Exam 1 Review Sheet: Basic Atomic and Nuclear Physics
Review Sheet – Exam 1: Basic Atomic and Nuclear Physics
Nuclear Binding Energies
Nuclear Binding Energy: Refers to the energy required to remove an atom’s nucleus into individual nucleons, representing the stability of the nucleus.
Binding energy per nucleon is often discussed to evaluate the stability of different isotopes.
Isotopes, Isotones, Isobars, Isomers
Isotopes: Atoms of the same element with different numbers of neutrons.
Isotones: Atoms that have the same number of neutrons but different numbers of protons.
Isobars: Atoms that have the same mass number (neutrons + protons) but different atomic numbers (protons).
Isomers: Nuclei with the same number of protons and neutrons but differing energy states.
Nuclear Stability
Stability Belt: A graphical representation that indicates the stable isotopes in terms of neutron-to-proton (N/P) ratio.
Modes of decay are classified based on the nuclide’s position relative to this stability belt.
Nuclides with low N/P ratio: Tend to increase neutron numbers and decrease proton counts through positron emission and electron capture.
Nuclides with excess N/P ratio: Typically undergo beta emission to achieve stability.
Computers in Nuclear Medicine
PACS (Picture Archiving and Communication System): A medical imaging technology for storing, transmitting, and displaying images.
Advantages of PACS: Enhanced accessibility, reduced physical storage needs, and improved workflow efficiency.
Disadvantages of PACS: High initial costs and risks related to data security and system obsolescence.
DICOM (Digital Imaging and Communications in Medicine): A standard for transmitting, storing, and sharing medical images and related information.
A system is DICOM compatible if it can read, store, or transmit DICOM files without data loss.
Network Performance
Important metrics in network performance include:
Packets: Units of data transmitted over the network.
Collisions: Occurs when two packets are sent simultaneously, resulting in data loss.
Latency: The time delay in transmitting data across a network.
Statistics
Systematic Error vs. Random Errors:
Systematic Error: Consistent, repeatable errors that occur due to a flaw in the measurement system or method.
Random Errors: Fluctuations that can occur unpredictably during measurements.
Usefulness of Statistics in Nuclear Medicine Technology (NMT): Enables better understanding and interpretation of measurement data.
Two major statistical applications utilized by NMTs are quality control in imaging and dosimetry evaluations.
Calculating Median with Even Measurements: The median is the average of the two middle values when data sets have an even number of observations.
Mode Definition: The value that appears most frequently in a data set.
Standard Deviation from Variance: To determine the standard deviation ($ ext{SD}$) from variance ($ ext{Var}$), use the formula: ext{SD} = ext{sqrt}( ext{Var}).
Statistical Percentile: Ninety-five percent of all measurements fall within two standard deviations from the mean (±2 SD).
Coefficient of Variation (CV): Allows assessment of the relative variability of the count data. A lower CV indicates more consistency in the counts we want in our images.
Radioactivity Calculation: The decay equation is derived from:
R = R0 e^{- rac{ ext{t}}{ au}} where $R0$ is the initial radioactivity, $R$ is the remaining radioactivity, $t$ is time, and $ au$ is the decay constant.
Interactions with Matter
Excitation vs. Ionization:
Excitation: The process in which electrons in atoms are raised to higher energy levels without ejection from the atom.
Ionization: Removal of electrons from atoms resulting in charged particles (ions).
Alpha Particle Path Predictability:
Alpha particles have predictable paths due to their larger mass and positive charge, which limits scattering and interaction compared to beta particles that exhibit variable course due to their smaller mass.
Main Photon Interactions with Matter:
Photons can interact through:
Photoelectric Absorption
Compton Scattering
Pair Production
Photoelectric Absorption:
The process whereby a photon energy is fully absorbed, leading to the ejection of an inner shell electron.
After electron ejection, an electron from a higher energy level fills the vacancy, releasing energy that may be emitted as an Auger electron (an electron emitted from the atom instead of a photon).
Probability decreases as photon energy increases, with exceptions at certain energy thresholds related to elemental absorption edges.
Pair Production:
Occurs when a photon with an energy surpassing $1.022 ext{ MeV}$ can produce a particle-antiparticle pair (electron and positron).
This is the dominant interaction for photon energies used in nuclear medicine.
Radiation Detectors
A detector must engage a photon, resulting in the production of an electric signal.
