High-energy electron measurements with thin Si detectors

A technique for measuring high-energy electrons using Si detectors of various thicknesses that are much smaller than the range of the examined electrons is presented. The advantages of the method are discussed on the basis of electron-positron pair creation recently studied in deuteron-deuteron fusion reactions at very low energies. Careful Geant 4 Monte Carlo simulations enabled the identification of the main spectral contributions of emitted electrons and positrons resulting from the energy loss mechanisms and scattering processes within the target, detector and their holders. Significant changes in the intensity of the detected electrons, depending on the detector thickness and the thicknesses of absorption foils placed in the front of the detector could be observed. The corresponding correction factors have been calculated and can be used for different applications in basic and applied research

Enhancement of the Deuteron-Fusion Reactions in Metals and its Experimental Implications

Recent measurements of the reaction d(d,p)t in metallic environments at very low energies performed by different experimental groups point to an enhanced electron screening effect. However, the resulting screening energies differ strongly for divers host metals and different experiments. Here, we present new experimental results and investigations of interfering processes in the irradiated targets. These measurements inside metals set special challenges and pitfalls which make them and the data analysis particularly error-prone. There are multi-parameter collateral effects which are crucial for the correct interpretation of the observed experimental yields. They mainly originate from target surface contaminations due to residual gases in the vacuum as well as from inhomogeneities and instabilities in the deuteron density distribution in the targets. In order to address these problems an improved differential analysis method beyond the standard procedures has been implemented. Profound scrutiny of the other experiments demonstrates that the observed unusual changes in the reaction yields are mainly due to deuteron density dynamics simulating the alleged screening energy values. The experimental results are compared with different theoretical models of the electron screening in metals. The Debye-H\"{u}ckel model that has been previously proposed to explain the influence of the electron screening on both nuclear reactions and radioactive decays could be clearly excluded.Comment: 22 pages, 12 figures, REVTeX4, 2-column format. Submitted to Phys. Rev. C; accepte

Genetic inactivation of the Fanconi anemia gene FANCC identified in the hepatocellular carcinoma cell line HuH-7 confers sensitivity towards DNA-interstrand crosslinking agents

Background: Inactivation of the Fanconi anemia (FA) pathway through defects in one of 13 FA genes occurs at low frequency in various solid cancer entities among the general population. As FA pathway inactivation confers a distinct hypersensitivity towards DNA interstrand-crosslinking (ICL)-agents, FA defects represent rational targets for individualized therapeutic strategies. Except for pancreatic cancer, however, the prevalence of FA defects in gastrointestinal (GI) tumors has not yet been systematically explored. Results: A panel of GI cancer cell lines was screened for FA pathway inactivation applying FANCD2 monoubiquitination and FANCD2/RAD51 nuclear focus formation and a newly identified FA pathway-deficient cell line was functionally characterized. The hepatocellular carcinoma (HCC) line HuH-7 was defective in FANCD2 monoubiquitination and FANCD2 nuclear focus formation but proficient in RAD51 focus formation. Gene complementation studies revealed that this proximal FA pathway inactivation was attributable to defective FANCC function in HuH-7 cells. Accordingly, a homozygous inactivating FANCC nonsense mutation (c.553C > T, p.R185X) was identified in HuH-7, resulting in partial transcriptional skipping of exon 6 and leading to the classic cellular FA hypersensitivity phenotype; HuH-7 cells exhibited a strongly reduced proliferation rate and a pronounced G2 cell cycle arrest at distinctly lower concentrations of ICL-agents than a panel of non-isogenic, FA pathway-proficient HCC cell lines. Upon retroviral transduction of HuH-7 cells with FANCC cDNA, FA pathway functions were restored and ICL-hypersensitivity abrogated. Analyses of 18 surgical HCC specimens yielded no further examples for genetic or epigenetic inactivation of FANCC, FANCF, or FANCG in HCC, suggesting a low prevalence of proximal FA pathway inactivation in this tumor type. Conclusions: As the majority of HCC are chemoresistant, assessment of FA pathway function in HCC could identify small subpopulations of patients expected to predictably benefit from individualized treatment protocols using ICL-agents

Medically unexplained symptoms, illness perception and childhood experience in neurology outpatients

AbstractObjectives: Up to one third of patients presenting to neurology outpatients clinics have medically unexplained symptoms, but the aetiology of such symptoms is not well understood. In the current study we sought to investigate the role of anxiety, depression, cognitive factors and early experience in the development of medically unexplained symptoms.Method: Fifty-seven new patients presenting to a neurology outpatients clinic were studied. Demographic details were recorded and a Hospital Anxiety and Depression Scale, an Illness Perception Questionnaire, and a Childhood Development Questionnaire were administered. An assessment was made by trained medical investigators as to whether the patients symptoms were medically unexplained or accounted for by organic pathology.Results: We found that 17 out of 56 patients (30%) had medically unexplained symptoms. Such patients complained of a greater number of symptoms, were more anxious, were more likely to have a past history of depression, and were more likely to attribute their illness to stress than patients with a presumed organic basis for their disease. They were also more likely to have been in foster care as children. High levels of depression and anxiety were strongly associated with the number of physical symptoms and the perceived negative consequences of the illness.Conclusions: The recognition and treatment of anxiety and depressive disorders may contribute to the management of patients with medically unexplained symptoms. Open discussion of beliefs regarding aetiology are also likely to be of benefit regardless of the presence or absence of organic pathology.</jats:p

Screening and resonance enhancements of the

The $^{2}\text{H(d,~p)}^{3}\text{H}$ reaction cross-section has been measured for deuteron energies below 25 keV in a deuterized Zr target under improved ultra-high-vacuum conditions and controlled target surface contamination. The increase of reaction enhancement factors towards lower energies is much weaker than that determined before and can result not only from the electron screening effect but also from a suggested 0+ threshold resonance in 4He. The cross-section calculations performed within the T-matrix approximation enable to estimate a coherent resonance contribution and explain the observed energy dependence of the enhancement factors. Additionally, indications for the increase of the screening energies due to impurities at the target surface could be found

Experiments on screening effect in deuteron fusion reactions at extremely low energies

The enhanced electron screening effect in nuclear reactions taking place in dense astrophysical plasmas is extremely important for determination of stellar reaction rates in terrestrial laboratories as well as in prediction of cross sections enhancement in interiors of stars such as White and Brown Dwarfs or Giant Planets. This effect resulting in reduction of the nuclear Coulomb potential by the atomic electrons has been confirmed in many laboratory experiments. Unfortunately, experimental screening energies are much higher than the theoretical predictions and the reason for that remains unknown. Here, we present absorbing results of the experiment studying d + d nuclear reactions in different deuterized metallic targets under ultra high vacuum conditions. The total cross sections and angular distributions of the 2H(d,p)3H and 2H(d,n)3He reactions have been measured using a deuteron beam of energies between 8 and 30 keV provided by the electron cyclotron ion source. The atomic cleanness of the target surface has been secured by combining Ar sputtering of the target and Auger electrons spectroscopy. Due to application of an on-line analysis method, the homogeneity of the implanted deuteron densities could be continuously monitored. We will discuss probable causes of the large discrepancy between theoretical and experimental data