Kolling Stefan, Oborn Bradley M, Keall Paul J, Horvat Joseph
Sydney Medical School, University of Sydney, NSW 2006, Australia.
Illawarra Cancer Care Centre (ICCC), Wollongong, NSW 2500, Australia and Centre for Medical Radiation Physics (CMRP), University of Wollongong, Wollongong, NSW 2500, Australia.
Med Phys. 2014 Jun;41(6):061707. doi: 10.1118/1.4873679.
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.
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.
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.
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.
鉴于当前对磁共振成像引导放射治疗的关注，放射治疗中常用材料的磁性能变得越来越重要。本文给出了一系列用于辐射屏蔽和准直的烧结重钨合金的磁化强度（BH）曲线的测量结果。
烧结重钨合金通常含有>90%的钨和<10%的铁、镍和铜粘结剂的组合。研究了八种不同等级、粘结剂含量不同的烧结重钨合金样品。使用超导量子干涉探测器磁力计，测量每个样品的感应磁矩m作为外加磁场H0的函数，并得出BH曲线。
发现合金中的铁含量起主导作用，直接影响磁化强度M，进而影响BH曲线的非线性。一般来说，饱和磁化强度随合金中铁含量的增加而增加。此外，对于所有不含铁的合金，尽管含有高达6%的镍，也未发现可测量的磁化强度。对于来自不同制造商但标称元素组成相同（95%W、3.5%Ni、1.5%Fe）的两个样品，测量到的磁化强度相对差异为11%-16%。
测量曲线表明，烧结重钨合金的磁性能强烈依赖于铁含量，而在不含铁的情况下添加镍没有可测量的影响。由于观察到来自不同制造商的标称组成相同的两个样品的BH曲线存在差异，因此每当对磁性能有准确了解至关重要时，建议对每一批重钨合金测量其BH曲线。所获得的BH曲线可用于有限元模拟，以预测烧结重钨合金的磁影响。
