Thallium Target Research Articles

Optimized Methods for the Production of High-Purity 203Pb Using Electroplated Thallium Targets.

203Pb is a surrogate imaging match for 212Pb. This elementally matched pair is emerging as a suitable pair for imaging and targeted radionuclide therapy in cancer care. Because of the half-life (51.9 h) and low-energy γ-rays emitted, 203Pb is suitable for the development of diagnostic radiopharmaceuticals. The aim of this work was to optimize the production and separation of high-specific-activity 203Pb using electroplated thallium targets. We further investigated the radiochemistry optimization using a suitable chelator, tetraazacyclododecane-1,4,7-triacetic acid (DO3A), and targeting vector, VMT-α-NET (lead-specific chelator conjugated to tyr3-octreotide via a polyethylene glycol linker). Methods: Targets were prepared by electroplating of natural or enriched (205Tl) thallium metal. Scanning electron microscopy was performed to determine the structure and elemental composition of electroplated targets. Targets were irradiated with 24-MeV protons with varying current and beam time to investigate target durability. 203Pb was purified from the thallium target material using an extraction resin (lead resin) column followed by a second column using a weak cation-exchange resin to elute the lead isotope as [203Pb]PbCl2 Inductively coupled plasma mass spectrometry studies were used to further characterize the separation for trace metal contaminants. Radiolabeling efficiency was also investigated for DO3A chelator and VMT-α-NET (a peptide-based targeting conjugate). Results: Electroplated targets were prepared at a high plating density of 76-114 mg/cm2 using a plating time of 5 h. A reproducible separation method was established with a final elution in HCl (400 μL, 1 M) suitable for radiolabeling. Greater than 90% recovery yields were achieved, with an average specific activity of 37.7 ± 5.4 GBq/μmol (1.1 ± 0.1 Ci/μmol). Conclusion: An efficient electroplating method was developed to prepare thallium targets suitable for cyclotron irradiation. A simple and fast separation method was developed for routine 203Pb production with high recovery yields and purity.

Application of Ion Exchange, Solvent Extraction, and Ion-Imprinted Methods for Separation of 203Pb

Lead-203 was produced by proton bombardment of natural thallium target. For producing 203Pb, natTl was electroplated on copper backing as target and was bombarded by energetic proton beam. After bombardment, the target was dissolved in 1 M HNO3. Ion exchange, solvent extraction, and nanomagnetic ion-imprinted polymer methods were used for separating 203Pb from thallium. The separation efficiency of these methods was studied. γ-Ray spectroscopy was applied for evaluating 203Pb and others radionuclides. The separation efficiency was determined from the γ-ray spectra. The separation efficiency of the methods using ion exchange, solvent extraction, and nanomagnetic ion-imprinted adsorbent was 98, 99.3, and 96.4%, respectively.

Magnetized ion-imprinted polymer-coated nano-particles for selective separation and trace detection of 203Pb using gamma-ray spectrometry

Lead-203 is produced from the proton bombardment of natural thallium target. The application of novel Pb(II) ion-imprinted polymer coated on magnetic nano-particles was investigated for separation and detection of ultra-trace of Pb(II) ions. This novel sorbent was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. Effects of various factors were considered in this study. In order to examine the selectivity of the sorbent for absorbing Pb(II) ions, the effects of variety of competitor ions interfering on preconcentration and recovery of Pb(II) ions were also investigated. The recovery of the method was obtained 96.4% by 2.5 mL of appropriate eluent. Finally, the sorbent was applied for separation and determination of 203Pb(II) ions.

Production cross section of At radionuclides from7Li+natPb and9Be+natTl reactions

Earlier we reported theoretical studies on the probable production of astatine radionuclides from $^{6,7}$Li and $^{9}$Be-induced reactions on natural lead and thalliun targets, respectively. For the first time, in this report, production of astatine radionuclides has been investigated experimentally with two heavy ion induced reactions: $^{9}$Be+$^{\textrm{nat}}$Tl and $^{7}$Li+$^{\textrm{nat}}$Pb. Formation cross sections of the evaporation residues, $^{207,208,209,210}$At, produced in (HI, xn) channel, have been measured by the stacked-foil technique followed by the off-line $\gamma$-spectrometry at the low incident energies ($<$50 MeV). Measured excitation functions have been explained in terms of compound nuclear reaction mechanism using Weisskopf-Ewing and Hauser-Feshbach model. Absolute cross section values are lower than the respective theoretical predictions.

