Medical physics Flashcards
What causes atoms to be radioactive?
he nucleus has an excess of internal energy. Instability of an atom’s nucleus may result from an excess of either neutrons or protons.
A radioactive atom will attempt to reach stability by ejecting nucleons (neutrons or protons) as well as other particles, or by releasing energy in other forms
Elements with Z>82 have too many what and will emit what to become stable
Any element with Z >82 has too many protons for the SNF (strong nuclear force) to keep it stable. It will emit alpha radiation to become stable
Any alpha or beta decay of ten leaves a nuclide in a metastable position “M”. When this happens further decay may occur by releasing what
Any alpha or beta decay of ten leaves a nuclide in a metastable position “M”. When this happens further decay may occur by releasing the excess energy as a gamma particle
Nuclide
The nucleus that protons and neutrons -which are called nucleons- make up is called nuclide.
Isotope
is an atom that contains the same number of protons but different number of neutrons that another atom with the same number of protons
Z
Number of protons
N
The number of neutrons
X
the chemical symbol for the element
A
the sum number of proton and neutrons
Radioactivity
Radioactivity is the property of some unstable atoms (radionuclides) to spontaneously emit nuclear radiation usually alpha or beta particles accompanied by gamma-rays
Fundamental law of physics
states that charged particles have a force acts on them that causes them to move if the force is not balanced. This is known as the coulomb force or electrostatic force. The force is repulsive for two particles of the same charge, and attractive for two particles of opposite charge.
3 Important aspects of SNF are
- One of the four fundamental forces / other are electromagnetic or coulomb force, gravity and the WNF
- It is mostly an attractive force
- It acts in the nucleus
It acts a very short distances of up to 1 fm (10-15m) on adjacent nucleons
The more protons there are in a nucleus the larger what which must also act on neutrons to keep the nucleus from flying part
SNF
strong nuclear force
types of decay
alpha, beta gamma
Alpha decay
Alpha decay occurs when a heavy, radioactive nucleus becomes more stable by emitting an alpha particle.
alpha decay emits what particles
two protons and two neutrons
what are the two types of beta decay
beta positive and beta negative
what force is responsible for both types of decay
weak nuclear force
beta negative decay releases what particles
electron, antineutrino
beta positive releases what particles
positron, and a neutrino;
neutrino
A neutrino is a tiny neutral and almost massless particle that always seen in association with a proton
antineutrino
An antineutrino has the almost the same properties as a neutrino but is always seen in association with a electron
gamma decay
Rather than the nucleus undergoing a change in number of nucleons, gamma decay reduce the amount of energy an unstable nucleus has by emitting a gamma ray.
what does gamma decay release
gamma ray
Half life
Time taken for half of the original amount to decay.
Wavelength
distance between two identical sections on adjacent waves
Amplitude
distance equal to how high the crest compared to the crest (intensity)
the number of waves that pass a point per second
Frequency
the time taken for a wave to pass a point
period
energy is proportional to what
Frequency
what are cyclotrons used to produce
cyclotrons are used to produce radioactive isotopes for medical diagnosis.
Rank the following in order of increasing wavelengths: radio waves, x-rays, visible light
x-ray, visible light, radio waves
nuclear reactor purpose
The main job of a reactor is to house and control nuclear fission—a process where atoms split and release energy
what are cyclotrons
A cyclotron is a type of particle accelerator
Scintigraphy
A procedure that produces pictures (scans) of structures inside the body, including areas where there are cancer cells. Uses gamma radiation to form images
what appears dark gray on the film in a x-ray
The soft tissues in the body (such as blood, skin, fat, and muscle)
what appears white on a x-ray
A bone or a tumor, which is more dense than soft tissue,
what is advantage and disadvantage of x-rays
quick, versatile and cheaper but details are often vague and can only see side views of what in the body
benefits of a CT scan
Unlike conventional x-rays, CT scanning provides very detailed images of many types of tissue as well as the lungs, bones, and blood vessels.
Unlike MRI, an implanted medical device of any kind will not prevent you from having a CT scan.
disadvantages of CT scan
During a CT scan, you’re briefly exposed to ionizing radiation. The amount of radiation is greater than you would get during a plain X-ray
what appears white in a CT scan
blood vessels, intestine or other structures
MRI
takes pictures of places in your body that contain water, proton density
advantages to MRI
provides better soft tissue contrast than CT and can differentiate better between fat, water, muscle, and other soft tissue than CT
DISADVANTAGES to MRI
People with implants, particularly those containing iron, cant get one
and noise
what cells show up as bright spots on PET scans because they have a higher metabolic rate than do normal cells.
cancer
what does a PET scan do
imaging technique that quantifies brain function by measuring glucose levels,
what does a ultrasound show
As a diagnostic tool, ultrasound can show the density differences in tissue.
disadvantages to US
- Increased depth means a lower frequency is required for optimal imaging. Resolution is weaker at greater depth
- Bone blocks US waves, can’t see through air
Advantages to US
• Patients aren’t exposed to ionizing radiation
Ultrasound captures images of soft tissues that don’t show up well on X-rays
