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Proton (¹H) NMR: Chemical Shift

Proton (¹H) NMR: Chemical Shift

Organic molecules primarily contain carbon and hydrogen atoms. While all the hydrogen isotopes are NMR-active, protium or hydrogen-1 is the most abundant. It has a significant energy separation between its nuclear spin states due to its large gyromagnetic ratio. As per Boltzmann's distribution, an increase in the energy separation implies a greater excess population of nuclei available for excitation, resulting in a strong NMR absorption signal.
Absorption signals of all the protium nuclei...

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Related Experiment Video

Updated: Mar 2, 2026

Setting Limits on Supersymmetry Using Simplified Models

Setting Limits on Supersymmetry Using Simplified Models

Published on: November 15, 2013

SU-E-T-232: Proton Source Modeling for Geant4 Monte Carlo Simulations.

S Barnes^1,2, G McAuley^1,2, A Wroe^1,2

¹Loma Linda University, Loma Linda, CA.

Medical Physics

|May 19, 2017

Summary

This summary is machine-generated.

A point source model more accurately simulates proton beam characteristics in therapeutic nozzles compared to a Gaussian distribution, especially for large apertures. This finding is crucial for precise proton therapy dose calculations.

Keywords:

Monte Carlo methods Protons Scattering measurements Therapeutics

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Area of Science:

Medical Physics
Radiation Oncology
Computational Physics

Background:

Proton therapy offers precise dose delivery.
Accurate modeling of proton beam characteristics is essential for treatment planning.
Monte Carlo simulations are widely used for simulating radiation transport.

Purpose of the Study:

To evaluate the impact of initial proton source placement and angular distribution on dose distribution in a proton therapy nozzle.
To compare two simulation models: a 2D Gaussian distribution versus a point source for proton generation.

Main Methods:

Geant4 Monte Carlo simulations were employed to model a passively scattered proton treatment nozzle.
Two proton source models were investigated: a 2D Gaussian distribution and a point source, both calibrated to measured beam properties.
Depth dose curves and orthogonal beam profiles were analyzed to assess differences between the models.

Main Results:

The point source model demonstrated superior agreement with measured data for orthogonal beam profiles, especially with large apertures (up to 6.5% difference).
Depth dose curves and profiles for small apertures were not significantly affected by the source model.
For large apertures, the point source model achieved average and maximum differences of 0.7% and 1.6% compared to measured data, respectively.

Conclusions:

A point source model provides a more realistic representation of proton distribution and direction correlation within the nozzle.
Accurate Monte Carlo simulations, particularly using the point source model, are necessary for precise dose calculations in proton therapy, especially for large apertures and specific scattering configurations.