Radiochemical procedures, detection limits

The NAA measurements on the paper samples were made at the Breazeale Nuclear Reactor Facility at the Pennsylvania State University with a TRIGA Mark III reactor at a flux of about 1013 n/cm2-sec. Samples were irradiated from 2 to 20 min and counted for 2000 sec, after a 90 min decay time for Ba and a 60 hr decay for Sb, Analyses were performed instrumentally, without radiochemical separation, using a 35cm3 coaxial Ge-Li detector and a 4096-channel pulse height analyzer. With these procedures, detection limits for Ba and Sb were 0.02ug and 0.001 ug, respectively. These sensitivities are comparable to those obtained by GA s radiochemical separation procedure, and are made possible by the use of the higher neutron output from the more powerful reactor and in combination with the higher resolution solid state detector... 

Long-lived radionuclides occur at extremely low concentrations, especially in environmental samples, therefore several authors have proposed matrix separation and enrichment of the analytes before analysis.21,24,26,3 39 Radiochemical methods often require very careful and time consuming separation and enrichment processes and measurement procedures of a-, (3- and -emitting radioactive species at the trace and ultratrace level using conventional radioanalytical techniques 40-43 Trace/matrix separation, which is performed offline or online in order to avoid possible isobaric interferences, matrix effects and to reduce the detection limits for the determination of long-lived radionuclides, is also advantageous before ICP-MS measurements as the most widely applied mass spectrometric technique. 

But the question remains as to what const outes no residue." Currie (] ) examined the corresponding problem of detection limits in radiochemical procedures and was frustrated by the differences in terminology and definitions which resulted in a range of three orders of magnitude for detection limits calculated for the same system. Figure 4, taken from his paper, shows the situation with respect to a specific radioactivity process. The horizontal lines indicate three specific levels L, "decision limit," the level a signal must exceed to permit a decision as to whether or not the result of an analysis indicates detection Lj), "detection limit," the level above which an analytical procedure can be relied upon to lead to detection and Lq, "determination limit," the level above... 

For Tc, the low-level energy jS-particles emitted (Emax = 292 keV) and the low concentrations in environmental samples represented an analytical challenge prior to the late 1970s. Based on a radiochemical procedure developed in 1969, the activity concentrations of Tc in waters ranged from 0.019 to 1.8Bql , and the detection limit was reached for 80% of the samples ( =150). For rainwater samples collected in 1967, the activity concentrations... 

During the last decades methods such as Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), Inductively Coupled Plasma Mass Spectroscopy (ICP-MS), and Resonance Ionization Mass spectrometry (RIMS) have decreased the need for selective radiochemical procedures. Many long-lived radionuclides today have lower detection limits if using, e.g., ICP-MS than if performing radiometric measurements with reasonable measuring times. At present, the half-life limit is a few hundred years, i.e., nuclides with longer half-hfe (e.g., Tc, Np, or Pu) should preferably be measured by ICP-MS and more short-... 

Kucera et al. [161] performed a comparative analysis of three procedures for determining I in food. Their accuracy and precision were checked against reference materials based on food products. The limit of detection was 1 pg/kg. Instrumental NAA (INAA) and replicate sample INAA (RSINAA) were used in Portugal to test a wide assortment of food products for their total Se content [162], INAA and radiochemical NAA (RNAA) were also used to assess the quality of bottled water sold in Greece [163]. Elements such as U, Ba, La, Sb, Ca, Cr, Zn, K, As, Br, Se and... 

Radiochemical and INAA procedures for the determination of the low level trace elements in human fivers established the limits of detection of seven critical low level trace elements (Cr, As, Se, Mo, Ag, Sn, 122Sb and 124Sb). For silver, the value 0.7 pg kg-1 is given354. These limits represent concentrations at which a sample would generate a detectable signal355. 

Chemistry used in the recovery of plutonium from irradiated fuel must provide a separation from all these elements, other fission and activation products, and the actinides (including a large amount of unburned uranium), and still provide a complete recovery of plutonium. The same issues apply to the recovery of uranium from spent thorium fuel. Most of the processes must be performed remotely due to the intense radiation field associated with the spent fuel. As in the enrichment of uranium, the batch size in the later steps of the reprocessing procedure, where the fissile product has become more concentrated, is limited by the constraints of criticality safety. There is a balance between maximizing the yield of the precious fissile product and minimizing the concentrations of contaminant species left in the final product These residual contaminants, which can be detected at very small concentrations using standard radiochemical techniques, provide a fingerprint of the industrial process used to recover the material. 

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