Radioactivity
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5.2.1 Detection of radioactivity
## Radioactivity Detection
Radioactivity is the process of releasing radiation from an unstable atomic nucleus. We are all exposed to radiation from various sources every day. Let's discuss some important things about radioactivity:
## Background Radiation Sources
Background radiation comes from a variety of sources, both natural and artificial:
- Cosmic rays from the sun
- Radon gas in the air
- Radon-containing granite rocks
- Potassium-40 in food
- Medical procedures that use radioisotopes
- Nuclear power plants and the rest of the nuclear bomb tests
## Ionization Effect
Radiation can cause ionization, which is the process of releasing electrons from atoms or molecules. This can be evidenced by:
Electroscope Experiments:
- When a fire or radium source is brought close to a charged electroscope, the charge is lost
- Fire or radiation causes air molecules to lose electrons and become positive ions
- These ions then neutralize the charge on the electroscope
## Geiger-Müller tube
A Geiger-Müller (GM) tube is a device for detecting radiation by:
- Radiation enters through thin mica windows or tube walls
- Radiation ionizes argon gas inside the tube
- Ions and electrons move to the electrode and produce pulses of electric current
- Pulses are amplified and calculated by a counter or ratemeter
## Hash Rate Correction
To get accurate measurement results:
- The chopping rate from radioactive sources must be corrected by reducing background radiation
- Background radiation is measured by recording the chopping rate at a location far from radioactive sources
- Measurements are taken for a few minutes to get an average value
The discovery of radioactivity happened by accident by Henri Becquerel in 1896 when he discovered that uranium compounds could penetrate black paper and ionize gases. Since then, radioactivity has been widely utilized in various fields such as industry, medicine, and research. This research was continued by Marie Curie who found other radioactive elements such as radium.
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5.2.2 The three types of nuclear emission
## Three Types of Radioactive Radiation
Radioactive substances can emit three different types of radiation. Let's discuss the properties of each of them:
## Radiasi Alfa (α)
- Is a double-positively charged particle (helium ion without electrons)
- Has the following properties:
- Very weak penetration, only a few centimeters in the air
- Can be stopped by a thick sheet of paper
- The ionizing power is strongest because its positive charge can attract electrons
- Deflected by an electric field towards the negative plate
- Moves at about 1/20 the speed of light
## Radiasi Beta (β)
- It is a negatively charged high-energy electron
- Has the following properties:
- Penetration is stronger than alpha, can reach several meters in the air
- Can be stopped by aluminum plate several millimeters
- Weaker ionizing power than alpha
- Deflected by an electric field towards the positive plate
- Can move at speeds close to the speed of light
## Gamma Radiation (γ)
- It is a very high-energy electromagnetic wave
- Has the following properties:
- The strongest penetrating power, it takes thick lead to stop it
- Not electrically charged so it is not affected by electric / magnetic fields
- Weakest ionizing power
- Moving at the speed of light
- Has a very short wavelength such as X-rays
## How to Detect Radiation
- Geiger-Müller (GM) tubes can detect high-energy beta, gamma and alpha radiation
- Charged electroscopes can only detect alpha radiation
- Fog rooms can show traces of radiation:
- Alpha produces a thick, straight trail
- Fast beta results in a thin straight trail
- Slow beta produces a thick winding trail
- Gamma results in a trail of electrons that radiate in all directions
Keep in mind that this radiation is harmful to living things, so it needs special handling with appropriate protective equipment when working with radioactive materials.
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5.2.3 Radioactive decay
## Radioactive Decay
Radioactive decay occurs when the nucleus of an atom is unstable and releases particles to achieve stability. Let's discuss this process:
## Basic Process of Decay
- Occurs randomly and spontaneously
- Cannot be controlled or influenced by external conditions
- Generate new and different elements
- It can occur in three main ways:
1. Alpha decay (α)
2. Beta decay (β)
3. Pancaran gamma (γ)
## Alpha decay (α)
- Releases alpha particles (helium nuclei)
- Alpha particles are made up of 2 protons and 2 neutrons
-Consequently:
- Mass number reduced by 4
- Atomic number reduced by 2
- Example: Radium-226 to Radon-222
## Beta Decay (β)
- Neutrons turn into protons and electrons
- Electrons emitted as beta particles
-Consequently:
- Mass number remains the same
- The atomic number increases by 1
- Example: Carbon-14 to Nitrogen-14
## Pancaran Gamma (γ)
- Occurs after alpha or beta decay
- It is a radiant of energy in the form of electromagnetic waves
- Does not change the mass number or atomic number
- Only releases excess energy
## Unstable Atom
The stability of the atomic nucleus is determined by:
1. Number of protons (Z)
2. Number of neutrons (N)
The stable atomic nucleus is characterized by:
- For light atoms: number of protons = number of neutrons
- For heavy atoms: number of neutrons > number of protons
- Most have an even number of protons and neutrons
An unstable atomic nucleus will:
- Decay to approach the stability line
- If there are too many neutrons: it has negative beta decay
- If there are too many protons: beta positive decay
- If it has more than 82 protons: it is likely to undergo alpha decay
The decay process will continue until a stable atomic nucleus is formed.
