Lauri Kaihola

QUANTITATIVE DETERMINATION BY 14C ANALYSIS OF THE BIOLOGICAL COMPONENT IN FUELS

Radiocarbon analysis was performed by liquid scintillation counting (LSC) and accelerator mass spectrometry (AMS) to assess whether the content of biological components in hydrocarbon fuels could be derived. Different fuel mixtures were prepared containing bioethanol, fossil ethanol, and fossil gasoline. The specific 14C activity of these mixtures was obtained from LSC measurements and directly related to the concentration of carbon originating from the bioethanol (biocar- bon). The results were checked via standardized carbon dating procedures and AMS. A good linear correlation exists between the fuel mixtures specific 14C activity and the concentration of biocarbon. Also, the biocarbon fraction of the fuel mixture (the ratio biocarbon : total carbon) and the normalized fraction of biocarbon (%M) showed good linear correlation. Therefore, both relations provide a possibility to quantitatively determine a fuels biocarbon content by 14C analysis. When the sample com- position is known (e.g. resolved by gas chromatography-mass spectroscopy (GC-MS) and nuclear magnetic resonance (NMR)), the amount of particular biological components in a fuel sample can be derived subsequently. For mixtures of bio- ethanol, fossil ethanol, and gasoline with bioethanol contents in the range of 0.5-2% m/m, it was found that errors in the nor- malized fraction of biocarbon (%M) were in the range of 25-10%, respectively. For samples with a higher bioethanol content (up to pure bioethanol), the errors in %M were <10%. Errors might be larger if substantial changes in the concentration of atmospheric 14C took place during the growth period of the biofuel feedstock. By taking into account the variation in specific 14C activity of carbon over the last decades, and by modeling simple tree-growth, it could be illustrated that this effect becomes significant only if the biofuel feedstock stopped growing more than 1 decade ago, e.g. with wood from constructions.

Cosmic background reduction in the radiocarbon measurements by liquid scintillation spectrometry at the underground laboratory of Gran Sasso

Radiocarbon measurements by two 1220 Quantulus ultra low background liquid scintillation spectrometers were performed at the underground laboratory of Gran Sasso and the Radiocarbon Laboratory of E.N.E.A.-Bologna to study the efficiency and background variations related to measurement sites. The same configuration setup, i.e. the same center of gravity of the 14 C spectrum (SQP(I) = 410 ± 1) was obtained in both instruments. Many different background and modern standards with pure analytical benzene were used and spectra for 40 one-hour periods were obtained. The data indicates a background reduction of approximately 65% between the surface and underground laboratories, with no differences in the efficiency. Recording similar efficiencies in both spectrometers is probably due to fairly identical photomultiplier characteristics. The cosmic noise reduction observed at the laboratory of Gran Sasso makes it possible to perform high precision 14 C measurements and to extend for these idealized samples the present maximum dating limit from 58,000 BP to 62,000 BP (5 mL, 3 days counting).

A Minivial for Small-Sample 14C Dating

We have designed a 0.3-m1 Teflon minivial for 14C dating of small samples in a liquid scintillation counter. We use a special adapter of standard vial size to optimize the position of the vial with respect to the phototubes and to intercept the light path between them, thus reducing optical cross-talk. Better performance can be achieved by using customized vials than by diluting small samples for counting in large vials. We have achieved counting efficiencies up to 80% in 0.3-ml vials typically with 0.05 cpm background.

Time series analysis of low level gas counting data.

ABSTRACT. We demonstrate the feasibility of pulse time of arrival information for early detection of periodic events in low level counting. Time of arrival data allows us to apply time series analysis and serial correlation tests which, in graphic form, give the user an illustrative view of the parameters affecting the validity of counting statistics. The decision to discontinue counting can already be made on the basis of less than 100 counts from the time information alone if more than 10 of these are non-Poisson periodic counts. The analyses also serve as a means of quality control for low level counting, being directly based upon the interval distribution of the Poisson process.

Gamma Flux in 14C Laboratories

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 Na! 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.

An evaluation of shielding characteristics applicable to mini-gas-proportional counter-based (super 14) C dating systems.

A mini-gas-proportional counter prototype of lOml capacity (at NTP) was constructed of oxygen-free Finnish copper. The counter tube will be one of 16 equivalent tubes of a smallsample gas counting system, which is equipped with passive graded shield made of lead, cadmium, and copper and a dual active anticoincidence shield, consisting of an external cosmic gas-proportional and an internal plastic scintillation guard. The aim of this study was to evaluate the parameters leading to the design of a cost-effective and compact shielding package for mini-counters.