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Physics of nuclear medicine

الكلية كلية طب حمورابي     القسم الكلية ذات القسم الواحد     المرحلة 1
أستاذ المادة نادية حسين صاحب طاهر       07/06/2018 00:22:55
Lecture:Physics of nuclear medicine
Objectives:
1. To get information about physical laws and their applications in medical physics.
2. Ability to; identify relevant principles and laws when dealing with
certain investigational tools in both and disease state.

Introduction:
The radioactive element is unstable nuclei that disintegrate to emit various rays and particles, like :
The Alpha (?) particles, are positively charged, helium nucleus (24 He) have range of energy stop in a few cm of air.
Beta particles (?):
?- are negatively charged are called negatron, are more penetrating but can be stooped in a few meters of air or few millimeters
of tissue , they are high- speed electrons.
?+ positive beta or positron is produced by cyclotrons.
?+ is physically identical to an electron except that it has a positive charge.
Gamma- rays (?) Electromagnetic radiation, identical to X- ray but ?-rays have much higher energies and they very penetrating
than ? and ?.
Isotopes, nuclei of a given element with different numbers of neutron:
Stable isotopes (They are not radioactive like 12C)
Unstable isotopes (They are radioactive nuclei like 11C , 14C and 13C)


The radioactive element is used in medicine for: research , diagnostic and therapy for cancer.
Radioactive decay: decay the nuclei of unstable isotopes to its daughter, which is also radioactive, is formed each daughter
decays until the final daughter (stable isotope) after emitting the radioactive rays (?, ?, and ?)

The use of radioactivity in medicine was development of nuclear reactor during 2nd world war in the connection with the atomic bomb project the most useful of radionuclides for nuclear medicine those that emit gamma rays since gamma rays are very penetrating.
The most common emission from radioactive elements are beta particles and gamma rays. Since beta particles are not very penetrating, they are usually absorbed in the body and are generally of little use for diagnoses. However some beta emitting radionuclides such as H3 C14 play an important role in medical research.
P32 is used for diagnosis of tumors in the eye because some of its beta particles have enough to emerged from the eye.
All of gamma emitting radionuclide of the common organic elements carbon, nitrogen & oxygen are short lived, which makes their use in clinical medicine difficult without accelerator.

Each radionuclide decays at fixed rate commonly indicated by half-life T1/2, the time needed for half of radioactive nuclei to decay.

It’s usually convenient to plot the activity on a semi loge graph. If the graph shows straight line you can be reasonably sure only one radionuclide is present, a curved line indicate the presence of more than one.
The basic equation for describing radioactive decay is:

A = A? e – ?t
A is the activity A? is the initial activity
? decay constant t is the time since that activity was if t measured in hr.
? in hr-1

A = ? N
N is the number of radioactive atoms
T1/2 = 0.693 / ?


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