General chemistry
Al-Farahidi University / Medical
technical college
Anesthesia Department
Lecture 4
Radio activity and radioactive isotopes
Radio activity and radioactive isotopes
Introduction:
• All substances are made of atoms.
• These have electrons (e-) around the outside (negatively
charged) and a nucleus in the middle.
• The nucleus consists of protons (positively charged) and
neutrons (neutral).
• The mass number is the (atomic number of an atom is the
number of protons) + (neutrons) in its nucleus.
Mass Number (A) = P+N
Figure 1: The Atom
Isotopes:
Isotopes are nuclides with the same atomic number, but a
different mass numbers.
Figure 2: Isotopes of Hydrogen
Figure 3: Isotopes of Carbon
Figure 4: Isotopes of Uranium-238 VS Uranium-235
Radiation:
It refers to particles or waves coming from the nucleus of the
atom through which the atom attempts to attain a more stable
configuration.
Figure 5: Radiation
Radioactivity:
The process in which an unstable isotope undergoes changes
until a stable state is reached and in the transformation emits
energy in the form of radiation (alpha particles, beta particles
and gamma rays). The elements which undergo this process are
called (radioactive isotopes, radioisotopes, radionuclides).
Figure 6: Radio activity decay
Radioactive Isotopes properties:
• It has same chemical properties
• It has different physical properties
• Emits radiation
• Half-life (t 1/2).
• Penetration property.
Half-life of radioisotopes:
• Half-life of radioisotopes is the time period required for
radio nuclide to decay to one half the amounts originally
present.
• Abbreviated (t1/2).
• T1/2 = 0.693/λ.
• λ is decay constant, a characteristic of given isotope
decaying in unit time.
Table 1: Half-Life of some radioactive isotopes
Differences between stable isotopes and radioactive
isotopes:
Measurement of radioactivity:
• Gas ionization detectors.
• Autoradiography.
• Fluorescent scintillation.
Applications of Radioactive Isotopes:
• Scientific research.
• Analytical.
• Diagnostic.
• Therapeutic.
Uses:
• Radioisotopes are widely used in study of the mechanism
and rate of absorption, accumulation & translocation of
inorganic and organic compounds in the animal.
• Radiolabeled drugs are useful in pharm-kinetic studies
(site of accumulation, rate of accumulation, rate of
metabolism & metabolic products).
Analytical application of radioisotopes:
• Virtually any enzyme reaction can be assayed using
radioactive tracer methods
• Radioisotopes have been used in study of:
1. The mechanism of enzyme action.
2. In studies of ligand binding to membrane receptors.
• Isotopes dilution analysis: when a known amount of
radioactive tracer is introduced into unknown volume,
after thorough mixing, the concentration of radio tracer is
estimated.
V =N/n
V: Volume to be measured.
N: Total number of counts injected.
n: Number of counts per ml.
• By isotope dilution analysis plasma volume, total body
water, E.C.F volume, RBC cell volume, total exchangeable
sodium can be measured.
• 131
I labeled human serum albumin useful in diagnosing
protein losing enteropathy.
• 51
Cr labeled RBC are given intra venously if there is any
GI blood loss radioactivity can be measured.
• Radio immune assays (RIA) are useful in analysis of
hormones, growth factors, tumour markers, cytokines,
bacterial antigens, Vitamin D and various biological
molecules.
• In RIA either antigen or antibody is radiolabeled.
• Radiolabelling must not interfere in the binding of antigen
and antibody, has to be compared with unlabeled ones.
Radioisotopes used in diagnostic purposes:
• Radioactive iodine uptake and imaging reveals the
functional status of thyroid tissue, including modules,
whole thyroid gland.
• 131
I is used for thyroid cancer imaging and management.
• 123
I is used for thyroid.
• Xenon 133 is useful in lung function tests and in
diagnosing malfunctions of lung ventilation.
• 133
I iodohippuric acid used in diagnosis of kidney
infections, kidney blockages or imbalance of function
between two kidneys.
Therapeutic uses of radioisotopes:
• Radioisotopes have role in management of malignancies.
• Tumor tissues are attacked by beam of radiation.
• From outside the patient's body (External sources).
• From within the body (Internal sources).
Radiation hazards:
• Radiation may cause the following:
1. Deposit energy in body.
2. Cause DNA damage.
3. Create ionization in body leading to free radicals.
• These hazards which may lead to biological damage.
Radiation safety and protection:
• The most popular triad radiation protection is (time,
distance and shield (TDS).
• Minimum possible time should be spent near the radiation
zone.
• Handling of radioactive material should be done from
maximum possible distance.
• Person should be shielded by lead.
• Minimize the time and you will minimize the dose.
• Pre-plan the experiment to minimize exposure time.
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