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Related Concept Videos

Electric Field of Two Equal and Opposite Charges01:30

Electric Field of Two Equal and Opposite Charges

Atoms generally contain the same number of positively and negatively charged particles, protons, and electrons. Hence, they are electrically neutral. However, the centers of the positive and negative charges do not always coincide. In such a scenario, the electric field of an atom may not be zero.
A separation of the positive and negative charges can lead to a weak, remnant effect of the positive and negative charges. The expectation is that the more the distance between the positive and...
Calculation of Electric Flux01:25

Calculation of Electric Flux

Consider the electric field of an oppositely charged, parallel-plate system and an imaginary box between those plates. Let the bottom face of the box be ABCD, and the top face be FGHK. The electric field between the plates is uniform and points from the positive plate toward the negative plate. The calculation of this field's flux through the box's various faces shows that the net flux through the box is zero. Why does the flux cancel out here?
Electric Field of a Continuous Line Charge01:19

Electric Field of a Continuous Line Charge

In physics, symmetry in a system means that something in the considered system remains unchanged due to a specific operation to which it is subjected. For example, consider a horizontal square. The square looks the same if its right and left sides are interchanged. Hence, it is symmetric under a right-left interchange.
In calculations of electric fields, symmetry is of great use. For example, while calculating electric fields of continuous charge distributions.
Consider a line element with a...
Crystal Field Theory - Tetrahedral and Square Planar Complexes02:46

Crystal Field Theory - Tetrahedral and Square Planar Complexes

Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
Determining Electric Field From Electric Potential01:12

Determining Electric Field From Electric Potential

The electric field and electric potential are related to each other. If the electric field at various points in the region of interest is known, it can be used to calculate the electric potential difference between any two points. Similarly, if the electric potential is known for various points, then it is possible to calculate the electric field.
In general, regardless of whether the electric field is uniform, it points in the direction of decreasing potential because the force on a positive...
Finding Electric Potential From Electric Field01:13

Finding Electric Potential From Electric Field

For a system of charges, it is easy to calculate the system's potential because potential is a scalar quantity. However, in some instances where calculating the electric field is more straightforward than finding the potential, the electric field is used to calculate the system's potential. For a positive charge, the electric field is radially outward, and the potential is positive at any finite distance from the positive charge. In such an electric field, the motion away from the positive...

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Updated: May 10, 2026

Characterization of Recombination Effects in a Liquid Ionization Chamber Used for the Dosimetry of a Radiosurgical Accelerator
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Determination of square equivalent field for rectangular field in electron therapy.

Mohammad J Tahmasebi Birgani1, Mohammad A Behrouz, Saeedeh Aliakbari

  • 1Department of Medical Physics and Radiation Therapy, University of Jundi Shapoor, School of Medicine, Ahwaz, Iran.

Journal of Medical Physics
|June 19, 2013
PubMed
Summary

This study defines equivalent fields for electron beams using pencil beam theory and multiple scattering. Findings show circular fields larger than lateral scattering equilibrium are equivalent, validated by experimental data.

Keywords:
Dosimetryelectron therapyfield equivalencemass angular scattering powerpencil beam theory

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Published on: February 20, 2021

Area of Science:

  • Medical Physics
  • Radiation Oncology
  • Dosimetry

Background:

  • Electron beam therapy relies on accurate dose calculations, often simplified using equivalent field concepts.
  • The Fermi-Eyges model describes electron beam dose profiles as Gaussian, necessitating understanding electron scattering.
  • Accurate determination of mean square radial displacement scattering is crucial for dose distribution modeling.

Purpose of the Study:

  • To investigate the concept of equivalent fields for electron beams using pencil beam theory.
  • To incorporate backscattered electrons and multiple scattering theories into calculating electron scattering parameters.
  • To determine the relationship between field dimensions, depth, and electron beam scattering for treatment planning.

Main Methods:

  • Utilized pencil beam theory and the Fermi-Eyges model for electron beam dose distribution.
  • Applied multiple scattering theories to account for backscattered electrons in calculating mean square radial displacement.
  • Analyzed electron scattering at depths where mean square radial displacement is extremum for rectangular fields.
  • Employed analytical calculations and validated findings with experimental measurements of Percentage Depth Dose (PDD) and output factors.

Main Results:

  • Developed a formula for equivalent fields based on electron scattering properties.
  • Demonstrated that circular fields with radius greater than or equal to lateral scattering equilibrium (LSE) are equivalent broad fields.
  • Analytical calculations showed good agreement with experimental data for 6, 9, 12, and 15 MeV electron beams.
  • Experimental validation confirmed the equivalence of calculated fields using PDD and output factor measurements.

Conclusions:

  • The study provides a method for defining equivalent fields in electron beam therapy based on scattering characteristics.
  • Lateral scattering equilibrium (LSE) is a critical parameter for determining field equivalence in electron dosimetry.
  • The findings support the use of analytical models and experimental validation for optimizing electron beam treatment planning.