Facebook Instagram Youtube Twitter

What is Cross-Section of Photoelectric Effect – Definition

At small values of gamma ray energy the photoelectric effect dominates. The cross-section curve have sharp discontinuities. Cross-Section of Photoelectric Effect

Photoelectric Effect

Cross-Sections of Photoelectric Effect

At small values of gamma ray energy the photoelectric effect dominates. The mechanism is also enhaced for materials of high atomic number Z. It is not simple to derive analytic expression for the probability of photoelectric absorption of gamma ray per atom over all ranges of gamma ray energies. The probability of photoelectric absorption per unit mass is approximately proportional to:

τ(photoelectric) = constant x ZN/E3.5

where Z is the atomic number, the exponent n varies between 4 and 5. E is the energy of the incident photon. The proportionality to higher powers of the atomic number Z is the main reason for using of high Z materials, such as lead or depleted uranium in gamma ray shields.Although the probability of the photoelectric absorption of gamma photon decreases, in general, with increasing photon energy, there are sharp discontinuities in the cross-section curve. These are called “absoption edges” and they correspond to the binding energies of electrons from atom’s bound shells. For photons with the energy just above the edge, the photon energy is just sufficient to undergo the photoelectric interaction with electron from  bound shell, let say K-shell. The probability of such interaction is just above this edge much greater than that of photons of energy slightly below this edge. For gamma photons below this edge the interaction with electron from K-shell in energetically impossible and therefore the probability drops abruptly. These edges occur also at binding energies of electrons from other shells (L, M, N …..).

Cross section of photoelectric effect.Cross section of photoelectric effect.

See also:

Definition of Photoelectric Effect

See also:

Photoelectric Effect

We hope, this article, Cross-Section of Photoelectric Effect, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about radiation and dosimeters.

What is Definition of Compton Scattering – Definition

Definition: Compton scattering is the inelastic or nonclassical scattering of a photon by a charged particle, usually an electron. Radiation Dosimetry

Compton Scattering

Key characteristics of Compton Scattering

  • Compton scattering dominates at intermediate energies.
  • It is the scattering of photons by atomic electrons  
  • Photons undergo a wavelength shift called the Compton shift.
  • The energy transferred to the recoil electron can vary from zero to a large fraction of the incident gamma ray energy

Definition of Compton Scattering

Compton Scattering
In Compton scattering, the incident gamma-ray photon is deflected through an angle Θ with respect to its original direction. This deflection results in a decrease in energy (decrease in photon’s frequency) of the photon and is called the Compton effect.
Source: hyperphysics.phy-astr.gsu.edu

Compton scattering is the inelastic or nonclassical scattering of a photon (which may be an X-ray or gamma ray photon) by a charged particle, usually an electron. In Compton scattering, the incident gamma ray photon is deflected through an angle Θ with respect to its original direction. This deflection results in a decrease in energy (decrease in photon’s frequency) of the photon and is called the Compton effect. The photon transfers a portion of its energy to the recoil electron. The energy transferred to the recoil electron can vary from zero to a large fraction of the incident gamma ray energy, because all angles of scattering are possible. The Compton scattering was observed by A. H.Compton in 1923 at Washington University in St. Louis. Compton earned the Nobel Prize in Physics in 1927 for this new understanding about the particle-nature of photons.

See also:

Compton Scattering

See also:

Compton Formula

We hope, this article, Definition of Compton Scattering, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about radiation and dosimeters.

What is Compton Formula – Definition

The Compton formula was published in 1923 in the Physical Review. Compton explained that the X-ray shift is caused by particle-like momentum of photons. Compton wavelength

Compton Scattering

Compton Scattering Formula

Compton Scattering
In Compton scattering, the incident gamma-ray photon is deflected through an angle Θ with respect to its original direction. This deflection results in a decrease in energy (decrease in photon’s frequency) of the photon and is called the Compton effect.
Source: hyperphysics.phy-astr.gsu.edu

The Compton formula was published in 1923 in the Physical Review. Compton explained that the X-ray shift is caused by particle-like momentum of photons. Compton scattering formula is the mathematical relationship between the shift in wavelength and the scattering angle of the X-rays. In the case of Compton scattering the photon of frequency f collides with an electron at rest. Upon collision, the photon bounces off electron, giving up some of its initial energy (given by Planck’s formula E=hf), While the electron gains momentum (mass x velocity), the photon cannot lower its velocity. As a result of momentum conservetion law, the photon must lower its momentum given by:As a result of momentum conservetion law, the photon must lower its momentum given by this formula.So the decrease in photon’s momentum must be translated into decrease in frequency (increase in wavelength Δλ = λ’ – λ). The shift of the wavelength increased with scattering angle according to the Compton formula:The shift of the wavelength increased with scattering angle according to the Compton formulawhereλ is the initial wavelength of photonλ’ is the wavelength after scattering,h is the Planck constant = 6.626 x 10-34 J.sme is the electron rest mass (0.511 MeV)c is the speed of lightΘ is the scattering angle.The minimum change in wavelength (λ′λ) for the photon occurs when Θ = 0° (cos(Θ)=1) and is at least zero. The maximum change in wavelength (λ′λ) for the photon occurs when Θ = 180° (cos(Θ)=-1). In this case the photon transfers to the electron as much momentum as possible.The maximum change in wavelength can be derived from Compton formula:The maximum change in wavelength can be derived from Compton formula. Compton lengthThe quantity h/mec is known as the Compton wavelength of the electron and is equal to 2.43×10−12 m.

See also:

Definition of Compton Scattering

See also:

Compton Scattering

See also:

Cross-Sections of Compton Scattering

We hope, this article, Compton Formula, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about radiation and dosimeters.

