radio activity and nuclear chemistry

Radio activity and nuclear chemistry

Radio activity: is a term given to describe the emission of radiation from samples (atoms) of certain elements. The elements which have isotopes some are stable and others unstable, the nuclei of unstable isotopes undergo nuclear reaction (decay) which cause new nucleus and energy. The new nucleus either stable or unstable, the unstable decay and give a stable nucleus.


Types of Radiation: Rutherford discovered three different types of radiation, when he put a piece of radio active substance in electric field:1- α-ray (heavy particles) +ve (proton).2- β-ray (light particles) –ve (electron).3- γ-ray (not affected) not charged.


- Alpha emission (α-ray particle): It consist of a stream of positively charged nuclei of He atoms called alpha particles.Its common for atoms have atomic mass more than 209, and atomic no. greater than 82 - it reduced the no. of {p} by – 2- and the no. of {n} by – 2 – {24He}. This type of radiation travel with a speed about one-tenth the speed of light and have very slight penetrating power as a result do little damage to internal organs, because they can not penetrating the skin but if substance that emit α – ray gets inside the body by swallowed or inhaled, the α-par. Can then damage internal organs.


Ex.:- 23892U 23490Th +42He 21084Po 20682Pb +42He- β –emission (β –ray particles):- It consist of a stream of electron or β-particles.The no. of neutrons (n) is decreased by – 1 – and the no. of protons (p) is increased by – 1 - , so the ratio of n/p is decreased, but the mass no. is not changed β-emission travel much faster than (α) can penetrate the skin and causes the skin to appear burned.


This type of rad. traveled as fast as light and have intermediate penetrating power. During β-decay one of neutron changed into proton (stay in nuclei) and electron (emitted) which lead to increase in atomic no. but mass no. not change. Ex.:- 8235Br β-decay 8236Kr + 0-1e 146C β-decay 147N + 0-1e 2712Mg β-decay 2713Al + 0-1e


- γ–emission:- Its not a particle but a form of energy similar to light waves or x-ray. This rad. Has high energy and occurs along with α & β emission and can penetrate deep in the body and cause serious damage to the cells. This kind has a higher penetrating power, it can be stopped by block of lead, Ex.:- 24094Pu 23692U + 42He + γ 22688Ra 22286Rn + 42He + γ There are two types of radiation less common but still important. 1- neutron 2-positron emission (+ve electron) 0+1e.



Positron emission: means ejection of +ve electron from the nucleus, it has the same mass as an electron with opposite charge (01e). It arises from the conversion of a nuclear proton into neutron, as a result a decrease by – 1 – in no. of proton and increase by one in no. of neutron, but no change in mass no. occur Ex.:- 3819K 3818Ar + 01e 158O 157N + 01e 2312Mg 2311Na + 01e

Effect of radiation on the living system

Ionizing radiation: Radiation from radio active isotop which can ionize the matter. The effect of radiation on living system causes damage to the cells. When the living molecules are affected such as RNA or DNA, this damage will happen by two ways 1-direct effect. when the radiation changes the structure or break down the living macromolecules which will cause a damage of the living cells: x+ + y – (Two ionic parts) DNA or RNA hט radiation x . + y . ( Two or more free radicals )


2- Indirect effect:- When the radiation break down the non living molecules which can be replaced or substituted or reformed again. In this case no damage will happen for ex: H2O hט OH - + H+ or: H2O hט H. +OH.But if these ions or free radicals hits the living molecules, living cell will be affected or damaged. By the high energy ions or free radicals or others. if the DNA destroyed, the cell will not divide and it will be die. But if DNA is damage it will cause abnormal division to produce new cells with altered DNA


Such cells will not be under control of the body called cancer cells which grow and divide under fission and destroying the normal cells. Its clear that exposure to radiation is dangerous? According to one theory called 1) Threshold theory no damage occurs below a certain level of radiation. Opposed to this is the 2) Linear theory according to this the risk of damage is proportional to exposure even down to very low levels of radiation. The radiation can not be detected by human body because we can not feel, smell or see ionized radiation but we have methods to detect this radiation. 1- Geiger counter. 2- Scintillation counter. 3- Photographic method. Each person wears a badge containing a piece of film.