Wade Moore's Radiation Physics EXAM 3

The Atom

fundamental unit of matter made up of Protons(+) Neutrons(+,-) Electrons (-)

Binding energy

what holds electrons in shell or the amount of energy needed to boot an electron from it's shell.

*Specific to ind. atoms and the shell where electron is located.

J to eV

1eV=1.6x10^-19J

SI Unit

J

Common Unit

erg

Influence chemical properties

Number and distribution of electrons

Determines stability and configuration of electrons

Number and distribution of protons and neutrons (nucleons)

Atomic Mass Unit (amu)

1/12 the mass of a C-12 atom.

1 AMU

1.66 x 10^-27 kg

AMU to MeV

1 amu = 931 MeV

Proton amu

1.0073 amu

Neutron amu

1.0087

Electron amu

0.00055

Atomic Mass of Atom

Addition of Protons and Neutrons

Strong Nuclear Force

the powerful attractive force that binds protons and neutrons together in the nucleus.

Nuclear Binding Energy

the energy required to decompose an atomic nucleus into its component protons and neutrons

Mass of Atom vs. Mass of its parts

Protons (amu) + Neutrons (amu) + Electrons (amu) = a mass higher than the atomic mass, therefore the mass of its parts is more than the mass of the atom.

Mass Defect

the difference between the mass of an atom and the sum of the masses of its protons, neutrons, and electrons. "missing" mass has been converted into the binding energy that holds the nucleus together.

If Carbon's mass defect is 0.09894amu, how much energy is created when this mass is converted into binding energy?

0.09894 amu x 931 MeV = 92 MeV

Expression of the relationship between energy and mass

E=mc^2

Speed of light

c=2.998x10^8 m/s

X superscript

A=Atomic Mass (# of protons + neutrons)

X subscript

Z=Atomic Number (# of protons)

As Mass Number increases (more protons)

it gets harder for atom to stay together.

How does atom compensate for increase mass number.

Nuclear Fission

Nuclear Fusion

Nuclear Fission

A nuclear reaction in which a massive nucleus splits into smaller nuclei with the simultaneous release of energy.

(Nuclear reactors and weapons)

*Waste and Heat byproduct

Fission Reaction

add neutron to U-235 to make U-236 = very unstable and begins fission, creating a "chain reaction."

U-236 breaks apart into different elements and release energy, the extra neutrons from this continually feed U-235 and create chain reaction.

Nuclear Fusion

a nuclear reaction in which atomic nuclei of low atomic number fuse to form a heavier nucleus with the release of energy. (Powers the stars)

*No waste, but engineering not capable yet. For now takes more energy than it creates.

Hydrogen Bombs

Combo of nuclear fission and fusion

Isotope

Atomic # (Z): Same

Neutrons: Different

Mass # (A): Different

Isotones

Atomic # (Z): Different

Neutrons: Same

Mass # (A): Different

Isobars

Atomic # (Z): Different

Neutrons: Different

Mass # (A): Same

Isomers

Atomic # (Z): Same

Neutrons: Same

Mass # (A): Same

99mTc and 99Tc

Isomers

m in 99mTc

Metastable

Basic unit for measuring radioactivity

disintegration per unit of time (dps)

Common Unit for radioactivity

Curie (Ci)

MI Unit for radioactivity

Becquerel (Bq)

Conversions for radioactivity

1Bq = 1dps

1Ci = 3.7x10^10 dps or Bq

Activity formula

A=λN

λ=decay constant or 0.693/T^1/2

N=number of atoms

Decay formula

At=AoE^-λt

Secondary Decay formula

At=Ao/2^n

n=# of half lives

Half Life

length of time required for half of the radioactive atoms in a sample to decay.

Physical Half Life

the time required for 50% of its atoms to decay to a more stable state

Biological Half Life

the time it takes for excretion processes to lower the amount of unchanged medication by half

Effective Half Life

the difference between the physical half-life and the biological half-life

Effective Half Life formula

Te=(Tp)(Tb)/Tp+Tb

Tp= Physical half life

Tb= Biological half life

Secular Equilibrium

Half life of parent is much longer than the daughter.

Over time daughter activity builds up to activity of parent and appear to have equivalent half lives. The daughter activity builds up quickly because the parent's decay is so long that it is constantly feeding new daughters.

Transient Equilibrium

If the parent half-life is longer than the child half-life but is not that long.

Daughter activity appears the same as the parent because the parent's decay is feeding the production of the daughter but since their half-lives are similar enough, the eventually come to a point of equilibrium with a decay curve following the same line.

Transient Equilibrium in Nuclear Medicine

In 99Mo (T1/2=66hr) --> 99mTc (T1/2=6hr)--> 99Tc, the peak time is about 24 hours. That is, we should extract 99mTc activity from the generator once a day at the same time.

