Low-level gas multicounter for C-14 dating of small samples: Electronic, numerical and shielding optimisation

Up to 14 methane samples can be dated simultaneously in our compact gas multicounter. Sample detectors are 10 ml (NTP) in volume each. They are made of copper and linked to form two 7 detector rigid assemblies which are filled in situ. Monitoring of the counting conditions is enabled through multichannel analysis of the cosmic pulse height spectrum, which shows the changes in gas amplification due to impurities or leakage. HV is set (and adjusted) automatically using the cosmic peak. All individual events are stored on disc, including pulse height (PH), risetime (RT) (both 256 Ch), time of arrival (TA), detector identification, anticoincidence status and elapsed and live time. Software programs analyse and validate data. Numerical discrimination and manipulations of counting parameters can be performed without destroying the original data set. Statistical quality control is based on chi-square and Poisson distribution of count rates around their mean in user defined energy regions as weil as time of arrival of pulses mode. TA analysis offers the user an early means for recognizing some types of system malfunction that otherwise might remain undetected for Jong periods of time. RT analysis is used to discriminate sample beta pulses from environmental radiation pulses, resulting in a low background with compact and relat ively inexpensive shielding. The automatic high voltage setting, PH, RT and TA electronics as weil as the liquid scintillation anticoincidence systems are applicable to all existing gas counting systems. Delivery of the gas multicounter to the Australian National University is to take place at the end of the year 1984

Blood-based cerebral biomarkers in preeclampsia: Plasma concentrations of NfL, tau, S100B and NSE during pregnancy in women who later develop preeclampsia - A nested case control study

OBJECTIVE: To evaluate if concentrations of the neuronal proteins neurofilament light chain and tau are changed in women developing preeclampsia and to evaluate the ability of a combination of neurofilament light chain, tau, S100B and neuron specific enolase in identifying neurologic impairment before diagnosis of preeclampsia. METHODS: A nested case-control study within a longitudinal study cohort was performed. 469 healthy pregnant women were enrolled between 2004–2007 and plasma samples were collected at gestational weeks 10, 25, 28, 33 and 37. Plasma concentrations of tau and neurofilament light chain were analyzed in 16 women who eventually developed preeclampsia and 36 controls throughout pregnancy with single molecule array (Simoa) method and compared within and between groups. S100B and NSE had been analyzed previously in the same study population. A statistical model with receiving characteristic operation curve was constructed with the four biomarkers combined. RESULTS: Plasma concentrations of neurofilament light chain were significantly increased in women who developed preeclampsia in gestational week 33 (11.85 ng/L, IQR 7.48–39.93 vs 6.80 ng/L, IQR 5.65–11.40) and 37 (22.15 ng/L, IQR 10.93–35.30 vs 8.40 ng/L, IQR 6.40–14.30) and for tau in gestational week 37 (4.33 ng/L, IQR 3.97–12.83 vs 3.77 ng/L, IQR 1.91–5.25) in contrast to healthy controls. A combined model for preeclampsia with tau, neurofilament light chain, S100B and neuron specific enolase in gestational week 25 displayed an area under the curve of 0.77, in week 28 it was 0.75, in week 33 it was 0.89 and in week 37 it was 0.83. Median week for diagnosis of preeclampsia was at 38 weeks of gestation. CONCLUSION: Concentrations of both tau and neurofilament light chain are increased in the end of pregnancy in women developing preeclampsia in contrast to healthy pregnancies. Cerebral biomarkers might reflect cerebral involvement before onset of disease

Performance of new technology liquid scintillation counters for 14C dating

The results are presented of an investigation comparing the performance of commercially available liquid scintillation spectrometers claiming 'low-level' radioisotope detection abilities. Determination of ¹⁴C at naturally occurring concentrations was carried out in both old and new technology liquid scintillation counters using a ¹⁴C labelled benzene sample with butyl-PBD as scintillant. The signal to noise ratio and the ¹⁴C detection efficiency were evaluated. The results show a wide range of merit for radiocarbon dating of so called 'low-lever instruments