Assessment of personnel absorbed dose at production of medical radioisotopes by a cyclotron

The medical radioisotope (201)Tl is produced by a cyclotron through the (203)Tl(p, 3n)(201)Pb reaction in the nuclear medicine research group of Agricultural, Medical and Industrial Research Schools in Iran. The produced (201)Pb decays to (201)Tl by electron capture. One of the most important problems that may occur is malfunction of a part of target or beam line, so that it needs the bombardment to be stopped and the problem fixed. In this work, induced radioactivity of the target, aluminium case of target, beam line and concrete walls of the thallium target room were calculated by Monte Carlo method. Then by using the results of the Monte Carlo simulation, the whole body absorbed dose to cyclotron personnel during repair and after stopping the bombardment, were assessed at different places of target room.

Production and separation of no-carrier-added 208,209,210At produced from heavy ion activation on natural thallium target

No-carrier-added (nca) 208,209,210At was produced for the first time from 9Be induced reaction on thallium carbonate target at BARC-TIFR pelletron, Mumbai, India. The target of 4 mg/cm2 thickness was prepared by centrifugation technique. Nca At was separated from the thallium target by liquid–liquid extraction using liquid cation exchanger HDEHP dissolved in cyclohexane and liquor ammonia.

Analysis and improvement of cyclotron thallium target room shield

Because of high neutron and gamma-ray intensities generated during bombardment of a thallium-203 target, a thallium target-room shield and different ways of improving it have been investigated. Leakage of neutron and gamma ray dose rates at various points behind the shield are calculated by simulating the transport of neutrons and photons using the Monte Carlo N Particle transport computer code. By considering target-room geometry, its associated shield and neutron and gamma ray source strengths and spectra, three designs for enhancing shield performance have been analysed: a shielding door at the maze entrance, covering maze walls with layers of some effective materials and adding a shadow-shield in the target room in front of the radiation source. Dose calculations were carried out separately for different materials and dimensions for all the shielding scenarios considered. The shadow-shield has been demonstrated to be one suitable for neutron and gamma dose equivalent reduction. A 7.5-cm thick polyethylene shadow-shield reduces both dose equivalent rate at maze entrance door and leakage from the shield by a factor of 3.

Yield and excitation function measurements of some nuclear reactions on natural thallium induced by protons leading to the production of medical radioisotopes201Tl and203Pb

Excitation functions for201Pb,202mPb,203Pb and204mPb radionuclides which are formedviaproton induced reactions with natural thallium target have been measured from their respective threshold (Ethr) to 27.5 MeV using activation technique. Natural copper foils were used to monitor the cyclotron beam. The integral yields (MBq/μA h) of the produced radionuclides were calculated from the measured excitation functions. The optimum proton energy range for the production of203Pb with low amount of impurities is (16–10 MeV) after 5 h of EOB. The experimental cross-sections fornatTl(p,xn) reactions were compared with the cross-sections recommended by the IAEA and with earlier published data when it was possible.

Investigation of [formula omitted] nuclear reaction in a cyclotron accelerator as a neutron source

