Evaluating the intensity of the 803-keV γ ray of 210Po using a 4παß(LS)-γ(HPGe) measurement system.

The absolute intensity for the 803-keV γ ray of 210Po was evaluated by α-γ coincidence technique. A liquid sample with a known amount of 210Po embedded in scintillation fluid was measured in a coincidence-based system that comprises a Liquid Scintillator (LS) detector and a High-Purity Germanium (HPGe) detector. A photo-reflector assembly that contains the 210Po sample provides 100% efficiency for detecting the α particles. The combination between the HPGe and the LS detectors allows to reject non-coincident α-γ events while maintaining high resolution γ spectroscopy. Consequently, the faint 803-keV photopeak from 210Po could be observed in a background-free environment, and its intensity could be evaluated with good accuracy. Sample measurements were carried out over nine months to gather statistics and verify the reliability of the experimental procedure. The absolute intensity of the 803-keV line was found to be (1.22 ± 0.03) × 10-5, in excellent agreement with the adopted value in a recent data compilation and consistent with previous experimental works.

Stellar

The ^{36}Ar(n,γ)^{37}Ar (t_{1/2}=35 d) and ^{38}Ar(n,γ)^{39}Ar (269 yr) reactions were studied for the first time with a quasi-Maxwellian (kT∼47 keV) neutron flux for Maxwellian average cross section (MACS) measurements at stellar energies. Gas samples were irradiated at the high-intensity Soreq applied research accelerator facility-liquid-lithium target neutron source and the ^{37}Ar/^{36}Ar and ^{39}Ar/^{38}Ar ratios in the activated samples were determined by accelerator mass spectrometry at the ATLAS facility (Argonne National Laboratory). The ^{37}Ar activity was also measured by low-level counting at the University of Bern. Experimental MACS of ^{36}Ar and ^{38}Ar, corrected to the standard 30 keV thermal energy, are 1.9(3) and 1.3(2) mb, respectively, differing from the theoretical and evaluated values published to date by up to an order of magnitude. The neutron-capture cross sections of ^{36,38}Ar are relevant to the stellar nucleosynthesis of light neutron-rich nuclides; the two experimental values are shown to affect the calculated mass fraction of nuclides in the region A=36-48 during the weak s process. The new production cross sections have implications also for the use of ^{37}Ar and ^{39}Ar as environmental tracers in the atmosphere and hydrosphere.

Demonstration of a high-intensity neutron source based on a liquid-lithium target for Accelerator based Boron Neutron Capture Therapy.

A free surface liquid-lithium jet target is operating routinely at Soreq Applied Research Accelerator Facility (SARAF), bombarded with a ~1.91 MeV, ~1.2 mA continuous-wave narrow proton beam. The experiments demonstrate the liquid lithium target (LiLiT) capability to constitute an intense source of epithermal neutrons, for Accelerator based Boron Neutron Capture Therapy (BNCT). The target dissipates extremely high ion beam power densities (>3 kW/cm(2), >0.5 MW/cm(3)) for long periods of time, while maintaining stable conditions and localized residual activity. LiLiT generates ~3×10(10) n/s, which is more than one order of magnitude larger than conventional (7)Li(p,n)-based near threshold neutron sources. A shield and moderator assembly for BNCT, with LiLiT irradiated with protons at 1.91 MeV, was designed based on Monte Carlo (MCNP) simulations of BNCT-doses produced in a phantom. According to these simulations it was found that a ~15 mA near threshold proton current will apply the therapeutic doses in ~1h treatment duration. According to our present results, such high current beams can be dissipated in a liquid-lithium target, hence the target design is readily applicable for accelerator-based BNCT.

Note: Proton irradiation at kilowatt-power and neutron production from a free-surface liquid-lithium target.

