Radio-activity, characteristics

To take radio-activity alone. .. perhaps there is no discovery of modern times which has so disorganized the fertile but by no means plastic brain and imagination of the workers in physical science as this bomb which overthrew with a mighty force all current and reputable theories of the constitution of Matter and its inherent quality. It was the assumption that Matter existed alone in the dense ponderable condition, which we have been told by generations of scientists is its main characteristic, that caused them to fabricate the Mechanical Theory of Nature. (550)... 

Characteristics of Carbon.— The dominant position of carbon in the fabric of life is due to unique chemical properties having biochemical consequences, and it has even been suggested by Jeans that life organisation is a latent property of carbon, which is biogenic in the sense that iron is magnetic or ra um is radio-active. 

Within its orbit, which has some of the characteristics of a molecular orbital because it is shared with electrons on the surrounding atoms, the electron has two possible spin multiplicity states. These have different energies, and because of the spin-multiplicity rule, when an (N-V) center emits a photon, the transition is allowed from one of these and forbidden from the other. Moreover, the electron can be flipped from one state to another by using low-energy radio-frequency irradiation. Irradiation with an appropriate laser wavelength will excite the electron and as it returns to the ground state will emit fluorescent radiation. The intensity of the emitted photon beam will depend upon the spin state, which can be changed at will by radio-frequency input. These color centers are under active exploration for use as components for the realization of quantum computers. 

Because at any given field strength each nucleus has a characteristic resonant frequency, we can tune the radio dial to any nucleus we are interested in observing. We can think of the various NMR-active nuclei in the sample as radio stations that we can tune into very accurately, just as stations come into tune in a very narrow range of frequencies on an FM radio. Having chosen a station to listen to, what can we learn by observing a particular type of nucleus The resonant frequency is always, always, always proportional to the magnetic field ... 

A particular nucleus (e.g. H, C, P) absorbs characteristic radiofrequencies, i.e. it resonates at a characteristic frequency. If an NMR spectrometer is tuned to a particular resonance frequency, only a selected NMR active nucleus is observed. For example, only H nuclei are observed if a 400 MHz spectrometer is tuned to 400 MHz, but if the same spectrometer is retuned to 162MHz, only nuclei are observed. This is analogous to tuning a radio and receiving only one station at a time. 

Sources of sex pheromones have now been described in several species of fish, and whenever urine has been examined, it has been shown to have pheromonal activity (Liley 1982 Liley Stacey 1983 Stacey et al 1986 Stacey et al. 1994 Appelt, Sorensen Kellner 1995 Vermeirssen, Scott Liley 1997). This is notable because both studies which have described temporal characteristics of urinary release in fish have found urine to be released in a pulsatile manner (Fletcher 1990 Curtis Wood 1991). Unfortunately, neither study used fish known to be releasing pheromones. In a study of a freshwater fish, Curtis and Wood (1991) used external catheters and a radio-label to demonstrate that rainbow trout (Oncorhynchus my kiss) held individually in laboratory tanks urinated approximately every 30 min. In a study of a marine fish, the plaice (Pleuronectes platessa), Fletcher (1990) demonstrated that isolated plaice held in laboratory tanks urinate once every few days. The primary objective of this study was to determine whether a link between pheromones and pulsatile urinary release exists. 

In radio-release methods, the nonradioactive test substance is brought into contact with a radioactive reagent. As a result of an appropriate chemical reaction, a portion of the activity of the radioactive agent is released, i.e., it passes from the sofid to the liquid or gas phase, or from the liquid to the gas phase. A characteristic feature of radio-release methods is that the radioactive substance leaves the solid or the liquid phase without any nonradioactive substance replacing it. 

Shot noise This is a type of circuit noise, which is not temperature dependent, and which is not white noise in the sense that it tends to diminish at higher frequencies. This usually occurs in components whose operation depends on a mean particle residence time for the active electrons within the device. The cutoff frequency above which noise disappears is closely related to the inverse of this characteristic particle residence time. It is called shot noise because in a radio it can make a sound similar to buckshot hitting a drum, as opposed to white noise, which tends to sound more hke hissing (due to the higher-frequency content). 

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