History and Nature of Radioactivity

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Questions and Answers

What is the half-life of Carbon-14?

5730 years

How can scientists determine the age of an object containing carbon?

By measuring the ratio of Carbon-12 to Carbon-14.

What are two medical uses of radioisotopes?

Killing cancerous cells and sterilizing medical instruments.

What fraction of caesium-137 remains after 90 days if it has a half-life of 30 days?

1/8 Signup and view all the answers

Define radioactivity.

Spontaneous random decay of a nucleus. Signup and view all the answers

What is a radioisotope?

A radioactive isotope. Signup and view all the answers

What is a property of beta particles?

They have a negative charge and negligible mass. Signup and view all the answers

What is one use of Americum-241 in everyday life?

It is used to detect smoke in smoke alarms. Signup and view all the answers

Who discovered radioactivity and how did it come to light?

Henri Becquerel discovered radioactivity while studying uranium salts, finding that they fogged a photographic plate left in darkness. Signup and view all the answers

What elements did Pierre and Marie Curie isolate from pitchblende?

The Curies isolated polonium and radium from pitchblende through extensive recrystallisations. Signup and view all the answers

Describe the composition and charge of alpha particles.

Alpha particles are composed of two protons and two neutrons, carrying a double positive charge. Signup and view all the answers

How do alpha particles behave in terms of penetrating power?

Alpha particles have low penetrating power and can be stopped by a few centimeters of air or paper. Signup and view all the answers

What transformation occurs to create beta particles?

A neutron in an unstable nucleus is transformed into a proton and an electron, with the electron being ejected as a beta particle. Signup and view all the answers

Compare the speed and penetrating ability of alpha and beta particles.

Beta particles travel faster than alpha particles and possess greater penetrating ability due to their smaller mass. Signup and view all the answers

What is gamma radiation, and how does it differ from alpha and beta radiation?

Gamma radiation is high-energy electromagnetic radiation that does not consist of charged particles and is not deflected in electric or magnetic fields. Signup and view all the answers

What role does gamma radiation play in the stability of an unstable nucleus?

An unstable nucleus emits gamma radiation to lose surplus energy and achieve stability. Signup and view all the answers

What are gamma rays and where are they commonly used?

Gamma rays are a type of radiation with high penetrating ability and are commonly used in radiotherapy, such as Cobalt-60, to kill cancer cells. Signup and view all the answers

How do nuclear reactions differ from chemical reactions?

Nuclear reactions involve changes in the atomic nucleus and can form new elements, whereas chemical reactions involve the transfer of electrons and do not produce new elements. Signup and view all the answers

What is the definition of half-life?

The half-life of an element is the time required for half of the nuclei in a sample to decay. Signup and view all the answers

Calculate the remaining amount of Carbon-14 after two half-lives if starting with 10g.

After two half-lives, 2.5g of Carbon-14 will remain. Signup and view all the answers

What happens to the amount of a radioactive isotope as it undergoes decay?

The amount of the radioactive isotope decreases over time as it transforms into a different element. Signup and view all the answers

Why is it important to understand half-life in nuclear reactions?

Understanding half-life is important for comparing the decay rates of radioactive isotopes and for applications in nuclear medicine and dating techniques. Signup and view all the answers

What type of radiation is released during nuclear reactions?

Nuclear radiation, such as alpha, beta, and gamma radiation, is released during nuclear reactions. Signup and view all the answers

What is the significance of Cobalt-60 in medical applications?

Cobalt-60 is significant in medical applications as it emits gamma rays, which are utilized in radiotherapy to target and kill cancer cells. Signup and view all the answers

Study Notes

History of Radioactivity

Radioactivity was discovered by Henri Becquerel, a French physicist.
Becquerel was studying the effect of sunlight on uranium salts.
He left uranium salts on a photographic plate wrapped in black paper.
The plate became fogged near the uranium salt, indicating radiation.
Pierre and Marie Curie further investigated uranium ore (pitchblende).
They isolated polonium and radium through recrystallisation.

Nature of Radioactive Radiation

Three types of radiation were identified based on their behavior in electric and magnetic fields.
Alpha particles:
- Groups of two protons and two neutrons.
- Carry a double positive charge (2+).
- Represented as ⁴₂He.
- Emitted from the unstable nucleus of a radioactive element.
- Relatively large mass, travel slower than other types.
- Low penetrating power (stopped by a few cm of air or paper).
- Example: Americium-241 (used in smoke detectors) is an alpha particle. Helium is the alpha particle.
Alpha Decay:
- An unstable nucleus emits an alpha particle to become more stable.
- Example: ²³⁸₉₂U → ⁴₂He + ²³⁴₉₀Th

Beta Particles

Fast-moving electrons.
Formed when a neutron in an unstable nucleus transforms into a proton and an electron.
The electron is ejected from the nucleus.
Represented as ⁰₋₁e.
Lighter than alpha particles; hence, travel faster and have higher penetrating power.
Example: Carbon-14 is an element that emits beta particles and is used in carbon dating.

Gamma Radiation

High-energy electromagnetic radiation.
Consists of no charged particles; hence, not deflected in electric or magnetic fields.
Emitted by an unstable nucleus to lose surplus energy.
High penetrating power; can penetrate bricks and metal.
Stopped only by a thick slab of lead.
Example: Cobalt-60 is used in radiotherapy.

Nuclear Reactions

Nuclear reactions alter the composition, structure, or energy of an atomic nucleus.
Chemical reactions involve electrons; nuclear reactions involve atomic nuclei.
Nuclear reactions produce new elements whereas chemical reactions do not.
Nuclear reactions release nuclear radiation while chemical reactions do not.

Half-Life

Half-life is the time taken for half of the nuclei in a sample to decay.
Radioactive isotopes decay at different rates.
Scientists use half-life to compare decay rates of isotopes.

Uses of Radioisotopes

Medical:
- Gamma rays used to kill cancerous cells.
- Used to sterilize instruments.
- Iodine-131 measures iodine uptake by the thyroid gland.
Archaeological:
- Radiocarbon dating determines the age of objects containing carbon (based on the Carbon-12 to Carbon-14 ratio).
Agricultural:
- Study fertilizer uptake by plants.
Food:
- Treating food with gamma rays to kill disease-carrying organisms.
Smoke Alarms:
- Americium-241 detects smoke.

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Description

Explore the key discoveries in the history of radioactivity, from Henri Becquerel's initial experiments to the groundbreaking work of Pierre and Marie Curie. Understand the nature of radioactive radiation, including the characteristics and behavior of alpha particles. This quiz will test your knowledge of these fundamental concepts in radioactivity.