Cerebral Biomarkers and Blood-Brain Barrier Integrity in Preeclampsia

Cerebral complications in preeclampsia contribute substantially to maternal mortality and morbidity. There is a lack of reliable and accessible predictors for preeclampsia-related cerebral complications. In this study, plasma from women with preeclampsia (n = 28), women with normal pregnancies (n = 28) and non-pregnant women (n = 16) was analyzed for concentrations of the cerebral biomarkers neurofilament light (NfL), tau, neuron-specific enolase (NSE) and S100B. Then, an in vitro blood–brain barrier (BBB) model, based on the human cerebral microvascular endothelial cell line (hCMEC/D3), was employed to assess the effect of plasma from the three study groups. Transendothelial electrical resistance (TEER) was used as an estimation of BBB integrity. NfL and tau are proteins expressed in axons, NSE in neurons and S100B in glial cells and are used as biomarkers for neurological injury in other diseases such as dementia, traumatic brain injury and hypoxic brain injury. Plasma concentrations of NfL, tau, NSE and S100B were all higher in women with preeclampsia compared with women with normal pregnancies (8.85 vs. 5.25 ng/L, p < 0.001; 2.90 vs. 2.40 ng/L, p < 0.05; 3.50 vs. 2.37 µg/L, p < 0.001 and 0.08 vs. 0.05 µg/L, p < 0.01, respectively). Plasma concentrations of NfL were also higher in women with preeclampsia compared with non-pregnant women (p < 0.001). Higher plasma concentrations of the cerebral biomarker NfL were associated with decreased TEER (p = 0.002) in an in vitro model of the BBB, a finding which indicates that NfL could be a promising biomarker for BBB alterations in preeclampsia

Surface and underground ultra low-level liquid scintillation spectrometry

Cosmic background and its variation have been removed in the Gran Sasso National Laboratory (National Institute of Nuclear Physics) by its 1400-m rock overburden. Stable, high-performance liquid scintillation counting conditions are obtained when any remaining variable components of the environmental background, such as radon, are eliminated. The ultra low-level liquid scintillation spectrometer Quantulus(TM) has an anti-Compton guard detector (guard for short) that allows monitoring of gamma radiation in the background. The guard detector efficiency in radiocarbon background reduction is 8% in the Gran Sasso National Laboratory, while 80% is observed in surface laboratories. Thus, atmospheric pressure variations in surface laboratories cause variation in cosmic radiation flux. The Quantulus anti-Compton detector is highly efficient in detecting cosmic radiation, and the sample count rate remains stable in long-term counting. Also, correlation of sample backgrounds with environmental gamma radiation in various laboratories is examined

Radiocarbon measurements by liquid scintillation spectrometry at the Gran Sasso National Laboratory

The background of a liquid scintillation spectrometer for radiocarbon measurements was investigated in the Gran Sasso National Laboratory (National Institute of Nuclear Physics), where 1400 m rock overburden (3800 m w.e.) absorbs most of the cosmic radiation. Comparisons were made with measurements carried out in surface laboratories (Radiocarbon Laboratory of ENEA, Bologna, Italy; PerkinElmer Life and Analytical Sciences, Turku, Finland) using Teflon and optimised copper–Teflon vials. The residual radioactivity of phototubes and the role of radon were a larger fraction of the total background signal in the Gran Sasso underground laboratory

Liquid scintillation spectrometry at Gran Sasso National Laboratory: radiocarbon measurements

Radiocarbon measurements using a Quantulus™ ultra low-level liquid scintillation spectrometer were performed at the Gran Sasso National Laboratory (National Institute for Nuclear Physics) to study the efficiency and background related to the measurement site (Plastino et al. 2001). Cosmic background and its variation have been removed in the Gran Sasso laboratory by its 1400-m rock overburden. Stable, high-performance liquid scintillation counting conditions are obtained when any remaining variable components of the environmental background, such as radon, are eliminated. The ultra low-level liquid scintillation spectrometer Quantulus has an anti-Compton guard detector, which allows for the monitoring of gamma radiation in the background. Guard detector efficiency in 14C background reduction is 8% at Gran Sasso, while 80% is observed on the surface (Plastino and Kaihola 2004). The big difference in the guard detector efficiency between surface laboratories and Gran Sasso is due to the absence of cosmic and associated lower energy Compton radiation (Plastino and Kaihola 2006). The cosmic noise reduction observed at the Gran Sasso laboratory makes it possible to perform high-precision 14C measurements and to extend for these ideal samples the present maximum dating limit from 58,000 to 62,000 BP (5 mL, 3 days of counting) (Plastino et al. 2001)

Differentiation between fossil and biofuels by liquid scintillation beta spectrometry - direct method

Liquid scintillation spectrometry of 14C in gasoline/ethanol and diesel oil was carried out using QuantulusŽ and straight mixtures of fuel and an organic scintillation cocktail. A linear correlation was found between the concentration of carbon that originates from the bioethanol (biocarbon) and the fuel mixture’s 14C activity in the range 0–100% (m/m) bioethanol content. Because of these good linear correlations, quantitative determination of a fuel’s biocarbon content can be made by 14C analysis. The direct method is also applicable to analysis of the bio-based materials dissolvable in solvents, which can be mixed with scintillation cocktails