Appendix CRF - Part 3 - Northamptonshire County Council

3 RESULTS
3.1 Cobalt-60 case
NOT PROTECTIVELY MARKED
The contact dose rate from high density (2 g/cm 3 ) soil containing 200 Bq/g 60 Co
covered with 30 cm of uncontaminated soil was determined for a series of soil material
densities from 1.0 to 1.6 g/cm 3 . The results are given in Table 1.
Soil material
density (g/cm 3 Contact dose rate
) (Sv/hr)
1.0 18.35
1.2 13.02
1.4 9.28
1.6 6.63
Table 1: Contact dose rates for various soil material densities
The resulting dose rate above the shielding layer of soil will be between 18.35 Sv/hr
for loose soil and 6.63 Sv/hr if the shielding surface soil has been compacted.
3.2 Caesium-137 case
The contact dose rate from high density (2 g/cm 3 ) soil containing 200 Bq/g 137 Cs
covered with 30 cm of uncontaminated soil was determined for a series of soil material
densities from 1.0 to 1.6 g/cm 3 . 137 Cs is a beta emitter. Its daughter, 137m Ba is the
source of the gamma radiation. Where a source containing 137 Cs was specified, its
daughter product 137m Ba was also included in equilibrium concentration with 137 Cs.
Since the half-life of 137m Ba is short (2.5 minutes), it will almost always be found in
equilibrium with its parent radionuclide. The results are given in Table 2.
Soil material
density (g/cm 3 Contact dose rate
) (Sv/hr)
1.0 2.58
1.2 1.67
1.4 1.08
1.6 0.70
Table 2: Contact dose rates for various soil material densities
The resulting dose rate above the shielding layer of soil will be between 2.58 Sv/hr for
loose soil and 0.70 Sv/hr if the shielding surface soil has been compacted.
WS010001/ENRMF/CONSAPPCRF 712
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