Radioactivity and Geiger-Müller Tubes

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Questions and Answers

What is the role of centripetal force in circular motion?

It increases the speed of the object in a circular orbit.

It keeps the object moving in a linear path.

It keeps the object moving in a circular path towards the center. (correct)

It acts outward, pushing the object away from the center.

What two forces keep stars in balance throughout their life cycle?

Gravity and thermal expansion (correct)

Centripetal and centrifugal forces

Magnetic and kinetic forces

Radiation pressure and gravitational collapse

Which type of stars has five stages in their life cycle and is comparable in size to our solar system?

Solar mass stars (correct)

Neutron stars

Red giants

Massive stars

What does the Doppler effect describe?

The apparent change in frequency and wavelength of a moving object. (D) Signup and view all the answers

What shift occurs in galaxies moving away from an observer?

Galactic RedShift (B) Signup and view all the answers

What is the definition of half-life in the context of radioactive isotopes?

The time taken for the count rate to fall to half of its initial reading (D) Signup and view all the answers

What is a significant reason for using isotopes with a short half-life as medical tracers?

They minimize harmful effects by decaying quickly (D) Signup and view all the answers

What is the process of carbon dating primarily used for?

Estimating the age of organic materials and fossils (A) Signup and view all the answers

Which of the following best describes asteroids?

Small rocky objects that orbit the sun (D) Signup and view all the answers

Which of the following statements is true about gravitational field strength?

It varies depending on the mass of the larger object (A) Signup and view all the answers

What characteristic distinguishes comets from asteroids?

Comets have tails formed by melting ice (A) Signup and view all the answers

What is the implication of the geocentric model contrasted with the heliocentric model?

The geocentric model indicates the sun revolves around the Earth (C) Signup and view all the answers

Which statement about circular motion is correct?

The direction of motion changes continuously while distance remains constant (C) Signup and view all the answers

What is the primary characteristic of alpha particles?

They consist of 2 protons and 2 neutrons. (A) Signup and view all the answers

Which type of radiation has the strongest ionizing effect?

Alpha particles (B) Signup and view all the answers

Which of the following radiation types is deflected in a magnetic field?

Alpha and beta particles (D) Signup and view all the answers

What is the effect of radiation penetration for gamma rays?

Reduced but not completely stopped by lead (A) Signup and view all the answers

In terms of half-life, what does the term refer to?

The time taken for a radioactive nuclei to decay to half its original size. (C) Signup and view all the answers

What is the primary result of nuclear fission?

Splitting of an atomic nucleus into smaller nuclei (B) Signup and view all the answers

Which particle has a charge of -1?

Beta particle (D) Signup and view all the answers

What characterizes the penetration effect of alpha particles?

Low penetration, blocked by paper (B) Signup and view all the answers

Which of the following is true about gamma rays?

They are an electromagnetic wave similar to X-rays. (C) Signup and view all the answers

What happens during the process of nuclear fusion?

Atomic nuclei combine to form a heavier nucleus. (D) Signup and view all the answers

Study Notes

Radioactivity

Radioactivity is the process where unstable atomic nuclei release energetic subatomic particles.
The SI unit for radiation is Becquerel (Bq).
Radiation cannot be detected by the five senses; special detectors are needed.
Several devices have been developed to detect radiation across generations.
Examples include cloud chambers, electroscopes, and Geiger-Müller tubes.

Geiger-Müller Tube

The Geiger-Müller (GM) tube is a useful and sensitive radiation detection device.
Radiation enters the tube through a thin mica window.
Argon atoms become ionized into electrons and argon ions.
Free electrons accelerate towards the central wire (anode).
These accelerated electrons collide with other argon atoms, causing further ionization (an "avalanche" of electrons).
This enhances the current pulse.
The amplifier measures and rates the count rate.

Three types of radioactive emissions

Unstable nuclei release tiny particles randomly.
Alpha particles:
- Highest ionizing power, but low penetration.
- Composed of two protons and two neutrons.
- Identical to a helium nucleus (He2+ or α).
- Can be blocked by paper.
Beta particles:
- Moderate ionizing and penetration power.
- High-speed electrons.
- Released by radioactive isotopes like potassium-40.
- Represented as β⁻¹ or β.
Gamma rays:
- Lowest ionizing power and highest penetration.
- Electromagnetic waves similar to X-rays.
- Cannot be considered particles.
- Represented as γ⁰.
- Most harmful.
- Lead and thick concrete reduce penetration.

Deflection of Radioactive Emissions

Alpha particles are positively charged, deflecting towards the negative cathode in an electric field.
Beta particles are negatively charged, deflecting towards the positive anode in an electric field. Gamma rays have no charge and aren't deflected.
In a magnetic field, alpha particles show a small deviation, beta particles a larger deviation, and gamma rays show no deviation.

Radioactive Decay

Radioactive decay is the spontaneous and random emission of radiation from unstable nuclei.
Each decay of radioactive nuclei reduces the radioactive activity.
The rate of decay is described by half-life.

Nuclear Equations

The numbers for atomic number and mass must balance.
Alpha decay represents a helium nucleus (He2+).
Alpha decay increases the atomic mass by 4 and decreases the atomic number by 2.

Beta Decay

One proton is subtracted from the atomic number when a neutron decays into a proton.
This explains the increase in atomic number and no change in atomic mass.

Gamma Emission

Even after alpha and beta decay, the nucleus can be in an excited state.
Energy is released in the form of a gamma ray to lower the energy status,.

Nuclear Fission and Fusion

Nuclear fission is the splitting of an atom's nucleus into two or more smaller atoms, along with some by-products.
Nuclear fusion is the joining of multiple atomic nuclei to create a heavier nucleus, releasing or absorbing energy.

Uses of Radioactive Isotopes

Radioactive isotopes are used in medical tracers, detecting leaks, and carbon dating.

Precautions

Wearing protective clothing (e.g., lead-lined suits).
Maintaining distance from radioactive materials.
Enclosing radioactive materials (in lead containers).
Limiting exposure time.

Detecting Leaks

Use a short-lived radioisotope, releasing it into the pipe, and using a Geiger-Müller (GM) tube to detect its movement and signal leaks.

Carbon dating

Carbon-14, with a long half-life, is present in living organisms.
The amount of Carbon-14 decreases after death at a predictable rate, allowing estimation of the organism's age.
Carbon dating is not suitable for non-living materials.

Astrophysics

Weight is the force acting on an object due to gravity.
Planets have strong gravitational fields.
Gravitational field strength is the force acting on a unit of mass.
The Solar System is composed of the Sun, planets, and other celestial bodies.
Rocky planets include Mars, Earth, Venus, and Mercury; gas planets include Jupiter, Saturn, Uranus, and Neptune.
An asteroid belt lies between the rocky and gas planets.
Satellites are celestial objects orbiting larger celestial objects: Natural (e.g., the Moon) and Artificial (e.g., communication satellites).
Asteroids are small rocky objects orbiting the Sun; comets are made of dust and ice; the ice melts to form a tail when they approach the Sun.

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Description

Explore the fascinating topic of radioactivity, understanding the principles behind this process and how radiation is detected. Dive into the workings of the Geiger-Müller tube, a sensitive device used for measuring radiation, and learn about different types of radioactive emissions.