understanding mass transport in fuel cells using neutron imaging dr. david l. jacobson national...

Understanding mass transport in fuel cells using neutron imaging

Dr. David L. Jacobson

National Institute of Standards and Technology

100 Bureau Drive - Stop 8461

Bldg 235, Rm B185

Gaithersburg, MD 20899-8461

Phone: (301)975-6207

Fax: (301)926-1604

Email: david.jacobson@nist.gov

Overview

• Who are we and what is our mission

• Radiography

• Neutron Radiography

• NIST fuel cell role

• NIST Center for Neutron Research

• Fuel cell testing infrastructure

• Future goals and direction

• Access to the NIST facilities

Radiography

• Roentgen Hand (1898) formed using xrays

• Contrast is due to attenuation of radiation

• Scattering density of material can be extracted

• N - density of sample atoms per cm3

• I0 - incident neutrons per second per cm2

- neutron cross section in ~ 10-24 cm2

Radiography

0I tNeII 0

Sample

t

x-ray cross sectionH D C O Al Si Fe

neutron cross section

Radiography

• Neutrons are the able to see hydrogen through heavy elements

• Comparison of the relative size of the x-ray and thermal neutron scattering cross section for various elements.

Image Geometry

• Images are formed

ij

• CCD images each pixel is a count value proportional to the light from the scintillator.• The transmission image below each pixel is a color or grayscaled value proportional to the

fraction of neutrons that make it through the sample.

What an image is

Picture of the detector and sample holder assembly

Pinhole collimator

Neutron beam

Fuel cell Light tight box

Mirror

Lens

CCD chip

neutron to light converter

Computer

Neutron Camera

Neutron Imaging Facility

Neutron Image Quality

• Images are formed as shadows• Edges will be blurred by various effects• CCD camera and lens• Neutron to