TNAG-1508-FCO40-2066-Guangdong-nuclear-power-station-project-at-Daya-Bay-safety-c-1987 — Page 52

Positron annihilation technology:

Positron is the anti-

particle of electron. When shot into the material, the

positron combines with the electron therein and thus is

annihilated and emits two Y-photons. By measuring the energy and

exit-angles of these two Y-photons and the life-span of the

positron, what can be indicated include the electronic density in

the medium, electron-momentum longitudinal-component change, as

well as the information about the inner state and structure.

This method is a new-type probe of the microscopic structure

of material, capable of detecting the atomic fault, even one

or several atomic holes, which are imperceivable under electronic

microscopes. Its capacity includes: detecting the minute fault

on the broken section or surface of a work piece, such as the

wing of air-plane and the rotating axle; determining the

cavity in the material destruction; studying the ion compounds,

the impurity inclusion effect of semi-conductor; the phase-

change and crystallization in high polymer and non-crystalline

alloys; chemical reaction dynamics. In bio-medical science,

this technology can be used to quantitatively study the physio-

logical process, blood circulation, and the blood volume in

heart and brain. In the laminal scanning for diagnosing tumors,

this technology demonstrates a high sensitivity and precision

and no harm to human body. Therefore, this is a technology

with a great future in the field of medical science.

P. 8

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