Ch 6 Nuc Med I

Charged Particles and Electromagnetic Radiation

The two classifications of radiation emitted during radioactive decay

Alpha Particles and Beta Particles

Most common two particles used in nuclear medicine

X-rays and Gamma Rays

The electromagnetic radiation that we use in nuclear medicine

transfer energy

Both types of radioactive decay _______ to matter as they pass through it

heat

majority of the energy from ionization and excitation is lost as _____

atomic and molecular vibrations

heat lost in ionization and excitation is ___

ionizing radiations

the radiation emitted during radioactive decay are ____

slow down

high energy charged particles lose energy and ____ as they pass through matter, as a result of collisions with atoms and molecules

collisions with atoms and molecules

what forces alpha and beta particles lose energy ans slow down as they pass through matter

high energy electrons

what are byproducts of alpha and beta collisions with atoms and molecules

when gamma rays and x rays interact with matter and emitted in internal conversion and the Auger effect

When are high-energy electrons generated?

identical

forces experienced by positive and negative electrons are ____

internal conversion event

ICE stands for

high-energy electrons

B+ and B- are ___

not important in nuclear medicine

there are slight differences in +/_ electron interactions however:

both the positive and negative charged particle

concerning interactions with matter, the term “electron” is going to include:

No

Do actual true physical/mechanical collisions occur?

electrical forces of attraction or repulsion

The collisions that occur between a charges particle and atoms or molecules involve:

be separated (or ejected) from the atom, causing ionization

suppose a charged partile passes near an atom and exerts electrical forces on the orbital electrons. If close enough, the forces may be sufficient to cause an orbital electron to …

to overcome the binding energy of the electron, and the rest is converted into kinetic energy to the ejected secondary electron.

During an ionizing interaction (a collision) between a charged particle and orbital electron, why does the particle lose energy

a positive electron (positron) loses all of its kinetic energy and is stopped.

What happens in an annihilation effect?

the emission of characteristic x-rays or auger electrons

Ionization involving an inner-shell electron leads to

outer-shell electrons

most ionization interactions involve:

secondary ionization

The secondary electron may be sufficiently energetic to cause a ____

delta ray

a secondary electron that causes a secondary ionization is called a

excited state; atomic or molecular excitation

encounters that are not as close can cause an orbital electron to be raised to an ____ causing _____

secondary electron

What is B?

Bremsstrahlung

What is A?

Bremsstrahlung

The interaction that occurs when the charged particle penetrates the orbital electron cloud of an atom and interacts with the nucleus

a particle interacts with the nucleus, is rapidly decelerated and loses energy, the energy appears as a photon called a bremsstrahlung

What creates a bremsstrahlung

braking radiation

bremsstrahlung is German for

transmutational reactions

for heavy charged particles with enough energy, like alpha particles or protons, ______ can occur during nuclear interactions

deflection by strong electrical forces

What is more likely to happen when a heavy particle or electron interacts with the nucleus, transmutation or deflection?

the particle rapidly decelerates and loses energy from this interaction

What happens when “breaking” happens?

bremmstrahlung

The electromagnetic radiation that is released when a particle interacts with the nucleus

nearly zero, slightly deflected or maximum energy, equal to the full energy of the particle which the particle is virtually stopped

Bremsstrahlung energy range

Characteristic x-ray , discrete energy

describe #4 and its energy

bremsstrahlung, maximum energy

describe #3 and its energy

collisional losses

energy losses incurred by a charged particle in ionization and excitation events are called

energy losses incurred by a charged particle in ionization and excitation events

what are collisional losses

radiation losses

energy losses incurred in nuclear encounters, resulting in bremsstrahlung production are called

energy losses incurred in nuclear encounters, resulting in bremsstrahlung production

what are radiation losses

increasing particle energy and increasing atomic number of the ABSORBING medium

radiation losses increase with ____

collisional losses

in nuclear medicine, which of the two, radiation or collisional losses, are by far the more dominating factor of the two?

Beta particles

which particles can be blocked with a small amount of plastic as shielding

the bremsstrahlung photons they generate are much more penetrating than the Beta particle

why would additional shielding be needed around the primary Beta particle shielding?

lead

what is an example of a high Z-material used in shielding bremsstrahlung emissions

82

what is the atomic number of Lead

very small

Bremsstrahlung production and radiation losses for alpha and other heavy charged particles are ______

the amount of bremsstrahlung production is inversely proportional to the mass of the incident charged particle.

why are bremsstrahlung and radiation losses very small in alpha particles and other heavy charged particles?

alpha particle

what is heavier, an alpha particle or electron?

