Alpha activity

Most chemical iavestigations with plutonium to date have been performed with Pu, but the isotopes Pu and Pu (produced by iatensive neutron irradiation of plutonium) are more suitable for such work because of their longer half-Hves and consequendy lower specific activities. Much work on the chemical properties of americium has been carried out with Am, which is also difficult to handle because of its relatively high specific alpha radioactivity, about 7 x 10 alpha particles/(mg-min). The isotope Am has a specific alpha activity about twenty times less than Am and is thus a more attractive isotope for chemical iavestigations. Much of the earher work with curium used the isotopes and Cm, but the heavier isotopes... 

W Predominant alpha activity (more than 50% of the epoch) mixed with EEG beta Slow and rapid High... 

Alpha activity is replaced by predominant low-voltage, mixed-frequency background activity sometimes with vertex sharp waves Slow Decreased from wake... 

From the alpha-activity remaining in the supernatant liquid after the final precipitation as a fluoride, it can be calculated, using 30,000 years as the half-life of 94239, that this salt of 94 has a solubility of the order of magnitude of 10 mg of the element per liter of 6 N HF solution. This value is necessarily somewhat tentative. 

Analyses. Plutonium was determined radiometrically. A weighed sample of a compound was dissolved in 2M H2S0lt with a few drops of 90% HNOj to oxidize organic material, and an aliquot of this solution counted for alpha activity. 

Wang X, Li C, Chen Y, Hao Y, Zhou W, Chen C, Yu Z (2008) Hypoxia enhances CXCR4 expression favoring microglia migration via HIF-1 alpha activation. Biochem Biophys Res Commun 371 283-288... 

Early measurements of " Th were on seawater samples and Th was co-precipitated from 20-30 L of seawater with iron hydroxide (Bhat et al. 1969). This procedure may not recover all of the " Th in the sample, and an alpha emitting Th isotope (e g., °Th or Th) is added as a yield monitor. Following chemical purification of the Th fraction by ion exchange chromatography, the Th is electrodeposited onto platinum or stainless steel planchets. The planchets are then counted in a low background gas-flow beta detector to measure the beta activity and subsequently with a silicon surface barrier detector to determine the alpha activity of the yield monitor. The " Th activity is thus determined as ... 

Burcham, W. E., and B. C. Haywood The alpha activity induced in Platinum... 

Fruchart JC, Duriez P, Staels B. Peroxisome proliferator-activated receptor-alpha activators regulate genes governing lipoprotein metabolism, vascular inflammation and atherosclerosis. Curr Opin Lipidol 1999 10 245-257. 

The variations in the background, the sensitivity to moisture, the alpha activity of the chamber itself and the influence of recombination were discussed by Hultqvist. The standard deviation due to counting statistics was estimated to be about 3 % (in a few measurements 6 %). The calibration was made by counting each alpha particle by a proportional counter specially designed at the Department for this purpose. The statistical uncertainty of the calibration of the equivalent radon concentration was estimated to be 12 %. 

Figure 1 Alpha activity versus time from radon progeny plated-out on several materials.

Activated carbon alpha activity, 282 conditions for optimal performance, 568 contaminants adsorbed, 568 feasibility for indoor radon control, 560-568... 

The differences found by these two EEG studies may be due to methodological factors. Kunkel (1993) prescreened subjects for high alpha activity (70% or more of the recording period), whereas Itil and colleagues did not. Kunkel also used lower doses (40, 80, and 160 mg) than Itil and colleagues (240 mg). 

Not all of the biochemical events in this complex pathway from PPAR-alpha activation to tumors are completely understood, but much is known. It seems that at least some peroxisome-proliferating chemicals that also produce tumors in rodent livers do so through this pathway. If it can be demonstrated that such a mechanism is at work, then it seems that the risk of tumorigenicity for such compounds would be limited to doses that are sufficient to activate PPAK-alpha sufficiently to initiate the dangerous cascade of events within the cell. Experts have developed a number of experimental criteria that should be met if a compound is to be put in this class of carcinogens. Study of P PAR-alpha activation as a route of carcinogensis is an extremely active area of research. 

Gravitt KR, Ward NE, Fan D, Skibber JM, Levin B, O Brian CA (1994) Evidence that protein kinase C-alpha activation is a critical event in phorbol ester-induced multiple drug resistance in human colon cancer cells. Biochem Pharmacol 48 375-381... 

Kolch W, Heidecker B, Kochs G, Hummel R, Vahidi M, Mischak H, Finkenzeller G, Marme D, Rapp UR (1993) Protein kinase C alpha activates RAF-1 by direct phosphorylation. Nature 364 249-252... 

Dent P, Reardon DB, Park JS, et al. Radiation-induced release of transforming growth factor alpha activates the epidermal growth factor receptor and mitogen-activated protein kinase pathway in carcinoma cells, leading to increased proliferation and protection from radiation-induced cell death. Mol Biol Cell 1999 10 2493-2506. 

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