Inverse-collimated proton radiography for imaging thin materials.

Area of Science:

• Physics
• Materials Science
• Imaging Technology

Background:

• Relativistic, magnetically focused proton radiography is effective for imaging dense objects (>20 g cm⁻²).
• Existing methods have limitations in imaging very low areal density materials.

Purpose of the Study:

• To detail and demonstrate an inverse-collimation scheme for proton radiography.
• To enhance the sensitivity of proton radiography for imaging thin media (<100 mg cm⁻²).

Main Methods:

• Utilized the 800 MeV LANSCE proton beam at Los Alamos National Laboratory.
• Implemented an inverse-collimation scheme at the Fourier plane to remove unscattered protons.
• Imaged Xenon gas shocked by an aluminum plate at Mach 8.8 using a 5-mrad inverse collimator.
• Employed Geant4 simulations for proton transport modeling and inverse-collimator design optimization.

Main Results:

• Achieved high sensitivity to areal densities below 100 mg cm⁻², discerning a 49 mg cm⁻² change across a shock front with a contrast-to-noise ratio of 3.
• Expanded the sensitive areal density range of proton radiography to approximately 25 mg cm⁻² to 100 g cm⁻² (over three orders of magnitude).
• Demonstrated the capability to simultaneously image both dense structures and thin ejecta materials.

Conclusions:

• The inverse-collimation technique significantly enhances proton radiography's sensitivity for thin materials.
• This method broadens the applicability of proton radiography for characterizing a wider range of areal densities in dynamic experiments.
• Optimized inverse-collimator design, guided by simulations, is crucial for specific experimental conditions and improved performance with reduced beam emittance.