Particulate radiation

tiny particles of matter that possess mass and travel in straight lines and at high speeds

Alpha Particles ⍺

⍺ (2p & 2n) charge is +2 and its massive from atomic perspective; 4amu.

neutron/proton (n/p) ratio too low

always release 2 electrons

*Atomic # of parent greater 82, get ⍺ release.

Very low penetration.

Energy released formula for Alpha particle

Q=Mp-Md-M⍺-2Me

*don't forget to convert amu to MeV

Energy of the ⍺ particle formula

E⍺=Q/1+M⍺/Md

⍺ particle decay scheme

down and to the left.

⍺ are mono-energetic in that an atom releases the same amount of energy every time it decays.

Pure β emitters

does not result in gamma only β

Beta Particles β-

very small with a - charge, same as electron except they originate in the nucleus, specifically a neutron.

(no neutrons or protons; same mass of electron)

Occurs when neutron/proton (n/p) ratio is too high.

Intermediate penetration power.

Neutrino v

uncharged infinitely small particle that go through essentially everything.

*Share energy release with β

Energy released for a β- particle formula

Q=Mp-Md-Mβ-+e

Mβ and e cancel out and formula becomes

*Q=Mp-Md (don't forget to convert amu to MeV)

β- spectrum, Mean energy

1/3 Emax or Q

*rare that they occur at max energy because β and v share the energy.

β- decay scheme

down and to the right because the atomic # went up.

Positron β+

positive charge beta particle. Neutron/proton (n/p) ratio too low but atomic # is less than 82.

Intermediate penetration power.

Energy released for a β+ particle formula

Q=Mp-Md-Mβ+-Me

Decay scheme for β+

down and to the left, *but they don't occur in nature because β+ and e are attracted to each other and instantly destroy themselves.

Annihilation Radiation

When β+ and e collide they always release energy at 180 degree angles and allow us to do PET imaging. (Helps determine where an event occurred in the body)

*Result in 2, 511 keV photons.

Example of ⍺

Example of β-

Example of β+

Electromagnetic radiation

a kind of radiation including radio waves, infrared, visible light, UV, X- ray, and gamma rays that have wave (photon) and particle behavior but have no mass.

Electron capture

When n/p ratio is too low but instead of releasing β+, an inner orbital electron is captured by the nucleus of its own atom.

When k-shell e pulled to nucleus, L-shell e moves down to replace it, releasing energy in an X-ray.

Characteristic X-rays

x-rays produced by transitions of orbital electrons from outer to inner shells.

Have distinct energies from atom to atom.

Bremsstrahlung x-rays

Produced when a projectile electron or β- is slowed by the nuclear field of a target atom nucleus. A spectrum of energies that also generate heat.

*e or β- interact with matter

Bremsstrahlung x-rays and Atomic # of the medium its passing.

directly proportional, Atomic # ⬆️ = Bremsstrahlung ⬆️

X-ray and high atomic number materials

generate more x-rays. (Lead, Tungsten)

X-rays and low atomic number materials

generate lower energy x-rays (Carbon)

How we use x-ray

electrons are accelerated from the cathode to a rotating tungsten anode, where their kinetic energy is converted into x-rays. The rotating anode helps dissipate heat. X-rays are emitted in all directions but are directed through a window and collimator towards the patient. Filters remove low-energy radiation to reduce patient exposure.

Gamma Rays (ɣ)

high energy photons emitted from excited nuclei (high energy state), following the beginning of a radioactive decay. (no such thing as a pure gamma-emitter, nucleus must undergo another type of decay first, such as alpha or beta). No change in atomic number or mass.

Gamma Ray example

Auger Electron (Competing Event)

Inner shell electron gets ionized, another drops down, emits energy but this energy ejects another (outer shell) electron from atom. No characteristic x-rays produced.

Conversion Electron (Competing Event)

Starts from within the nucleus. Instead of a gamma ray the nucleus transfers excess energy directly to an inner shell electron and is ejected from the atom.

Gamma Rays can result in......

conversion electrons, auger electrons, and characteristic x-rays.

Ionizing Radiation

incident radiation with enough energy to knock electrons off atoms or molecules, producing ions

Ion pair

Original atom & emitted orbital electron

Ionizing potential & binding energy relationship

all ionization potentials are binding energies but not all binding energies are ionization potentials.

Ionizing potential

The amount of energy required to ionize (remove) the least tightly bound electron in an atom of that element (outermost shell). If the free electron has enough energy it can also cause ionizations.

Excitation

instead of electron emitting out of atom, it can just move up a shell, losing energy. It will eventually drop back down to its ground state giving off photons of visible light.

Specific Ionization

number of ion pairs formed per unit distance, traveled by the incident radiation.

Linear Energy Transfer (LET)

average energy deposited per unit length/distance traveled by the incident radiation.

High LET

Alpha particles, a lot of energy in a short distance.

*pose internal risk, but are not penetrating so are not an external risk. (easy to shield).

Low LET

Beta particles, x-rays and gamma rays