Using cyclotron accelerator (at Cyclotron Dept. in Karaj) the radioisotope 201Tl is produced through the Tl ( p,3n ) 81 201 Pb 82 201 → Ec, β + Tl 81 201 reaction. The main objective of this paper is to calculate the intensity, energy spectrum and angular distribution of the neutrons produced from the above reactions. The reason is that, if the neutron characteristics are reasonable enough then at the same time that 201Pb (and subsequently 201Tl) is produced, the above nuclear reaction can be considered as a neutron source, which in turn can be applied for different purposes. Of course depends on the application, the neutrons must be collimated and thermalized (if thermal neutron is needed for example for neutron activation analysis). Besides, the knowledge about the characteristics of the emitted neutrons can help us to predict the activity of the concrete walls and equipments in the target room. And also it is possible to design shielding for these sorts of neutron sources. In this paper the intensity, energy spectrum and angular distribution of neutrons produced from the above mentioned reaction is investigated. In our investigation the thickness of thallium layer assumed to be 70 μm coated on copper sub-layer. The target (thallium) was bombarded by protons with energy 28.5 MeV and 200 μA current. By using the computational code SRIM2000 the average proton energy at different points of the traveling path was calculated and then by using computational code ALICE91 and reaction rate equation, the neutron intensity from the Tl ( p,3n ) 81 203 Pb 82 201 reaction was determined to be 1.26 × 10 13 n/s. With the same method, the neutron intensity produced from the copper sub-layer i.e. from 63Cu + p → 63Zn + n nuclear reaction was calculated to be 9.19 × 10 12 n/s. As a result, the total neutron intensity from thallium target and its copper sublayer was determined to be 2.179 × 10 13 n/s, which is comparable with some conventional neutron sources such as Am–Be neutron source, and is high enough to be applied for different purposes. Our calculations also showed that the neutron energy spectrum from thallium target and its copper sub-layer has a peak around 1 MeV region. The angular distribution of produced neutrons, has its maximum value at angle 0–2.5° and decreases slowly as the angle of neutron emission increases, and its minimum value occurs at backward direction, i.e. 177.5–180°. It means that the produced neutrons, are mostly emitted in the forward direction.

Spin-orbit and interference asymmetries in elastic scattering of electrons from heavy one-electron atoms

Two asymmetries in the differential cross section for elastic scattering of electrons from one-electron atoms are discussed. Numerical results for the standard left-right asymmetry (electrons polarised, atoms unpolarised) and the interference asymmetry (electrons unpolarised, atoms polarised) are presented for caesium and thallium targets. For electron-thallium scattering, it is found that the former left-right asymmetry is predominantly due to spin-nonconserving processes in the electron-core interaction, even for very low scattering energies. This result explains the relatively small importance of the fine-structure effect (based on exchange between the continuum and the target electrons) for this particular collision system.

The quantification of Tl and Cu concentrations in 201Tl solutions using anodic stripping voltammetry

Thallium-201 is a cyclotron produced isotope which is used in nuclear medicine for myocardial function studies. Thallium-201 is prepared by the (p, 3n) reaction on 203Tl to form 201Pb which decays by positron emission to 201Tl. Prior to irradiation the thallium target is electro-deposited onto a copper cathode. After irradiation the target is processed by leaching the cathode with dilute acid and passing the leachate through ion exchange resins. Pharmocopoeia monographs on pharmaceutical grade 201Tl define limits on the concentrations of Tl and Cu which may be present in solutions of 201Tl. It is therefore important from a quality control viewpoint to have a rapid, accurate means of analysis of quantify levels of these metals in radioactive solutions of 201Tl. We have developed a procedure utilizing anodic stripping voltammetry to quantify concentrations of Tl and Cu in solutions of 201Tl.

Separation of lead-203 from cyclotron-bombarded thallium targets by ion-exchange chromatography

A simple method is presented for the separation of lead-203 from copper-backed thallium cyclotron targets. The procedure involves cation-exchange chromatography in hydrochloric acid and hydrochloric acid—acetone mixtures. Further purification involves anion-exchange chromatography in nitric acid—hydrobromic acid mixtures. A cation-exchange column containing 3.0 g of resin can handle as much as 15 g of thallium and 160 mg of copper. An anion-exchange column containing 3.0 g of resin can separate lead from up to 200 mg of thallium and 10 mg of copper. Separations are extremely sharp and less than 0.1 μg of thallium and less than 0.1 μg of copper remain in the lead-203 fraction.

