Lecture 4: Isotopes - University of the Prophets PDF

‫د رياض حنيوه‬ ‫جامعه وارث االنبياء‬ lecture 4 ‫كليه الطب‬ ‫قسم الكيمياء الحيوية والطبية‬ Isotopes isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and...

‫د رياض حنيوه‬ ‫جامعه وارث االنبياء‬ lecture 4 ‫كليه الطب‬ ‫قسم الكيمياء الحيوية والطبية‬ Isotopes isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) due to different numbers of neutrons in their nuclei. While all isotopes of a given element have almost the same chemical properties, they have different atomic masses and physical properties. The number of protons within the atom's nucleus is called atomic number and is equal to the number of electrons in the neutral (nonionized) atom. Each atomic number identifies a specific element, but not the isotope; an atom of a given element may have a wide range in its number of neutrons. The number of nucleons (both protons and neutrons) in the nucleus is the atom's mass number, and each isotope of a given element has a different mass number. For example, carbon-12, carbon-13, and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13, and 14, respectively. The atomic number of carbon is 6, which means that every carbon atom has 6 protons so that the neutron numbers of these isotopes are 6, 7, and 8 respectively. 1 ‫جامعه وارث االنبياء‬ ‫د رياض حنيوه‬ ‫كليه الطب‬ ‫‪lecture 4‬‬ ‫قسم الكيمياء الحيوية والطبية‬ ‫‪2‬‬ ‫د رياض حنيوه‬ ‫جامعه وارث االنبياء‬ lecture 4 ‫كليه الطب‬ ‫قسم الكيمياء الحيوية والطبية‬ Isotope Facts       All elements have isotopes. There are two main types of isotopes: stable and unstable (radioactive). There are 254 known stable isotopes. All artificial (lab-made) isotopes are unstable and therefore radioactive; scientists call them radioisotopes. Some elements can only exist in an unstable form (for example, uranium). Hydrogen is the only element whose isotopes have unique names: deuterium for hydrogen with one neutron and tritium for hydrogen with two neutrons. Stable Isotopes Stable isotopes have a stable proton-neutron combination and do not display any sign of decay. This stability comes from the amount of neutrons present in an atom. If an atom has too many or too few neutrons, it is unstable and tends to disintegrate. Since stable isotopes do not decay, they do not produce radiation or its associated health risks. A radioactive isotope is an isotope whose nucleus readily decays, giving off subatomic particles and electromagnetic energy. Different radioactive isotopes (also called radioisotopes) differ in their half-life, the time it takes for half of any size sample of an isotope to decay. For example, the half-life of tritium—a radioisotope of hydrogen—is about 12 years, indicating it takes 12 years for half of the tritium nuclei in a sample to decay. Excessive exposure to radioactive isotopes can damage human cells and even cause cancer and birth defects, but when exposure is controlled, some radioactive isotopes can be useful in medicine. 3 ‫د رياض حنيوه‬ ‫جامعه وارث االنبياء‬ lecture 4 ‫كليه الطب‬ ‫قسم الكيمياء الحيوية والطبية‬ Medical Applications Nuclear medicine uses radioactive isotopes in a variety of ways. One of the more common uses is as a tracer in which a radioisotope, such as technetium-99m, is taken orally or is injected or is inhaled into the body. The radioisotope then circulates through the body or is taken up only by certain tissues. Its distribution can be tracked according to the radiation it gives off. The emitted radiation can be captured by various imaging techniques, such as single photon emission computed tomography (SPECT) or positron emission tomography (PET), depending on the radioisotope used. Through such imaging, physicians are able to examine blood flow to specific organs and assess organ function or bone growth. Radioisotopes typically have short half-lives and typically decay before their emitted radioactivity can cause damage to the patient’s body. Radioactive isotopes have numerous medical applications—diagnosing and treating illness and diseases. One example of a diagnostic application is using radioactive iodine-131 to test for thyroid activity. The thyroid gland in the neck is one of the few places in the body with a significant 4 ‫د رياض حنيوه‬ ‫جامعه وارث االنبياء‬ lecture 4 ‫كليه الطب‬ ‫قسم الكيمياء الحيوية والطبية‬ concentration of iodine. To evaluate thyroid activity, a measured dose of radioactive iodine-131 is administered to a patient, and the next day a scanner is used to measure the amount of radioactivity in the thyroid gland. The amount of radioactive iodine that collects there is directly related to the activity of the thyroid, allowing trained physicians to diagnose both hyperthyroidism and hypothyroidism. Iodine-131 has a half-life of only 8 d, so the potential for damage due to exposure is minimal. Technetium-99 can also be used to test thyroid function , Bones, the heart, the brain, the liver, the lungs, and many other organs can be imaged in similar ways by using the appropriate radioactive isotope. 5 ‫د رياض حنيوه‬ ‫جامعه وارث االنبياء‬ lecture 4 ‫كليه الطب‬ ‫قسم الكيمياء الحيوية والطبية‬ Isotope Use P cancer detection and treatment, especially in eyes and skin 59 Fe anemia diagnosis 60 Co gamma ray irradiation of tumors 32 99m Tc* 131 I 133 Xe brain, thyroid, liver, bone marrow, lung, heart, and intestinal scanning; blood volume determination diagnosis and treatment of thyroid function lung imaging 6 ‫جامعه وارث االنبياء‬ ‫د رياض حنيوه‬ ‫كليه الطب‬ ‫‪lecture 4‬‬ ‫قسم الكيمياء الحيوية والطبية‬ ‫‪Isotope‬‬ ‫‪Use‬‬ ‫‪liver disease diagnosis‬‬ ‫‪198‬‬ ‫‪Au‬‬ ‫‪END OF THE LECTUER 3‬‬ ‫‪7‬‬