Sources of Photons

The sources of photons include radioisotopes, nuclear reactions, and brems-strahlung radiation. 

There are many radioisotopes that emit gamma rays. The most useful ones are as follows  

Na with a 15-h half-life emitting y s with energy 1.37 and 2.75 MeV 

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For a radio astronomer, a star is a source of noise this noise can be detected and correlated from antenna to antenna in order to position precisely the source. For optical observer, the star is a source of photons, the unique photon goes through a variety of optical paths and materialize on the focal plane detector. 

Photons that are scattered, absorbed or emitted by a catalyst form a versatile source of information. Figure 1.4 shows the electromagnetic spectrum, along with a number of techniques involving photons. In addition to the common sources of photons (lamps, lasers, helium discharge and X-ray sources) available for laboratory... 

X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) are the two main techniques based on electron spectroscopy. In XPS, a source of photons in the X-ray energy range is used to irradiate the sample. 

On one level it is a quantum effect, and can be described in terms of photon—phonon scattering. The incident NIR beam is a source of photons, and the energy from the piezotransducer provides a source of lattice phonons that propagate through the crystal. As in all collision processes, the twin principles of conservation of momentum and conservation of energy apply. The momentum of a quantum particle is linked to its wavevector by hk. The energy is linked to its frequency by hjj. 

The experimental setup requires a source of photons which can be tuned through the K-edge of the element of interest. For all of the studies presented in this paper, this is the carbon K-edge at —285 eV. If the orientation of the a or it or-... 

Consider a source of photons surrounded by a cloud of nebular gas. The gas particles are ionized by those photons with energies above the ionization threshold. Once ionized, the particles tend to recombine with the free electrons, and an equilibrium stage is eventually established in which the rate of ionization equals the rate of recombination... 

Since in most experiments one source of photons is used, we can substitute the angular frequencies Wj and u>2 for 0.5... 

The simplest quantum source of photons is the atomic transition, creating, according to the selection mles, multipole photons. The simplest model of the interaction of an atom with the electromagnetic radiation is associated with the notion of so-called two-level atom [64]. In fact, this model originates from the famous study of radiation kinetics by Einstein [65]. With the development of laser, the notion of two-level atom entered firmly into the practice of quantum optics. The fact is that, using lasers as sources of electromagnetic radiation, one... 

Problem 4-15. An Application of Optical Scattering/Fluorescence. A currently active area of research is the application of optical scattering and fluorescence for the noninvasive location of tumors. The patient is injected with a fluorescent dye that preferentially absorbs into a tumor. A portion of the patient s skin located near the suspected tumor is illuminated with a source of photons, such as a laser diode. The wavelength or energy of the photons is such that the absorbed dye fluoresces, and the emitted photons are then detected by a photomultiplier also located on the patient s skin. This optical response is then analyzed to determine the location and extent of the tumor. 

We will study a ID model problem to understand quantitatively how we might analyze such a response. Assume that the surface of the skin is located atx = 0 and that a tumor is located at x > L. Note we are neglecting any variations parallel to the surface of the skin or tumor. The surface of the skin is exposed to a sinusoidal source of photons such that... 

To induce X-ray fluorescence of elements in a sample, a source of photons or particles of sufficient energy is required. Generally these sources are produced by X-ray tubes of variable power or, for portable instruments, by radioisotopic sources. If the term of X-ray fluorescence is considered in the broadest sense of X-ray emission, other excitation processes employing particles (e , a) can be used. 

Several properties of lasers make them an ideal source of photons. For example, laser light is monochromatic, available in wavelengths ranging from the UV to the infrared depending on... 

Since photons have, essentially, an infinite range, the previous calculation for charged particles does not apply. A source of photons located anywhere in the body will deliver some dose to all the other parts of that body. The calculation of the dose rate proceeds as follows. 

In Sect. 4.4, we examined the effect of the illumination of semiconductor-electrolyte junctions, using a light source of photon energy greater than the band gap of semiconductor. We shall now try to develop a model to get a quantitative estimation of the photocurrent from the magnitude of the concentration of photogenerated carriers. 

Collision termc ksJ j f x,m ) pa m m )dm. It represents the source of photons in the phase space volume dxdm in relation to photons with propagation direction m that are scattered at x in the direction m (see Fig. 8D). c ksj[x,m )dxdm is the rate at which photons within dxdm are scattered, andpsi m m ) is the probabifity density for their scattering direction to be soHd angle accounts for all incoming directions m. ... 

The basic act of counting a steady source of photons with any radiation detector has been shown to have associated with it a standard counting error a = /N,... 

High-energy photons can remove an electron from a sample molecule and generate a molecular ion. Inexpensive gas discharge lamps, originally developed for photoionization detection in gas chromatography, are suitable sources of photons, e.g., 10.0 eV photons from a krypton discharge lamp. 

Photons may be used as activation particles. The nuclear reactions depend on the atomic number of the target and on the energy of the photons used for irradiation. The source of photons for PAA is nearly always the bremsstrahlung radiation (synchrotron radiation) produced with electron accelerators. The photon energies are commonly 15-20 MeV, predominantly inducing the (y,n) reaction. Other reactions that can be used include (y,p), (y,2n), and (y,a). The method is complementary to INAA, and the determination of light elements C, N,... 

More useful in spectroscopic terms is the process of coherent Stokes Raman scattering (CSRS) or anti-Stokes Raman scattering (CARS). This involves radiation from two laser sources of photon energy hvi>hv2 that irradiate the sample simultaneously. 

XPS is based on the photoelectric effect principle of the ejection of electrons from a surface when the photons impinged upon it. The source of photon energies used is A1 Ka. The energy of the photoelectrons leaving the surface of a specimen gives a spectrum with a series of photoelectron peaks in terms of binding energy... 

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