Radiochemical scintillation counter

Radioactivity of uranium can be measured by alpha counters. The metal is digested in nitric acid. Alpha activity is measured by a counting instrument, such as an alpha scintillation counter or gas-flow proportional counter. Uranium may be separated from the other radioactive substances by radiochemical methods. The metal or its compound(s) is first dissolved. Uranium is coprecipitated with ferric hydroxide. Precipitate is dissolved in an acid and the solution passed through an anion exchange column. Uranium is eluted with dilute hydrochloric acid. The solution is evaporated to near dryness. Uranium is converted to its nitrate and alpha activity is counted. Alternatively, uranium is separated and electrodeposited onto a stainless steel disk and alpha particles counted by alpha pulse height analysis using a silicon surface barrier detector, a semiconductor particle-type detector. 

Beta-emitters such as tritium (H-3) or carbon-14 (C-14) are the most commonly used radioisotopes in drug metabolism, agricultural metabolism, and toxicology studies. In HPLC, the radiochemical detector can be off-line or on-line. Off-line detection requires coupling the chromatograph to a fraction collector. The collected fractions are combined with a suitable liquid scintillation cock-tail and then counted by a liquid scintillation counter. This method allows for... 

All reagents are added in excess, and the mixture is equilibrated overnight with the GTP sample, so that the quantity of PEP(14C) produced is limited by the quantity of GTP present in the sample and the equilibrium constants of the enzymatic reactions. The labeled PEP is then separated by anion-exchange chromatography and quantitated in a scintillation counter. The assay for GDP is conducted using the same reactions in reverse (both enzymes are reversible, and yield an equilibrium mixture of reactants and products), and labeled PEP as a reagent. This reaction is followed by the separation and quantitation of labeled aspartate. Note that all radiochemical enzymatic assays require a separation step prior to quantitation. 

CPT was determined using a radiochemical isotope forward assay as described previously. In brief, the assay system contained lOmM Tris-HCl-buffer (pH 7.6), 0,1% fatty acid-free bovine serum albumin, 1 mM dithiothreitol, 0.08 mM palmitoyl-CoA and 5 mM [ CJ-camitine in a final volume of 1 ml and the assay temperature was 30 °C. Experiments were performed either in the presence or in the absence of 0.4 mM malonyl-CoA to inhibit CPT I. Concentration of L-AC was varied between 0 and 30mM. Incubations were started by the addition of homogenate and stopped after lOmin by addition of ammonium sulfate and isobutanol. Labelled pahnitoylcamitine was measured after separation of the organic phase using a scintillation counter (Beckmann LS 6500). 

As a commercial company that provides analytical services for the determination of radionuclides for a wide variety of clients, AMEC required a more accurate and reliable method to be developed. It needed to use relatively low hazard chemicals, have improved accuracy and precision and utilise common radiochemical analytical laboratory equipment such as liquid scintillation counters and gravity fed chromatography columns. In addition, the process must have realistic and commercially viable batch sizes, operator time and turnaround times, so that samples can be analysed in a cost-effective manner. Ideally the whole process for a batch of samples should not exceed more than one working week. As part of the validation process both internal and external quality control (QC) samples were used along with statistical tests, such as zeta (Q scores and student t-tests , to determine the accuracy of the improved method. In addition, elution profiles for iodine and chlorine and decontamination tests for potentially interfering radionuclides were also carried out in order to further validate the process. 

The radiochemical method quantifies gross a activity utilizing either a gas flow proportional counter or a scintillation detection system following chemical separation. In the EPA radiochemical method, the uranium is co-precipitated with ferric hydroxide, purified through anion exchange chromatography, and converted to a nitrate salt. The residue is transferred to a stainless steel planchet, dried, flamed, and counted for a particle activity (Krieger and Whittaker 1980). 

Gamma spectroscopy is a radiochemical measurement method that allows identification and quantitative determination of activity of radionuclides, which emit gamma radiation or x-rays. The equipment used in gamma spectroscopy includes an energy-sensitive radiation detector, such as semiconductors, scintillators or proportional counters, and a multichannel analyzer. The energies and the photon yields are characteristic for specific nuclides. 

Sr deserves special attention since it is released by nuclear power facilities, accumulates in organisms and replaces Ca (mainly in bones) and has a long half life. °Sr is a pure beta emitter and before measurement (liqiud scintillation counting, proportional counters, etc.) a laborious and time-consuming procedure for radiochemical separation has to be performed (IAEA, 1989). This is practically the best way for reliable determination of this radionuclide (IAEA, 1989). 

All chromatographic methods (liquid, liquid-liquid, liquid-solid, gas, gas-liquid, and gas-solid chromatography) are used in radiochemical analysis of food and environmental samples. Equipment for the evaluation of paper and thin-layer radiochromatograms is commercially available. The radiation detectors used vary according to the type and energy of the radiation emitted by the measured radionuclides. Use is made of ionization chambers, proportional counters, and Geiger-Miiller, scintillation, and semiconductor detectors. 

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