NuclearPharmacy 3

 Electron Capture Decay

A parent nucleus may capture one of its own electrons and emit a neutrino (proton is converted to a neutron) with the release of gamma rays. 

7Be4 + 0e-1 7Li3 + γ Berilium Lithium

The following particle reaction occurs

1P1 + 0e-1 1n0 + γ

Electron capture is one form of radioactivity. A parent nucleus may capture one of its orbital electrons and emit a neutrino. This is a process which competes with positron emission and has the same effect on the atomic number. Most commonly, it is a K-shell electron which is captured, and this is referred to as K-capture.

 Electron Capture Decaywith gamma ray emission

Isomeric transition

In this reaction, an unstable nuclide, with higher energy, decays to a suitable isomeric nuclide of lower energy with the emission of gamma rays

In this case, Protons and Neutrons are rearranged within the nucleus leading to change in energy level of the nuclide.

The more excited isomeric state is called metastable which is indicated adding letter "m" to the atomic mass

Example; metastable Technetium 99mTc 

99mTc 99Tc + γ

decay scheme of Tc-99m

RADIATIONThere are two types of radiation have been employed, non-ionizing and

ionizing radiationA. Non-Ionizing Radiation The non-ionizing radiations have an older history and two important

forms of this are infrared and ultraviolet radiations. Infrared radiation destroys by the heat it generates. Ultraviolet radiation kills by excitation of atoms and chemical reactions

in the cell components. The penetrating power of both these radiations is very low. Though still

used selectively, the two processes, in general, can cause undesirable chemical reaction in some pharmaceuticals and surgical supplies.

However, ultraviolet radiation is popular for its germicidal action and finds extensive use in disinfecting pharmaceutical manufacturing basis.

 B. Ionizing Radiation

Over the last two decades, there has been a progressive recognition that ionizing radiation in the form of high energy electrons or gamma radiations can offer significant and real advantages in the pharmaceutical processing technology.

Ionizing radiation especially high energy electrons and gamma radiations are lethal to microorganisms.

They have some clear advantages over the other methods in that they have unrestricted permeability through the packaged product. Sterilization can therefore be carried out on the finally packaged product.

Ionizing radiation is radiation that has sufficient energy to remove electrons from atoms, creating ions.

The result of this ionization is the production of negatively charged free electrons and positively charged ionized atoms.

Ionizing radiation can be classified into two groups: photons (gamma and X-rays) and particles (alpha, beta, and neutrons(

Ionized atoms (free radicals), regardless of how they are formed, are much more active chemically than neutral atoms.

Units of radioactivityA. Activity units:Curie (Ci): it is the quantity of a radionuclide that is decaying at a rate of 3.7 X 1010 disintegration per second

(dps); 

1 Ci = 3.7 X 1010 dps1 millicurie (mCi) = 3.7 X 107 dps1 microcurie (µCi) = 3.7 X 104 dps

 

B. Dose units:1. Exposure dose:**Roentgen;

Is the quantity of radiation which will produce one unit of change of 1 cm3 of air

Is a unit of exposure dose to X or γ radiation which is the commonly used in radiotherapy.

Is not a unit of α or β radiation

B. Dose units:1. Exposure dose:**Roentgen;

Is the quantity of radiation which will produce one unit of change of 1 cm3 of air

Is a unit of exposure dose to X or γ radiation which is the commonly used in radiotherapy.

Is not a unit of α or β radiation

2. Absorbed dose

The absorbed dose is the amount of energy absorbed per unit mass of irradiated material

The SI (System International) unit for absorbed dose is Joules per kilogram (Jkg-1), which is given the special name gray (Gy)

Units used previously were the rad; Where 1 rad = 0.01 Gy= 0.01 Jkg-1 and, less frequently,

the electronvolt per gram (eVg-1) and electronvolt per cubic centimeter (eV cm-3)

The absorbed dose rate is the absorbed dose per unit time and has the units gray per unit time, e.g., Gy S-1 or Gy min-1

The absorbed dose is a direct measure of energy transferred to the irradiated material that is capable of producing physical changes.

Sources of radioisotopes1. Natural sources:

Naturally occurring radioisotopes are those that were formed in the earth and decay so slowly that they still present today e.g. Uranium-238 (238U), and Potassium-40 (40K)

They disintegrate through a series of decay processes until stable nuclear configuration are reached.

2. Artificial sources: A. By Fission Certain heavy radionuclide like 238U can be

caused to fission by introduction of a neutron into the nucleus leading the production of radioactive fission products like 131I.

This process is performed in a nuclear reactor.

B. By Activation

Many radioactive nuclides are prepared by neutron activation by placing a suitable target element in a nuclear reactor where it is bombarded by neutrons

For example, radioactive Phosphorus (32P) can be prepared by neutron bombardment of the stable phosphorus (31P).

Nuclear reactor

C. By Acceleration

It is the Cyclotron produced isotopes Certain radioisotopes are produced by

accelerating charged particles like proton, deuterons or alpha particles in an accelerator by applying a high voltage.

The highly energetic accelerated are caused to bombard a target element.

123I is an example of this type. It is obtained by deuteron bombardment of 122Te.

Cyclotron1- Two flat hollow objects called dees.The dees are part of an electrical circuit.2- On the other side of the dees are large magnets that (drive) steer the injected charged particles (protons, deuterons, alpha and helium) in a circular path

Mechanism The charged particle follows a circular path until the particle has sufficient energy that it passes out of the field and interact with the target nucleus.Why can we use only with charged particles such as:, protons, deuterons, or alpha particles It depends upon the interaction of magnetic and/or electrostatic fields with the charge of the particle undergoing acceleration.When the particles have been accelerated to a high velocity, they are caused to strike a target, containing the atoms to be bombarded.

Gamma Radiation Sources Gamma emitting radionuclides are the most

widely used radiation sources. The penetrating power of gamma photons has

many applications. However, while gamma rays penetrate many materials, they do not make them radioactive.

Examples of radionuclides by far most useful are:

Cobalt-60Technetium-99m

One of the most useful gamma sources for radiation processing because of its availability, high gamma energy (1.17 MeV and 1.33 MeV), long half life (5.27-years), and great penetrability capacity.

Cobalt-60 is produced in nuclear reactor. Natural Cobalt, Cobalt-59, has 27 protons and 32 neutrons.

When inserted in a stream of slow neutrons, Cobalt-59 absorbs a neutron and becomes Cobalt-60, which is radioactive.

It emits an electron, a β-particles, from the nucleus and is transformed from Cobalt-60 to Nickel-60.

Cobalt-60

Cobalt-60 uses

sterilize medical equipment in hospitals pasteurize certain foods. gauge the thickness of metal in steel mills.

Technetium-99m

TC-99m is the most widely used radioactive isotope for diagnostic studies. It has a short half-life and as a result it doesn't remain in the body for long

Different chemical forms are used for brain, bone, liver, spleen and kidney imaging and also for blood flow studies.

The "short" physical half-life (6h)of the isotope and its biological half-life of 1 day (in terms of human activity and metabolism) allows for scanning procedures which collect data rapidly but keep total patient radiation exposure low. The same characteristics make the isotope suitable only for diagnostic but never therapeutic use.