Lead

what shielding is required for Beta particles?

since alpha particles and protons are thousands of times heavier than electrons, they dissipate only a few hundredths of 1% or less of their energy as radiation losses

describe radiation losses in alpha particles and protons

collisional losses

even at energies up to 100 MeV, alpha particles and protons dissipate nearly all of their energy as ______

secondary electrons and ionized atoms

A charged particle passing through matter leaves a track of _______ and ________ in its path

100 um

how wide are tracks in soft tissue and materials of similar density

energetic delta rays

occasionally, longer sidetracks can be generated by _______

microns

alpha particle track lengths are in the order of ____

centimeters

beta particle track lengths are in the fractions of ________

unchanged; only a small fraction of its energy

when an alpha particle or other heavy particle collides with an orbital electron, its direction is virtually _____ and loses ____

bowls ball and a pin

what is the analogy used for a heavy particle like an alpha particle and its charged-particle track?

it is a rather straight track and experience an almost continuous slowing down, losing tiny amounts of energy from large number of individual collisions.

due to an alpha particles few bremsstrahlung collisions and only a small fraction of its energy being dissipates, describe their trach pathway

deposit its energy in the surrounding area

When a heavy particle runs out of energy from traveling, it will _____

the amount of energy that they deposit in the surrounding tissues and cells.

the reason alpha particles are so toxic in biological tissues is due to ______

large angle deflections

charged particle tracks: an electron can undergo _______ with orbital electrons

a large fraction of their energy to be lost in these collisions

The large angle deflections electrons undergo will cause _____

billiards

the analogy used for electron charged-particle tracks

are deflected through large angles and bremsstrahlung radiation is emitted

electrons also undergo occasional collisions with nuclei in which they _____

unpredictable

due to the large angle deflections of electron and nuclei interactions, electron tracks are ____

an alpha particle

This is a charged-particle track of __

an electron or Beta particle

This is a charged-particle track of __

for a given kinetic energy, an electron travels at a much faster speed

Besides charged-particle track, what is another difference between electrons and heavy particles

10%

at 4 MeV, an alpha particle will travel at ____ of the speed of light

4 MeV

at _____, an alpha particle will travel at 10% of the speed of light

90%

at 1 MeV, an electron will travel at ____ of the speed of light

1 MeV

at ____, an electron will travel at 90% of the speed of light

this is due to the low mass size and decreased probability of nuclear interactions with atoms

Why does an electron travel faster than an alpha particle

an electron only carries 1- unit of charge whereas an alpha particle carries 2+

why are the forces an electron exerts weaker than those of the alpha particles?

electrons

which particle experiences less frequent interactions and lose their energy much more slowly?

electron

which particle travels further before they are stopped

alpha particle

which particle is stopped sooner in their charged-particle track?

electron

which particle is much less densely ionizing?

how far it will travel and how dense the ionization along its track will be

the rate at which the charged particle diminishes energy determines ____

the rate at which the charged particle diminishes energy

what determines how far it will travel and how dense the ionization along its track will be

the type of particle and its initial energy (and on the composition and density of the absorbing medium)

the rate at which the charges particle diminishes energy depends on ___

differently

1 MeV of an alpha particle and 1 MeV of an electron act ____

energy loss

density of ionization affects the ___

how closely it interacts with the atoms in its path

density of ionization affects the energy loss due to ____

10 MeV

For nuclear medicine, we deal with energies at or below ____

increase linearly with the density of the absorbing medium

in the cases of energies at or below 10 Mev for nuclear medicine, energy loss rates for charged particles _____

electrons

which charged particle has a longer track length

MeV/cm

the total energy loss rate of a charged particle is expressed in ___

the linear stopping power

he total energy loss rate of a charged particle (MeV/m) is also known as ___

linear energy transfer

LET stands for

Linear energy transfer (LET)

the amount of energy deposited along the track

the amount of energy deposited along the track

Linear energy transfer (LET) is

it is tied to high radiation toxicity for cells when the LET is large

Why is LET parameter important in nuclear medicine

Cerenkov Effect

a phenomenon that occurs when a charged particle travels in a medium at a speed faster than the speed of light in the same medium

No

can a particle travel faster than the speed of light in a vacuum?

0.8 C

In water, a 1 MeV beta particle is able to travel with the velocity of ____