Radioactivity I

Basic Science JSS3 Third term

Sub-theme: You and energy

Theme: Science and development

WEEK 1

Radioactivity I

Performance Objectives

The student should be able to:

1. Define Radioactivity
2. Name some Radioactive elements

Content

Radioactivity

Everything on Earth is made of atoms, but you can see that not everything on Earth is the same. This is because everything is made of different types of atoms called elements. Atoms are really, really small, but each atom of an element is made of even smaller subatomic particles. These are the protons, neutrons, and electrons of the atom.

The nuclei of some certain elements are not stable, hence they disintegrate and simultaneously emit certain kinds of radiation, and in the process, change into the nuclei of other elements. This phenomenon is known as radioactivity.

Radioactivity is the spontaneous disintegration of atomic nuclei by the emission of subatomic particles called alpha, beta, and electromagnetic rays called X-rays or gamma rays.

A brief history on the discovery of radioactivity

In 1896 Henri Becquerel was using naturally fluorescent minerals to study the properties of x-rays, which had been discovered in 1895 by Wilhelm Roentgen. He exposed potassium uranyl sulfate to sunlight and then placed it on photographic plates wrapped in black paper, believing that the uranium absorbed the sun’s energy and then emitted it as x-rays. This hypothesis was disproved on the 26^th-27^th of February when his experiment "failed" because it was overcast in Paris. For some reason, Becquerel decided to develop his photographic plates anyway. 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 had discovered radioactivity.

Becquerel used an apparatus similar to that displayed below to show that the radiation he discovered could not be x-rays. X-rays are neutral and cannot be bent in a magnetic field. 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 classes of radioactivity: 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.

Radioactive elements

This is a list or table of elements that are radioactive. Keep in mind, all elements can have radioactive isotopes. If enough neutrons are added to an atom, it becomes unstable and decays. A good example of this is tritium, a radioactive isotope of hydrogen naturally present at extremely low levels. This table contains the elements that have no stable isotopes. Each element is followed by the most stable known isotope and its half-life.

Note increasing atomic numbers doesn't necessarily make an atom more unstable. Scientists predict there may be islands of stability in the periodic table, where super heavy transuranium elements may be more stable (although still radioactive) than some lighter elements.
This list is sorted by increasing atomic number.

Radioactive Elements

Element	Most Stable Isotope	Half-life of Most Stable Isotope
Technetium	Tc-91	4.21 x 106 years
Promethium	Pm-145	17.4 years
Polonium	Po-209	102 years
Astatine	At-210	8.1 hours
Radon	Rn-222	3.82 days
Francium	Fr-223	22 minutes
Radium	Ra-226	1600 years
Actinium	Ac-227	21.77 years
Thorium	Th-229	7.54 x 104 years
Protactinium	Pa-231	3.28 x 104 years
Uranium	U-236	2.34 x 107 years
Neptunium	Np-237	2.14 x 106 years
Plutonium	Pu-244	8.00 x 107 years
Americium	Am-243	7370 years
Curium	Cm-247	1.56 x 107 years
Berkelium	Bk-247	1380 years
Californium	Cf-251	898 years
Einsteinium	Es-252	471.7 days
Fermium	Fm-257	100.5 days
Mendelevium	Md-258	51.5 days
Nobelium	No-259	58 minutes
Lawrencium	Lr-262	4 hours
Rutherfordium	Rf-265	13 hours
Dubnium	Db-268	32 hours
Seaborgium	Sg-271	2.4 minutes
Bohrium	Bh-267	17 seconds
Hassium	Hs-269	9.7 seconds
Meitnerium	Mt-276	0.72 seconds
Darmstadtium	Ds-281	11.1 seconds
Roentgenium	Rg-281	26 seconds
Copernicium	Cn-285	29 seconds
Nihonium	Nh-284	0.48 seconds
Flerovium	Fl-289	2.65 seconds
Moscovium	Mc-289	87 milliseconds
Livermorium	Lv-293	61 milliseconds
Tennessee	Unknown
Oganesson	Og-294	1.8 milliseconds