Loading and unloading of conveyor (A) takes place 
Trays of sutures move to ir- 
beside controls (B). 
Engineering Corp. and embarked on an 
extensive research project. 
We established the minimum killing 
dose for over 150 different species of 
microorganisms and found the maxi- 
mum dose that could be safely tolerated 
by catgut. We chose 2.5 megarads as 
our sterilizing dose. This is 40% above 
the minimum to kill the most resistant 
microorganism. Catgut can tolerate 
5.0 megarads before showing properties 
inferior to heat-sterilized gut. 
Although we knew that the 2-Mev 
cate 9 tae 
ew: 
oe 
Ethicon's linac. 
Van de Graaff would not have enough 
production capacity, we later bought 
the unit for our expanding research 
program in the field of irradiation. We 
have since installed the linac that we 
use routinely for sterilization. Cur- 
rently we are installing a 3-Mev Van de 
Graaff. 
Setting specifications. As our in- 
vestigations progressed we began to 
have more enthusiasm for radiation 
sterilization. Simultaneously we began 
establishing our requirements. 
OLD AND NEW PACKAGES. Aluminum-foil package shown in front and back views 
at bottom is more convenient than glass package it replaced 
electron beam from linac (D). 
maintenance workshop are on mezzanine (E) 
radiation room at lower level (C) to pass under 
Power supplies and 
If radiation is to be used in produc- 
tion-line sterilization, the source must 
satisfy the following requirements: 
© Adequate dose delivery 
® Complete and uniform coverage of 
the product 
© Adequate penetration 
Dose is determined mainly by beam 
current. Coverage is ensured by the 
proper scan width, which is determined 
by scanning coil current. Penetration 
is determined by accelerating voltage 
or, more generally, by electron energy. 
The energy must be great enough for 
complete penetration. 
Total penetration is the depth of 
complete absorption of electrons. For 
our purpose we define ‘‘useful penetra- 
tion” as the thickness such that exit 
dose is equal to entrance dose (Fig. 2). 
With monoenergetic electrons the en- 
trance dose is ~60% of the maximum 
in this energy range. 
Having met the penetration require- 
ment one seeks a source delivering the 
largest number of electrons of a speci- 
fied energy per unit time. Usually 
beam current then determines produc- 
tion capacity. For each scan width, 
beam current tells us at what rate the 
product can move under the source for 
a specific minimum dose. 
If one is dealing with a homogeneous 
material like grain or a fluid, dimen- 
sions can be varied for maximum beam 
utilization. However, the majority of 
145 
