USES OF RADIOACTIVE TRACERS

Definition: substances with atomic or nuclear, physical, chemical or biological properties that can help identify, observe or follow the behaviour of various physical, chemical or biological processes

Advantage:

  • Easy to detect and measure with high precision to sensitivities of 10^-16 to 10^-6 g
  • Radioactivity is independent of pressure, temperature, chemical and physical state
  • Do not affect the system and can be used in nondestructive techniques
  • The radiation can be measured independently of the matrix, eliminating the need for calibration curves.

Basic Assumption for Tracer Use

  • The primary assumption is that radioactive isotopes are chemically identical with stable isotopes of the same element.
  • The second assumption is that the radioactive nature of the isotope does not change the chemical and physical properties.

Isotopic Exchange

  • involving the redistribution of the isotopes of an element between reacting substances

Absorption

  • Solutes in contact with surfaces have a tendency to be absorbed on the surface

Radiocolloid

  • A mixture containing small particles, in the range of 10-1000nm

Equilibrium Reaction

  • The low concentration of radioactive tracers can lead to the formation of solute species that are not observed at equilibrium with macro amounts.

Precipitation & Crystallization

  • Co-precipitation - simultaneous precipitation of a normally soluble component with a macro-component from the same solution by the formation of mixed crystal, by absorption, occlusion or mechanical entrapment.

Tracer Separation Methods

  • Solvent extraction and various forms of partition chromatography methods have been found to be particularly advantageous in this connection since they are selective, simple and fast
  • Liquid-liquid extraction is a technique for selectively transferring a species between an aqueous solution and an organic phase by equilibrating the aqueous phase with an organic solvent.

Analytical Chemistry

  • Studies and uses instruments and methods used to separate, identify, and quantify matter

Radiochemical Methods

Radiometric Analysis

  • The use of a radioactive reagent of known activity to isolate the analyte from the other components of the sample.
  • The activity of the product is directly proportional to the amount of the analyte.

Isotopic Dilution

  • Involves the preparation of the analyte in a radioactive form
  • A known weight of this compound labeled with isotope is then mixed with the mixture containing the compound to be analyzed.

Activation Analysis

  • The sample is irradiated with neutrons
  • After that, the gamma or beta spectrum is obtained, depending on the type of emission produced by the irradiated element.

Application of Radioactive Tracers to Life Sciences

Radiotraces in Biological Affinity

  • To study how living species interact with the environment, ecology.

Technique

Autoradiography

  • alternative to using the blackening of a photographic film for radiation detection based on semiconductor array detectors

Radioimmunoassay

  • technique for determining antibody levels by introducing an antigen labelled with a radioisotope and measuring the subsequent radioactivity of the antibody component.

DNA Analysis

  • DNA profiling is the process of determining an individual's DNA characteristics.

Radiotraces in Transmission Computer Tomography (TCT)

  • nuclear medicine imaging provides unique information that often cannot be obtained using other imaging procedures and offers the potential to identify disease in its earliest stages.

Radiotraces in Emission Computer Tomography (ECT) and Diagnosis

  • includes Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT)
  • plays the same role as in the TCT

Radiotraces in Radiation Therapy with Internal Radionuclides

  • To develop monoclonal antibodies, which will seek out particular types of cancer cells and bind to them
  • Patients receiving this type of radiopharmaceutical experience swift lowering of pain levels.

Industrial Uses of Radiotracers

Mixing

  • by adding a radionuclide to the mixing vessel or by labelling one of the components, the approach to mixing equilibrium can be followed either by external measurement or taking samples at different time intervals

Liquid Volumes & Flows

  • to calculate liquid volume of a closed system from external container dimensions
  • to determine the volume of tanks through which there is a known constant flow

Wear & Corrosion

  • wear and materials transfer are easily followed if the material undergoing wear is made radioactive
  • It is important that the surface undergoing wear has a high specific radioactivity
    ~ Corrosion in gas and oil pipelines on the sea floor is monitored by welding patches containing a series of long-lived radionuclides at different material.

Chemical Processing

  • radioactive tracers are used to seek information of flow and mixing patterns for:
    1) Parameter evaluations
    2) Fluid dynamics
    3) Chemical reaction engineering

Environmental Applications

Movement of Water

  • By measurement on T, Sr-90, Cs-137, and other fission products it has been possible to follow movements of water from land via lakes and rivers into the sea, as well as to study the water streams of the oceans and the exchange between surface and deep water.

In Hydrology

  • to determine the volume of natural water reserves
  • to map the movement of ground and surface water as well as effluent pathways.

Gamma Scanning

  • scanning pipelines for blockage or build-up