*Atomic Spectroscopy DOI: http://dx.doi.org/10.5772/intechopen.89269*

#### **Figure 3.**

*Modern Spectroscopic Techniques and Applications*

provide a better performance for both AES and sample introduction into an inductively coupled plasma. Traditional sources usually include arcs and sparks but modern instruments use argon or some other inert gas to create plasma. The plasma may

by seeding ions from a high-voltage spark—and is sustained from a radio frequency generator in the area of the induction coil. This is known as *inductively coupled plasma* (ICP). Plasma exists at temperatures of up to 10,000 K and the instrument prevents the torch from melting. XRF requires that sample should be irradiated by high energy photons. In most instruments, the source is the polychromatic primary beam from *X-Ray tubes*. Of interest to biological applications, however, it is the use

An ideal *wavelength selector* has a high throughput of radiation and a narrow effective bandwidth. There are two major types of wavelength selectors —**filters and monochromators**. A simple example of an absorption filter is a piece of colored glass. Absorption filters provide effective bandwidths of 30–250 nm, although the throughput can be only 10% of the source's emission intensity at the low end of this range. Interference filters constructed of a several optical layers deposited on a glass or transparent material. Typically, effective bandwidth is 10–20 nm, with maximum throughputs of at least 40% [11]. *A monochromator* is used to convert a polychromatic source of radiation at the entrance slit to a monochromatic source of restricted effective bandwidth at the exit slit. These devices are classified as either fixed-wavelength or scanning. The wavelength selects by manually rotating the grating in a fixed-wavelength monochromator. A scanning monochromator includes a drive mechanism that continuously rotates the grating, allowing sequen-

*Detectors* use a sensitive **transducer** that converts a signal comes from light energy into electrons An ideal detector produces signal, *S*, is a linear function of the

S = kP + D

where *k* is the detector's sensitivity and *D* is the detector's **dark current**, or the

Phototubes and photomultipliers include a photosensitive surface that absorbs radiation in the *UV-visible*, or near-IR, generating an electrical current proportional to the number of photons reaching the transducer (**Figure 4**). Other *photon* 

background current when no radiation of source reached to the detector.

of radioactive isotopes such as 244Cm, 241 Am, 55Fe, and 109Cd [11, 12].

tial wavelengths to exit from the monochromator (**Figure 3**) [11].

electromagnetic radiation's power, *P*,

+ 2e<sup>−</sup>—a process generated

be produced when gas atoms are ionized, Ar + e<sup>−</sup> → Ar1

**4**

**Table 1.**

*The most common kinds of light sources.*

*Schematic diagram of wavelength selectors: (a) filters and (b) a diffraction grating monochromator.*

#### **Figure 4.**

*Diagram of a phototube and a photomultiplier tube.*

*detectors* use a semiconductor compound as the photosensitive surface. One advantage of the Si photodiode manufactured utilizing semiconductor process is that it is easy to miniaturize. Infrared photons do not have enough heat to generate a measurable current with a photon transducer [11].

A transducer's electrical signal is sent to a **signal processor** where it is displayed in a form that is more convenient *to* explain. The analog meters, digital meters, recorders, and computers equipped with data acquisition boards are good examples of signal processors. A signal processor is used in calibrating the detector's


**Table 2.** *Examples of detectors for spectroscopy.*

response, amplificating the transducer's signal, removing noise by filtering, or mathematically transforming the signal [11] (**Table 2**).
