Classification of Radiation and Physics Constants

Introduction to Radiation and Constants

Radiation refers to the transport of energy through space via electromagnetic waves or atomic particles. Radiation can be classified into two main categories depending on its ability to ionize matter. The ionization potential of atoms, which is the minimum energy required to ionize an atom, varies widely. The ionization potentials for atoms range from a few electron volts (eV) for alkali metals to 24.6 eV for noble gases like helium.

Types of Radiation

Non-Ionizing Radiation

Non-ionizing radiation cannot ionize matter because its energy per quantum is below the ionization potential of atoms. These types of radiation have lower energy compared to ionizing radiation. Examples include:

  • Near ultraviolet radiation
  • Visible light
  • Infrared photons
  • Microwaves
  • Radio waves

Ionizing Radiation

Ionizing radiation has sufficient energy to ionize matter, either directly or indirectly, because its quantum energy exceeds the ionization potential of atoms. This type of radiation can remove electrons from atoms, causing ionization. Examples include:

  • X-rays
  • Gamma rays (γ rays)
  • Energetic neutrons
  • Electrons
  • Protons
  • Heavier atomic particles

Detailed Examples of Radiation

Here are detailed examples of various types of electromagnetic radiation, including their energy, frequency, and wavelength.

X-rays

X-rays are a form of ionizing radiation with high energy. They are commonly used in medical imaging. X-ray photons have wavelengths ranging from about 0.01 to 10 nanometers (nm), corresponding to frequencies between 3 × 1016 Hz to 3 × 1019 Hz. Their energy can be calculated using the equation:

E = hν

Where:

  • h = 6.626 × 10–34 J·s (Planck's constant)
  • ν = frequency of the photon (in Hz)

For example, if the frequency of an X-ray is 1 × 1018 Hz, the energy is:

E = (6.626 × 10–34 J·s) × (1 × 1018 Hz) = 6.626 × 10–16 J

Gamma Rays

Gamma rays have even higher energy than X-rays, with wavelengths typically less than 0.01 nm and frequencies greater than 3 × 1019 Hz. Gamma rays are used in cancer treatments and have energies on the order of 1 MeV to 10 MeV. For example, with a frequency of 1 × 1020 Hz, the energy can be calculated as:

E = hν = (6.626 × 10–34 J·s) × (1 × 1020 Hz) = 6.626 × 10–14 J

Ultrasound

Ultrasound is a type of non-ionizing radiation, typically used in medical imaging. It has frequencies above 20 kHz (kilohertz), often in the range of 1 MHz to 20 MHz. Since ultrasound is not electromagnetic radiation, it doesn't have a wavelength in the electromagnetic spectrum but is related to the propagation of sound waves. A common frequency used in medical ultrasound is 5 MHz. The corresponding wavelength is:

λ = v / f

Where:

  • v = speed of sound in the medium (approx. 1540 m/s in human tissue)
  • f = frequency (in Hz)

For a frequency of 5 MHz (5 × 106 Hz), the wavelength is:

λ = (1540 m/s) / (5 × 106 Hz) = 0.000308 m = 0.308 mm

Physics Constants and Calculations

Below are some key physical constants, their values, and sample calculations. These constants are fundamental in understanding various phenomena in radiation and physics.

Important Physics Constants

Physical Constant Symbol Value Units
Avogadro's Number NA 6.022 × 1023 mol–1
Speed of Light c 2.998 × 108 m/s
Electron Charge e 1.602 × 10–19 C (coulombs)
Planck's Constant h 6.626 × 10–34 J·s
Gravitational Constant G 6.674 × 10–11 m3·kg–1·s–2

Sample Calculations

Below are a couple of examples showing how these constants are used in calculations:

1. Calculation of Energy of a Photon

The energy E of a photon is related to its frequency ν by the equation:

E = hν

Where:

  • h = 6.626 × 10–34 J·s (Planck's constant)
  • ν = frequency of the photon (in Hz)

If the frequency of the photon is 5 × 1014 Hz, the energy of the photon is:

E = (6.626 × 10–34 J·s) × (5 × 1014 Hz) = 3.313 × 10–19 J

2. Calculation of Gravitational Force Between Two Objects

The gravitational force F between two objects is given by Newton's law of gravitation:

F = G (m1m2) / r2

Where:

  • G = 6.674 × 10–11 m3·kg–1·s–2 (Gravitational constant)