ION SELECTIVE ELECTRODE

Typical Number in Hospital:

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References: 5

Measurement of the concentration of specific ions in solutions (both in vivo and in vitro) can be made by selective electrodes. Examples are hydrogen (pH), chloride, potassium, sodium, calcium, etc.

There are two main types. Direct measurement electrodes measure the activity or concentration of an ion in water or plasma. Indirect types measure the activity or concentration in a dilution of the original sample. The direct measurement types are independent of the effects of abnormal levels of lipids or plasma proteins, and can be used with whole blood.

IRTX

IONIZATION CHAMBER n=5 c=1 r=3

Ionizing radiation can be detected by the small electric current which can be made to flow between two electrodes when particles of the gas between them become ionized. The electrodes and gas are often in a sealed glass envelope to allow the gas pressure to be reduced, which makes the device more sensitive. The Geiger- Muller (GM) tube is a special type of ionization chamber which contains low-pressure neon or argon, and a very high voltage is applied between specially shaped electrodes. Ionization chambers are used to measure X-ray and gamma-ray radiation levels.

Small radiation monitors employing ionization chambers are available for personal dose monitoring, and GM tube instruments are available with a dose rate alarm. However, these instruments are not suitable for monitoring the dose rate to large numbers of individuals and so film badge monitors or thermoluminescent dosimetry devices are used.

IXRT

IONIZING RADIATION r=3,4

Electromagnetic and particulate radiations may have sufficient energy to remove electrons from atoms (ionization). The energy of electromagnetic radiation is related to the frequency (or wavelength). Ionization of some atoms begins with rays of about 10 eV which corresponds to waves in the ultraviolet region. Thus visible light (1 eV), microwaves (0.0001 eV) and lower frequencies may be considered to be non-ionizing.

Ionization in human tissues is caused deliberately in radiotherapy using X-rays (0.1-10 MeV) and gamma rays (up to 100 MeV). Particulate radiations of beta particles (electrons), alpha particles, neutrons, and heavy nuclei may also be used.