Monitoring Content of Food

Monitoring Thickness of Steel/paper Sheet

Detecting Underground Leakage

Measuring the Wearing Rate of Engine

Pest Control

1. Male insect is sterilised by exposing to radioactive radiation and then released back to the ecosystem.
2. This can ensure that their reproducing effort do not generate new generation and hence reduces the population of the insect.

Tracer

1. The metabolism of phosphorus by plants can be studied using phosphate fertilisers that contain phosphorus-32. 
2. A small amount of phosphorus-32 is used in fertilisers. 
3. The radiation produced by phosphorus-32decay is detected by a Geiger-Muller counter. 
4. This method can trace the passage of phosphate ions in plants.
5. Carbon-14 is used to study the passage of carbon during photosynthesis in plants.

Develop New Species of Plant

1. Radioactive radiation is targeted to the seeds of plants and hence causes mutation to the genes.
2. By chance, this may develop some superior agricultural products.

Preserve Food

1. The gamma rays from cobalt-60 are used to kill bacteria in food to make fresh vegetables and fruits last longer without any change in quality, flavour and texture of food.
2. Gamma rays are used to inhibit budding in potatoes.

Radiotherapy

Tracer to Detect Blood Clots or Tumour

1. A small amount of sodium-24 is injected into the patient's body. 
2. Radioactive imaging is then used to detect accumulation of sodium-24 and therefore detect tumours and blood clots before they become dangerous.

Sterilising Medical Instrument

1. Gamma ray emitted from radioactive cobalt-60 can kill germs such as bacteria and fungus. 
2. Medical instruments such as surgical equipment, syringes and bandages can be sterilised by using gamma rays.

Heart Pacemaker

(Heart Pacemaker)

1. A heart  pacemaker is a medical device which uses electrical pulses to contract the heart muscles, and hence to regulate the beating of the heart. 
2. Plutonium-238 in a nuclear battery is used to produce small electric shocks in the heart pacemaker. 
3. People with irregular heartbeats need to have a heart pacemaker implanted inside their chest.

Tracer to Investigate Activities of Thyroid Glands

1. There are two types of isotopes, namely
   1. the stable isotopes (non-radioactive)
   2. the non-stable isotopes (radioactive).
2. Unstable isotopes go through radioactive decay and emit radiation and they are known as radioisotopes.
3. Radioisotopes have many applications in the following field
   1. Industri
   2. Medical
   3. Agriculture
   4. Archeology

Half-life

1. The half-life (T_½ ) of a quantity subject to exponential decay is the time required for the quantity (mass, number of atom or activity) to decay to half of its initial value.
2.  The decay curve of a radioactive source can be found experimentally - provided the activity of the source decreases over a practicable time period (minutes, hours or days for example). 
3. The corrected count-rate is then plotted against time to give the decay curve. The half-life of the source can be found from the curve as indicated above.

(Decay Curve)

Example 1
A radioisotope has half-life of 8 hours. Initially, there were 3.6 x 10¹⁸ radioisotope atoms in a sample. How much time is taken for the number of atoms of the radioisotope to fall to 4.5 x 10¹⁷?

Answer:

The sample take 3 half-life to decay from 3.6 x 10¹⁸ radioisotope atoms to 4.5 x 10¹⁷. Therefore, the time taken
t = 3T_½
t = 3(8) = 24h

Example 2

The diagram shows the graph of the activity of a radioisotope, X, against time. What is the half-life of the radioactive substance?

Answer:
The half-life is the time taken for the activity to decrease to become half of the initial value.

From the graph we can see that the radioisotope take 6 days for the activity to become half. Therefore

Half-life = 6 days

Alpha Decay

1. During an alpha decay, a radioactive atom X decay and emits an alpha particle ($He$ ).
2. Atom X losses 2 neutron and 2 proton and become atom Y.

Beta decay

1. A beta particles is an electron emitted from a nucleus.
2. The beta particles are very small and move with very high speed.
3. During a beta decay, a radioactive atom X decay and emits a beta particle ($e$ ).
4. One of the neutron is disintegrated to become proton and electron. The electron is emitted out from the nucleus whereas the proton stay in the nucleus.
   
5. Therefore proton number increase by 1 and the nucleon number remain unchanged.

Gamma Emission 

3 Types of Radioactive Emission

Alpha Particle

• carries positive charge.
• most strongly ionizing of the nuclear radiations. 
• least penetrating. Range in air is only a few centimetres, and can be stopped by a thick sheet of paper.

Beta Particle

• carry a negative charge. 
• much less ionizing than alpha emission.
• more penetrating than alpha emission..
• have a range of a metre or so in air,
• can be stopped by a few millimetres of Perspex or aluminium.

Gamma Radiation

• often emitted at the same time as an alpha or beta particle.
• least ionizing of the nuclear radiations, 
• most penetrating.
• their intensity is greatly reduced by several centimetres of lead, but they are never completely absorbed.

Ionising Effect

• All alpha, beta and gamma emission can cause ionising effect.
• Alpha particle has high ionizing power.Beta particle has low ionizing power.
• Gamma ray has very low ionizing power.

Penetrating Power

Deflection in Electric Field

Deflection in Magnetic Field

• Alpha and beta emission can be deflected by a magnetic field.
• The direction of deflection can be determined by using Fleming’s Left Hand Rule.
• Beta particle deflected more compare to alpha particle due to its much smaller mass.

Summary

Series Decay

1. Sometimes after a radioactive decay, the daughter nuclide formed is still unstable.
2. It will further decay into another nuclide which may also unstable.
3. This process continues until a stable nuclide is reached. This is called a series decay.
4. Each decay will emit either an alpha particle or a beta particle and may be gamma ray.
5. Figure below shows a series decay started from plutonium-241 to formed Thallium-205 eventually.

(This image is created by Johantheghost under creative common licence)

[Can detect: Alpha particles only]

1. Alpha radiation can be detected using a charged electroscope as in on the left. The more intense the radiation, the faster the leaf falls. 
2. The method isn't suitable for detecting beta and gamma-radiation as these cause insufficient ionization of the air.

1. All the α-particle, β-particle and γ-ray can be detected by a photograph film.
2. The ionisation effect by the radioactive rays will decompose silver bromide crystal on the film.
3. Films are kept in the badges worn by workers as a tracer device of radioactive rays.
4. The main disadvantages of using a film as a radioactive tracer is that it needs to be processed in order to prove the presence of radioactive rays)

[Can detect: Alpha particles only]

1. A spark-chamber detector is a particle detector, that is, a device used in particle physics for detecting electrically charged particles. 
2. Spark-chamber detectors consists of metal plates placed in a sealed box filled with gas (for example, helium, neon or a mixture of the two); as a particle travels through the detector, it will ionize the gas between the plates, and a trigger system is used to apply high voltage to the plates to create an electric field immediately after the particle went through the chamber, producing sparks on its exact trajectory.