Spectral analysis gamma

Re-analysis with better purification should be considered if the count rate is unexpectedly high or the observed half life and radiation energies are not those of the radioanalyte. Contaminant radionuclides may be tolerated if they do not interfere with counting the radioanalyte, or can be subtracted from the count rate with only a minor increase in detection uncertainty. In spectral analysis of alpha particles and gamma rays, for example, contaminant radionuclides are tolerated in the sample if they do not interfere with counting the characteristic spectral peaks of the analyte. 

Earlier methods used in the analysis of radium isotopes in water required labor-intensive radiochemical separations and subsequent measurement of alpha particles for 226Ra and beta particles for 228Ra. The method used in this experiment applies simpler gamma-ray spectral analysis of the progeny of both 226Ra and 228Ra. 

Proper preparation of biological solids for radiochemical analysis is essential for obtaining valid radioanalytical chemistry results. The samples often must be large because the radioactivity levels are low. Gamma-ray spectral analysis is the preferred method of radiation measurement because it requires little preparation. If gamma-ray spectral analysis of the untreated sample is not feasible because few or no gamma rays are emitted, the sample must be dissolved. Dissolution is almost always required for alpha- and beta-particle analysis. The first step usually reduces the mass of the solid sample and prepares it for dissolution. 

Gamma-ray Spectral Analysis of a Solution of Mixed Fission Products 143... 

A sample from a suspected nuclear incident is processed by gamma-ray spectral analysis. The sample does not contain any "Mo, or at least none is observed. Also, the sample contains large amounts of 60Co and 137Cs but no other radionuclides detectable by gamma-ray emission. What do you conclude ... 

Keller, P.E. and Kouzes, R.T., Gamma Spectral Analysis via Neural Networks, Nuclear Science Symposium and Medical Imaging Conference, IEEE Conference Record, I, 341, 1994. 

A similar simation is presented by a sample of soil or rock from which the radioactive progeny Rn of Ra leaves as a gas. The gas may be collected for counting as a purified radionuclide or its loss can cause an erroneous result in counting the sample by gamma-ray spectral analysis. 

Milk samples should be refrigerated and delivered to the laboratory within 1-2 days. For longer storage, the milk sample should be frozen or a preservative added such as methiolate, formaldehyde, or thimerosal (DOE 1987, EPA 1984), as indicated in Table 5.1. Preservatives may interfere with radioiodine separation (Murthy and Campbell 1960), but can be added if radioiodine is measured directly by gamma-ray spectral analysis. 

Radiobioassay is the determination of the kind, quantity, and location of radionuclides in the body by direct measurement (in vivo) or by in vitro analysis of material excreted from the body. Spectral analysis permits rapid analysis of radionuclides that emit gamma rays. Computer systems with data analysis in terms of metabolic models support routine use of bioassay procedures for assessing internally deposited radionuclides. The whole-body counter is an example of an in vivo procedure. 

Air filters and gummed deposition collection films first are measured by gross alpha- and beta-particle counting and gamma-ray spectral analysis. Usually, 1/2 of the sample then is dissolved to perform radiochemical analysis of the deposited radionuclides. The filter can be dry ashed, and then totally dissolved with an HNO3-HF treatment. 

Airborne Rn collected in a scintillator-coated Lucas cell is placed on a photomultiplier tube in the laboratory and counted (see discussion for Ra analysis by radon measurement in Section 6.4.1). Radon collected on a charcoal cartridge or other sorbent is measured by gamma-ray spectral analysis. In both cases, a 4-h period of ingrowth is needed to accumulate the radon progeny that contribute to the count rate. 

The sample may arrive unliltered or separated as filtered water and the filter that contains the solids. The water sample is preserved with dilute acid or a preservative suitable for a radionuclide such as 1 that may be lost from an acid solution. Water without suspended solids is ready for evaporation to measure the gross alpha- and beta-particle activity, measure gamma rays by spectral analysis, and perform radiochemical analysis. The solids usually are counted similarly and then processed for dissolution as described in Section 6.2.1 for subsequent radionuclide analysis. 

Many persons consume milk soon after collection, and the pathway for a few radionuclides from origin to milk includes accumulation steps due to large-area grazing by cows and their lactation process. Before the advent of gamma-ray spectral analysis, the radionuclides Sr, °Sr, 1, Cs, and were measured after chemical separation. Today, only the Sr pair requires chemical separation. 

Urine samples are measured directly by spectral analysis for radionuclides that emit gamma rays. To measure radionuclides that emit only alpha or beta particles, a general approach for urine pretreatment is boiling to dryness and then ashing. The ash is dissolved in mineral acid to prepare the aqueous solution for analysis (Chieco 1997). Other bioassay samples are pretreated similarly. 

Paper or cloth smears are used, often in response to regulations, to wipe surfaces of specified area (e.g., 100 cm ) to check for removable radionuclides. The smears are counted directly by gamma-ray spectral analysis. For gross alpha- or beta-particle measurements, thin smears are counted in a proportional counter or immersed in a cocktail for LS counting. Further analysis for a radionuclide of interest that emits... 

Although isotopic tracers are preferred, application of nonisotopic tracers provides more choices for selecting a radionuclide with suitable radiation, e.g., Ba tracer by gamma-ray spectral analysis for Ra by counting alpha particles. As stated in the preceding section, tests must be performed to determine whether yields for the two nonisotopic radionuclides are identical or have a constant ratio. 

Once gamma-ray spectral analysis became available, the 0.660-MeV gamma ray of the 2.55-min daughter was counted for identification, distinction from... 

For tracing plutonium yield, Pu is available. The plutonium isotope peaks are measured with a Si diode and alpha-particle spectral analysis. The Pu activity is calculated from the product of the Pu activity and the Pu peak area ratio. The Pu activity includes any contribution from Pu because the energies of their peaks are almost identical. Other plutonium isotopes (except " Pu) are measured at the same time in terms of characteristic peak areas at the energies listed in Table 6.3. A mass spectrometer is used to separate Pu from " °Pu if they must be reported separately. As indicated in Table 6.3, the emitted gamma rays can be used for intense sources but are too weak for sensitive measurements. 

The other cited radioisotope pairs among fission products are measured simultaneously by gamma-ray spectral analysis. Before such analysis became available in the 1950s, these pairs were distinguished after chemical separation by dual measurements such as those described above for 9/90gj. gfore and after an interval during which the shorter-lived radionuclides had decayed sufQciently to measure the difference with the needed precision. 

The radionuclides in this category that emit beta particles also emit gamma rays that can be detected by spectral analysis. Short-lived radionuclides that emit alpha particles occur in the natural decay chains and usually are identified by other members of the decay chain that emit gamma rays. One caution to consider is that air filters and other surfaces in the environment collect particulate progeny of °Rn and Rn that emit alpha particles, beta particles, and gamma rays with half-lives of minutes to hours. Observation of such emissions and decays has misled unprepared observers into attributing these radiations to man-made radionuclides. 

Many sources can be prepared directly for gamma-ray spectral analysis. Exceptions are sources that require concentration, stabilization, or radionuclide purification. Concentration improves detection sensitivity, stabilization should prevent changes in source configuration or content, and purification can eliminate interference with counting characteristic peaks. 

---