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5.2.4 Half-life
## Half-Life
The half-life is the time it takes for half of the number of nuclei of radioactive atoms in a sample to decay. Let's discuss this concept :
## Basic Definition
- Radioactive decay occurs randomly and spontaneously
- Cannot be affected by temperature or outside conditions
- Each radioactive element has a different half-life
- Half-life ranges from microseconds to millions of years
## How to Calculate Half-Life
The half-life can be calculated by:
1. Measure the count rate at a certain time interval
2. Create a decay graph
3. Find the time needed to reduce activities by half
Example: If the initial activity of an isotope is 200 counts/minute and after 25 minutes it becomes 100 counts/minute, then the half-life is 25 minutes.
## Background Radiation Correction
In the measurement of half-life it is necessary to pay attention to:
- Background radiation must be measured first
- The value of background radiation must be deducted from the measurement result
- Graphs are created using corrected values
## Random Nature of Decay
- Decay occurs spontaneously and randomly
- It is impossible to predict which atoms will decay
- Cannot be influenced or controlled
- It is certain that only half of the total number of atoms will decay in a single half-life
## Decay Curve
When activity is measured at various times, we can create a decay curve that shows the decrease in activity over time. This curve shows that activity decreases by the same fraction in the same time interval.
### Example of Decay Curve
- If the activity drops from 80 to 40 disintegrations per second in 10 minutes, then from 40 to 20 in the next 10 minutes, then the half-life is 10 minutes.
## The Use of Radioactivity in Daily Life
## Smoke Detector
- Uses americium-241 which emits alpha particles
- Has two ionization chambers: one open and one closed
- When smoke enters an open space, the electric current is reduced
- This change in current triggers an alarm
- Alpha particles are chosen because their range is short so they are safe
- Uses isotopes with long half-lives to keep their activity stable
## Sterilization
- Uses gamma radiation to kill bacteria
- Used for sterilization of medical devices and food preservation
- Safe because radioactive materials do not enter the food
- Gamma radiation is chosen because of its high transgression
- Can penetrate the packaging without opening it
## Thickness Gauge
- A radioactive source is placed on one side of the material
- GM detector on the other side
- Used to control the thickness of paper, plastic, and metal
- For thin materials use beta transmitters
- For thick materials use gamma emitters
- Can also detect defects in materials
## Cancer Diagnosis and Treatment
- Gamma radiation is used for imaging cancer
- For diagnosis in vivo using short-lived isotopes
- For therapy using high-energy gamma radiation beams
- Radiation beams are rotated around the body to minimize damage to healthy tissues
## Tracer
- Weak radioactive isotopes are injected into the system
- Used for:
- Detects brain tumors and internal bleeding
- Study the absorption of fertilizer by plants
- Measuring fluid flow in pipes
- The half-life of the isotope is adjusted to the duration of the experiment
## Arkeologi
- Using carbon-14 to determine the age of ancient objects
- Carbon-14 has a half-life of 5,700 years
- Can determine the age of objects between 1,000-50,000 years
- The same principle is used to determine the age of rocks
- Example: Viking ships can be dated to around 800 AD
All these uses must pay attention to the radiation safety aspect and choose the type of radiation and half-life that suits the needs.
5.2.5 Safety precautions
## Safety Measures in the Use of Radiation
Although radiation has many benefits, exposure to radiation can be harmful to health. Here is an explanation of the dangers and how to secure them:
## Radiation Hazards
- Radiation can damage the cells and tissues of the body
- May cause genetic mutations
- Risk of cancer and cell death
- Alpha particles are harmful if they enter the body
- Beta and gamma radiation can cause burns and cataracts
- High exposure can result in radiation sickness and death
## Three Basic Principles of Radiation Safety
1. Time:
- Minimize radiation exposure time
- The shorter the exposure, the smaller the dose received
2. Distance:
- Keep as far away as possible from radiation sources
- The greater the distance, the less intense the radiation
- Double spacing will reduce exposure by a quarter
3. Protector:
- Use appropriate protective gear (lead, concrete, water)
- Lead is effective at resisting gamma radiation and X-rays
- Protective thickness adjusted to the type of radiation
## Practical Safety Measures
- Use long clamps to handle radioactive materials
- Store in a lead-plated container
- Wear a dosimeter badge to monitor the display
- Use personal protective equipment (PPE):
- Laboratory coat
-Glove
- Safety glasses
- Thyroid shield if needed
## Storage and Disposal
- Low-activity waste is stored in steel containers and concrete bunkers
- High-activity waste is immobilized in glass or synthetic rock
- Store underground to avoid leakage
- Avoid contamination of water sources and food chains
## School Usage
For weak radiation sources in schools:
- Lift with clamps
- Keep out of sight
- Store in a special box when not in use
By applying these safety principles, the risk of radiation exposure can be minimized while still taking advantage of the usefulness of radiation in a variety of fields.
