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Related Concept Videos

¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule

In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the others.
¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)01:20

¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)

When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...
¹³C NMR: ¹H–¹³C Decoupling01:04

¹³C NMR: ¹H–¹³C Decoupling

The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...
NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...

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High-speed Continuous-wave Stimulated Brillouin Scattering Spectrometer for Material Analysis
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Creating a spread-out Bragg peak in proton beams.

David Jette1, Weimin Chen

  • 1ICT Radiotherapy Services, Livingston, NJ 07039, USA. Department of Medical Physics, Rush University, Chicago, IL 60612, USA. dave@jettes.org

Physics in Medicine and Biology
|May 12, 2011
PubMed
Summary

Researchers modified a proton beam model to achieve a flat spread-out Bragg peak (SOBP). Monte Carlo simulations determined optimal parameters for various energies and widths, improving proton therapy dose calculations.

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Area of Science:

  • Medical Physics
  • Radiation Oncology
  • Particle Beam Therapy

Background:

  • The Bortfeld and Schlegel model often produces tilted spread-out Bragg peaks (SOBP).
  • Achieving a uniform dose distribution is critical for effective radiation therapy.
  • Proton beam characteristics influence dose deposition and treatment outcomes.

Purpose of the Study:

  • To modify the Bortfeld and Schlegel model for improved SOBP generation.
  • To determine optimal parameters for creating satisfactory SOBPs using proton beams.
  • To provide data for accurate dose calculations in proton therapy.

Main Methods:

  • Arbitrarily varied the energy-range parameter 'p' in the Bortfeld and Schlegel model.
  • Utilized MCNPX Monte Carlo simulations to calculate proton beam interactions.
  • Tabulated optimal 'p' values and a correction factor for various beam energies and SOBP widths.

Main Results:

  • Successfully generated satisfactory, non-tilted SOBPs by adjusting the 'p' parameter.
  • Determined optimal 'p' values for maximum beam energies from 50 to 250 MeV and SOBP widths from 15% to 40%.
  • Demonstrated the model's application in analyzing deuteron and alpha particle dose deposition.

Conclusions:

  • The modified model effectively produces uniform SOBPs, enhancing proton therapy precision.
  • The tabulated data serves as a valuable resource for treatment planning and dose verification.
  • The methodology can be extended to analyze dose distributions for other charged particles.