Target and Its Processing
Various types of targets have been designed and used for both reactor and
cyclotron irradiation. In the design of targets, primary consideration is given
to heat deposition in the target by irradiation with neutrons in the reactor
or charged particles in the cyclotron. In both cases, the temperature can rise
to 1000°C, and if proper material is not used or a method of heat dissipa-
tion is not properly designed, the target is likely to be burned or melted.
For this reason, water cooling of the cyclotron probe to which the target is
attached is commonly adopted. In the case of the reactor, the core cooling
with heavy water is sufficient to cool the target. Most often, the targets are
designed in the form of a foil to maximize heat dissipation.
The common form of the target is metallic foil, for example, copper,
aluminum, uranium, vanadium, and so on. Other forms of targets are oxides,
carbonates, nitrates, and chlorides contained in an aluminum tubing, which
is then flattened to maximize the heat loss. Aluminum tubing is used
because of its high melting point. In some cases, compounds are deposited
on the appropriate metallic foil by vacuum distillation or by electrodeposi-
tion, and the plated foils are then used as targets. In specific cases, high-
pressure gases (e.g.,^124 Xe for^123 I production) and liquid targets (e.g., H 218 O
for^18 F production) are also used.
Equation for Production of Radionuclides
While irradiating a target for the production of a radionuclide, it is essen-
tial to know various parameters affecting its production, preferably in a
mathematical form, to estimate how much of it would be produced for a
given set of parameters. These parameters are therefore discussed below.
Equation for Production of Radionuclides 49Table5.1.Continued
g-ray Common
Physical Mode of g-ray energy* abundance production
Nuclide half-life delay (%) (MeV) (%) method
(^13354) Xe 5.3 days b−(100) 0.081 37 235 U(n, f) (^133) Xe
(^13755) Cs 30.0 yr b−(100) 0.662 85 235 U(n, f) (^137) Cs
(^20181) TI 73 hr EC (100) 0.167 9.4 (^203) TI(p, 3n) (^201) Pb
X-ray 93 201 Pb^201 TI
(0.069–0.083)
*g-rays with abundance less than 4% have not been cited.
d, deuteron; EC, electron capture; f, fission; IT, isomeric transition; n, neutron; p, proton.
Data from Browne E, Finestone RB.Table of Radioactive Isotopes. New York: Wiley; 1986.
EC
93.hr→