Download Chemistry Lecture No.4______By : Asst. Led Tariq-H-AL

Chemistry Lecture No.4______By : Asst. Led Tariq-H-AL-Mgheer
A bombardment reaction occurs when particles of atomic or subatomic size strike
atoms of an element and change them into another element. For example, the
reaction between an alpha particle and a beryllium atom forms a carbon atom and a
neutron according to the following equation:
4Be
9
-
2He
4——> C12
6
+
For a bombardment reaction to occur, the bombarding particles must have enough
energy to overcome the highly charged nucleus of the target atom, especially when
the target atom has a high atomic mass. Most particles emitted by natural radioactive
isotopes do not have enough energy to do this, so their energies must be increased.
This can be done by an accelerator, a device that increases the speed of a charged
atomic or subatomic particle. Increasing the speed of a particle increases its energy
and therefore increases its effect on the atom it hits. MEDICAL USES OF
RADIOACTIVE ISOTOPES
Radiation from radioactive isotopes is used extensively in medicine to treat
cancer. The radiation is directed at the cancer cetis from either outside or inside the
body, depending on the type of cancer. The most widely used external source of
radiation is cobalt-60. This isotope of cobalt has a half-life of 5.5 years and is .3
powerful beta and gamma emitter. The sample of cobalt-60 is placed in a lead
container with an opening that allows its radiation to be directed to the site of the
cancer.
The use of radioactive isotopes internally to treat cancer is based on the fact that all
isotopes of an element, radioactive or not, have identical electron arrangements and
consequently identical chemical properties .For example, when taken internally, the
iodide ion from sodium iodide is eventually concentrated in the thyroid gland. Use is
made of this fact to treat thyroid cancer. Iodine-131, a radioactive isotope of iodine is
used. A patient is given a drink of water containing sodium iodide. Some of the iodide
ions are radioactive. When these, ions are absorbed by the thyroid gland, radiation
from their decay destroys the cancer cell. Other radioactive isotopes used to treat
cancer are given in Table3
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