Radiation sensitivity, definition

Although the use of ionizing radiation has contributed to a definite picture of certain chemisorptions and catalyses, in other cases it has run into difficulties that have not yet been resolved. With several oxides, for example, water or some other poison is required for radiation sensitivity, and the role of the poison has not been clarified. Because this behavior seems to be fairly widespread, it is important to understand it more fully, and considerable attention could well be given to irradiation of such oxides in a high state of purity and with varying degrees of surface coverage. 

Extensive discussion of radiobiological principles is beyond the scope of this chapter, yet a few definitions will be mentioned. The response of tumors to radiotherapy is determined by several factors such as repopulation, reoxygenation, number of clonogenic cells, and their intrinsic radiosensitivity. Since the introduction of mammalian cell survival curves, the parameters D and N have been used as quantitative measures of inherent radiation sensitivity, as was the shoulder width Dq (Thames and Suit 1986). Today the ratio alpha/beta is the most common parameter for characterization of cell survival curves. It is also a measure of fractionation sensitivity. 

Polymer films that are sensitive to light, x-rays, or electrons— known as photoresists—are nsed extensively to transfer the pattern of an electronic circuit onto a semiconductor surface. Such films must adhere to the semiconductor surface, cross-link or decompose on exposure to radiation, and nndergo development in a solvent to achieve pattern definition. Virtually all aspects of photoresist processing involve surface and interfacial phenomena, and there are many outstanding problems where these phenomena mnst be controlled. For example, the fabrication of multilayer circuits requires that photoresist films of about 1-pm thickness be laid down over a semiconductor surface that has already been patterned in preceding steps. 

B) Phase-shift methods. The phase shift method for determining fluorescence lifetimes is based on the principle that if fluorescence is excited by suitably modulated light source, emitted radiation will also be similarly modulated. With reference to a scattering substance, emission from a fluorescent substance will introduce a time lag due to finite time between absorption and emission. This, by definition is the lifetime of the excited state. The time lag will cause a phase-shift relative to the exciting light. Phase fluorimetry requires a modulated light source and a phase sensitive detector. 

When spectroscopy with polarized light or other optical polarization measurements are performed the studied sample becomes one element of the optical train which transmits the beam from the radiation source to the detector. Four optical phenomena might take place in a sample sensitive to polarized radiation. We list them below together with their physical definition ... 

We became interested in poly(l-trimethylsilyl-l-propyne) [poly(TMSP)] after the initial report of its synthesis (9). Poly(TMSP) possesses many of the qualities needed in a practical deep-UV resist material a high silicon content (—25%) thermal stability excellent film-forming properties and a chromo-phore, the conjugated backbone, that absorbs strongly in the deep-UV region. Our initial work with poly(TMSP) showed that it had one serious drawback its sensitivity toward degradation by deep-UV radiation was poor, and doses of >1 J/cm are required for the definition of a positive-tone pattern. 

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