The separation of 203Pb from a thallium target

The separation of 203Pb from a thallium target

Study of the Energy Levels ofTl203Using (γ,γ′) Reaction

Elastic and inelastic nuclear resonant scattering of monochromatic photons from $^{203}\mathrm{Tl}$ has been studied using a 20-cc Ge(Li) detector. The $\ensuremath{\gamma}$ source was obtained from thermal-neutron capture in titanium. The scattering isotope was identified by using an isotopically enriched thallium target. The energy of the resonance level in $^{203}\mathrm{Tl}$ was found to be 6.418 MeV. Assuming the high-energy lines to be primary transitions deexciting the resonance level, some 14 energy levels were found from the ground state up to 2.9 MeV, 4 of which may be identified with recently reported levels.By measuring the angular distribution of the scattered radiation, the spin of the 6.418-MeV level was determined to be \textonehalf{}, and thus, based on the assumption of dipole transitions, the spins of several low-lying levels were found to be either \textonehalf{} or $\frac{3}{2}$. The total radiative width of the resonance level was determined and found to be ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}=0.32\ifmmode\pm\else\textpm\fi{}0.06$ eV and $\frac{{\ensuremath{\Gamma}}_{0}}{{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}}=0.026$. The spectral shape of scattered radiation was found to have a strong intensity bump at about 5 MeV; this is discussed in the light of similar bumps obtained in ($n,\ensuremath{\gamma}$) and ($d,p\ensuremath{\gamma}$) reactions on nuclei in the same mass region.

Study of the Energy Levels ofTl205Using the (γ,γ′) Reaction

Both elastic and inelastic scatterings of monochromatic photons were used for studying the energy levels of $^{205}\mathrm{Tl}$; the photons were produced by thermal-neutron capture in iron, and the resonantly scattered spectrum was measured using Ge(Li) detectors. The scattering isotope was identified by using an isotopically enriched thallium target. The energy of the resonance level in $^{205}\mathrm{Tl}$ was found to be 7.646 MeV. The spectral shape of the scattered radiation was found to have a strong intensity bump above about 4.5 MeV. Energies and intensities of several $\ensuremath{\gamma}$ lines were measured in the region 1.0-7.7 MeV. Assuming the high-energy lines to be primary transitions deexciting the resonance level, 25 energy levels were found from the ground state up to 3.4 MeV, 8 of which may be identified with recently reported levels. By measuring the angular distribution of the scattered radiation, the spin of the scattering level was found to be \textonehalf{}. The width of the resonance level was determined and was found to be $\ensuremath{\Gamma}=0.98\ifmmode\pm\else\textpm\fi{}0.09$ eV, and $\frac{{\ensuremath{\Gamma}}_{0}}{\ensuremath{\Gamma}}=0.58$. The E1 character of the scattered radiation was inferred from the systematics of the radiation widths of highly excited levels, and the resonance level was interpreted as being associated with the tail of the giant electric-dipole resonance. The $^{205}\mathrm{Tl}$ levels are discussed in terms of the predictions of the shell model. The anomalous intensity bump in the $\ensuremath{\gamma}$ spectrum is discussed in the light of similar bumps obtained in the ($n,\ensuremath{\gamma}$) reaction on nuclei in the same mass region.

Alpha-Decay Properties of Neutron-Deficient Isotopes of Emanation

Isotopes of emanation (element 86) with 126 or fewer neutrons were prepared at the Heavy Ion Linear Accelerator by bombardment of platinum, gold, mercury, and thallium targets with $^{16}\mathrm{O}$, $^{14}\mathrm{N}$, and $^{12}\mathrm{C}$ nuclei. Several techniques were developed for isolation of the gaseous products. Si(Au) surface-barrier detectors were used to measure $\ensuremath{\alpha}$ particles emitted by emanation isotopes and by their polonium and astatine daughters. Mass- number assignments of new isotopes of mass 201 through 205 were based on genetic relationships and on excitation functions. The probable nature of the isomerism observed in $^{203}\mathrm{Em}$ is discussed. Properties of isotopes with masses 206 through 212 were confirmed.