Anodized Manufacturing Technique
The activity is incorporated in the top surface of an aluminium foil resulting in a source which has an active layer only 5 µm (0,8mg/cm²) in depth. The source is also robust. To produce anodized foil sources, micropores are etched into the surface of a 0,3 mm thick aluminium foil. The micropores are less than 0,01 µm in diameter, and are 4-10 µm deep.
The active material is then incorporated in the pores in an insoluble chemical form. The pores are chemically sealed to produce a thin layer which is mechanically robust and chemically resistant. To construct a rigid source, the aluminium foil is mounted on a backing plate.
Measurement of emission rate and uniformity
The quantity of interest for wide area reference sources is the particle emission rate. This quantity is used to calibrate the instruments, and the calibration is related back to the quantity of radiological importance (the activity of the radionuclide) following the procedure in ISO7503 or national recommendations. The particle emission rate is measured using a high efficiency windowless and/or windowed proportionalcounter, which is calibrated using a Class 1 source. All particles which are emitted from the surface with an energy greater than 590eV are detected. A particle emitted by a decaying nucleus can be scattered by the source material, or can lose energy in a series of inelastic collisions. The probability of high angle scattering of an alpha particle is very low, and the energy loss in inelastic collisions is low (until the alpha particle reaches the end of its range). For an alpha source, the emission rate is therefore approximately half the activity. Beta particles are deflected relatively easily, and low energy beta particles can quickly lose energy. Consequently, backscatter from the source backing plate and self-absorption of particles in the source material are more significant, and the emission rate can be greater or less than half of the activity, depending on the end-point energy of the beta particles. Typical ratios are shown below:
Beta end-point energy[MeV]
Ratio of particle emissionrate to activity (source efficiency)
|Sr-90/Y-90||0,546 / 2,280||0,63|
The uniformity of each EZN class 2 or EZN class 2 equivalent source is checked.
The reported uncertainty is based on a standard uncertainty multiplied by a coverage factor k=2, providing a level of confidence of approximately 95%. Sources are offered with a choice of DAkkS certificate (measurement uncertainty less than 5%) or Eckert & Ziegler Nuclitec GmbH certificate (EZN certificate, measurement uncertainty less than 10%).
Sources that are greater than 100cm2 in area are in addition classified as EZN class 2 or EZN working sources in. For EZN class 2 sources, the uncertainty in the particle emission rate and activity is equal to or less than ±5% (k=2). For natural uranium sources the uncertainty in the activity is ±10%.
For EZN working sources, the uncertainty in the particle emission rate and activity is equal to or less than ±10%.
Each source is supplied with a certificate of calibration which states:
• Serial number
• Reference time and date
• Measured particle emission rate into 2pi
• Measured activity*
• Measurement uncertainties
• Date of leak test
• ISO classification
*As the Tritium (H-3) activity cannot be calibrated, it is stated as a nominal value.
The maximum deviation of the delivered activity from the nominal activity is ±30%. Other tolerances are available on request.
The sources are calibrated in accordance with the requirements of ISO8769 and all measurements are traceable to national standards.
The sources are manufactured in a facility which operates a quality management system which has been independently audited and approved to ISO9001:2008.
The sources are tested to ISO2919 which is equivalent to ANSI N542 1977. The assessed classification for the sources is ISO/12/C34645.
Advice on handling of sources and replacement
Sources should be recalibrated at regular intervals in accordance with national recommendations. Abrasion of the top surface of the aluminium foil will inevitably remove activity, although only from the sections of the source that has been physically damaged. Sources may be cleaned by wiping with a lint-free cloth moistened with ethanol. Detergents or abrasive compounds such as metal polish should not be used.To prevent loss of C-14 due to exchange of carbon with the atmosphere, C-14 sources should be kept in their storage box and kept out of strong sunlight and high humidity atmospheres when not in use.Regular improvements in source design and measurement mean that it would be good working practice to renew the sources within 10 years.
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