linear accelerator drift tube. positive ion cyclotron operation
TRANSCRIPT
Linear Accelerator Drift Tube
Positive Ion Cyclotron Operation
CS-15 Positive Ion CyclotronWashington University School of
Medicine
Target
Targets for Cyclotron
1. Metals:111Cd(p,n)111In (111In-DTPA)201Hg(d,2n)201Tl (201Tl-chloride)
68Zn(p,2n)67Ga (67Ga-citrate)
2. Gases:14N(d,n)15O (H2
15O, 15O2)14N(p,)11C (11C-acetate, 11C-
palmitate, 11C- glucose)
3. Liquids:16O(p,)13N (13N-ammonia)18O(p,n)18F (18F-FDG)
Simple X-ray Tube
• Fast neutrons (E of 1.5 MeV) have a low probability of interaction with other nuclei.• They are thermalized or slowed down (0.025 eV) to interact with other nuclei.• Moderators (low MW materials like heavy water, beryllium or graphite) are distributedin spaces between fuel rods
University of Missouri Research Reactor (MURR)Columbia, MO
Nuclear Fission
235U144 + n 236U144
236U144144Ba88 + 89Kr53 + 3n
99Mo42 + 135Sn50+ 2n
• 236U unstable - undergoes fission immediately
• wide range of fission products - usually 1/3 and 2/3 split of the mass number
Fission products useful in nuclear medicine include:99Mo, 131I, 133Xe, 137Cs and 90Sr
Mo-99 I-131
Reactor-Produced Radionuclides:Thermal Neutron Reactions
• (n, reaction: formed by reactions between targets and thermalized neutrons
YAz + n Y+1Az +
A=target; A=isotope producedsame atomic number, different mass
• (n, reaction– not carrier-free, since target and product are same– radioisotopic purity can be high if cross section is
sufficiently large (e.g. 176Lu(n,)177Lu)
Reactor-Produced Radionuclides:Thermal Neutron Reactions, cont’d
• (n, p reaction: formed by reactions between targets and thermalized neutrons
YAz + n YBz-1 + p
A=target; B=isotope produceddifferent atomic number, same mass
• (n, p reaction– carrier-free, since target and product are different– example: 64Zn(n,p)64Cu
Fisson/Reactor Products Cyclotron Products
• Generally decay by - emission because of excess neutrons
• Not many are useful for diagnostic imaging, but several are useful for radiotherapy
• Generally decay by + emission or electron capture because of excess protons
• Many are useful for diagnostic imaging
(gamma scintigraphy or positron emission tomography)
Photoelectric Effect:The energy of an incoming gamma ray is completely absorbed by the atom, and the energy absorbed is used to eject an electron from the atom.
Pair Production:The energy of an incoming gamma ray (>1.02 MeV) is completely absorbed by the nucleus, and the energy absorbed is used to eject an electron and a positron from the atom.
Alpen, E.L. (1998) Radiation Biophysics Academic Press, San Diego, p. 87
Alpen, E.L. (1998) Radiation Biophysics Academic Press, San Diego, p. 105
Hall, E.J. (1994) Radiobiology for the Radiologist J.B. Lippincott Company, Philadelphia, p. 154
Latorre Travis, E. (1989) Primer of Medical Radiobiology Year Book Medical Publishers, Inc.,Chicago, p. 92
LET
RB
E
Hall, E.J. (1994) Radiobiology for the Radiologist J.B. Lippincott Company, Philadelphia, p. 160
Hall, E.J. (1994) Radiobiology for the Radiologist J.B. Lippincott Company, Philadelphia, p. 160
Alp
en, E
.L. (
1998
) R
adia
tion
Bio
phys
ics
Aca
dem
ic P
ress
, San
Die
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