Name
Email

1.3 FEECOM/BIECOM Results

g-shielding for a 60Co-source

Shielding calculations for a 60Co-source resulted in the following half value layers and tenth value layers for lead, steel, bismuth-epoxy composite (BEC), and iron-epoxy composite (IEC):

Half value layer x1/2:

  • Lead     10 mm
  • Steel     30 mm
  • BEC     24 mm
  • IEC     59 mm

Shielding calculations for a 60Co-source resulted in the following tenth value layers for shielding material:

Tenth value Layer x1/10:

  • Lead     40 mm
  • Steel     98 mm
  • BEC     95 mm
  • IEC     198 mm

g-shielding for a 137Cs-source

Shielding calculations for a 137Cs-source resulted in the following half value layers and tenth value layers for lead, steel, BEC, and IEC:

Half value layer x1/2:

  • Lead     5 mm
  • Steel     13 mm
  • BEC     10 mm
  • IEC     24 mm

Tenth value Layer x1/10:

  • Lead     20 mm
  • Steel     50 mm
  • BEC     46 mm
  • IEC     87 mm

1.4 Conclusion

Ten measurements were carried out for each point of measurement, and the measurements appear to diverge from the mean value by a maximum of 4 %. For a 95 % confidence interval, the error in measurement amounts to 3 %. In comparison to the reference material steel, the BEC plates achieved better results. Although the BEC plates have a 50% lower density, they show 2 – 5 % better shielding compared to steel plates of equal thickness. The IEC plates show significantly inferior shielding in comparison to the steel plates of equal thickness, but are much lighter. Where space is not a consideration, the IEC plates can be used to achieve the same shielding if they are of double the thickness. This would have the advantage of a 5 % reduction in the entire shielding weight. As the cost of iron powder is much lower then of steel, lead or bismuth powder, the manufacture of IEC in the form of plates or other shapes would be economical and competitive. For this reason IEC plates will be a serious alternative as g-shielding.

These results from the exponential function are valid for the determined half value layers as well as for the computed tenth value layers.

2. Investigations of homogeneity of the moulded plates

The investigations of homogeneity of the new shielding material plates were conducted with 60Co-sources. The plates with a diameter of 150 mm and a thickness of 30 mm were divided into 55 small fields. At each field the attenuation of the radiation was measured. Theoretically, all 55 fields will have the same radiation exposure, i.e. 100 % homogeneity across the plates. The attenuation of the g-radiation, in particular for energy lines at 1.17 MeV and 1.33 MeV including the Compton underground radiation was determined, with an average energy of Eg = 1.25 MeV.


Figure 3: Arrangement of the measurement points on the plates

As the test plates have a round shape, only 55 measure points for each plate were available. In order to obtain representatives results, two values were determined for each measure point and the mean value was calculated. The other measuring conditions were as following:

  • Area source under the entire sample for simulation a gammadefectoscopie
  • Trigger count tube with detection electronic
  • 110 measurements for each plate
  • Measuring time 60 s
  • Underground correction of the count rates
  • Error in measurements amounts more or less 5 %

2.1 Measurements with a 60Co-source (area source) of the BEC plates

Figure 4 shows the inhomogeneity of the density. The inhomogeneity was calculated from the divergence from the mean attenuation factor I/I0 and the local differences of the mean value.


Measurement points

  • Bismuth-epoxy composite plate 213/1
  • Bismuth-epoxy composite plate 213/2
  • Bismuth-epoxy composite plate 215/2
Figure 4: Diagram of the divergence from the mean value of the attenuation factor I/I0 - BEC plate

2.2 Measurements with a 60Co-source (area source) of the IEC plates

Figure 5 shows the inhomogeneity of the density of IEC plates. The inhomogeneity was calculated from the divergence from the mean attenuation factor I/I0 and the local differences from the mean value. For presenting the divergence of inhomogeneity of the IEC plates, the same measuring conditions as for the BEC were used. Also the attenuation of the g-radiation was determined with an average energy line Eg = 1.25 MeV.


Measurement points

  • Iron-epoxy composite plate 209/2
  • Iron-epoxy composite plate 209/4
  • Iron-epoxy composite plate 209/6
Figure 5: Diagram of the divergence from the mean value of the attenuation factor I/I0 – IEC plate

2.3 Conclusion

The homogeneity of density was determined by the divergence from the mean value of the attenuation factor I/I0. The error of measurements could be reduced to 4 % by performing a double measurement for each measurement point. The measurement points on the rim diverge clearly from the centre points. This is not a result of manufacturing inhomogeneities, but can be attributed to the scattering of the g-radiation around the rim of the plate. The inhomogeneity caused by manufacturing amounts to 8 %. This means that the composites of polymers and metal powder can be made dense, without any porosity. Furthermore the plates show only small holes of 1 – 3 mm depth, but the influences of the shielding effects is insignificant considering the thickness of the plates.

Reference:
Engelmann 19.06.04
1. and 2. Shielding material

For more information regarding FEECOM/BIECOM, please fill out the inquiry form here.