What is Cross-Section of Compton Scattering – Definition

The angular distribution (cross-sections) of photons scattered from a single free electron is described by the Klein-Nishina formula. Cross-Section of Compton Scattering

Compton Scattering

Compton Scattering – Cross-Sections

The probability of Compton scattering per one interaction with an atom increases linearly with atomic number Z, because it depends on the number of electrons, which are available for scattering in the target atom. The angular distribution of photons scattered from a single free electron is described by the Klein-Nishina formula:The angular distribution of photons scattered from a single free electron is described by the Klein-Nishina formulawhere ε = E0/mec2 and r0 is the “classical radius of the electron” equal to about 2.8 x 10-13 cm. The formula gives the probability of scattering a photon into the solid angle element dΩ = 2π sin Θ dΘ when the incident energy is E0.

Compton scattering experiment
The wavelength change in such scattering depends only upon the angle of scattering for a given target particle.
Source: hyperphysics.phy-astr.gsu.edu/
compton scatteringCross section of compton scattering of photons by atomic electrons..Compton scattering - Angle distributionEnergies of a photon at 500 keV and an electron after Compton scattering.

See also:

Compton Formula

See also:

Compton Scattering

See also:

Compton Edge

We hope, this article, Cross-Section of Compton Scattering, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about radiation and dosimeters.

What is Compton Edge – Definition

In spectrophotometry, the Compton edge is a feature of the spectrograph that results from the Compton scattering in the scintillator or detector. Radiation Dosimetry

Compton Scattering

Compton Edge

In spectrophotometry, the Compton edge is a feature of the spectrograph that results from the Compton scattering in the scintillator or detector. This feature is due to photons that undergo Compton scattering with a scattering angle of 180° and then escape the detector. When a gamma ray scatters off the detector and escapes, only a fraction of its initial energy can be deposited in the sensitive layer of the detector. It depends on the scattering angle of the photon, how much energy will be deposited in the detector. This leads to a spectrum of energies. The Compton edge energy corresponds to full backscattered photon.

Compton edge of 60Co on gamma spectrometer Na(Tl).
Compton edge of 60Co on gamma spectrometer Na(Tl).

See also:

Cross-Section of Compton Scattering

See also:

Compton Scattering

See also:

Inverse Compton Scattering

We hope, this article, Compton Edge, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about radiation and dosimeters.

What is Inverse Compton Scattering – Definition

Inverse Compton scattering is the scattering of low energy photons to high energies by relativistic electrons. Radiation Dosimetry

Compton Scattering

Inverse Compton Scattering

Inverse Compton scattering is the scattering of low energy photons to high energies by relativistic electrons. Relativistic electrons can boost energy of low energy photons by a potentially enormous amount (even gamma rays can be produced). This phenomenon is very important in astrophysics.

Inverse Compton scattering
source: venables.asu.edu

See also:

Compton Edge

See also:

Compton Scattering

We hope, this article, Inverse Compton Scattering, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about radiation and dosimeters.

What is Linear Attenuation Coefficient – Definition

The sum of the three partial cross-sections is called the linear attenuation coefficient. Gamma rays attenuation. Radiation Dosimetry
The total cross-section of interaction of a gamma rays with an atom is equal to the sum of all three mentioned partial cross-sections:σ = σf + σC + σ
  • σf – Photoelectric effect
  • σC – Compton scattering
  • σp – Pair production

Depending on the gamma ray energy and the absorber material, one of the three partial cross-sections may become much larger than the other two. At small values of gamma ray energy the photoelectric effect dominates. Compton scattering dominates at intermediate energies. The compton scattering also increases with decreasing atomic number of matter, therefore the interval of domination is wider for light nuclei. Finally, electron-positron pair production dominates at high energies.Based on the definition of interaction cross-section, the dependence of gamma rays intensity on thickness of absorber material can be derive. If monoenergetic gamma rays are collimated into a narrow beam and if the detector behind the material only detects the gamma rays that passed through that material without any kind of interaction with this material, then the dependence should be simple exponential attenuation of gamma rays. Each of these interactions removes the photon from the beam either by absorbtion or by scattering away from the detector direction. Therefore the interactions can be characterized by a fixed probability of occurance per unit path length in the absorber. The sum of these probabilities is called the linear attenuation coefficient:

μ = τ(photoelectric) +  σ(Compton) + κ(pair)

Linear Attenuation Coefficient

The attenuation of gamma radiation can be then described by the following equation.

I=I0.e-μx

, where I is intensity after attenuation,  Io is incident intensity,  μ is the linear attenuation coefficient (cm-1), and physical thickness of absorber (cm).

The materials listed in the table beside are air, water and a different elements from carbon (Z=6) through to lead (Z=82) and their linear attenuation coefficients are given for three gamma ray energies. There are two main features of the linear attenuation coefficient:

  • The linear attenuation coefficient increases as the atomic number of the absorber increases.
  • The linear attenuation coefficient for all materials decreases with the energy of the gamma rays.

AttenuationDependence of gamma radiation intensity on absorber thickness.Gamma rays attuenuationThe relative importance of various processes of gamma radiation interaction with matter.Linear Attenuation CoefficientsTable of Linear Attenuation Coefficients (in cm-1) for a different materials at gamma ray energies of 100, 200 and 500 keV.

Absorber 100 keV 200 keV 500 keV
Air   0.000195/cm   0.000159/cm   0.000112/cm
Water 0.167/cm 0.136/cm 0.097/cm
Carbon 0.335/cm 0.274/cm 0.196/cm
Aluminium 0.435/cm 0.324/cm 0.227/cm
Iron 2.72/cm 1.09/cm 0.655/cm
Copper 3.8/cm 1.309/cm 0.73/cm
Lead 59.7/cm 10.15/cm 1.64/cm

Read more