Half-Life Determination: Graphical Method

This section explains how to calculate half-life from a graph in chemistry and physics.

The process involves:

1. Selecting two points on the count rate axis, with one being half the other.
2. Noting the time between these two points on the graph.
3. Repeating this process for multiple pairs of points and averaging the results.

Example: Using a graph of count rate vs. time, the half-life is determined to be 1.2 hours by analyzing multiple pairs of points.

Highlight: When selecting points, choose those that land nearly on exact values for more accurate results.

Experimental Measurement of Half-Life

This page outlines an experiment to measure the half-life of a radioactive material, which is essential for understanding how to measure half-life of radioactive material experimentally.

Key steps in the experiment include:

1. Setting up apparatus: Radioactive source, Geiger-Müller tube, counter, and clock.
2. Measuring decays over a given time period.
3. Calculating count rate using the formula: count rate = number of decays / time in seconds.
4. Repeating measurements at regular intervals.
5. Measuring and subtracting background radiation.
6. Plotting a graph of activity vs. time and using the graphical method to determine half-life.

Highlight: It's crucial to measure and subtract background radiation to get accurate results.

Dosimetry: Absorbed Dose

This section introduces the concept of dosimetry and absorbed dose in nuclear physics.

Definition: Absorbed dose is the energy absorbed per unit mass of the absorbing material.

Key points:

1. Dosimetry quantifies the biological effect of radiation on humans.
2. Absorbed dose is calculated using the formula: D = E / m, where D is absorbed dose, E is energy absorbed, and m is mass of absorbing tissue.
3. Absorbed dose is measured in Grays $Gy$.

Example: A person undergoing hospital treatment where an organ of mass 250g absorbs 20J of energy receives an absorbed dose of 80 Gy.

Highlight: The absorbed dose is higher if the energy is concentrated on a smaller mass of tissue.

Dosimetry: Equivalent Dose

This page expands on dosimetry by introducing the concept of equivalent dose.

Definition: Equivalent dose is a measure of the biological effect of radiation, taking into account radiation type, absorbed dose, and exposed body organs or tissue.

Key points:

1. Equivalent dose is calculated by multiplying absorbed dose by the radiation weighing factor.
2. The formula is H = D × W_r, where H is equivalent dose, D is absorbed dose, and W_r is the radiation weighing factor.
3. Equivalent dose is measured in Sieverts $Sv$.
4. Different types of radiation have different weighing factors, e.g., alpha particles have a factor of 20, while gamma rays have a factor of 1.

Example: A worker in a nuclear power station receiving 10 mGy of slow neutrons and 2.5 mGy of gamma rays in a year has a total equivalent dose of 0.055 Sv.

Highlight: Equivalent dose provides a more accurate representation of radiation's biological effects compared to absorbed dose alone.

Practical Applications of Dosimetry

This final section explores the practical applications of dosimetry in various fields, emphasizing its importance in radiation protection and medical physics.

Key applications of dosimetry include:

1. Radiation Protection in Nuclear Facilities: Monitoring worker exposure in nuclear power plants Ensuring safety in radioactive waste management
2. Medical Imaging: Optimizing radiation doses in X-ray and CT scans Balancing image quality with patient safety
3. Radiation Therapy: Planning and delivering precise radiation doses to tumors Minimizing exposure to healthy tissues
4. Environmental Monitoring: Assessing radiation levels in areas affected by nuclear accidents Monitoring natural background radiation
5. Space Exploration: Protecting astronauts from cosmic radiation during space missions

Highlight: Accurate dosimetry is crucial in maintaining the ALARA principle $As Low As Reasonably Achievable$ in radiation protection.

Example: In radiation therapy, dosimetrists use sophisticated planning systems to calculate the optimal radiation dose distribution, ensuring that the tumor receives the prescribed dose while minimizing exposure to surrounding healthy tissues.

Understanding and applying dosimetry principles is essential for professionals working in radiation-related fields, ensuring the safe and effective use of ionizing radiation in various applications.

Page 7: Equivalent Dose in Radiation Protection

This section covers equivalent dose calculations and radiation weighing factors.

Formula: Equivalent Dose = Absorbed Dose × Radiation Weighing Factor

Vocabulary: Sievert $Sv$ - unit for equivalent dose Gray $Gy$ - unit for absorbed dose

Example: Calculation of total equivalent dose for a nuclear power station worker exposed to multiple radiation types.

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Page 8: Dosimetry Rates and Calculations

Covers the calculation of dose rates and practical applications in radiation safety.

Example: Calculating equivalent dose rate for a radiation worker exposed to 120 µSv over a working week.

Formula: Absorbed dose rate = Absorbed Dose / Time

Half-Life Determination: Numerical Method

This section introduces the concept of half-life and demonstrates how to calculate it numerically.

Definition: The half-life of a radioactive source is the time taken for the activity to fall to half its previous value.

The page covers three main types of problems:

1. Finding Initial Activity: Given the current activity and half-life, calculate the activity at a previous time.
2. Finding Final Activity: Given the initial activity and half-life, determine the activity after a specific time period.
3. Finding Half-Life: Given initial and final activities over a time period, calculate the half-life.

Example: A source with an activity of 1024 Bq and a half-life of 3 days will have an activity of 32 Bq after 15 days.

Highlight: Always start calculations from time zero and halve the activity for each half-life period.