Agriculture Reference
In-Depth Information
Table 10.1.
Major irradiation technologies—advantages and disadvantages
Factors
Electron Beam
X - ray
Gamma
Source
Electric power
Electrons are
generated using
electronics and
accelerated to high
energy using
magnetic fi elds,
5 - 10 MeV
a
. When
accelerator is powered
off, no radiation is
emitted.
Electric power
Created when high-energy
electrons (up to 5 MeV)
strike a metal plate (e.g.,
tungsten or tantalum
alloys); typical conversion
effi ciency is 5-10%.
When accelerator is
powered off, no radiation
is emitted.
Radioisotopes
Radioactive decay of
60
cobalt (2.5 MeV) or
137
cesium (0.51 MeV).
Radioisotope source
is always emitting
radiation — shielding
of source must be the
default position.
Mechanism
High - energy electrons
cleave water
molecules, creating
oxygen and hydroxyl
radicals that damage
DNA, membranes.
Direct cleavage of
DNA also occurs.
High - energy photons
stimulate atoms within
target to release
high - energy electrons,
which cleave water
molecules into radicals.
Direct cleavage of DNA
also occurs.
High - energy photons
stimulate atoms
within target to
release high - energy
electrons, which
cleave water
molecules into
radicals. Direct
cleavage of DNA also
occurs.
Infrastructure
required
Shielding:
>
2 m concrete
Shielding:
>
2 m concrete or
Shielding:
Depending
on design,
or
<
1 m steel/iron/
1 m steel/iron/lead
Cooling:
extensive for
high - voltage electronics
and accelerator; additional
cooling systems required
for plate target
Ventilation:
for ozone
removal while unit is
operating
<
>
5 m water
lead
Cooling:
extensive for
high - voltage
electronics and
accelerator
Ventilation:
for ozone
removal while unit is
operating
or
>
2 m concrete or
1 m steel/iron/lead.
Cooling:
moderate for
control equipment
Ventilation:
at all times
for ozone removal
when source is
exposed to air
<
Speed
b
Seconds
Seconds
Minutes
(depending on
source strength)
Penetrability
c
6 - 8 cm
, suitable for
relatively thin or
low - density products
30 - 40 cm
, suitable for all
products
30 - 40 cm
, suitable for
all products
a
MeV = million electron volts.
b
Speed of dose delivery. The desired dose will vary depending on the target organism and commodity
irradiated.
c
Penetrability in food, avg. density approximately 1 g/cm
3
. This fi gure will vary for individual commodities
due to localized variation in density associated with bone, voids, fi brous matter, etc.
and extend shelf life. The FDA is currently considering the approval of additional fruit
and vegetable commodities listed in a petition fi led by the Food Irradiation Coalition
that would allow the produce industry to use irradiation to improve the safety of fresh
and fresh-cut fruits and vegetables. If approved, treatments of up to 4.5 kGy could be
applied.
