The Story of Radioactivity

Author: Deepanshu S. (IG: @quantum.man)

SCG ID: 1606201903

Introduction

Radioactivity is the process by which an unstable atomic nuclei loses energy in form of α – particles, β – particles or γ – radiation to attain stability.

Story of discovery

It was the year 1896 when Antoine Henri Becquerel was trying to studying the properties of x-rays by using potassium uranyl sulfate [K2(UO2)(SO4)2], a naturally fluorescent mineral.

He exposed potassium uranyl sulfate [K2(UO2)(SO4)2] to sunlight and then placed it on photographic plates wrapped in black paper. He placed this setup near the window in his laboratory, believing that the uranium will absorb the sun’s energy and then emit it as x-rays. By placing the setup for several hours in enough sunlight, he placed the system in dark for a few hours. After this, he developed his photographic plates, which were wrapped in the black paper.

The results satisfied his expectations, there were traces of any kind of radiation emitted by uranium. He believes that this radiation is x-rays, so he announced to demonstrate his finding during a public lecture in Paris on the 26th-27th of February.

But his hypothesis was disproved when he refused to perform the experiment because it was overcast in Paris during those two days, and believed that sunlight was crucial for his experiment.

He went back to his laboratory and placed the experimental setup in a dark drawer of his study desk. After some days Becquerel decided to develop his photographic plates anyways. To his surprise, the images were strong and clear, proving that the uranium emitted radiation without an external source of energy such as the sun. Becquerel was surprised to see the results.

Now he was sure that the radiation coming out of the uranium was not x-rays, but something else.

“He discovered radioactivity.”

Becquerel used an apparatus to show that the radiation he discovered are not x-rays because x-rays are neutral and do not bend in magnetic field, whereas the new radiation was bent by the magnetic field so that the radiation must be charged and different than x-rays. When different radioactive substances were put in the magnetic field, they deflected in different directions or not at all, showing that there were three types of radiations: negative, positive, and electrically neutral.

The term radioactivity was actually coined by Marie Curie, who together with her husband Pierre, began investigating the phenomenon recently discovered by Becquerel. The Curies extracted uranium from ore and to their surprise found that the leftover ore showed more activity than the pure uranium. They concluded that the ore contained other radioactive elements. This led to the discoveries of the elements polonium and radium. It took four more years of processing tons of ore to isolate enough of each element to determine their chemical properties.

Ernest Rutherford, who did many experiments studying the properties of radioactive decay, named this alpha, beta, and gamma particles, and classified them by their ability to penetrate matter.

Cause of Radioactivity

Radioactivity is caused in the same way but appears in three different types: alpha, beta and gamma. In alpha decay, alpha particles are identical to helium nuclei, which are made of two protons and two neutrons bond together. Initially, the alpha particle escapes the nucleus of a parent atom and is further repelled from its sources by various processes of quantum mechanics. These processes change the original atom from an alpha particle into a different element, which lowers its mass and atomic numbers.

Beta radioactivity occurs in two types. During the first type of decay, emissions occur from the transformation of one of a nucleus' neutrons into a proton, an electron and an antineutrino. The second type of beta decay is similar in process but involves the transformation of a proton into a neutron, neutrino and positron.

Gamma decay takes place after a nucleus undergoes alpha or beta decay and results in the hyperstimulation of a nucleus. Gamma radiation is the most intense form of radioactivity and has strong penetrating capacities.

Types of Radioactive decay

• α – decay

• β – decay

• γ – decay

α – decay

In alpha decay the nucleus emits a 4He nucleus, an alpha particle. Alpha decay occurs most often in massive nuclei that have too large a proton to neutron ratio. An alpha particle, with its two protons and two neutrons, is a very stable configuration of particles. Alpha radiation reduces the ratio of protons to neutrons in the parent nucleus, bringing it to a more stable configuration.

Also, a Q-Value is also produces which is indeed the measure of vibration/thermal energy produced during this decay.

Example -

β – decay

β – decay is of two types –

Example –

Example –

γ – decay

In gamma decay a nucleus changes from a higher energy state to a lower energy state through the emission of electromagnetic radiation (photons).

The number of protons (and neutrons) in the nucleus does not change in this process, so the parent and daughter atoms are the same chemical element. In the gamma decay of a nucleus, the emitted photon and recoiling nucleus each have a well-defined energy after the decay. The characteristic energy is divided between only two particles.

Example –

Applications –

1. Transmutation is achieved by the notion of radioactivity. Lead has been converted into Gold, moreover, the production cost was so high that it is not an economically beneficial process.

2. Medical applications and improvement in drug delivery mechanism. Advancement in treatments for cancer is a blooming research topic.

3. Advancement in electricity and fuel production.

Resources:

https://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Nuclear_Chemistry/Radioactivity/Discovery_of_Radioactivity

http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/electromagnetic_spectrum/electromagneticspectrumrev5.shtml

http://www2.lbl.gov/abc/wallchart/chapters/03/4.html

http://www.radioactivity.eu.com/site/pages/Important_nuclei.htm

Books and Articles:

1. Naomi Pacachoff, Marie Curie and the Science of Radioactivity, Oxford University Press, 1997.

2. Bjorn Walhstrom, Understanding Radiation, Medical Physics Pub. Corp., 1996.