AATEC TT EAN / 
y 
SY 
y 
4 
SORIDRTLLEIRDILIIDE A 
Z 
oAv eee neeennmets 
ESS 
BSS 
SESS 
B 
vA 
A 
Z 
A 
y 
oN 
z 
Plain view 
of Co source 
FIG. 2, IRRADIATOR has ~600 curies of Co® in 8 flat plates 
cobalt is in 2 X 4g X 13-in. stainless-steel-clad flat strips, 
produced by Brookhaven National Laboratory. Eight 
source strips are supported in a compartmented double- 
walled stainless-steel can with an effective radius of ~3.5 
in. This array gives a cylindrical volume of 2.8 liters 
(~12.7 cm radius, 18.3 cm high) over which the dose-rate 
variation is ~10%. 
There are six irradiators, four of which are shown in 
Fig. 3. The cobalt loading varies from 540 to 660 curies 
in each irradiator with a total of 3,600 for the six units (7). 
Average dose rate varies from 788 to 910 r/min. To take 
adequate account of biological variability, possible varia- 
tion in the physiological pupal age, etc., exposure times 
were as long as 12-14 min. 
Irradiation Procedure 
Operation of an irradiator is essentially automatic. 
Pupae are measured by volume into canisters that hold 
~18,000 each. The operator attaches the canisters to 
the elevator-conveyor. Then automatic controls take 
over, move the canister into position, open the cover, insert 
FIG. 3. COBALT ROOM HAS 6 IRRADIATORS, each of which 
performs 13-min irradiation automatically once operator has 
inserted canister and started operation 
the material for irradiation during a preset time, remove 
the canister, close the port and return the canister to the 
load position. 
Manual operation is also possible with electrical controls 
and in case of power failure hand operation bypasses all 
controls. Interlocks prevent driving the canister against 
the closed port or opening the port when the canister is not 
in position. 
The shielding casks and handling mechanisms were fabri- 
cated by Knapp-Mills, Inc., Wilmington, Delaware. 
Safety 
Such devices have an obvious disadvantage: upon open- 
ing the port there emerges a cone of fairly intense radiation 
(several hundred milliroentgens per hour). This requires 
considerable vertical clearance and relatively light con- 
struction to minimize scatter. In the Sebring installation 
the eave line is ~14 ft higher than the top of the cask, and 
the roof is corrugated aluminum sheet on wood framing. 
Personnel exposure has not been a serious problem since 
the general radiation level is ~2 mr/hr. For a fraction of 
a second during insertion and removal of pupae measured 
intensity of scattered radiation at the operator’s position 
is 12-20 mr/hr. Film-badge and monitoring records indi- 
cate, however, that workers usually receive less than 50 mr 
per week. Special circumstances account for rare expo- 
sures as great as 75 mr. 
Value and Cost 
In 1957, its most successful year since it got into Florida 
in 1933, the screwworm was able.to infest an estimated 
80-85 % of all cattle wounds in the state. Weunds are not 
hard to find—punctures, scratches, wire cuts, brands, fly 
bites and even navels of newborn animals. 
Losses from such a rate of infestation were costing $10- 
million/year in Florida and $20-million/year in the South- 
east. Shipment of infested animals and natural migration 
caused further loss in states as far north as New Jersey even 
though infestations in the north were checked by winter 
weather. 
In comparison, Federal appropriations to support 
elimination of the fly have totaled $6.76-million. The 
Florida legislature appropriated $3-million for the two- 
year period ending in June, 1960. Substantial amounts 
were also expended by the states of Georgia, South 
Carolina, Alabama and Mississippi in support of the 
program. Approximately $425,000 went to remodel 
the plant; $584,000 went into equipment, including $106,- 
000 for cobalt, shields, and handling and control mecha- 
nisms. Operating costs accounted for the rest. Exten- 
sive surveys and animal inspection are still being conducted 
to determine the effectiveness of accomplishments and 
protect the region from reinfestation. 
BIBLIOGRAPHY 
1. Screwworm eradication program, Bulletins No. 1 and 2 (Florida Infor- 
mation Office, July and November, 1958); U. S. Dept. of Agriculture, 
Picture stories No. 108 (1958) and 116 (1959) 
2. E. F. Knipling, J. Econ. Entomol. 48, 459 (1955); Sci. Monthly 86, 195 
(1957); Science 130, 902 (1959) 
8. R. C. Bushland, D. E. Hopkins, J. Econ. Entomol. 44, 726 (1951); ibid. 
46, 462 (1953) 
4. A. H. Baumhover et al., J. Econ. Entomol. 48, 462 (1955) 
§. R.C. Bushland. Advances in pest control research (to be published) 
6. E. B. Darden, Jr., E. Mayens, R. C. Bushland, nucLEonics 12, No. 12, 
60 (1954) 
7. Survey of gamma facilities in U. S. and Canada—an updating, NUCLE- 
onics 17, No. 7, 88 (1959) 
184 
