Radioactivity

The periodic table is an arrangement of all the elements known to man in accordance with their increasing
atomic number and recurring chemical properties.
The modern periodic table, the one we use now, is a new and improved version of certain models put forth
by scientists in the 19th and 20th century. Dimitri Mendeleev put forward his periodic table based on the
findings of some scientists before him like John Newlands and Antoine-Laurent de Lavoisier. However,
Mendeleev is given sole credit for his development of the periodic table.

What Makes a Substance Radioactive?

1. Unstable Nucleus:
o Inside every atom, there's a nucleus, which is made up of protons and neutrons. In some
elements, the nucleus is unstable, meaning it is not in its most stable form.
o Why unstable? The forces inside the nucleus aren't balanced, so it breaks apart over time,
releasing energy in the form of radiation.
2. Spontaneous Emission:
o The process of a radioactive substance emitting radiation is spontaneous, which means it
happens naturally without needing any outside energy or force.
o The radiation can be in the form of particles (alpha and beta particles) or energy waves
(gamma rays).

How Does Radioactivity Work?

 Decay of Unstable Nucleus: Over time, the unstable nucleus will undergo a process called
radioactive decay. During this decay, the atom’s nucleus breaks down and releases radiation.
 Types of Radiation: The radiation emitted can be one of three types:
o Alpha radiation (α): Large particles made of 2 protons and 2 neutrons.
o Beta radiation (β): High-energy electrons or positrons.
o Gamma radiation (γ): High-energy electromagnetic waves (like X-rays, but much stronger).
In 1889, a scientist named Rutherford discovered that there are two types of radiation emitted by a
substance called radium. These are called alpha radiation and beta radiation. Later, a scientist named
Willard discovered a third type, called gamma radiation.

To study these types of radiation, Rutherford did an experiment in 1902 where he passed the radiation
through two charged plates—one plate was negatively charged, and the other was positively charged. He
wanted to see how the radiation would behave when placed in this electric field.

Here’s what they found:

 Alpha rays: These rays were attracted slightly towards the negatively charged plate. This told
Rutherford that alpha rays have a positive charge because they were attracted to the negative plate
(opposites attract).
 Beta rays: These rays were attracted strongly towards the positively charged plate. This meant that
beta rays have a negative charge because they were drawn to the positive plate.
 Gamma rays: Gamma rays didn’t get attracted to either plate at all. This told Rutherford that
gamma rays are neutral and have no charge because they didn't respond to the electric field.

In simple terms, alpha rays are positively charged, beta rays are negatively charged, and gamma rays
have no charge at all. This experiment helped scientists understand that there are different types of
radiation, each with different properties!

In 1896, a French scientist named Henri Becquerel was studying a substance called pitchblende, which
contains uranium. He was also working with some unused photographic plates, which are special plates
used to take pictures, and kept them in a cardboard box in a drawer. There was a key lying on top of the
box, and Becquerel didn’t think much about it at the time.

By mistake, Becquerel left the uranium compound on the box for a few days. Later, he went to check the
photographic plates and washed them. To his surprise, the plates were cloudy and showed the shape of the
key—even though the plates had been kept in the dark.

This was very strange because the plates usually only get exposed to light, and there was no light in the
drawer. Becquerel thought that the uranium compound might be emitting invisible rays (similar to x-
rays) that could pass through the cardboard and the key, and expose the photographic plates. These rays
were later called Becquerel rays.

A few days after this discovery, another scientist, Marie Curie, found out that other substances, like
thorium, also had similar properties. These substances could also emit invisible rays without needing any
light.

In simple words, Becquerel accidentally discovered that uranium could give off invisible rays that could
expose photographic plates, even in the dark. This led to the discovery of radioactivity, and Becquerel rays
were named after him. Later, Madame Curie found that thorium also had this property.

Characteristics of alpha, beta and gamma rays

1. Nature

 Alpha Rays (α): These are made up of alpha particles, which consist of 2 protons and 2 neutrons.
You can think of them as tiny, heavy particles.
 Beta Rays (β): These are made up of beta particles, which are electrons (small, fast-moving
particles with a negative charge).
  Gamma Rays (γ): These are electromagnetic radiation (like light or X-rays) but with much higher
energy. They don’t have particles, just energy.

