Physics Form 5 : chapter 5

5.3 UNDERSTANDING THE USES OF RADIOISOTOPES

By: Name : Nur Khairina Binti Khairu NajhanClass : 409/509

College number : 13272

RADIOISOTOPES• Isotopes : Atoms of with the same number of protons but

different number of neutrons.• Radioactive isotopes are called radioisotopes.• Some radioisotopes exist naturally. For example;

– Carbon-14: Used to measure the age of water (up to 50,000 years)– Chlorine-36: Used to measure sources of chloride and the age of water (up to 2

million years)– Lead-210: Used to date layers of sand and soil up to 80 years– Tritium (H-3): Used to measure 'young' groundwater (up to 30 years)

• Others are produced artificially by transmutation in a nuclear reactor.

a) A stable nucleus is bombarded by high speed alpha particles, neutrons or protons to produce artificial radioisotopes.

b) The bombarding particles are trapped in the nucleus creating a radioisotope.

• For example;

1. Americium-241:Used in backscatter gauges, smoke detectors, fill height detectors and in measuring ash content of coal.

2. Caesium-137:Used for radiotracer technique for identification of sources of soil erosion and deposition, in density and fill height level switches.

3. Chromium 57:Used to label sand to study coastal erosion.

4. Cobalt-60, Lanthanum-140, Scandium-46, Silver-110m, Gold-198:Used together in blast furnaces to determine resident times and to quantify yields to measure the furnace performance.

5. Cobalt-60: Used for gamma sterilisation, industrial radiography, density and fill height switches.

6. Gold-198 & Technetium-99m:Used to study sewage and liquid waste movements, as well as tracing factory waste causing ocean pollution, and to trace sand movement in river beds and ocean floors.

7. Gold-198:Used to label sand to study coastal erosion.

8. Hydrogen-3 (Tritiated Water): Used as a tracer to study sewage and liquid wastes

9. Iridium-192Used in gamma radiography to locate flaws in metal components.

• Emits radioactive radiation.• Radioactive radiation can kill cells.• Radioactive radiations can cause cell

mutation.• Radioactive radiations can ionise

molecules.• Its activity decreases with time.• Radioisotopes have the same chemical

properties as non-radioactive isotopes of the same element.

Properties of radioisotopes

Uses of Radioisotopes

Medicine• Sodium iodide labelled with radioactive iodide – ssstreat overactive thyroid gland and thyroid cancer.• Sodium-24 injected into bloodstream to detect sssposition of blood clots or thrombosis in blood sssvessels.• Phosphorus-32 – detect and treat brain tumor.• Iron-59 – study circulation of iron in blood• Cobalt-30 – Destroy cancer cells in radiotheraphy

Sterilize medical equipments.

RADIOISOTOPES HALF-LIFE APPLICATION

Sodium-24 15 hours Plasma volume

Iodine-131 8 days Thyroid function

Iodine-125 60 days Vein flow

Technetium-99m 60 hours Thyroid uptake

Industry1. Monitoring Content of Food

2. Monitoring Thickness of Steel/paper Sheet

3. Detecting Underground Leakage

4. Measuring the Wearing Rate of Engine

Agriculture• Pest can be killed using radioactive rays

especially gamma rays• Nitrogen-15 and phosphorus-32 use as

tracers in study of effectiveness of fertilizers.– These radioisotopes are added to soil

water.– After plant absorb soil water, the

radioisotopes can track uptake of fertiliser from roots to leaves in a plant

• Radioactive radiation is also used to in duce genetic mutation in plant to produce better strain (higher resistance against disease).

Archeology• To determine age of artefacts. • Method : carbon dating• Carbon dating is a variety of radioactive dating which is

applicable only to matter which was once living and presumed to be in equilibrium with the atmosphere, taking in carbon dioxide from the air for photosynthesis.

• Cosmic ray protons blast nuclei in the upper atmosphere, producing neutrons which in turn bombard nitrogen, the major constituent of the atmosphere . This neutron bombardment produces the radioactive isotope carbon-14. The radioactive carbon-14 combines with oxygen to form carbon dioxide and is incorporated into the cycle of living things.

• The carbon-14 forms at a rate which appears to be constant, so that by measuring the radioactive emissions from once-living matter and comparing its activity with the equilibrium level of living things, a measurement of the time elapsed can be made.

• Presuming the rate of production of carbon-14 to be constant, the activity of a sample can be directly compared to the equilibrium activity of living matter and the age calculated. Various tests of reliability have confirmed the value of carbon data, and many examples provide an interesting range of application.

• Carbon-14 decays with a halflife of about 5730 years by the emission of an electron of energy 0.016 MeV. This changes the atomic number of the nucleus to 7, producing a nucleus of nitrogen-14. At equilibrium with the atmosphere, a gram of carbon shows an activity of about 15 decays per minute.

• The low activity of the carbon-14 limits age determinations to the order of 50,000 years by counting techniques. That can be extended to perhaps 100,000 years by accelerator techniques for counting the carbon-14 concentration.

• Measuring geological time:a) During the formation of rocks, some

radioisotopes such as Uranium-238 are trappedb) As decay continues, the proportion of uranium-

238 decreases slowly resulting in the equally slow growth of its product, lead-206.

c) An estimate of the age the rock can be inferred from the relative proportions of lead and uranium in the rock.

EXAMPLE OF OBJECTIVE QUESTION

• Example:1) A piece of wood found in a cave of an archaeology site has a carbon-14 activity 25% of the activity from a live plant. Estimate the age of the wood. [Half-life of carbon-14 = 5730 years]

A 15162 C 12589B 11460 D 11580

• Answer:100% → 50% → 25%

Carbon-14 take 2 half-life to decay from 100% to 25%, hence the age of the wood= 2(5730)= 11460 years (B)

• 2) It is found that 98.4375% of Carcon-14 in an archeological artefact has disintegrated. Determine the age of the artefact if the half life of carbon14 is 5600 years.

A 35805 C 39025B 38056 D 33600

SolutionPercentage of carbon-14 remaining = 100 – 98.4375

= 1.5625%Let the final amount of carbon-14 = NThe final amount of carbon-14 = 1/64 N

* The age of the artefact = 6 x 5600 years = 33600 years (D)

• 3)The table shows the half-lives of the radioisotopes G,H, I and J.

Which of the radioisotopes is NOT suitable as a tracer in the human body?A G C IB H D J

Radioisotopes Half-life

G 9 days

H 62 days

I 82 days

J 5.5 years

CommentsThe radioisotopes used must have a half-life long enough for it to act as a tracer but not too long because it will give side effects to the patients.Answer : D

THE END