Understanding Radioactivity: Discovery, Definition, Types, and Units | 10th Science

Radioactivity - Discovery, Definition, Types, Units

1. Discovery of radioactivity

In 1896, French physicist Henri Becquerel finished his research for the week and stored a certain amount of uranium compound away in a drawer for the week end. By chance, an unexposed photographic plate was also stored in the same drawer. After a week he returned and noticed that the film had been exposed to some radiation. He discovered that he could reproduce the effect whenever he placed uranium near a photographic film. Apparently, uranium radiated something that could affect a photographic plate. This phenomenon was called as Radioactivity. Uranium was identified to be a radioactive element.

Two years later, the Polish physicist Marie Curie and her husband Pierre Curie detected radioactivity in 'Pitchblende', a tiny black substance. They were not surprised at the radioactivity of pitchblende, which is known as an ore of uranium. Later, they discovered that the radiation was more intense from pure uranium. Also, it was found that the pitchblende had less concentration of uranium. They concluded that some other substance was present in pitchblende. After separating this new substance, they discovered that it had unknown chemical properties and it also emitted radiations spontaneously like uranium. They named this new substance as 'Radium'. The radioactive elements emit harmful radioactive radiations like alpha rays or beta rays or gamma rays.

2. Definition of radioactivity

The nucleus of some elements is unstable. Such nuclei undergo nuclear decay and get converted into more stable nuclei. During this nuclear reaction, these nuclei emit certain harmful radiations and elementary particles. The phenomenon of nuclear decay of certain elements with the emission of radiations like alpha, beta, and gamma rays is called 'radioactivity' and the elements, which undergo this phenomenon are called 'radioactive elements'.

3. Natural Radioactivity

The elements such as uranium and radium undergo radioactivity and emit the radiations on their own without any human intervention. This phenomenon of spontaneous emission of radiation from certain elements on their own is called 'natural radioactivity'.

The elements whose atomic number is more than 83 undergo spontaneous radioactivity. Eg: uranium, radium, etc. There are only two elements, which have been identified as radioactive substances with atomic number less than 83. They are technetium (Tc) with atomic number 43 and promethium (Pm) with atomic number 61.

4. Artificial Radioactivity (or) Induced Radioactivity

The phenomenon by which even light elements are made radioactive, by artificial or induced methods, is called 'artificial radioactivity' or 'man-made radioactivity'.

This kind of radioactivity was discovered by Irene Curie and F.Joliot in 1934. Artificial radioactivity is induced in certain lighter elements like boron, aluminium etc., by bombarding them with radiations such as 'alpha particles' emitted during the natural radioactivity of uranium. This also results in the emission of invisible radiations and elementary particles. During such a disintegration, the nucleus which undergoes disintegration is called 'parent nucleus' and that which is produced after the disintegration is called a 'daughter nucleus'.

The particle, which is used to induce the artificial disintegration is termed as projectile and the particle which is produced after the disintegration is termed as ejected particle. When the projectile hits the parent nucleus, it is converted into an unstable nucleus, which in turn decays spontaneously emitting the daughter nucleus along with an ejected particle.

If you denote the parent and daughter nuclei as X and Y respectively, then the nuclear disintegration is represented as follows: X (P,E) Y. Here, P and E represent the projectile particle and ejected particle respectively.

Comparison between Natural and Artificial Radioactivity

Natural radioactivity

1. Emission of radiation due to self-disintegration of a nucleus.

2. Alpha, beta and gamma radiations are emitted.

3. It is a spontaneous process.

4. Exhibited by elements with atomic number more than 83.

5. This cannot be controlled.

Artificial radioactivity

1. Emission of radiation due to disintegration of a nucleus through induced process.

2. Mostly elementary particles such as neutron, positron, etc. are emitted.

3. It is an induced process.

4. Exhibited by elements with atomic number less than 83.

5. This can be controlled.

Example:

In the above nuclear reaction, ₆C^13* is unstable and is radioactive. This reaction can be represented as ₄Be⁹ (α, n) ₆C¹²

5. Units of Radioactivity

Curie: It is the traditional unit of radioactivity. It is defined as the quantity of a radioactive substance which undergoes 3.7 × 10¹⁰ disintegrations in one second. This is actually close to the activity of 1 g of radium 226.

1 curie = 3.7 × 10¹⁰ disintegrations per second.

Rutherford (Rd): It is another unit of radioactivity. It is defined as the quantity of a radioactive substance, which produces 10⁶ disintegrations in one second.

1 Rd = 10⁶ disintegrations per second.

Becquerel (Bq): It is The SI unit of radioactivity is becquerel. It is defined as the quantity of one disintegration per second.

Roentgen (R): It is The radiation exposure of γ and x-rays is measured by another unit called roentgen. One roentgen is defined as the quantity of radioactive substance which produces a charge of 2.58 × 10^-4 coulomb in 1 kg of air under standard conditions of pressure, temperature and humidity.

Marie Curie

Contributions, life, and interesting facts

Marie Curie was a scientist who studied physics, chemistry, and mathematics. She was born on November 7, 1867, in Warsaw, Poland. Marie was the youngest of her family, and had 3 sisters and 1 brother. She had two children, and her husband was Pierre Curie. Her children are Irene Joliot-Curie, and Eve Curie. (Both dead now. Eve died in 2007.) Marie died on July 4, 1934, at the Sancellemoz Sanatorium in Passy, in Haute- Savoie.

Marie Sklodowska Curie was a chemist. Marie created a theory of radioactivity. She discovered the element polonium, which is number 84 in the Periodic Table of Elements. Mrs. Curie also founded radium, number 88 in the PTE (For PTE, see previous sentence.)Radium steadily emits rays. It was also under her personal direction that the world’s first studies were conducted into treatment on neoplasms (cancers).

Curie helped soldiers during World War I. Mrs. Curie used mobile radiography units for the treatment of wounded soldiers in World War I. She also used X-rays. A little later, Curie began to use a technique pioneered in Dublin to collect Radon--- a radioactive gas that radium steadily emits. Later on, during the spring of 1919, she offered radiology courses to a group of American soldiers who remained in France while awaiting passage home.

Marie helped raise funds for an institute.  Marie founded the Radium Institute in her hometown (Warsaw). At first it was called the Radium Institute, but now it is called the Maria Sklodowska-Curie Institute of Oncology. She toured the US in 1921 to raise funds for radium research, and succeeded in equipping this institute. (Do you get it? The fund is the 3rd contribution.)

Some interesting facts about her is that she died from aplastic anemia due to exposure to radiation, won 2 Nobel Prizes, won a Davy Medal, won a Matteucci Medal, people made a statue in honor of her in Lublin, Poland, and she and her husband used some of her Nobel Prize money to install modern plumbing with a bathroom and replace the wallpaper in their Parisian home.