RADON INHALATION EXPERIMENTS TO TEST RADON EXHALATION KINETICS.

Three experiments were conducted with a volunteer to test the kinetics of the 222Rn exhalation after a short-time exposure to an elevated 222Rn air concentration. Radon concentration in an exhaled air was measured, complemented by whole body counting of 222Rn decay products in a body. Exhaled activities are compared with the prediction of the recent ICRP biokinetic model for radon. While a rapid equilibration of the exhaled radon activity concentration with that in the air inhaled corresponded with the model, the measured 222Rn exhalation rate was significantly less than modelled. Five hours after termination of the inhalation phase, the radon concentration in the exhaled air decreased to levels expected for non-elevated indoor radon activity concentration. Whole body activities of the 222Rn decay products were found higher than expected. Inhalation of the unattached fraction or residual activity of decay products in the air inhaled may be the explanation.

A preclinical Talbot-Lau prototype for x-ray dark-field imaging of human-sized objects.

PURPOSE: Talbot-Lau x-ray interferometry provides information about the scattering and refractive properties of an object - in addition to the object's attenuation features. Until recently, this method was ineligible for imaging human-sized objects as it is challenging to adapt Talbot-Lau interferometers (TLIs) to the relevant x-ray energy ranges. In this work, we present a preclinical Talbot-Lau prototype capable of imaging human-sized objects with proper image quality at clinically acceptable dose levels. METHODS: The TLI is designed to match a setup of clinical relevance as closely as possible. The system provides a scan range of 120 × 30 cm2 by using a scanning beam geometry. Its ultimate load is 100 kg. High aspect ratios and fine grid periods of the gratings ensure a reasonable setup length and clinically relevant image quality. The system is installed in a university hospital and is, therefore, exposed to the external influences of a clinical environment. To demonstrate the system's capabilities, a full-body scan of a euthanized pig was performed. In addition, freshly excised porcine lungs with an extrinsically provoked pneumothorax were mounted into a human thorax phantom and examined with the prototype. RESULTS: Both examination sequences resulted in clinically relevant image quality - even in the case of a skin entrance air kerma of only 0.3 mGy which is in the range of human thoracic imaging. The presented case of a pneumothorax and a reader study showed that the prototype's dark-field images provide added value for pulmonary diagnosis. CONCLUSION: We demonstrated that a dedicated design of a Talbot-Lau interferometer can be applied to medical imaging by constructing a preclinical Talbot-Lau prototype. We experienced that the system is feasible for imaging human-sized objects and the phase-stepping approach is suitable for clinical practice. Hence, we conclude that Talbot-Lau x-ray imaging has potential for clinical use and enhances the diagnostic power of medical x-ray imaging.

Electron ionization of helium droplets containing C60 and alcohol clusters.

We report a mass spectrometric investigation of (C60)n clusters mixed with either methanol or ethanol clusters inside helium nanodroplets. The abundance of ion products produced by electron ionization shows marked differences compared with pure methanol/ethanol clusters without C60 [M. Goulart, P. Bartl, A. Mauracher, F. Zappa, A. M. Ellis and P. Scheier, Phys. Chem. Chem. Phys., 2013, 15, 3577], where clusters containing in excess of a hundred alcohol monomers were observed. In contrast, under identical conditions concerning He droplet size and alcohol pickup pressure, only a small number of alcohol molecules become attached to the fullerene ions. Our results suggest that each fullerene cluster acts as a charge sink, which hampers alcohol cluster formation, as well as intra-cluster ion-molecule reactions. The appearance of specific 'magic number' peaks suggests an enhanced probability for the attachment of small alcohol rings to (C60)n+ clusters.

Adsorption of hydrogen on neutral and charged fullerene: experiment and theory.

Helium droplets are doped with fullerenes (either C60 or C70) and hydrogen (H2 or D2) and investigated by high-resolution mass spectrometry. In addition to pure helium and hydrogen cluster ions, hydrogen-fullerene complexes are observed upon electron ionization. The composition of the main ion series is (H2)(n)HC(m)(+) where m = 60 or 70. Another series of even-numbered ions, (H2)(n)C(m)(+), is slightly weaker in stark contrast to pure hydrogen cluster ions for which the even-numbered series (H2)(n)(+) is barely detectable. The ion series (H2)(n)HC(m)(+) and (H2)(n)C(m)(+) exhibit abrupt drops in ion abundance at n = 32 for C60 and 37 for C70, indicating formation of an energetically favorable commensurate phase, with each face of the fullerene ion being covered by one adsorbate molecule. However, the first solvation layer is not complete until a total of 49 H2 are adsorbed on C60(+); the corresponding value for C70(+) is 51. Surprisingly, these values do not exhibit a hydrogen-deuterium isotope effect even though the isotope effect for H2/D2 adsorbates on graphite exceeds 6%. We also observe doubly charged fullerene-deuterium clusters; they, too, exhibit abrupt drops in ion abundance at n = 32 and 37 for C60 and C70, respectively. The findings imply that the charge is localized on the fullerene, stabilizing the system against charge separation. Density functional calculations for C60-hydrogen complexes with up to five hydrogen atoms provide insight into the experimental findings and the structure of the ions. The binding energy of physisorbed H2 is 57 meV for H2C60(+) and (H2)2C60(+), and slightly above 70 meV for H2HC60(+) and (H2)2HC60(+). The lone hydrogen in the odd-numbered complexes is covalently bound atop a carbon atom but a large barrier of 1.69 eV impedes chemisorption of the H2 molecules. Calculations for neutral and doubly charged complexes are presented as well.

