

Question 8

The critical difference between nonionizing and ionizing radiations is the size of the ( ) packets of energy, not the ( ) energy involved.

Answer 8

individual, total

Question 9

The potency of x-rays, then, is a function not so much of the ( ) energy absorbed as of the size of the ( ) energy packets.

Answer 9

total, individual

Question 10

In their biologic effects, electromagnetic radiations are usually considered ( ) if they have a photon energy in excess of ( ) eV, which corresponds to a wavelength shorter than about ( ) cm.

Answer 10

ionizing, 124 eV, 10^-6

Question 11

What equipment is needed to accelerate protons?

Answer 11

Cyclotron

Question 12

What are alpha-particles?

Answer 12

nuclei of helium atoms and consist of two protons + two neutrons, positively charge

Question 13

alpha particles are emitted during the decay of heavy, naturally occurring radionuclides, such as ( ) and ( ).

Answer 13

uranium and radium

Question 14

What is the major source of natural background radiation to the general public? What is the example? How many in the US is impacted by this?

Answer 14

alpha particles by Radon gas seeping out of the soil, it is estimated 10,000 - 20,000 cases of lung cancer mostly in smokers.

Question 15

What are the two classifications of radiation?

Answer 15

Directly or indirectly ionizing

Question 16

All of the charged particles are ( ) ionizing.

Answer 16

directly, which means they have sufficient kinetic energy that they can disrupt the atomic structure of absorber through which they pass directly and produce chemical and biological changes.

Question 17

Electromagnetic radiations (x and gamma rays) are ( ) ionizing.

Answer 17

Indirectly

Question 18

How does indirectly ionizing radiation cause chemical and biological damage?

Answer 18

When they are absorbed in the material through which they pass, they give up their energy to produce fast-moving charged particles that in turn are able to produce damage.

Question 19

Cobalt-60 (60Co) and caesium-137 (137Cs) are the most widely used sources of gamma radiation. Co produces gamma rays with energies of 1. ( ) MeV and has a half-life of ( ) years, whereas 137Cs produces gamma rays with an energy of ( ) MeV and has a longer half-life of ( ) years.

Answer 19

1. 1.173 and 1.332 Mev
2. 5.2 years
3. 0.662 Mev
4. 30.1 years

Question 20

What process dominates at high energies, characteristic of a cobalt-60 unit or a linear accelerator used for radiotherapy?

Answer 20

Compton

Question 21

In Compton process, the photon interacts with what is usually referred to as a ( ) electron, an electron whose binding energy is negligibly small compared with the photon energy.

Answer 21

free

Question 22

What is the net result production of Compton process?

Answer 22

The production of several fast electrons, many of which can ionize other atoms of the absorber, break vital chemical bonds, and initiate the change of events that ultimately is expressed as biologic damage.

Question 23

In the photoelectric process, the x-ray photon interacts with ( ) , for example, the K, L, or M shell of an atom of the absorbing material.

Answer 23

a bound electron in

Question 24

Unlike in Compton, in photoelectric process, the photon gives up ( ) of its energy to the electron; some is used to overcome the ( ) of the electron and release it from its orbit; the remainder is given to the electron as kinetic energy of motion.

Answer 24

all, binding energy

Question 25

In photoelectric process, the energy change from its electron’s movement from a loosely bound to a tightly bound shell represents a decrease of potential energy which is balanced by the emission of a photon of ( ) electromagnetic radiation

Answer 25

characteristic

Question 26

In soft tissue, characteristic radiation has a low energy, typically ( ) kV.

Answer 26

0.5 kV and is a little biologic consequence.

Question 27

Describe the “direct action” of radiation.

Answer 27

When any form of radiation x, gamma rays or charged or uncharged particles are absorbed in biologic materials and interact directly with the critical targets in the cells.

Question 28

Direct action of radiation is the dominant process if the radiations is ( ) linear energy transfer (LET).

Answer 28

high

Question 29

What are the examples of particles that can have high LET?

Answer 29

neutrons or alpha particles

Question 30

Define indirect action of radiation.

Answer 30

Radiation interacting with other atoms or molecules in the cell particularly water to produce free radicals that are able to diffuse far enough to reach and damage the critical targets.

Question 31

What are free radicals?

Answer 31

an atom or a molecule carrying an unpaired orbital electron in the outer shell.

Question 32

It is estimated that about ( ) the x-rays damage to DNA in mammalian cells is caused by ( ) radical.

Answer 32

2/3, hydroxyl

Question 33

Write down the indirect action of x-rays, the chain of events form the absorption of the incident photon to the final observed biologic change.

Answer 33

Incident x-ray photon –> Fast electron –> Ion radical –> Free radical –> Chemical changes from the breakage of bonds –> Biologic effects

Question 34

What is unique about the neutrons interaction with matters unlike x-rays?

Answer 34

Neutrons interact not with the planetary electrons but with the nuclei of the atoms that make up the tissue resulting in “recoil protons,” or in the case of higher energy neutrons “spallation products,” that is, a high energy neutron may hit a carbon atom which then breaks up into three alpha-particles, or may hit an oxygen atom to produce four alpha-particles.

Question 35

For heavy particles such as proton or carbon, unlike in x-rays, there is a shift in the balance between the two modes of action indirect vs direct. What is it?

Answer 35

For x-rays, indirect action is dominant, whereas for the neutrons or heavy ions, the direct action assumes greater importance, increasingly so as the density of ionization increases, that is, as the density of ionization increases, the probability of a direct interaction between the particle track and the target molecule increases.

Question 36

Radioprotective compounds by scavenging free radicals are quite effective for 1. ( ) but of little use for 2. ( ).

Answer 36

1. x- and gamma-rays

2. neutrons, alpha-particles, or heavier ions

Question 37

X- and gamma-rays are ( ) ionizing; the first step in their absorption is the production of ( ).

Answer 37

indirectly, fast recoil electrons

Question 38

Which other heavy particle is also a indirectly ionizing?

Answer 38

Neutrons

Question 39

Neutron is also ( ) ionizing; the first step in their absorption is the production of ( ), ( ), and heavier nuclear fragments.

Answer 39

indirectly, fast recoil protons, alpha-particles

Question 40

Discuss two major biologic effects of x-rays.

Answer 40

1. Direct action by the recoil electron directly ionizes the target molecule.
2. Indirect action by the recoil electron that interacts with water to produce an OH radical which diffuses to the target molecule.

Question 41

How much of the biologic damage by x-rays is caused by indirect action (e.g. involving free radicals)? And what can prevent that damage?

Answer 41

2/3, it can be modified by chemical protectors.

Question 42

Chemical protectors are less effective with ( ) LET radiations where most biologic damage is a result of the ( ) effect.

Answer 42

high, direct

Question 43

1. How long does the absorption process take?
2. How long does the chemistry take?
3. How long does the biology take?

Answer 43

1. 10^-15 seconds
2. Chemistry takes longer because the lifetime of the DNA radicals is about 10^-5 second
3. The biology takes hours, days, or months for cell killing, years for carcinogenesis, and generations for heritable effects.

Question 44

Classify types of radiation from non-ionizing vs ionizing

Answer 44

Non-ionizing radiation (cannot ionize matter)

Ionizing radiation can ionize matter either directly or indirectly:

• Directly ionizing radiation is usually charged particles including electrons, protons, alpha particles and heavy ions.
• Indirectly ionizing radiation is usually neutral particles such as photons, neutrons