Interaction of Radiation with Matter

Radiation is defined as the emission or transmission of energy either in the waveform or particle form. Life on earth has evolved with an ever-present background of radiation. On average, natural background radiation consists of emissions from radon gas (~50%), human body (~10%), rocks and soil (~10%), and cosmic rays (~12%). The artificial sources amount to ~18% of the total, which is still growing with the advancement of technologies. The electromagnetic spectrum covers a wide wavelength (or frequency range) from non-ionizing radiowaves, microwaves, terahertz, infrared, to ionizing ultraviolet, X-rays, and particle radiations. Although people have been studying and using the visible spectrum for centuries, both extremes (beyond violet and red) have lately shown an impressive list of applications. All of these applications include some interaction of radiation with various types of matter. Imaging was one of the original applications using the visible spectrum. However, we have now progressed past the visible spectrum, and infrared, far infrared (terahertz), X rays, and gamma rays are being developed for important specific applications. Hence, the importance of radiation interaction of matter keeps increasing with time. For example, infrared or far-infrared (terahertz) non-ionizing radiation detectors are heavily used in defense, security, commercial, and now in medical applications. Most airports are now in the process of replacing X-ray machines with terahertz machines. Infrared-based thermometers and glucose meters are also common occurrences. The vibrations due to infrared radiation absorption can identify chemical components due to their bonds. This idea is used in recent developments in minimally or noninvasive disease diagnostics using infrared radiation.

Ionizing electromagnetic radiation is an excellent way to study atomic systems in that the interaction is small (on the order of the fine-structure constant, ~1/137) and the photon disappears after the interaction. Theoretical and experimental studies of neutral atoms and ions conducted over the years have revealed a wealth of information about the photoabsorption process and the quantum mechanics of the transitions from bound to unbound states. More recently, attosecond time delay between the absorption of a photon and the emission of the subsequent photoelectron has attracted attention.

In recent years, there has also been a growing interest in cosmic ray flux measurements at the surface of the earth for important applications ranging from new technologies for space and earth weather monitoring, soil moisture monitoring, cosmic ray muon/neutron tomography, etc., allowing a better understanding between the level of cosmic ray radiation and the rate of cancer cell formation in living objects.

This Special Issue om “Interaction of Radiation with Matter” will focus on radiation covering the electromagnetic spectrum and their applications in physics, medicine, biology, chemistry, environmental studies, etc. The Special Issue will include but not be limited to the applications of radiation, such as infrared, visible, ultraviolet, X-rays and, gamma radiation (γ); cosmic rays, alpha (α), and beta radiation (β).

Dr. A. G. Unil Perera
Guest Editor

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• electromagnetic and particle radiation
• applications
• attosecond delays
• photon detectors
• disease diagnostics
• soil and moisture
• non ionizing and ionizing radiation
• imaging
• photoabsorbtion