（General use）

MLF Experimental Report
Project No.

Date of Report
2014/5/26
Name of person responsible for instrument

2013B0017

OIKAWA Kenichi, HARADA Masahide

Title of experiment

Name of Instrument/（BL No.）

Magnetic field imaging and Bragg-edge transmission using a

NOBORU (BL10)high-resolution, time-resolved neutron imaging detector based on

Date of Experiment

the muPIC micro-pixel chamber

2014/3/17-19

Name of principal investigator
PARKER Joseph Don
Affiliation
Kyoto University (*currently CROSS-Tokai)
Please report your samples, experimental method and results, discussion and conclusions.
tables for better explanation.

Please add figures and1. Name of sample(s) and chemical formula, or compositions including physical form.
We prepared a total of four samples for the experiment, consisting of Permalloy C metal (Ni 77%/Fe 14%/Cu
5%/Mo 4%) in 5cm x 5cm sheets with thicknesses of 0.2mm (2 sheets) and 0.5mm (2 sheets). Two sheets (oneof each thickness) were heat treated to optimize their magnetic shielding properties.
During the experiment, we also imaged samples provided by collaborator T. Shinohara consisting of a soft
magnetic iron-alloy foil (amorphous ribbon) with a thickness of 30μm. One sample was heat treated, while
the other was not.

2. Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

The experimental plan called for imaging a Permalloy sample using both magnetic imaging with polarized
neutrons and Bragg-edge imaging using the μPIC-based time-resolved neutron imaging detector (μNID).
The sample would be measured twice, before and after bending, allowing us to image the changes in both themagnetic domain structure and the physical crystal structure caused by the bending. Using the μNID, wecan achieve a spatial resolution of about 0.1mm. Polarized neutrons were provided by a polarizing apparatus
consisting of a super-mirror polarizer, spin flipper, two sets of two spin-rotator coils, super-mirror analyzer,and collimator. A magnetically shielded sample environment was also provided between the two sets of spinrotators. The combined polarization apparatus has a total length of about 1.7 m. The μNID was set about
30 cm downstream of the collimator and about 1 m from the sample position. The beam line setup was asfollows: rotary collimator large, duct-end collimator 32 x 32 mm2, upstream/downstream B4C slits 25 mm (y)x 18 mm (x).

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2. Experimental method and results (continued)
We began by measuring the heat-treated 0.2mm Permalloy sample. Unfortunately, we were not able tomeasure any magnetic field in the sample. We tried various combinations of incident and transmitted spinorientations (XX, YY, YZ, etc.) and even placed the sample inside a coil to create a guide field, but we wereunable to produce any contrast in the image. We are now studying the data to try and learn the reason for
the failure to image the magnetic field of the sample. Possible reasons are: the magnetic domains are toosmall, the sample is too thick, or our data analysis method is too simple or incomplete.
As a backup, we imaged a 30μm-thick amorphous foil composed of a soft magnetic iron alloy. Two samples
were measured, one with heat treatment and one without. Similar samples were measured previously using
the same polarizing setup and an RPMT as the imaging detector. The RPMT has limited spatial resolution of
only about 0.8mm. Then, we can hope to see more detail using the μNID with a spatial resolution of about0.1mm.
The two samples were measured for each of nine incident and transmitted neutron spin combinations (XX,YY, ZZ, XY, XZ, ...), with the spin flipper on and off, for a total of 18 measurements. Each of thesemeasurements was carried out for 45 minutes, for a total of 13.5 hours measurement time per sample. Thepolarization of the transmitted neutron beam could then be calculated for each spin combination as:
P(TOF) =𝑁𝑠𝑓𝑜𝑛 (𝑇𝑂𝐹) − 𝑁𝑠𝑓𝑜𝑓𝑓 (𝑇𝑂𝐹)
𝑁𝑠𝑓𝑜𝑛 (𝑇𝑂𝐹) + 𝑁𝑠𝑓𝑜𝑓𝑓 (𝑇𝑂𝐹)

where 𝑁𝑠𝑓𝑜𝑛 (𝑇𝑂𝐹), 𝑁𝑠𝑓𝑜𝑓𝑓 (TOF) are the measured neutron time-of-flight spectra with the spin flipper onand off, respectively. Figure 1 shows preliminary two-dimensional XX polarization distributions measured forthe foils without (left) and with (right) heat treatment for neutron TOF of 20 to 21 ms and a spatial resolutionof about 0.3 mm. The untreated sample shows a strong preference of the magnetic domains along thedirection in which the ribbon was drawn, while the heat treated sample shows no such preference. A moredetailed analysis including improved spatial resolution is ongoing.

Figure1. Two-dimensional XX polarization distributions for neutron TOF between 20 and 21 ms for amorphous foil samples
without (left) and with (right) heat treatment.

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