Lecture Notes on Radiation Safety and Measurement Apparatus

Overview

• Discussion on safety apparatus designed to prevent unauthorized opening of a radioactive source.
• Description of a rod and gripper mechanism holding a radioactive source, specifically sodium-22.
• Introduction of sealed sources as a safety measure.

Radioactive Source Characteristics

• Sodium-22:
  • Emits a positron with low kinetic energy.
  • Classified as a sealed source, reducing the need for stringent safety measures compared to unsealed radioactive materials.

Safety Measures

• Housing Design:
  • Made of lead; contains drilled holes to accommodate the radioactive source securely.
  • The source is held firmly within the housing to prevent accidental exposure.

Positron Emission and Annihilation

• Emission of positrons and their interaction with electrons.
• Formation of positronium (positron-electron pair) and its excited state.
• Positronium radiates until reaching a ground state before annihilation.

Radiation Measurement

• Measurement Setup:
  • Cosmic ray background measurement noted at 0.02 millirem per hour.
  • Comparison with localized measurements indicating a 20-fold increase near the source.

Positronium and Annihilation

• Discussion on positronium spins: 1s0 and 3s1 states.
• Annihilation in 1s0 state leads to emission of two gamma rays.
• 3s1 state decays to three gamma rays, with less probability of back-to-back emission.

Gamma and Compton Scattering

• Gamma Interaction:
  • Gamma rays scatter within the apparatus, interacting with aluminum through Compton scattering.
  • Scattering more likely at angles close to 90 degrees under specific conditions.

Polarization and Compton Scattering

• Polarization affects scattering direction due to interaction with electrons.
• Experimental setup aims to prove polarization correlation between emitted gamma rays.

Detector Apparatus

• Scintillator:
  • Sodium iodide detector setup to measure gamma interactions.
  • Encased to prevent light and moisture interference.

Pulse Processing and Analysis

• Pulse Height Analysis:
  • Amplification and threshold adjustments to capture specific pulse heights.
  • Coincidence detection for gamma-gamma emission verification.

Calibration and Data Collection

• Use of radioactive sources like cesium-137 for calibration.
• Adjustment of detector gain to optimize pulse height readings.

Coincidence Detection System

• Explanation of coincidence circuit setup to measure simultaneous events.
• Use of tracking and holding signals to stabilize pulse readings for computer analysis.

Experiment Preparation

• Suggestions for setting up the apparatus with attention to historical data and calibration runs.
• Emphasis on manual record-keeping due to limitations in digital interfacing.

Key Considerations

• Importance of understanding detector calibrations and adjustments for accurate radiation measurement.
• Addressing dead time corrections and random coincidences in data analysis.
• Ensuring safety protocols are followed during experiments to avoid radiation exposure.