GAMMA y RAYS

The penetrating power of gamma rays is approximately one hundred times greater than that of beta rays. For example, gamma rays can pass through a lead block several centimeters thick. They can only be stopped by concrete blocks of two to three meters thick. 

Since gamma rays are electrically neutral particles, they are not deflected by electric or magnetic fields and they do not have an ionizing effect. 

The mass and charge of gamma rays are accepted as zero. Therefore, the atomic mass number and the atomic number of an atom remain unchanged when it radiates a gamma (y) ray. 

For example, when the element transmutes into gQTh by radiating la ray, gamma (y) rays are also produced. 

The nuclear equation of this process is shown below  

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Figure 12.10 The electromagnetic spectrum covers a continuous range of wavelengths and frequencies, from radio waves at the low-frequency end to gamma (y) rays at the high-frequency end. The familiar visible region accounts for only a small portion near the middle of the spectrum.

A wide variety of solvents, reagents, and structural materials encountered normally in the trace-element analysis of seawater have been analyzed for trace-element impurities by neutron activation analysis and gamma (y)-ray spectrometry.17 Some of the results obtained for 10 trace elements are shown in Table 6.4 and indicate that many substances contain high impurity levels of various elements. Particular note should be made of the high concentrations of zinc in... 

Internal transition involves the emission of electromagnetic radiation in the form of gamma (y) rays from a nucleus in a metastable state and always follows initial alpha or beta decay. Emission of gamma radiation leads to no further change in atomic number or mass. 

Analytical applications have been found for all parts of the electromagnetic spectrum ranging from microwaves through visible radiation to gamma (y) rays (Table 1). The emission and absorption of electromagnetic radiation are specific to atomic and molecular processes and provide the basis for sensitive and rapid methods of analysis. There are two general analytical approaches. In one, the sample is the source of the radiation in the other, there is an external source and the absorption or scattering of radiation by the sample is measured. Emission from the sample may be spontaneous, as in radioactive decay, or stimulated by thermal or other means, as in flame photometry and fluorimetry. Both approaches can be used to provide qualitative and quantitative information about the atoms present in, or the molecular structure of, the sample. 

The major divisions of the spectrum are shown in color in the inside front cover of this book. Note that the visible portion, to which our eyes respond, is only a minute portion of the entire spectrum. Such different types of radiation as gamma (y) rays or radio waves differ from visible light only in the energy (frequency) of their photons. 

Gamma (y)-rays (velocity 3x10 m/s in free space), wavelength <0.1 nm, energy > 10 keV X-rays, wavelength 10-0.001 nm, energy 100 eV-1 MeV Neutrons (n)... 

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