ANSTO internship No. 3
- ANSTO Project supervisor : Andrew Manning
- Project duration: 3 months
- Nominal project commencement date: Flexible
Polarised neutron scattering is a powerful technique to gain unique information in scattering experiments with both magnetic and non-magnetic samples. To perform such experiments, existing neutron scattering instruments are modified with devices which filter and control the spin of the neutron beam, and the suitability of these devices is critical to the success of the experiment. At ACNS, we currently have a variety of setups which enable neutron polarisation experiments to be performed on six different instruments and are working to expand these capabilities. The project(s) offered can be tailored to the interests of the student across a variety of disciplines. Possible project topics include:
Project1: Polarised helium-3 gas transfer apparatus for Platypus detector tank
Suitable student disciplines: experimental physics, engineering
The polarised neutron reflectometer Platypus at ACNS can be used with a helium-3 spin-filter cell for polarisation analysis of off-specular scattering. This spin-filter cell is mounted inside the Platypus detector tank on a vertical translation stage, so that it can be moved in and out of the neutron beam as necessary. To use the cell, polarised helium-3 gas must be transferred from outside the detector tank through a magnetized tube to the cell in a way which does not result in the depolarization of the gas, while fitting within the geometrical and mechanical constraints of the instrument and minimizing the internal volume of the transfer line. This project involves the design (possibly with CAD software such as SolidWorks), prototyping and testing of a polarised helium-3 gas transfer apparatus suitable for this application.
Project2: Neutron guide fields for triple-axis spectrometer instruments
Suitable student disciplines: experimental physics, engineering
When using a polarised neutron beam on a triple-axis spectrometer (TAS) such as Sika or Taipan at ACNS, an important consideration is the relative orientation of the beam polarisation direction relative to the scattering vector Q. Existing setups use the versatile Pastis coil configuration, where a set of 3D Helmholtz-style coil windings are used to create a uniform field in any direction. However, this setup can be disadvantageous for TAS instruments due to the large range of scattering angles (2θ) used on such instruments, which can lead to the neutron beam being blocked by the coil windings. Furthermore, it can be difficult to maintain adequate continuity of the magnetic field profile from the spin-filter cells containing polarised helium-3 gas to the sample position over a range of angles. This project involves the design (with finite-element analysis software COMSOL), prototyping and testing of a new set of coils which provide a suitable magnetic field over a wide range of scattering angles on a TAS instrument, as well as compatibility with a variety of sample environments.
Project3: McStas simulations of polarised neutron instruments
Suitable student disciplines: experimental physics, theoretical physics
A powerful tool in the design of neutron scattering instrumentation is the use of ray-tracing software to benchmark the performance of various neutron optics components. McStas is a leading ray-tracing simulator software package dedicated to neutron scattering experiments, and the ability to calculate neutron polarisation features has recently been added to the software. This project involves using McStas to simulate polarised neutron scattering experiments on the six compatible instruments at ACNS (Pelican, Platypus, Quokka, Sika, Taipan and Wombat) to benchmark their performance and identify opportunities for improving the instrumentation on these beamlines.
Project4: Calibration methodology for polarised neutron experiments using Mantid
Suitable student disciplines: experimental physics, theoretical physics
An important aspect of polarised neutron scattering experiments is the need to correct the data collected to compensate for the characteristics of the helium-3 spin-filter cells. In particular, there is a pronounced time dependence to the data sets as a result of the spin-relaxation of the filter cells which alters their transmission and polarisation efficiency. Polarisation instrumentation can be calibrated with samples of known properties, such as a purely coherent nuclear scatterer. This project is to design a robust and efficient calibration methodology for polarisation analysis experiments, and to implement this using the Mantid software, which is a Python-based package for neutron scattering data.
Supervisor bio: Andrew Manning is the polarised helium-3 instrument scientist at ACNS, who works with instrument scientists for other neutron scattering instruments to achieve polarisation analysis experiments at ANSTO. Andrew’s primary responsibility is the metastable-exchange optical pumping station at ACNS, which produces spin-polarised helium-3 gas for use in neutron polarisation filters, along with the supporting infrastructure to enable polarisation analysis experiments.
- Project location: Lucas Heights Campus, B82
- Requirement for ANSTO site security clearance (requires 3 months advanced processing): Yes, and also access to an ANSTOnet IT account
- Option for to work remotely? In part, some lab-based work at Lucas Heights is required
- Will an interview step be required? Not necessarily, happy to discuss project informally with student
- Site attendance expectations: approx. 60% onsite, flexible
- Non-disclosure agreement required? (if so, this must be handled by the ANSTO affiliate itself) No