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

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

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

Gamma Flux in 14C Laboratories

From the 14th International Radiocarbon Conference held in Tucson, AZ, May 20-24, 1991.An informal collaborative group of radiocarbon dating laboratories, the Low-Level Club, has been established to measure the gamma radiation flux and to test the efficiency of the anticoincidence counting system in laboratories with a NaI detector unit. The detector will record gamma radiation from cosmogenic nuclides, muons and secondary y radiation formed in the passive shield by charged cosmic-ray particles. We present here the first phase of this work.This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202