Theoretical considerations predicted the feasibility of K-edge x-ray computed tomography (CT) imaging using energy discriminating detectors with more than two energy bins. This technique enables material-specific imaging in CT, which in combination with high-Z element based contrast agents, opens up possibilities for new medical applications. In this paper, we present a CT system with energy detection capabilities, which was used to demonstrate the feasibility of quantitative K-edge CT imaging experimentally. A phantom was imaged containing PMMA, calcium-hydroxyapatite, water and two contrast agents based on iodine and gadolinium, respectively. Separate images of the attenuation by photoelectric absorption and Compton scattering were reconstructed from energy-resolved projection data using maximum-likelihood basis-component decomposition. The data analysis further enabled the display of images of the individual contrast agents and their concentrations, separated from the anatomical background. Measured concentrations of iodine and gadolinium were in good agreement with the actual concentrations. Prior to the tomographic measurements, the detector response functions for monochromatic illumination using synchrotron radiation were determined in the energy range 25 keV-60 keV. These data were used to calibrate the detector and derive a phenomenological model for the detector response and the energy bin sensitivities.

Monte Carlo (MC) calculations are a fundamental tool for the investigation of ionization chambers (ICs) in radiation fields, and for calculations in the scope of IC reference dosimetry. Geant4, as used for the toolkit TOPAS, is a major general purpose code, generally suitable for investigating ICs in primary proton beams. To provide reliable results, the impact of parameter settings and the limitations of the underlying condensed history (CH) algorithm need to be known. A Fano cavity test was implemented in Geant4 (10.03.p1) for protons, based on the existing version for electrons distributed with the Geant4 release. This self-consistent test allows the calculation to be compared with the expected result for the typical IC-like geometry of an air-filled cavity surrounded by a higher density material. Various user-selectable parameters of the CH implementation in the EMStandardOpt4 physics-list were tested for incident proton energies between 30 and 250 MeV. Using TOPAS (3.1.p1) the influence of production cuts was investigated for bare air-cavities in water, irradiated by primary protons. Detailed IC geometries for an NACP-02 plane-parallel chamber and an NE2571 Farmer-chamber were created. The overall factor f as a ratio between the dose-to-water and dose to the sensitive air-volume was calculated for incident proton energies between 70 and 250 MeV. The Fano test demonstrated the EMStandardOpt4 physics-list with the WentzelIV multiple scattering model as appropriate for IC calculations. If protons start perpendicular to the air cavity, no further step-size limitations are required to pass the test within 0.1%. For an isotropic source, limitations of the maximum step length within the air cavity and its surrounding as well as a limitation of the maximum fractional energy loss per step were required to pass within 0.2%. A production cut of  ⩽5 μm or  ∼15 keV for all particles yielded a constant result for f of bare air-filled cavities. The overall factor f for the detailed NACP-02 and NE2571 chamber models calculated with TOPAS agreed with the values of Gomà et al (2016 Phys. Med. Biol. 61 2389) within statistical uncertainties (1σ) of<0.3% for almost all energies with a maximum deviation of 0.6% at 250 MeV for the NE2571. The selection of hadronic scattering models (QGSP_BIC versus QGSP_BERT) in TOPAS impacted the results at the highest energies by 0.3%  ±  0.1%. Based on the Fano cavity test, the Geant4/TOPAS Monte Carlo code, in its investigated version, can provide reliable results for IC calculations. Agreement with the detailed IC models and the published values of Gomà et al can be achieved when production cuts are reduced from the TOPAS default values. The calculations confirm the reported agreement of Gomà et al for [Formula: see text] with IAEA-TRS398 values within the given uncertainties. An additional uncertainty for the MC-calculated [Formula: see text] of  ∼0.3% by hadronic interaction models should be considered.

A search for the J π = 1/2 − spin-orbit partner of the J π = 3/2 − ground state in 7 He has been performed with the 7 Li(d, 2 He) chargeexchange reaction. The experimental results are incompatible with recent claims of such a state at very low excitation energy [M. Meister, et al., Phys. Rev. Lett. 88 (2002) 102501]. A decomposition of the spectrum is performed taking into account known resonances and quasifree charge-exchange reactions on 7 Li as well as on triton and 4 He clusters in the 7 Li ground state. A possible resonance at an excitation energy E x ≈ 1.45 MeV with a width Γ ≈ 2.0 MeV is suggested when the quasifree charge-exchange process on 7 Li is constrained by a measurement of the 6 Li(d, 2 He) reaction. Gamow-Teller strengths for transitions to the lowest states in 7 He deduced from the differential cross sections are in remarkable agreement with results from ab initio quantum Monte Carlo calculations.

Acquisition of quasi‐monoenergetic ("pristine") depth‐dose curves is an essential task in the frame of commissioning and quality assurance of a proton therapy treatment head. For pencil beam scanning delivery modes this is often accomplished by measuring the integral ionization in a plane perpendicular to the axis of an unscanned beam. We focus on the evaluation of three integral detectors: two of them are plane‐parallel ionization chambers with an effective radius of 4.1 cm and 6.0 cm, respectively, mounted in a scanning water phantom. The third integral detector is a 6.0 cm radius multilayer ionization chamber. The experimental results are compared with the corresponding measurements under broad field conditions, which are performed with a small radius plane‐parallel chamber and a small radius multilayer ionization chamber. We study how a measured depth‐dose curve of a pristine proton field depends on the detection device, by evaluating the shape of the depth‐dose curve, the relative charge collection efficiency, and intercomparing measured ranges. Our results show that increasing the radius of an integral chamber from 4.1 cm to 6.0 cm increases the collection efficiency by 0%–3.5% depending on beam energy and depth. Ranges can be determined by the large electrode multilayer ionization chamber with a typical uncertainty of 0.4 mm on a routine basis. The large electrode multilayer ionization chamber exhibits a small distortion in the Bragg Peak region. This prohibits its use for acquisition of base data, but is tolerable for quality assurance. The good range accuracy and the peak distortion are characteristics of the multilayer ionization chamber design, as shown by the direct comparison with the small electrode counterpart.PACS number: 87.55.Qr

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