title: Magnetization curves of sintered heavy tungsten alloys for applications in MRI-guided radiotherapy.
abstract: OBJECTIVE
  Due to the current interest in MRI-guided radiotherapy, the magnetic properties of the materials commonly used in radiotherapy are becoming increasingly important. In this paper, measurement results for the magnetization (BH) curves of a range of sintered heavy tungsten alloys used in radiation shielding and collimation are presented.
  
  
  METHODS
  Sintered heavy tungsten alloys typically contain >90% tungsten and <10% of a combination of iron, nickel, and copper binders. Samples of eight different grades of sintered heavy tungsten alloys with varying binder content were investigated. Using a superconducting quantum interference detector magnetometer, the induced magnetic moment m was measured for each sample as a function of applied external field H0 and the BH curve derived.
  
  
  RESULTS
  The iron content of the alloys was found to play a dominant role, directly influencing the magnetization M and thus the nonlinearity of the BH curve. Generally, the saturation magnetization increased with increasing iron content of the alloy. Furthermore, no measurable magnetization was found for all alloys without iron content, despite containing up to 6% of nickel. For two samples from different manufacturers but with identical quoted nominal elemental composition (95% W, 3.5% Ni, 1.5% Fe), a relative difference in the magnetization of 11%-16% was measured.
  
  
  CONCLUSIONS
  The measured curves show that the magnetic properties of sintered heavy tungsten alloys strongly depend on the iron content, whereas the addition of nickel in the absence of iron led to no measurable effect. Since a difference in the BH curves for two samples with identical quoted nominal composition from different manufacturers was observed, measuring of the BH curve for each individual batch of heavy tungsten alloys is advisable whenever accurate knowledge of the magnetic properties is crucial. The obtained BH curves can be used in FEM simulations to predict the magnetic impact of sintered heavy tungsten alloys.
authors.affiliation: Sydney Medical School, University of Sydney, NSW 2006, Australia.
authors.forename: Stefan
authors.initials: S
authors.lastname: Kolling
authors.affiliation: Illawarra Cancer Care Centre (ICCC), Wollongong, NSW 2500, Australia and Centre for Medical Radiation Physics (CMRP), University of Wollongong, Wollongong, NSW 2500, Australia.
authors.forename: Bradley M
authors.initials: BM
authors.lastname: Oborn
authors.affiliation: Sydney Medical School, University of Sydney, NSW 2006, Australia and Ingham Institute for Applied Medical Research, Liverpool, NSW 2170, Australia.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Keall
authors.affiliation: Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, NSW 2500, Australia and School of Physics, University of Wollongong, Wollongong, NSW 2500, Australia.
authors.forename: Joseph
authors.initials: J
authors.lastname: Horvat
mesh_terms: D000497:Alloys / Q000737:chemistry*; D003300:Copper / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D060328:Magnetic Phenomena; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009532:Nickel / Q000737:chemistry; D017711:Nonlinear Dynamics; D055618:Radiation Equipment and Supplies; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D014414:Tungsten / Q000737:chemistry*
chemical_list: D000497:Alloys; D003300:Copper; D009532:Nickel; D007501:Iron; D014414:Tungsten