Abstract
Through the use of Time-of-Flight Three Dimensional Polarimetric Neutron Tomography (ToF 3DPNT) we have for the first time successfully demonstrated a technique capable of measuring and reconstructing three dimensional magnetic field strengths and directions unobtrusively and non-destructively with the potential to probe the interior of bulk samples which is not amenable otherwise. Using a pioneering polarimetric set-up for ToF neutron instrumentation in combination with a newly developed tailored reconstruction algorithm, the magnetic field generated by a current carrying solenoid has been measured and reconstructed, thereby providing the proof-of-principle of a technique able to reveal hitherto unobtainable information on the magnetic fields in the bulk of materials and devices, due to a high degree of penetration into many materials, including metals, and the sensitivity of neutron polarisation to magnetic fields. The technique puts the potential of the ToF time structure of pulsed neutron sources to full use in order to optimise the recorded information quality and reduce measurement time.
Highlights
Where c = 4.632 × 1014 T−1 m−2 is the Larmor constant, and B is the magnetic field strength
We measured with a pulsed polychromatic neutron beam using the time-of-flight (ToF) information to determine the neutron wavelength, with the current in the spin rotators synchronised with the neutron pulse in order to achieve the proper neutron spin rotation for all neutron wavelengths
In order to reconstruct the measured magnetic field from the recorded polarimetric neutron tomographic data set, we have developed the reconstruction procedure presented
Summary
Through the use of Time-of-Flight Three Dimensional Polarimetric Neutron Tomography (ToF 3DPNT) we have for the first time successfully demonstrated a technique capable of measuring and reconstructing three dimensional magnetic field strengths and directions unobtrusively and nondestructively with the potential to probe the interior of bulk samples which is not amenable otherwise. As described in[11,12] tomographic reconstruction of a magnetic field is not as straight forward as standard attenuation tomography since the polarisation of a neutron beam passing through a region of various magnetic field directions and strengths cannot be calculated using a simple line integral because of the non-commuting properties of the neutron spin orientation along the path[3].
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