3. Outline
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4. Pion or pi meson is a subatomic particle consists of one quark
and one anti-quark. They hold the nucleus together
They have small rest mass, zero baryon number ,short lifetimes,
and antiparticles.
Decay
π⁺ –› μ⁺ + ν
π¯ –› μ¯ + ν͂
π° –› hν₁ + hν₂
Introduction
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5. the energy of the bombarding particle & target material must be appropriate
When the target is bombarded the pions are released nearly isotropitally
with different momenta.
Pions of specific momenta may be selected by magnetic fields.
Pions lose energy in flight through tissue
Mechanism of Pion Production
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7. When the π¯ reaches the tumour it has slowed down so much
that a nucleus captures it.
The nucleus is now unstable and breaks up violently into
smaller fragments.
These fragments damage surrounding cells within a small
radius
Negative pion in Radiotherapy
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8. As the pion comes to rest, it is captured by the nucleus.
Unstable nucleus explodes, producing short range, heavily ionizing
nuclear fragments and alpha particles, as well as neutrons, protons,
y-rays and pi-mesic X-rays
30 MeV of the total rest energy (139 MeV) of the pi-meson appears in
the form of heavy ions, alpha particles and protons.
Radiated particle & Radiation type
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9. Protons with 400-800 MeV energy produced in cyclotron or
linac are used for pion beam production for RT.
100 MeV pions are of interest in radiation therapy
Pions have low dose rate
Energy range & Dose rate
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10. First pion centre at Los Alamos, New Mexico closed in 1981,
Second in Switzerland & Another has opened in Canada
But this is only for clinical research, currently
Early results showed no better or worse than conventional Xray
therapy
Applications & Popularity
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