The free-surface Liquid-Lithium Target, recently developed at Soreq Applied Research Accelerator Facility (SARAF), was successfully used with a 1.9 MeV, 1.2 mA (2.3 kW) continuous-wave proton beam. Neutrons (~2 × 10(10) n/s having a peak energy of ~27 keV) from the (7)Li(p,n)(7)Be reaction were detected with a fission-chamber detector and by gold activation targets positioned in the forward direction. The setup is being used for nuclear astrophysics experiments to study neutron-induced reactions at stellar energies and to demonstrate the feasibility of accelerator-based boron neutron capture therapy.

Association between Chlamydia pneumoniae and atherosclerotic lesions.

There can no longer be any doubt that viable Chlamydia pneumoniae organisms are present in atherosclerotic lesions. Indeed, the endovascular presence of C. pneumoniae in coronary artery disease (CAD) is common. The fact that this lesion, which is the major cause of stroke, coronary heart disease ( CHD), peripheral vascular disease and aortic aneurysm, can no longer be regarded as sterile has prompted a good deal of study and speculation. Atherosclerotic lesions have been studied in detail, but until recently histological descriptions of the lesion have not included C. pneumoniae organisms. Reviews and analysis of the literature confirm the association between C. pneumoniae and atherosclerotic lesions and CHD. The possibility that C. pneumoniae plays a causal or contributory role in the development of atherosclerotic lesions has been debated. It is of major importance as there is already evidence that antibiotic therapy may be of clinical benefit in patients with CHD. Large clinical trials using antichlamydial agents have been embarked upon which may provide further evidence of a causal role for C. pneumoniae. The underlying mechanism of how C. pneumoniae contributes to lesions and the effect of antibiotic therapy on lesions remain unknown. The association between C. pneumoniae and atherosclerosis is reviewed. Particular attention is paid to the lesion itself and the presence of C. pneumoniae. Potential areas of study that may contribute to this rapidly expanding area of research is explored.

Myocardial infarction associated with Chlamydia pneumoniae.

A 39-year-old black South African man with no recognised risk factors for coronary hart disease (CHD) except hypertension, died of a myocardial infarct (MI). The case was unusual because although hypertension is common, MI is rare in black South Africans. Serology indicated that the subject had previously had a Chlamydia pneumoniae infection. The primary lesion in the left anterior descending branch of the coronary artery was a ruptured atherosclerotic plaque in which C. pneumoniae was indentified by immunocytochemical, electron microscopic and polymerase chain reaction techniques. The organisms were detected in smooth-muscle cells, foam cells and interstitially, but not in adjacent unaffected tissue. C. pneumoniae DNA was also detected in the myocardium of the left ventricle in an area of the infarct. It is postulated that debris from the ruptured plaque was deposited in the muscle. The observations support the association between C. pneumoniae and CHD; for the first time the organism is identified in a lesion that ruptured and caused an MI.

Histological and ultrastructural findings suggesting an initiating role for Chlamydia pneumoniae in the pathogenesis of atherosclerosis.

AIMS: An association between Chlamydia pneumoniae and atherosclerosis is now well established. The finding of C. pneumoniae in atherosclerotic lesions has led to the hypothesis that this organism may have an aetiological role in atherogenesis. The implications of such a concept are enormous, but to date the pathological features of the lesion have not been examined in the light of this new hypothesis. This study was designed to determine the pathological basis of the association between C.pneumoniae and atherosclerotic lesions. METHODS: The pathological features of 50 atherosclerotic lesions from 50 different patients, in which C.pneumoniae had been demonstrated by immunocytochemistry and PCR techniques, were examined using light and electron microscopy techniques. In 20 cases the lesions were fatty streaks, 20 were fibro-atheroma lesions, and 10 were advanced, complicated lesions. RESULTS: Intimal smooth-muscle cells infected with C. pneumoniae exhibit vacuolation, loss of myofilaments, an increase in lipid, rupture and fragmentation. Macrophages phagocytose these muscle cell fragments, lipid and C. pneumoniae. Large numbers of extracellular C. pneumoniae organisms were identified in the central necrotic core, in areas of fibrosis, in areas of fragmentation of the internal elastic lamina, and in ceroid bodies. Neither pathological changes nor organisms were seen in the endothelium. CONCLUSIONS : C. pneumoniae infection of intimal smooth&hypen; muscle cells is accompanied by cytoplasmic alterations and damage. The fatty streak appears to be formed by a macrophage response to this muscle damage. C. pneumoniae is found in early, mature and advanced lesions. This is the first study of the pathology of atherosclerosis suggesting that the lesion be interpreted as an infective chlamydial granuloma.

