Radiation incidents/emergencies

The selection rules help to predict the probability of a transition but are not always strictly followed. If the transition obeys the rules it is allowed, otherwise it is forbidden. A molecule can become excited in a variety of ways, corresponding to absorption in different regions of the spectrum. Thus certain properties of the radiation that emerges from the sample are measured. The fraction of the incident radiation absorbed or dissipated by the sample is measured in optical (ultraviolet and visible) absorption spectroscopy and some modes of nuclear magnetic resonance spectrometry (NMR). Because the relative positions of the energy levels depend characteristically on the molecular structure, absorption spectra provide subtle tools for structural investigation. 

The propagation of light through an excited gas was considered in detail in Chapter 10. If spontaneous emission is neglected, the intensity of radiation of angular frequency ( ) emerging from a column of gas of length L, Ij (L), is related to the intensity of radiation incident at z=0 by... 

Mass Absorption Coefficients. Radiation traversing a layer of substance is diminished in intensity by a constant fraction per centimeter thickness x of material. The emergent radiant power P, in terms of incident radiant power Pq, is given by... 

The light reflected by a powdered solid will consist of a specular reflection component and of a diffuse reflection component. The specular component represents reflection of the incident light by the surfaces of the component particles, and it is characterized by a complete absence of light transmission through the interiors of the particles. By contrast, diffuse reflectance is associated with the radiation that penetrates into the particles to some extent and that then emerges from the bulk solid. This light will exhibit spectral characteristics that are modified from those of the incident beam by the electronic transitions that took place within the solid phase and at the boundaries of the component particles. 

If the optically active medium is not transparent at the wavelength of the incident radiation, the transmitted intensity may be further reduced by an absorptive contribution to the index of refraction. Because of preferential absorption of either the left or the right circularly polarized component, the emerging beam would no longer be the sum of equal amplitudes and trace out an ellipse with ellipticity tp = (kt — kr). Practical details of the measurement and chemical applications of optical activity are discussed by Charney[34],... 

DOD Marine Corps Chemical Biological Incident Response Force, DOD Army Medical Research Institute for Infectious Diseases, DOD Naval Medical Research Institute, HHS National Medical Response Teams, HHS Disaster Medical Assistance Teams, HHS Metropolitan Medical Strike Teams, HHS Experts from Public Health Safety agencies, DOE Radiation Emergency Assistance Center and Training Site. 

The amount of radiation absorbed by a substance cannot be measured directly and it is usually determined by measuring the difference in intensity between the radiation falling on the sample (incident radiation, /0) and the residual radiation which finally emerges from the sample (transmitted radiation, /) (Figure 2.12). 

Quantitative analysis starts with Eq. (8.15) which gives the true total fluorescence flux of the sample relative to the flux of incident radiation. However, the true fluorescence is experimentally only rarely accessible, and questions of analytical interest are among others how much of / tot is emerging from the sample, how is the emerging part distributed between front and back surface, how are the parts related to the concentration of the fluorophore, how can multicomponent systems be analyzed, how is the fluorescence disturbed by interactions between fluorophore and substrate, how the fluorescence is decaying with time. 

Figure B3.6.5 The inner filter effect. A cuvette (10 x 10-mm) is represented in plan view, with the collimated incident beam from the monochromator having intensity /0. As a result of absorption by the protein solution, the intensity of the beam through the cuvette will decrease steadily, emerging with intensity /. The values are illustrated for a solution having an absorbance at the excitation wavelength of 0.1. The optics of the fluorescence detector are focused so that only fluorescence originating from the volume depicted by the heavily shaded square is seen by the photomultiplier. Thus the observed normalized fluorescence intensity will be less than that expected from the protein at infinite dilution. The fluorescence passes through the protein solution on its way to the detector and will be further decreased in intensity if the solution absorbs at the wavelengths of the emitted radiation.

The first four mirrors (>99.7% reflectance at 1.06 micron) act as a far field isolator which locates the multipass cavity 15 meters away from the laser and effectively isolates the laser from the potentially damaging retroreflected 1.06 micron radiation from the normal incidence beam splitter. The multipass cavity is aligned by monitoring the retroreflected 1.06 micron pulse which is found to emerge from the Nd YAG laser cavity, 120 nsec after the original pulse, when optimum alignment is achieved. 

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