Nucs Flashcards
What is the band of stability?
Happy place atoms go when they have a certain balance of protons and neutrons in the nucleus. Not exactly 1:1, but it’s close.
Depending on the imbalance of neutrons/protons different types of decays occur.
What kind of decay happens when you have lots of neutrons, not enough protons?
Beta minus decay
What is beta minus decay?
Have lots of neutrons, not enough protons
Take one of your neutrons and turn it into a proton - results in the emission of a “beta particle” from the nucleus - basically an electron emitted from the nucleus.
Need to change the charge of a neutron from neutral to positive (neutron is 1/2 negative and 1/2 positive - eject the negative, become all positive).
Need to balance out the energy loss - going from a neutron to proton - emit a massless “neutron” just to balance out the energy.
What is a “beta particle” and why is it ejected?
Ejected in beta minus decay when you have too many neutrons, not enough protons.
Basically an electron that comes from the nucleus.
- Ejected to change the charge of a neutron from neutral to positive (neutrons are basically 1/2 positive and 1/2 negative - eject the negative, then you become all positive).
- Balance out the energy loss - going from a neutron to proton, emit a massless particle called a “neutrino” just to balance out the energy.
What is emitted in beta minus decay?
Beta particle - negative particle
Neutrino - massless, to balance out the energy.
What kind of process is beta minus decay - chemistry term?
Isobaric transition - mass doesn’t change.
The atomic number changed (increased), but the mass of a neutron and proton are about the same - the mass number remained constant.
Is beta minus decay good for imaging?
No, but can cause some damage.
What kind of shielding do you want for a beta emitter?
Plastic b/c it has a low Z.
Lead’s high Z will result in Bremmstahlung x-rays.
What kind of decay happens when you have lots of protons and not enough neutrons?
Beta positive decay
Electron capture
What is Beta Positive Decay?
Too many protons and not enough neutrons.
The “rich guy” - has 1.02 MeV and not problem losing it.
A positively charged proton is converted into a neutral neutron by giving up a “positron” and a neutrino to keep the energy balanced.
Positron travels a very short distance and meets an electron - annihilate each other - results in two 511 keV photons emitted 180 degrees apart from each other.
511 keV is 1/2 of 1.02 MeV
What is Electron Capture?
Too many protons and not enough neutrons
The “poor guy” - don’t have the energy to kick out the positively charged proton to leave - adds a negative to a positive to make a neutral.
Pulls an electron into the neucleus from the K shell
What kind of process is Electron Capture - chemistry term?
Isobaric transition - just like beta minus and beta plus, mass does not change, but atomic number does - lose a proton.
Is Electron capture good for imaging?
Yes, it’s excellent b/c it’s often coupled to a process referred to as “isometric transition” which results in the emission of a characteristic gamma photons that can be imaged under a gamma camera.
After undergoing an isobaric transition (beta emission, positron emission, or electron capture), there is often left over energy - needs to be emitted to achieve final stability.
Isomeric transition - emitting energy and dropping to the ground state.
What is Gamma Emission from Isomeric Transition?
After undergoing isobaric transition (beta emission, positron emission, or electron capture), there is often left over energy - needs to be emitted prior to achieving final stability. Isomeric transition - emitting energy and dropping to the ground state.
Gamma Emimssion - the nucleus will emit its excess energy in the form of a gamma photon. The energy of these photons is variable and depends on the energy differences between the intermediate and final states of the nucleus undergoing isomeric transition. TOTAL energy emission for a given nuclei of a specific nuclide is the same - many times you have more than one intermediate state - with multiple energy gamma photons - why you see multiple peaks for different tracers.
What is Metastable?
In most cases the time spent in the intermediate state is very short. The transition from isobaric to isometric transitions is fast.
Situation where the intermediate state is prolonged - “metastable state”
The main value is the ability to separate out the electron radiation (bad) and the photon radiation (good). By using a nuclide that has already undergone an isobaric (electron emitting) transition - you can only expose the body to useful gamma emissions from the isometric transition.
Mo99 (isobaric transition via beta minus decay - emission of a beta particle (electron)) - Tc99m (hanging out in “metastable” limbo for a couple of hours) - Isometric transmission - emission of 140 keV photons - Tc99
What are the two types of isometric transition?
After undergoing isobaric transition (beta emission, positron emission, or electron capture), there is often left over energy - needs to be emitted prior to achieving final stability. Isomeric transition - emitting energy and dropping to the ground state.
Gamma Emission - nucleus emits its excess energy in the form of a gamma photon.
Internal Conversion - The energy you would normally get rid of via gamma emission can be transferred to an electron w/in the atom. Vacancy can lead to a downward cascade from a higher level - and either the transmission of a characteristic x-ray or an Auger electron. Bad b/c you are emitting particles which cause harm, not imageable gamma photons which contribute to the study.
What is Internal Conversion?
Type of isometric transition- left over energy from an isobaric transition (beta emission, positron emission, or electron capture) needs to be emitted.
The energy instead of being emitted via gamma emission, is transferred to an electron w/in the atom. Vacancy can lead to a downward cascade from a higher level - and either the transmission of a characteristic x-ray or an Auger electron. Bad b/c you are emitting particles which cause harm, not imageable gamma photons which contribute to the study.
What is Alpha Decay?
Tends to occur in heavier unstable atoms.
Alpha particles are basically Helium nuclei (2 protons, 2 neutrons). Slow and fat, can’t penetrate a piece of paper, worthless for imaging, but bad in close proximity.
Used in treatment situations - bone cancer mets with Radium 223.
Two types of tracer production?
Bombardment (nuclear reactor or cyclotron) and Fission
What is Bombardment type of tracer production?
Striking target elements with either neutrons (in a nuclear reactor), or with charged particles (alpha particles, protons, or deuterons) in a cyclotron.
Cyclotron has the advantage of producing elements via transmutation, therefore you don’t have any parents to clean up “carrier free”.
Have to clean up the left over parent element.
Difference between bombardment production in nuclear reactor vs cyclotron.
Nuclear Reactor: bombard with neutrons
Cyclotron: bombard with charged particles - usually results in transmutation, so you don’t have to clean up the parent - CARRIER FREE
What is Fission type of tracer production?
Neutrons are fired into large atoms (like Uranium and Plutonium) and split them into pieces - a lot of random stuff being made - I-131, Xenon-133, Strontium-90m, Molybdenum-99, Cesium-137.
The desired isotope also has a bunch of fission products (contaminants) which have to be separated out - can be done with chemistry. Can demonstrate a bunch of different decay methods.
What is Neutron Activation?
Target atoms eat up neutrons to form a new isotope - don’t need to be accelerated.
Products are isotopes of the target atoms, they cannot easily be separated from each other - NOT carrier free.
Neutron rich products tend to decay to beta emission.
Difference between physical, biologic, and effective half life?
Physical - Time necessary for a radionuclide to be reduced to half its existing activity.
Biologic- how long it takes to shit or piss half the tracer out.
Effective- takes both of these into consideration.