Radiation non-thermal

Today we can no longer ignore the idea that the extreme specialisation of the human eye is a severe handicap when surveying the Universe as a whole. For many stars are much colder or much hotter than our own. Not to mention sources of non-thermal radiation, whose spectra fall a long way outside the frequency bands in which stars tend to radiate. If we wish somehow to perceive this luminous otherness, then we must invent new tools, both mental and experimental, so that we may call ourselves astronomers of the invisible. 

Fig. 3.6. Synchrotron radiation. A fast-moving electron is forced to spiral along the line of force of a magnetic held and emits non-thermal radiation in the direction of motion of the particle. This type of radiation is confined to a narrow cone whose axis coincides with the direction of motion.

Polarimetric measurements provide essential information in space physics that cannot be found through other methods of observations. Obtained and analysed polarimetric results have shown that such measurements provide important information about a) diagnostics of non-thermal radiation mechanisms b) determination of spatial stracture of matter, a field of radiation and magnetic fields of small angular-size objects c) determination of optical, geometrical, physical and chemical properties of dust particles in space -circumstellar, interstellar, and intergalactic. 

This high degree of polarisation could be explained by non thermal radiation and indicates that some control over flare events might need to be exerted when measuring absolute brightness in the far IR. Yet, the experiment has not been able to measure the instrumental polarisation on a source of similar spatial extent as the Sun. 

Total Radiation Pyrometers In total radiation pyrometers, the thermal radiation is detec ted over a large range of wavelengths from the objec t at high temperature. The detector is normally a thermopile, which is built by connec ting several thermocouples in series to increase the temperature measurement range. The pyrometer is calibrated for black bodies, so the indicated temperature Tp should be converted for non-black body temperature. 

Keywords gamma rays bursts supernovae stars neutron radiation processes non-thermal ... 

We now have clear evidence of non-thermal processes in the sky. A whole panoply of violent activities is revealed to the watchful eye of our radio. X-ray and gamma-ray telescopes. Supernova remnants, pulsars, active galactic nuclei and gamma bursts emit radiation that has clearly nothing to do with thermal activity, for their spectra bear no resemblance to those of heated bodies. 

Seeing is not just a question of adjusting our eyes to the solar spectrum. We live close to a star called the Sun and at night, when it is hidden, we see only stars similar to our daytime star. This does not mean that darkness is absence. The chilled, the scorching and the non-thermal shine invisibly. The eye is in fact doubly solar, for it is made from the same atoms as our star, and it is the persistence and predominance of the Sun s light that have fashioned our sense of sight. The atmosphere is transparent to solar radiation. The maximal sensitivity... 

The fact that our eyes are so exclusively tuned to the Sun has thus blinded us to almost all forms of radiation. This includes radiation from media at very different temperatures, such as the relic cosmological background that filters down to us from the beginning of time, and the great majority of non-thermal emissions, such as the signals from pulsars and supernova remnants. 

Calculations which relate the concentration limits to losses by thermal radiation lead to the conclusion that, as the pressure is raised, the minimum possible propagation rate decreases proportionally to p-1/2. Unfortunately, we do not have the data necessary to compare this assertion with experiment. Reliable measurements of the flame velocity (especially for slow flames) at non-atmospheric pressures are rarely encountered. 

In the flame of a mixture of gas and air, the gas is also heated before the flame front, but this heating occurs in the presence of oxygen and the pieces of hydrocarbon molecules that could become the initial centers of formation of soot are immediately oxidized. As a result the thermal radiation of the flame of the mixture turns out to be significantly lower and the temperature significantly higher than in the flame of a non-premixed gas, although the... 

Although some of the speculation about non-thermal microwave effects appears to emanate from a misconception that microwave radiation can excite rotational transitions, the frequencies at which these occur are much higher than 2.45 GHz. For example, the first absorption lines of OCS, CO, HF and MeF occur at 12.2, 115, 1230 and 51 GHz, respectively. Internal bond rotations (torsional vibrations) also require higher frequencies, in the order of 100-400 cm-1 or 3000-12 000 GHz, for excitation61,62. 

Applications of thermal radiation spectroscopy to expins and pyrots are readily apparent. As a consequence of the highly exothermic nature of explns and flares, significant thermal radiation is emitted which can serve to characterize the reaction processes. The photometric properties of pyrots have been treated in Vol 8, P505-R. In practice, thermal radiation characteristics of explns do not always closely approximate black body properties since the system is non-equilibrium in nature and is time dependent. In addition, some pyrotechnically related materials such as aluminum oxide and magnesium oxide behave as gray bodies with emissivities well below unity. For such systems the radiant emission is reduced as shown in Fig 4... 

