Radioactivity

1. Radioactivity Its Nature, History, Uses and Effects

2. What is radioactivity? • Radioactivity describes an atom which undergoes radioactive decay. • Radioactive decay is when an unstable atom of an element emits radiations in the form of electromagnetic waves or particles; to stabilize itself.

3. Discovery of radioactivity • In 1896, Henri Becquerel, a French scientist, discovered radiation. He had had his thoughts about phosphorescent materials, which glowed in the dark after being exposed to light for an interval of time, and suspected they emitted radiations similar to x-rays or sunlight. He approached different chemicals, beginning with phosphorescent ones to a photographic plate, and found that it had blackened, in the dark, only when exposed to a Uranium salt. He then concluded that Uranium emits radiations, similar to light radiations that blacken photographic plates. • It was thought by early scientists that radiations emitted by substances like uranium were similar to x-rays, which were recently discovered at the time. However, work by future scientists, most notably the Curies and Ernest Rutherford, proved that these types of radiations were much more complex. • Marie and Pierre Curie, worked for several years and successfully discovered two radioactive elements: Radium and Polonium. Marie’s death was almost certainly due to prolonged exposure to radiation.

4. Isotopes • All atoms of the same element have the same number of protons and electrons. For example, all Chlorine atoms have 17 electrons and 17 protons in them. • However, some elements have atoms with different numbers of neutrons. Each atom with a certain number of neutrons is called an isotope. 18 Neutrons 20 Neutrons Chlorine Chlorine Isotope: Cl-35 Isotope: Cl-37

5. Why some Isotopes are unstable, thus radioactive • The protons and neutrons in the nucleus of an atom are affected by many interactions between them and electrons. • There are three main forces that affect them: • Electrostatic attraction force: Between electrons and protons (The attraction between positive and negative particles). • : Between protons and neutrons. • Weak nuclear force: Between particles in the nucleus. • Particles called pions are exchanged between the neutrons and the protons, maintaining the relative stability of the nucleus. • The strong nuclear force is only effective when the number of protons is roughly equal to the number of neutrons. • In some isotopes, this is not the case, which makes the repulsion between protons and the strong nuclear force work against each other, leading to instability in the atoms. • Thus alpha decay occurs, to stabilize the atoms. Strong nuclear force

6. α Alpha decay • The unstable atom ‘needs’ to get rid of some of its neutrons and protons to become more stable. • It emits alpha rays: a series of alpha particles, which are basically 2 Neutrons and 2 Protons together. Alpha decay turns the atom of an element into an atom of another element with 2 less protons. • Radium, a radioactive element, emits an alpha particle, losing 2 Protons and 2 Neutrons, which turns it into another radioactive element, Radon, an inert gas.

7. β Beta Decay • Due to weak nuclear interaction (force), when a nucleus is unstable, it emits beta rays, which are streams of beta particles. • There are two types of beta particles: • Beta Minus Particle, β-, which is an electron • Beta Plus Particle, β+, which is a positron.

8. Gamma Rays • Alpha particles are very unstable, or excited. • Unstable particles, such as alpha or some nuclei, emit gamma rays to stabilize themselves. • Gamma rays are electromagnetic waves, or light emissions, that have a very short wavelength, thus high energy, which makes them very hard to shield. • Although they have many uses, they could be very dangerous, and are carcinogenic.

9. Uses of radioactive isotopes • Uranium 235 can cause what is known as a fission chain reaction, which releases huge amounts of energy. This reaction could be contained and slowed down to release energy gradually, which is what happens in nuclear power plants. However, in nuclear weapons, it is left to react to a critical point, where a nuclear explosion occurs.

10. Uses of radioactive isotopes • Carbon 14 is used in carbon dating, to determine the age of carbonaceous materials with ages up to 40,000 years. • Radium produces radon gas, which when used properly in medicine, works as a cancer treatment. However, better treatments with radioactive isotopes of Cobalt and Caesium have come to use since the mid 90’s. • Isotopes like carbon-11, potassium-40, nitrogen-13, oxygen-15, fluorine-18, and iodine-12 are used in positron emission tomography, a technique for medical imaging. It produces a three-dimensional image or map of functional processes in the body, by utilizing gamma rays in a non-harmful exposure.

13. Uses of radioactive isotopes • Gamma rays kill living organisms when given in high doses, so they are used in sterilizing medical equipment (as an alternative to autoclaves or chemical means) and in removing decay-causing bacteria from many foodstuffs. • Despite their cancer-causing properties, gamma rays are also used to kill some tumors. In the procedure called Gamma Knife surgery, multiple concentrated beams of gamma rays are directed carefully on the tumor in order to kill the cancerous cells, but not any other cells.

14. Ionizing Radiation • Ionizing radiation is when radiation, in the form of particles or waves, causes atoms or molecules to turn into ions. This is what causes mutations and cancer, as molecules of DNA are sometimes damaged beyond repair. • Radiations in general, whether they were Alpha, Beta, Gamma, Ultraviolet or X-Ray, are ionizing if they have enough energy. • This has led scientists to predict that prolonged proximity with electromagnetic fields around electric devices is one of the reasons that lead to cancer. Other studies have linked excess ultraviolet radiation to skin cancer.

15. Shielding and The Geiger Counter • Alpha rays could be shielded with a sheet of paper. • Beta rays need at least a sheet of aluminum to be shielded. • Gamma rays are the hardest to shield, and require materials with high atomic numbers and high density, such as lead or concrete. This makes them the most feared kind of radiation. • Geiger counters are used to detect radiation, usually alpha and beta radiation, but also other types of radiation as well, through measuring ionizing radiation.

16. References/Sources • Google Images • Microsoft Encarta • Wikipedia Prepared and presented by Ahmed Ghoneim