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116 APPEN D IX IV
TABLE XXIX. RADIOACTIVITY IN Porphyra SEAWEED SAMPLED
IN THE VICINITY OF WINDSCALE, 1967-68
D istan ce from
C o n cen tratio n o f rad io a ctiv ity
Sam p lin g point p ip e -lin e (p C i/g (w et))
(m iles) 95Z r /95Nb i°6Ru 144C e
St. Bees 6 . 2 North 23 59 8 .4
Nethertow n 3. 5 North 60 119 13
Braystones North 2. 3 North 76 149 21
Braystones South 1. 2 North 203 249 66
S e lla fie ld (p ip e -lin e ) 0 41 116 14
S e lla fie ld (B a ile y bridge) 0. 9 South 52 146 23
S e a sca le 1. 9 South 50 127 18
Drigg 3 . 5 South 28 89 11
Eskm eals 8 . 9 South 22 60 7. 0
G utterby 12. 5 South 23 43 6 .3
W alney 24. 0 South 10 22 5 .0
by this means when concentrations are radiologic ally significant.
At low er concentrations a chem ical separation is needed, followed
by beta counting; in such circum stances, in view of its minor contribution
to the total radiation dose, a quarterly bulk at a few selected
positions is quite adequate. Recent measurements of these radionuclides
are shown in Table XXIX.
Sub-critical group of Ravenglass Estuary fishermen
For m ost waste disposals habits surveys by the laboratory
have confirmed that the circum stances of the critical group are
such that exposure of all other groups is on such a very much
lower scale that, if discharges are controlled to ensure safety of
the critical group, then all other groups will automatically be safeguarded
to a higher degree. However, there exists a group affected
by Windscale discharges that is only just sub-critical to the group
of laverbread eaters, and a small monitoring program me is undertaken
to keep this situation under review.