2. Mass

 Alpha Rays: The mass of alpha particles is about 4.0028 atomic mass units (u), which is relatively
heavy.
 Beta Rays: Beta particles (electrons) are much lighter, with a mass of 0.000548 u.
 Gamma Rays: Gamma rays don’t have any mass because they are pure energy.

3. Charge

 Alpha Rays: These particles have a positive charge (+2) because they have 2 protons, each with a
positive charge.
 Beta Rays: These particles have a negative charge (-1) because they are electrons, which carry a
negative charge.
 Gamma Rays: Gamma rays are electrically neutral, meaning they have no charge.

4. Velocity (Speed)

 Alpha Rays: Alpha particles move at about 1/5 to 1/20 the speed of light. They are slow compared
to other types of radiation.
 Beta Rays: Beta particles move much faster, about 1/5 to 9/10 the speed of light.
 Gamma Rays: Gamma rays travel at the speed of light, which is the fastest possible speed.

5. Deviation in Electric Field

 Alpha Rays: Alpha particles are positively charged, so they are attracted to a negatively charged
plate.
 Beta Rays: Beta particles (which are negatively charged) are attracted to a positively charged plate.
 Gamma Rays: Gamma rays have no charge, so they don’t get affected by electric fields. They don't
deviate or change direction.

6. Penetrating Power

 Alpha Rays: Alpha particles have low penetrating power. They can only go through very thin
materials (like an aluminum sheet of less than 0.02 mm thick). If you touch alpha-emitting
substances, they can be dangerous, but they are easily stopped by paper or skin.
 Beta Rays: Beta particles have more penetrating power than alpha particles. They can go through
aluminum sheets about 2 mm thick, which is 100 times more than alpha particles.
 Gamma Rays: Gamma rays have very high penetrating power. They can pass through 15 cm
thick lead, which is about 10,000 times more penetrating than alpha rays. That's why gamma rays
are so dangerous and difficult to shield against.

7. Ionization Power

 Alpha Rays: Alpha particles have very high ionization power. This means they can easily knock
electrons off atoms, creating charged particles (ions). Even though they can’t travel far, they can
cause a lot of damage to living cells in their path.
 Beta Rays: Beta particles have low ionization power compared to alpha particles. They can still
cause damage, but not as much as alpha rays.
 Gamma Rays: Gamma rays have very low ionization power. They are less likely to cause damage
directly by ionizing atoms but can still affect living tissue by passing through it.
8. Power to Produce Fluorescence

 Alpha Rays: Alpha particles have a very high ability to produce fluorescence, meaning they can
make certain materials glow brightly when they hit them.
 Beta Rays: Beta particles have a low ability to produce fluorescence.
 Gamma Rays: Gamma rays have a very low ability to produce fluorescence.

Summary of Key Differences

 Alpha Rays: Heavy, slow-moving, positive charge, low penetration, high ionization power, and can
make materials glow brightly.
 Beta Rays: Lighter, faster, negative charge, higher penetration than alpha rays, and low ionization
power.
 Gamma Rays: No mass or charge, travel at the speed of light, high penetration power, very low
ionization, and low ability to cause fluorescence.

Uses- Radioactive isotopes have many important uses, and they aren't just for making bombs. They are used
in different fields such as scientific research, medicine, agriculture, and industry. Radioactive substances can
be used in two ways:

1. By using the radiation alone: This means using the radiation (energy) that comes from the
radioactive material for various purposes, like detecting problems in machines or treating diseases.
2. By using the radioactive element itself: This involves using the actual radioactive material for its
properties, like helping in medical treatments or improving crop growth.

Natural radioactivity: Some elements, like those with atomic numbers between 82 and 92, naturally give
off radiation. These elements are called natural radioactive elements. They are found in nature and radiate
energy without any human intervention.

Artificial radioactive elements: In 1935, a couple named Frederic Joliot-Curie and Irene Joliot-Curie
discovered how to create radioactive elements in a lab. They bombarded certain elements with particles,
causing them to become radioactive. These are called artificial radioactive elements. Their invention was
so important that they won the Nobel Prize in 1935 for this discovery.

*Isotope- Atoms with the same number of protons but different numbers of neutrons are called
isotopes. They share almost the same chemical properties, but differ in mass and therefore in physical
properties.