In the late years of the 19th century scientists were interested in experiments about the rays that certain elements were emitting. After various experiments they found that there was a different ray then x rays which could go further and deeper and could pass thicker obstacles through experiments. Soon a scientist called Becquerel discovered that various substances containing uranium admixtures emitted such radiation. This new phenomenon was to be called radioactivity.

Rutherford and others began studying the nature of the rays emitted in radioactivity about They found that the rays could be classified into three distinct types according to their penetrating power. One type of the radiation could barely penetrate a piece of paper. The second type could pass through as much as 3mm of aluminum. The third was extremely penetrating: it could pass trough several centimeters of lead and still be detected on the other side. They named these three types of radiation alpha (α), beta (β) and gamma (γ), respectively, after the first three letters of the Greek alphabet.

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The alpha decay occurs when the nucleus of an element emits an alpha particle which is two protons and two neutrons. This is a simple helium atom with no electron present. An example of this is a uranium- 238 atom decaying into into a thorium-234 atom and an alpha particle (helium-4 nucleus, i.e. 2 protons and 2 neutrons).

p + Li Be + 2 He proton + lithium beryllium + 2 alpha particles ( )

As you may wonder; why does alpha decay occur? Alpha decay occurs because the strong nuclear force is unable to hold very large nuclei together. Because the nuclear force is a short- range force, it acts only between neighboring nucleons. For every nuclei, the large atomic number means the repulsive force becomes very large (Coulomb's law) and it acts between all protons. The strong nuclear force, since it acts only between neighboring nucleons, is overpowered and is unable to hold the nucleus together.

But if there is a repelling force between the protons why not all the protons leave the nucleus? This should be explained by another force holding them together called as Strong Nuclear Force.

Indeed, the question arises as how a nucleus stays together at all in the view of the fact that the electric force between protons would tend to break it apart since stable nuclei stay together,it is clear that another force must be acting.

Because this force is stronger than the electric force it is called the strong nuclear force. The strong nuclear force is an attractive force that acts between all nucleons-protons and neutrons - alike. Thus,protons attract each other via the nuclear force and at the same time they repel each other via the lectric force. Neutrons, since they are electrically neutral, only attract other neutrons or protons via the nuclear force. This way, the nucleus does not break apart and stay together.

Alpha decay is an exothermic process. As the nucleus becomes more stable, it liberates a net amount of energy due to this. Therefore, the tendency for minimum enthalpy is fulfilled. Also, the decay’s entropy can be said to be positive; the places the particles can exist increase. Under these conditions, it can be said that Alpha decay is always spontaneous.

This type of decay occurs naturally in uranium and is an example of "spontaneous decay". The uranium atom doesn't just break apart. As it decays, each of the two resulting elements (the thorium and α-particle) fly apart at high speed. In other words they both have kinetic energy. It is possible to measure the mass of the original uranium atom and the masses of the two resultant particles. This is done by measuring the momentum of each particle as it strikes a sensor. When these measurements are taken it is found that the total mass of the two smaller particles is less than the mass of the original uranium particle. Some mass must have been turned into (mostly kinetic) energy. So as we have said the mass and energy is not conserved during a radiation. Energy Changes in Alpha Decay

Write a balanced equation for the following process: Np (Np turns into Pa) Answer: Np Pa + He

Write a balanced equation for the process that is described below: Uranium (235); which is used in atomic bombs, decays initially by alpha particle production. U Th + He

When an alpha decay occcurs; 1) Mass number decreases by 2 2) It’s chemical properties change 3) Neutron number decreases by 2 Which of the following above statements are correct? A)Only 1 B)1 and 2 C) 2 and 3 D) 1 and 3 E) 1,2 and 3 Answer : C

When the atom Ra makes 3 alpha radiation what would be the neutrons number of the newly formed element? A) 214 B) 164 C) 142 D) 132 E) 82 Answer: Ra 3 He+ X 3 x 4= = x 2 = =82 X 214 – 82 = 132 So the answer is D.

QUESTION THAT WAS NOT ANSWERED... Why does in alpha decay a simple helium atom is emitted instead of saperate individual particles??

There was a lot of verbal and written mistakes. I did not talked deeply about the subjects such as energy change during alpha radiation which can last for a very long time. I could not answer some of the questions came from the class.

The subjects were presented in a very easy level. It was easy to understand the topics and contents but scientifically the presentation is not enough. Many subjects that should have been placed in the presentation was skipped so it was not sufficent.