C. Vermeulen

Imaging quality of 44Sc in comparison with five other PET radionuclides using Derenzo phantoms and preclinical PET

PET is the favored nuclear imaging technique because of the high sensitivity and resolution it provides, as well as the possibility for quantification of accumulated radioactivity. (44)Sc (T1/2=3.97h, Eβ(+)=632keV) was recently proposed as a potentially interesting radionuclide for PET. The aim of this study was to investigate the image quality, which can be obtained with (44)Sc, and compare it with five other, frequently employed PET nuclides using Derenzo phantoms and a small-animal PET scanner. The radionuclides were produced at the medical cyclotron at CRS, ETH Zurich ((11)C, (18)F), at the Injector II research cyclotron at CRS, PSI ((64)Cu, (89)Zr, (44)Sc), as well as via a generator system ((68)Ga). Derenzo phantoms, containing solutions of each of these radionuclides, were scanned using a GE Healthcare eXplore VISTA small-animal PET scanner. The image resolution was determined for each nuclide by analysis of the intensity signal using the reconstructed PET data of a hole diameter of 1.3mm. The image quality of (44)Sc was compared to five frequently-used PET radionuclides. In agreement with the positron range, an increasing relative resolution was determined in the sequence of (68)Ga<(44)Sc<(89)Zr<(11)C<(64)Cu<(18)F. The performance of (44)Sc was in agreement with the theoretical expectations based on the energy of the emitted positrons.

Carbon radioactivity of 223Ac and a search for nitrogen emission

A very intense 227Pa source was produced in order to study the possible 14C and 15N spontaneous emission from 223Ac. After the irradiation of a hemispherical, highly efficient array of nuclear track detectors, about 350 Carbon events were found leading to a branching ratio with respect to alpha decay B = 3.2 10−11. Comparison with other 14C emitters allows the study of the influence of even-odd effects on cluster radioactivity.

Separation of 103Pd from Rh and Ag by the macroporous AG MP-1 anion exchange resin in Ag targets

A radiochemical process is reported for the production of 103Pd from Ag targets for use in brachytherapy. The procedure, which is based on anion exchange chromatography, separates Pd from a large amount of target material (16 g Ag), as well as Rh radioisotopes (mainly 101Rh and 100Rh), which are produced from decays of their Pd parents. The AG MP-1 anion exchange resin was used for the process. For elution of Rh and Ag, 3M nitric acid solution was used and 5% ammonia solution was used to elute the Pd. The average recovery of Pd was 97.4%. An elution curve for Pd was set up and a panel for the radiochemistry designed and installed in a hot cell.

Excitation Functions and Production Rates of Radionuclides Produced in the Proton Bombardment of natPr and natLa

Excitation functions and production rates are presented for various radionuclides formed in the bombardment of natPr and natLa with protons. Comparisons are made with theoretical predictions based on the geometry dependent hybrid model. Alternative production routes for 139Pr and 139Ce are investigated.

Production of 28 Mg by bombardment of nat Cl with 200MeV protons: Proof-of-concept study for a stacked LiCl target

A stacked target consisting of ten Al-encapsulated LiCl discs, for producing (28)Mg via the (nat)Cl(p,X)(28)Mg process in the energy region 50-200MeV, is described. This target was irradiated with a 200MeV beam at an intensity of 100nA, providing information on both yield and outscattering losses. Results of a Monte Carlo modelling of the beam and target, by means of the code MCNPX, are also presented. Similar Al-encapsulated LiCl discs were individually irradiated with 66MeV proton beams of 65 and 90μA, respectively, to study their behaviour under high-intensity bombardment. Once removed from the Al encapsulation, the (28)Mg can be separated from the LiCl target material efficiently, using a 12.5cm x 1cm(2) column containing Purolite S950 chelating resin. The eluate contains (7)Be but no other measurable radio-contaminants. The removal of the (7)Be contaminant is performed by cation exchange chromatography in malate media, with (28)Mg being retained by the resin and (7)Be eluted.

Encapsulation methods for solid radionuclide production targets at a medium-energy cyclotron facility

The techniques employed at iThemba LABS for the encapsulation of solid radionuclide production targets, based on cold indentation welding, electron beam welding and laser welding, are described. Some aspects of the target holders and cooling requirements to bombard targets in a tandem configuration with a 66 MeV proton beam, with intensities up to nominally 250 A, are also briefly discussed. These techniques are inter alia suitable for a production regimen compatible with the new generation of commercial, high-intensity 70 MeV cyclotrons.The techniques employed at iThemba LABS for the encapsulation of solid radionuclide production targets, based on cold indentation welding, electron beam welding and laser welding, are described. Some aspects of the target holders and cooling requirements to bombard targets in a tandem configuration with a 66 MeV proton beam, with intensities up to nominally 250 A, are also briefly discussed. These techniques are inter alia suitable for a production regimen compatible with the new generation of commercial, high-intensity 70 MeV cyclotrons.

Concurrent spectrometry of annihilation radiation and characteristic gamma-rays for activity assessment of selected positron emitters

A method is described to determine the activity of non-pure positron emitters in a radionuclide production environment by assessing the 511keV annihilation radiation concurrently with selected γ-lines, using a single High-Purity Germanium (HPGe) detector. Liquid sources of 22Na, 52Fe, 52mMn, 61Cu, 64Cu, 65Zn, 66Ga, 68Ga, 82Rb, 88Y, 89Zr and 132Cs were prepared specifically for this study. Acrylic absorbers surrounding the sources ensured that the emitted β+-particles could not escape and annihilate away from the source region. The absorber thickness was matched to the maximum β+ energy for each radionuclide. The effect on the 511keV detection efficiency by the non-homogeneous distribution of annihilation sites inside the source and absorber materials was investigated by means of Monte Carlo simulations. It was found that no self-absorption corrections other than those implicit to the detector calibration procedure needed to be applied. The medically important radionuclide, 64Cu, is of particular interest as its strongest characteristic γ-ray has an intensity of less than 0.5%. In spite of the weakness of its emission intensity, the 1346keV γ-line is shown to be suitable for quantifying the 64Cu production yield after chemical separation from the target matrix has been performed.

Large discrepancies in the excitation function data of the 68Zn(p, x)64Cu reaction: A possible explanation

The excitation function of the 68Zn(p, x)64Cu reaction was investigated in an attempt to clarify a serious discrepancy in the recently published data. New measurements based on both a weak γ-line of 1345.8 keV (0.47%) as well as the 511 keV annihilation radiation were performed after radiochemically separating the Cu from the Zn target matrix. In the case of the 511 keV measurements, the method of decay-curve analysis was employed as the annihilation radiation is not specific for a particular radionuclide. The results from the two methods were found to be in excellent agreement. Simulations were also performed to test the method of 511 keV decay-curve analysis for the effects of possible intruder contaminants.