The electric signal generated indicates that a photon has been successfully detected.
Modes of Detector Operation:
Current Mode: This mode processes individual pulses of photons, treating each as a discrete event.
Energy Discrimination Mode: Differentiates incoming photon energies, allowing for the measurement of the energy spectrum of detected radiation.
Dead Time Definition: The period after a detection event during which a detector cannot record new events, usually due to the recovery needed for the detection circuitry.
Count Rate Trade-offs: While higher count rates can improve detection sensitivity, they risk overwhelming detectors during high exposure rates.
Gas-filled Detector Signal vs. Voltage Regions
Five regions of operation include:
Region I (Recombination): Detectors operate inefficiently, and signal corresponds to ion recombination.
Region II (Proportional): The current signal increases with photon energy adequately.
Region III (Geiger-Müller): Characterized by large current but lack of energy resolution.
Region IV (Continuous Discharge): High current that leads to continuous discharge making it unsuitable for accurate measurements.
Region V (Saturation): No increase in current; additional photons cannot be recorded.
Conditions Affecting Detector Operations: Temperature, pressure, and the type of gas used influence the ionization events and overall efficiency.
Recombination: The process by which free electrons and ions within the detector gas recombine instead of contributing to the electric current, resulting in reduced efficiency.
Scintillation Detectors
Scintillation Definition: A process in which a material emits light (scintillates) in response to incident radiation, which is then detected.
Desirable Properties of Good Scintillators:
High scintillation light yield
Fast response time
Good energy resolution
Chemical and mechanical stability
Photomultiplier Tube (PM Tube)
Doping NaI Crystals: Doping introduces impurities into sodium iodide (NaI) crystals to improve scintillation efficiency.
PM Tube Purpose: Converts scintillation light to an electrical signal and amplifies it for measurement.
Dynode Amplification Gain: The process where electrons released from the photocathode are accelerated towards a series of dynodes, resulting in a cascade of boosted electrons, greatly amplifying the initial signal.
Quality Control Procedures
Dose Calibrator QC: Essential QC procedures include verifying the instrument's performance before use.
The three preliminary steps before using the survey meter include: checking battery status, ensuring proper calibration, and confirming connection integrity.
Survey Meter Calibration Requirements:
Tolerance for check sources and calibration must adhere to specific regulations.
Calibration frequency requirements depend on usage and regulatory standards.
Dose Calibrator Operational Region: Typically operates in the Region III of the voltage curve in the current mode.
Considerations for Geometry: Geometry influences the accuracy and precision of dose measurements.
Four QC Procedures for Dose Calibrator:
Constancy: Check the consistency of the readings over time.
Must be performed daily with acceptable tolerance limits.
Accuracy: Assessing the precision against a known standard.
Accuracy checks need to be done at set frequencies and must involve multiple sources.
Tolerance for accuracy tests has to be maintained as per regulatory standards.
Linearity: Evaluating the response of the instrument over a range of activities.
Must be performed periodically and can utilize decay and Calicheck methods.
Linearity Testing Tolerance: Specific thresholds must maintain consistency with expected decay rates.
Well Counter and Thyroid Probe
Well Counter: A type of detector that's effective for small volume samples and low activities.
QC Procedures for Well Counter: Include maintenance, calibration, and performance checks.
Thyroid Probe: A specialized detector designed for measuring radioisotope activity from thyroid glands.
Energy Resolution in Detectors
Energy Resolution: The ability of a detector to distinguish between different energy levels of incoming radiation.
Measured as the full width at half maximum (FWHM) expression: ext{Energy Resolution} = rac{ ext{FWHM}}{ ext{Peak Energy}}.
Systems with 9% energy resolution have better performance over those with 12%.
Causes of Increased Energy Resolution: Can stem from improved crystal purity, temperature stability, and detector design.
Semiconductor Detectors
Semiconductor Detection Principle: Photon interactions within a semiconductor lead to the formation of electron-hole pairs that migrate to oppositely charged electrodes to generate measurable current.
Advantages of Semiconductor Detectors:
Enhanced stopping power, superior energy resolution, higher spatial resolution, and increased sensitivity compared to traditional detectors.
Disadvantages of Semiconductor Detectors:
Limitations in correcting for attenuation effects, smaller field of view (FOV), and inefficiency with larger body habitus.