Mrs: Aya Ahmed Abd alrahium saeed MSC &BSC Nuclear medicine Inaya medical science college Nuclear Medicine Physics and Equipment 243 RAD Mrs: Aya Ahmed Abd alrahium saeed MSC &BSC Nuclear medicine

Radioactivity

An unstable nucleus releases energy to become more stable Radioactivity Radioactivity refers to the particles which are emitted from nuclei as a result of nuclear instability. Radioactive decay: is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles (ionizing radiation). Henri Becquerel, 1896 Discovered uranium was radioactive by leaving it on photographic paper and finding the paper to be exposed There are numerous types of radioactive decay. The general idea: An unstable nucleus releases energy to become more stable

Isobars are nuclides that have equal weight (mass number) , & Families of nuclei Isotopes means specific elements with different forms of that elements each containing different numbers of neutrons. Isotones are atoms of different elements that have the same number of neutrons but having different number of protons e.g. , , & Isobars are nuclides that have equal weight (mass number) , & Isomers are atoms that have identical physical attributes as far as the number of protons, neutrons and electrons, they contain a different a mount of nuclear energy.

Isomers are identified by putting an M after the mass number. M means the atom is currently in metastable state form and will emit gamma radiation from the nucleus to achieve more stable energy configuration. The most common used radionuclide in nuclear medicine is an isomer. Other isomers that have been used in nuclear medicine are &

The decay, or loss of energy, results when an atom with one type of nucleus, called the parent radionuclide. Transforms to an atom with a nucleus in a different state, or a different nucleus, either of which is named the daughter radionuclide. Often the parent and daughter are different chemical elements, and in such cases the decay process results in nuclear transmutation. In an example of this, a carbon-14 atom (the "parent") emits radiation (a beta particle, antineutrino, and a gamma ray) and transforms to a nitrogen-14 atom (the "daughter").

By contrast, there exist two types of radioactive decay processes (gamma decay and internal conversion decay) that do not result in transmutation, but only decrease the energy of an excited nucleus. This results in an atom of the same element as before but with a nucleus in a lower energy state. An example is the nuclear isomer technetium-99m decaying, by the emission of a gamma ray, to an atom of technetium-99.

Nuclides produced as daughters are called radiogenic nuclides, whether they themselves are stable or not. The SI unit of activity is the Becquerel (Bq). One Bq is defined as one transformation (or decay) per second. Radioactivity was first discovered in 1896 by the French scientist Henri Becquerel, while working on phosphorescent materials

Different between radioactivity and chemical radiation The radioactivity can not affected by extra nuclear condition which affect rates of chemicals reactions such as: Temperature. Pressure. Chemical form. Physical state. So the radioactivity is in sensitivity to extra nuclear condition allows us to characterize radioactive nuclei by their: Period of decay (half life). Mode of decay. Energy of decay.

So radioactivity can be described by the equation :- Where: A B + X + Q A = parent nuclei B = daughter X = emitted particle Q = energy released

The decay rate, or activity, of a radioactive substance are characterized by: Constant quantities: half life — symbol t1/2 — the time taken for the activity of a given amount of a radioactive substance to decay to half of its initial value. mean lifetime — symbol τ — the average lifetime of a radioactive particle. decay constant — symbol λ — the inverse of the mean lifetime.

Activity measurements:- The units in which activities are measured are: Becquerel (symbol Bq) = number of disintegrations per second; curie (Ci) = 3.7 × 1010 disintegrations per second. Low activities are also measured in disintegrations per minute (dpm).

Activity The quantity of radioactive material, expressed as the number of radioactive atoms undergoing nuclear transformation per unit time (t), is called activity (A) Described mathematically, activity is equal to the change (dN) in the total number of radioactive atoms (N) in a given period of time (dt).

The SI unit is the Becquerel (Bq) The minus sign indicates that the number of radioactive atoms decreases with time. Activity is traditionally expressed in units of curies (Ci). In nuclear medicine, activities from 0.1 to 30 mCi of a variety of radionuclide's are typically used for imaging studies, and up to 300 mCi of iodine 131 are used for therapy. The SI unit is the Becquerel (Bq) 1 mCi = 37 MBq

Constant of proportionality is the decay constant (). Number of atoms decaying per unit time (dn/dt) is proportional to the number of unstable atoms (n). That are present at any given time: Constant of proportionality is the decay constant (). -dn/dt =  n The minus sign indicates that the number of radioactive atoms decaying per unit Time (the decay rate or activity of the sample) decreases with time. The decay constant is equal to the fraction of the number of radioactive atoms remaining in a sample that decay per unit time. The relationship between activity and  can be seen by considering equation and substituting a for -dn/dt in equation A =  N

The decay constant and the physical half-life are related as follows: Useful parameter related to the decay constant is physical half-life (T1/2 or Tp1/2) ; defined as the time required for the number of radioactive atoms in a sample to decrease by one half. The decay constant and the physical half-life are related as follows:  = ln 2/Tp1/2 = 0.693/Tp1/2 Physical half-life and decay constant are inversely related and unique for each radionuclide. Half-lives of radioactive materials range from billions of years to a fraction of a second. Radionuclide's used in nuclear medicine typically have half-lives on the order of hours or days.

Fundamental Decay Equation At = A0e-t where: At = activity at time t A0 = initial activity e = base of natural logarithm = decay constant = ln 2/Tp1/2 = 0.693/Tp1/2 t = time

precalibration factor Decay calculations Decay factor for 99mTc  Hours  Decay factor (DF)  precalibration factor 1.000 0.5 0.944 1.059 1 0.891 1.122 2 0.794 1.259 3 0.707 1.414 4 0.630 1.587 5 0.561 1.782 6 0.500 2.000 7 0.445 2.247 8 0.397 2.518 9 0.354 2.824 10 0.315 3.174 11 0.281 3.558 12 0.250 4.000

How much radioactivity was present 5 hours before for 10 mCi. Examples A vial contains 10 mCi of 99mTc; how much radioactivity remains after 2 hours? DF for 2 hours = 0.794 10 mCi × 0.794 = 7.94 mCi. How much radioactivity was present 5 hours before for 10 mCi. Precalibration DF for 5 hours = 1.782 10 mCi ×1.782 = 17.82 mCi. How much of the 10 mCi remains after 36 hours? 10 mCi × 0.250 × 3 = 0.156 mCi.

Example using general Eq. Calculate the activity of 5 mCi/ml of 201Tl after 48 hr (t1/2 = 73 hr). At = A0e-0693×t/t1/2 At = 5mCi/(ml)×e-0.9639×(48/73) At = 3.17mCi/(ml) A vial contains a mixture of 20 mCi of 124I (half life 4 days) and 6 mCi of 131I (half life 8 days). What will be the activity in the vial 8 days from now? A source of is delivered to the nuclear medicine department calibrated for 100 mCi at 8:00 AM on Monday. If this radioactivity is injected into a patient at noon on Tuesday, what radioactivity will the patient receive? A source of 18F (t1/2 = approximately 2 hr) is noted to contain 3 mCi at noon. What was the radioactivity at 8:00 AM that same day?

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