Accuracy of Pyrometers Most of the temperature estimation methods for pyrometers assume that the object is either a gray body or has known emissivity values. The emissivity of the non-black body depends on the internal state or the surface geometry of the objects. Also the medium through which the thermal radiation passes is not always transparent. These inherent uncertainties of the emissivity values make the accurate estimation of the temperature of the target objects difficult. Proper selection of the pyrometer and accurate emissivity values can provide a high level of accuracy. 

Several galaxy clusters show also an emission of extreme UV (Lieu et al. 1996, Durret et al. 2002) and soft X-ray (Bonamente et al. 2002, Kaastra et al. 2002) radiation in excess w.r.t. the thermal bremsstrahlung emission. This EUV emission excess may be consistent with both ICS of CMB photons off a non-thermal electron population (e.g., Lieu et al. 1999, Bowyer 2000) with Ee = 608.5 MeV (hv/keV)1/2 149 MeV for hv 60 eV, and with thermal emission from a warm gas at ksTe V 1 keV (Bonamente et al. 2002). In the case of Coma, the simple extrapolation of the ICS spectrum which fits the HXR excess down to energies 0.25 keV does not fit the EUV excess measured in Coma because it is too steep and yields a too high flux compared to the measured flux by the EUV satellite in the 0.065 — 0.245 keV band (Ensslin Biermann 1998). Thus, under the assumption that the HXR and the EUV emission of Coma is produced by ICS of CMB photons, the minimal requirement is that a break in the electron spectrum should be present in the range 0.3 — 2.8 GeV in order to avoid an excessive EUV contribution by the ICS emission and to be consistent with the radio halo spectrum. 

Very small grains and macromolecules are known to be present in the surface layers of some disks as well as in the ISM. They are usually revealed by emission features due to polycyclic aromatic hydrocarbons (PAHs, see also Chapter 6). These particles, with frameworks of six to several thousand carbon atoms, are so small that they can be excited by single ultraviolet photons. Subsequently, they will non-thermally re-radiate the energy in discrete, but broad, bands stretching across the mid-infrared wavelength region. They are found in protoplanetary disks when the ultraviolet radiation field is sufficiently high (Habart et al. 2004), but... 

As a future plan, we would like to explore a new field where atomic and nuclear physics are related in plasmas and systemize them. Extensions of our research to non-equilibrium, non-thermal and non-isotropic plasma, especially polarization spectroscopy are considered. We would like to develop quantum molecular dynamics for plasma-wall interactions, plasma radiation science, high-density plasma states, and atomic processes in high fields. These... 

If, however, the population of the energy state 2 ii> a consequence of a non-thermal process, then the emission of radiation as a result of a transition from 2 to 1 is referred to as luminescence. There are different types of luminescence ... 

Any object at a temperature above absolute zero emits thennal radiation, it is a thermal radiator. Ideally, its atoms or molecules are in a thennal equilibrium, the entire ensemble has a definite temperature. In contrast to lasers, thermal radiation sources produce non-coherent radiation. Its quanta have a random phase distribution, both spatially and temporarily. Planck s law defines the. spectral radiance of a black body the radiant power per solid angle, per area, and per wavelength L j (Eq. 3.3-2) or per wavenumber L j (Eq. 3.3-3) ... 

The radiant flux

thermal radiation source through a spectrometer is calculated by multiplying the spectral radiance by the spectral optical conductance, the square of the bandwidth of the spectrometer, and the transmission factor of the entire system (Eq, 3.1-9). Fig. 3.3-1 shows the Planck function according to Eq. 3.3-3. The absorption properties of non-black body radiators can be described by the Bouguer-Lambert-Beer law ... 

Pd(2-thpy)2 is dissolved in an n-octane matrix and is excited at low temperature (T < 2 K) by a c.w. source (non-pulsed, e.g. at A = 330 nm [61]). Additionally, microwave irradiation is applied and scanned in frequency. The microwave radiation can cause transitions between the triplet sublevels in the case of resonance, and thus, the previously different and non-thermalized steady state populations of the substates are usually altered. Under suitable conditions (see below) a change of the phosphorescence intensity will result due to microwave perturbation. Usually, this effect is very weak. Therefore, microwave pulse trains are applied, for example, with a repetition rate of 150 Hz. Thus, one can monitor the microwave-induced intensity changes by a phase-sensitive lock-in technique [90]. 

---