Plasma radiocarbon

Table III summarizes the results of tissue residue analysis. It is evident that the amount of radioactivity in tissues was not directly related to the length of chemical exposure. The average accumulation in fish exposed from 1 to 14 days was 1.35%. In general, liver, kidney, intestine, and bile contained the most 1 C. C-labeled materials accumulated in the liver at levels 3 to 5 times greater than [111C]molinate concentration in the water. The maximum radiocarbon level in the bile was 14.5 ppm and was reached by the 7th day. On the 14th day, the radiocarbon decreased to 6.09 ppm which was 30-fold higher than the [ 1 C]molinate water concentration. Blood contained negligible amounts of radioactivity, and little of that was associated with the plasma. Twenty percent of total blood radioactivity was detected in the erythrocytes within 4 days after treatment and by the 14th day, 69% of the radiocarbon in whole blood was present in the erythrocytes.

XPS will aid in understanding specifically the surface of the black deposit covering pictographs in Little Lost River Cave in Idaho. This work will complement other bulk analyses carried out with pyrolysis-GC-MS and thermally assisted hydrolysis /methylation (THM)-GC-MS (75). The objectives of this project were to use XPS to qualitatively determine the surface elemental composition of the black residue semiquantitatively characterize the surface, for comparison with other surface-related materials and examine the relationship between the chemistry and depth by using Ar+ sputtering. This, then, will aid in validating the radiocarbon date obtained through plasma-chemical oxidation and accelerator mass spectrometry by Steelman et al. (5). 

Whole blood concentrations represented approximately 80% of the plasma concentrations. Cmax = 1.33 tig-eq/mL, AUCinfinf = 32.7 ig-eq.h/mL. The mean half life, 20.2 h, was very close to the plasma half-life. There was radioactivity in the red blood cells and it declined with an elimination half-life similar to the half-lives in plasma and whole blood radiocarbon concentrations. 

FIGURE 14.7 Linear response curve of 14C AMS measurement to spiked 14C concentration in human plasma between 0.1 and 150 Modern. (Adapted from Zoppi, U. et al., Radiocarbon, 49, 171, 2007. With permission.)... 

After 24 hours, the arm is washed with soapy water followed with a swab soaked in acetone. Wash water and swab are saved and the latter extracted with solvent. The protective screens are also collected and washed with soap and water. The extracts and all the washes are assayed for radiocarbon content to determine the percent of dose recovered from the application site. The animals are returned to metabolism cages and daily urine, feces and plasma sanq[>les are collected. 

Figure 2. Plasma disappearance of radiocarbon from monkeys. Oryzalin (2.0 mg/kg) given in ethanol intravenously. N=4.

In exploring the question of the earliest date for human presence in Brazil, Steelman and coworkers apply the plasma chemical procedure to extract carbon from both the pigments of a rock painting from Toca do Serrote de Bastiana and the accretions covering its surface. The accretions were found to contain both monohydrate of calcium oxalate and calcium carbonate. The radiocarbon age of the oxalate carbon was determined to be 2540 60 B.P. while the radiocarbon age of carbon extracted from the pigment was determined to be 3730 90 B.P. These ages are much more recent than the 30,000-40,000 B.P. age determined by electron spin resonance and thermoluminescence of the accretions, but are consistent with dates of other pictographs in the same shelter. 

Given typically only 0.1 mg carbon is extracted from pictograph samples as CO2, we realized that we should be able to obtain non-destructive radiocarbon dates and stable isotopic carbon analyses on many perishable archaeological artifacts. Currently, for radiocarbon dating, subgram samples are removed from artifacts and destroyed during combustion extraction of CO2. Plasma extraction does not require the removal of material from an object for destructive analysis. The characteristics of plasma extraction have great potential for the study of artifacts associated with burials, where the least intrusive techniques are especially critical. Museum artifacts such as basketry,... 

For archaeological samples, CO2 extracted with 0-plasmas were sent to AMS laboratories for analyses. Radiocarbon dates were determined for three... 

Figure 3. Photographs before (left-a) and after (right-b) vacuum and four plasma exposures to the modern T-shirt label studied here. Some bleaching of the text color can be observed. Alterations were minor and no significant changes can be seen in the fabric. For scale, the height of the letter is approximately 0.5 cm. No change was observed when the material was subjected to a plasma sufficient for a radiocarbon and a stable carbon isotopic analysis.

Third International Radiocarbon Intercomparison (TIRI) standard wood samples (5,6,8) and four different archaeological charcoal samples (2,3J8) for comparison with dates previously determined at other laboratories using standard combustion methods. These measurements were utilized to demonstrate the viability of the plasma extraction technique for dating rock paintings from around the world with charcoal and inorganic pigments. 

Table 1. Radiocarbon dates from the plasma extraction technique compared to previously determined radiocarbon ages for charcoal and TlRl wood...

Figure 4. Photographs before (left a,c,e) and after (right-b,d,f) vacuum and plasma exposure to the 4500 year old TIRI wood studied here. For scale, the length of the wood piece shown in photographs a d is - 2 cm and 0.25 cm for e and f Only minor damage is detected and none after extraction sufficient for one radiocarbon date and one stable carbon isotopic analysis.

Procedures for chemically pretreating archaeological samples typically involve an acid-base-acid treatment 31, S2). However, we routinely eliminate both acid washes as we have shown them to be unnecessary with our plasma-chemical extraction technique. Carbonate and oxalate carbon are not extracted by the plasma only organic material was removed for radiocarbon measurements (33,34), Samples are immersed in -I M NaOH and placed in an ultrasound bath for an hour at 50 5 C. When the resulting supernatant was colored, subsequent NaOH washes were performed until the supernatant... 

Next, low-temperature (<150°C), low-pressure torr) oxygen plasmas oxidized organic components of the sample to CO2. Decomposition of inorganic carbon present (dolomitic limestone rock and calcite/calcium oxalate accretions) was prevented by running the plasmas at low-temperature. Carbon dioxide from the sample was flame-sealed into a glass tube cooled to liquid nitrogen temperature (-194°C), after water had been frozen out with a dry-ice/ethanol slurry (-58°C), and finally sent for radiocarbon analysis at the Center for Accelerator Mass Spectrometry at the Lawrence Livermore National Laboratory (LLNL-CAMS). It was necessary to utilize an AMS measurement due to the small sample size. 

Our oxalate radiocarbon determination is consistent with the era determined by radiocarbon dates on four other pictographs located in the same shelter. In fact, we have also obtained a direct radiocarbon date of 3730 90 years BP on organic material extracted from the same red figure covered by the oxalate accretion. This plasma-chemical process has been verified by successfully dating known age materials and pictographs with archaeologically constrained ages (39, 40). 

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