Electron ionization of different large perfluoroethers embedded in ultracold helium droplets: effective freezing of short-lived decomposition intermediates.

RATIONALE: Electron ionization of three perfluoroethers (PFEs), C(6)F(14)O(3), C(8)F(18)O(4), and C(10)F(20)O(5), is studied in the gas phase and when the molecules are embedded in ultracold helium (He) droplets. The molecules investigated are model compounds for perfluoropolyethers used as lubricants in technical applications. The present study gives insight into possible radiolysis pathways upon radiation exposure. METHODS: The experiments utilized a crossed electron/droplet beam apparatus consisting of a He droplet source and pick-up chamber combined with a commercial time-of-flight mass spectrometer. The doped droplets were ionized by electron ionization at 70 eV. RESULTS: The He environment strongly affects the ionization patterns in the way that both the molecular ion M(+) and high-mass fragment ions formed by the loss of light neutral species such as F([M-F](+)), or CF(3)OCF(2) ([M-CF(3)OCF(2)](+)), etc., became strong signals in the mass spectrum. These signals were not or only barely visible in the gas-phase experiment and were identified as short lived (< µs) dissociation intermediates which in the gas phase immediately decomposed into lower-mass fragment ions. CONCLUSIONS: Ionic fragmentation intermediates are frozen and subsequently stabilized in the He environment. Helium droplets can hence be viewed as a cryogenic laboratory transforming short-lived decomposition intermediates into stable fragment ions appearing as strong signals in the mass spectrum.

TH-9 (a theophylline derivative) induces long-lasting enhancement in excitatory synaptic transmission in the rat hippocampus that is occluded by frequency-dependent plasticity in vitro.

Dementia, especially Alzheimer's disease, is a rapidly increasing medical condition that presents with enormous challenge for treatment. It is characterized by impairment in memory and cognitive function often accompanied by changes in synaptic transmission and plasticity in relevant brain regions such as the hippocampus. We recently synthesized TH-9, a conjugate racetam-methylxanthine compound and tested if it had potential for enhancing synaptic function and possibly, plasticity, by examining its effect on hippocampal fast excitatory synaptic transmission and plasticity. Field excitatory postsynaptic potentials (fEPSPs) were recorded in the CA1 hippocampal area of naïve juvenile male Sprague-Dawley rats using conventional electrophysiological recording techniques. TH-9 caused a concentration-dependent, long-lasting enhancement in fEPSPs. This effect was blocked by adenosine A1, acetylcholine (muscarinic and nicotinic) and glutamate (N-methyl-d-aspartate) receptor antagonists but not by a γ-aminobutyric acid receptor type B (GABA(B)) receptor antagonist. The TH-9 effect was also blocked by enhancing intracellular cyclic adenosine monophosphate and inhibiting protein kinase A. Pretreatment with TH-9 did not prevent the induction of long-term potentiation (LTP) or long-term depression (LTD). Conversely, induction of LTP or LTD completely occluded the ability of TH-9 to enhance fEPSPs. Thus, TH-9 utilizes cholinergic and adenosinergic mechanisms to cause long-lasting enhancement in fEPSPs which were occluded by LTP and LTD. TH-9 may therefore employ similar or convergent mechanisms with frequency-dependent synaptic plasticities to produce the observed long-lasting enhancement in synaptic transmission and may thus, have potential for use in improving memory.

Large-scale production of lambda bacteriophage and purified lambda deoxyribonucleic acid.

Large amounts of a heat-inducible phage lambda mutant (lambdaCI857) may be obtained under standardized conditions. The phage is harvested by simple polyethylene glycol (C 6000) precipitation and purified by CsCl density gradient banding. Deoxyribonucleic acid (DNA) is extracted by cold phenol and purified by sucrose density gradient sedimentation to yield a homogenous population of unbroken lambda DNA molecules.