## 1 Introduction  
The isotope \({}^{89}\)Zr is one of several positron-emitting radiometals that are increasing in popularity as radiolabels for positron emission tomography (PET) [1; 2; 3; 4; 5]. A search of the PubMed database [6] found over 55 publications with \({}^{89}\)Zr mentioned in the title, 75% of which had been published since 2009. In particular, \({}^{89}\)Zr holds significant potential for immunoPET [4; 7; 8; 9; 10], a growing technique that uses radiolabelled antibodies, antibody fragments, and peptides for the _in vivo_ molecular imaging of antigens using PET [7; 11; 12; 13; 14]. \({}^{89}\)Zr is well-suited for this technique because it is a positron-emitter with a half-life (\(t_{1/2}\) = 3.27 days) that is long enough to accommodate the targeting time for these relatively large imaging agents, which is on the order of days. So far, the most prevalent application for \({}^{89}\)Zr has been cancer imaging, which is the focus of the majority of publications that used \({}^{89}\)Zr for _in vivo_ PET imaging. The information that is obtained using \({}^{89}\)Zr-immunoPET can be useful for cancer staging, therapy planning, and treatment monitoring, making \({}^{89}\)Zr a potentially valuable tool for personalized medicine. There are several properties of \({}^{89}\)Zr that make it an attractive radiolabel for immunoPET. Most importantly, the half-life of \({}^{89}\)Zr matches the biological half-life of antibodies. Additionally, \({}^{89}\)Zr emits positrons with a sufficient branching ratio (\(y\) = 23%) and provides good PET spatial resolution because it emits positrons at a low average energy (\(E_{\beta^{+},avg}\) = 396 keV), and therefore a lower positron range (1.2 mm [15]) compared to several other PET isotopes. Unfortunately, \({}^{89}\)Zr also emits a high energy (909 keV) gamma ray with a high branching ratio (99.0%). Thus, \({}^{89}\)Zr has a high gamma factor, \(\Gamma_{15\ keV}\) = 6.6 R\(\cdot\)cm\({}^{2}\cdot\)mCi\({}^{-1}\cdot\)h\({}^{-1}\) (weighted average of all gamma rays emitted) [16], meaning that the dose rate for this isotope is significant. The Zr\({}^{4+}\) ion prefers a coordination state of 6 to form a stable complex, and, so far, the most prevalent chelator of \({}^{89}\)Zr is desferrioxamine (DFO) [8; 17]. Table 1 summarizes chemical and nuclear decay properties of \({}^{89}\)Zr, including a simplified decay scheme. The vast majority of medical centers capable of producing medical isotopes do so using a low-energy \"biomedical\" cyclotron capable of bombarding a target with protons with energy (\(E_{p}\)) \(<\) 20 MeV (and alternatively deuterons with energy (\(E_{d}\)) \(<\)10 MeV). For these particles and energies, the highest cross-section is the (\(p\),\(n\)) reaction with a peak cross-section of \(\sim\)0.8 b at \(E_{p}\)-14 MeV. The (\(p\),\(n\)) reaction uses \({}^{89}\)Y target material, which is 100% naturally abundant and thus relatively inexpensive. For the above reasons, the \({}^{\rm nat}\)Y(\(p\),\(n\))\({}^{89}\)Zr reaction is the most common reaction route for \({}^{89}\)Zr production [18]. However, contaminants can also be produced in a \({}^{\rm nat}\)Y foil via the following common low-energy positron reactions: (\(p\),\(n\))\({}^{89m}\)Zr, (\(p\),2)\({}^{88}\)Zr, (\(p\),\(pn\))\({}^{88}\)Y, as shown in the Electronic Supplementary Information (ESI). Fortunately, high radionuclide purity can still be achieved using \(\sim\)15 MeV protons because \({}^{89m}\)Zr has a short half-life (\(t_{1/2}\) = 4.2 m) and a high degree of isomeric transition (IT = 93.8%) and because the (\(p\),\(2n\)) and (\(p\),\(pn\)) reactions require greater proton beam energies, so they have low cross-sections at \(E_{p}\)-15 MeV--less than 0.2 and 0.02 b, respectively [19]. The important characteristics of \({}^{89}\)Zr production in general are summarized in Table 2, and the parameters and results from eight publications [20, 21, 22, 23, 24, 25, 26, 27] about \({}^{89}\)Zr production are shown in the ESI.