Chlamydia pneumoniae in atheroma: consideration of criteria for causality.

AIMS: (1) To seek evidence of the existence of Chlamydia pneumoniae in a spectrum of atheromatous lesions in different types of arteries from individuals of different ages, using a polymerase chain reaction (PCR) assay supported by electron microscopy and immunocytochemistry; (2) to use electron microscopy to examine interactions between C pneumoniae and the cells present in the arterial tissue; (3) to assess the extent to which the data fulfil the criteria for causality. METHODS: At necropsy examination, 35 arterial specimens were taken from 25 subjects. The grade of atheroma was determined macroscopically and microscopically and the tissues coded and examined by the three techniques. RESULTS: Of the 35 specimens, 24 had macroscopic or microscopic atheromatous lesions of varying degree. Twenty two of the 35 specimens were examined by electron microscopy, C pneumoniae-like bodies being found in 11 (50%); seven specimens were examined by the immunocytochemical method, positive staining being detected in three; and all specimens were examined by the PCR technique, 15 (43%) being PCR positive. Overall, of the 24 specimens with lesions, 17 (71%) were positive by at least one of the three tests, whereas of the 11 specimens without lesions, only one was positive. The positive specimens comprised 10 of 19 aortas, three of six iliac arteries, and one coronary and one pulmonary artery. C pneumoniae was detected in four of six specimens in which there were early changes and in a 20 year old subject. Concerning the 25 subjects, of 17 who had atheromatous arteries, 14 (82%) were C pneumoniae positive and of the eight who had normal arteries, none was positive. CONCLUSIONS: There is a strong correlation between C pneumoniae and arterial atheromatous lesions. The organism may contribute to the disease process by damaging smooth muscle cells.

Serological response to Chlamydia pneumoniae in adults with coronary arterial fatty streaks and fibrolipid plaques.

The antigen-specific serological response to Chlamydia pneumoniae was studied in 45 adults with coronary artery atherosclerosis and compared with that in 40 adults with acute respiratory infection. C. pneumoniae antigen and DNA were detected in lesions more frequently in patients with low immunoglobulin G titers against C. pneumoniae than in those with high immunoglobulin G titers. Reactivities with the 42-kDa (46%) and 52-kDa (31%) proteins were observed more frequently in sera from seropositive individuals with atherosclerosis than in sera from patients with acute respiratory infection. Antibodies against the C. pneumoniae-specific 42- and/or 52-kDa protein may be a marker for chronic C. pneumoniae infection.

Demonstration of Chlamydia pneumoniae in atherosclerotic lesions of coronary arteries.

Chlamydia pneumoniae is a human respiratory pathogen that causes acute respiratory disease and approximately 10% of community-acquired pneumonia. The infections are geographically widespread. Antibody prevalence studies have shown that virtually everyone is infected with the C. pneumoniae organisms at some time and that reinfection is common. In addition to respiratory disease, seroepidemiologic studies have shown an association of this organism with coronary artery disease. C. pneumoniae was detected in coronary artery atheromas by immunocytochemistry (15/36) and by polymerase chain reaction (PCR) (13/30) in 20 of 36 autopsy cases from Johannesburg, South Africa. Sequence analysis of the C. pneumoniae rRNA genes amplified by PCR confirmed that the amplified gene products were C. pneumoniae. Electron microscopy revealed typical pear-shaped C. pneumoniae elementary bodies in 6 of 21 atheromatous plaques. These findings support the seroepidemiologic studies and offer further evidence that C. pneumoniae may be involved in the atherosclerotic process.