Utilizing High Energy Photons

We will first describe devices which use phosphors which respond to high energy photons like x-rays and gamma rays (high energy x-rays). 

---

As most of the free radicals are short-lived, direct monitoring of their reactions is not an easy task and powerful tools based on fast reaction techniques are required to follow such processes.Thus, fast reaction techniques utilize either short pulses of high-intensity flash of light or laser (in flash photolysis), or short pulses of charged particles and high-energy photons from accelerators (in pulse radiolysis). 

High-energy radiation may be classified into photon and particulate radiation. Gamma radiation is utilized for fundamental studies and for low-dose rate irradiations with deep penetration. Radioactive isotopes, particularly cobalt-60, produced by neutron irradiation of naturally occurring cobalt-59 in a nuclear reactor, and caesium-137, which is a fission product of uranium-235, are the main sources of gamma radiation. X-radiation, of lower energy, is produced by electron bombardment of suitable metal targets with electron beams, or in a... 

There will be a certain proportion of suitcases whose contents are so optically thick that it is impossible to achieve sufficient penetration to acquire a useful number of photons in the diffraction profile. This renders evaluation impossible. Such an impenetrable suitcase raises a dark (sometimes called shield ) alarm. Clearly, the most effective way of reducing the dark alarm rate is to raise the mean photon energy. It is in this respect that the HETRA method of diffraction profile analysis (Section 2.3.1.) may prove helpful as it utilizes photons at the high-energy limit, where the suitcase is most transparent. 

Several quantum cutting regimes have been utilized with most of them involving Gd " and Pr " since these ions have high energy levels from which the initial photon is released. However, these levels lie too high for effective absorption of solar energy. The emission from Yb " is just above the band gap of crystalline Si. Hence, the downconversion in which one blue photon ( 483 nm) is absorbed by Tb " and used to sensitize two Yb " ions for Vs/2 emission near 1 pm has... 

The unique phenomena originating from dressed photon exchange have been applied also to the development of novel high-resolution fabrication techniques. As has been described in Sect. 1.2 (refer to (1.3) and (1.4) and Fig. 1.3), the principle of fabrication utilizes the dressed photon, which carries the coherent phonon energy (DP-CP). Several examples are reviewed in this section. 

---