Counting alpha-particle

Radon-222 may be transported with a carrier gas into an ionization chamber and its alpha particles counted. Short-lived isotopes in a carrier gas stream are measured this way using a flow-type ionization chamber. 

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. 

To prepare a standardized plutonium tracer for use and compare its activity in 2 detector systems calibrated for alpha-particle counting efficiency. 

In this experiment, a known activity of 242Pu is diluted for use as tracer and its activity is checked with a detector that was previously calibrated for alpha-particle counting. This tracer will be used in Experiments 14 and 15 for the analysis of mPu... 

What are the assumptions in using the alpha-particle counting technique with regards to the different energies associated with different radionuclides ... 

Estimate the fraction of uranium that remained in the sample from the alpha-particle count rate compared to the count rate in the initial sample, adjusted for the amount of uranium in the solution. Do the same for thorium based on the comparison of beta-particle count rates. Estimate the efficiency of separating 234Th from 238U. 

For each alpha-particle count and beta-particle count, subtract the respective background to obtain the net count rate with its uncertainty. 

Plutonium is electrodeposited onto a stainless steel disk to obtain a thin and uniform source for counting alpha particles. Counting is by spectral analysis to identify the plutonium alpha particles by peak energy and determine their activity by the integral of the count rate at the peak. 

The sample then is prepared for alpha-particle counting by co-precipitation of plutonium with a small amount of lanthanum fluoride, which is collected... 

U-series nuclide activities can be measured directly by detection of their emitted nuclear particles, e.g., alpha particle counting by solid-state detectors (Ivanovich and Harmon, 1992). In contrast, measurements by mass-spectrometry do not require waiting for Nature to take its course. Atoms of the sample are ionized and accelerated so that charged particles of the nuclides themselves can be measured by Faraday cups or electron multipliers (see Goldstein and Stirling, 2003). Mass-spectrometry is hence a more rapid technique. Typically mass-spectrometry measurements take tens of minutes to hours, while counting methods require days to weeks. 

For the first three applications, a radionuclide- and mass-specific counting efficiency musf be selected. For the fourth application, a thin sample—below 2.5 mg/cm for alpha-particle counting—should be prepared so that efficiency values are similar af commonly encountered energies. For counting beta particles, the sample should not exceed 10 mg/cm. An intermediate-energy (e.g., 0.6-0.8 MeV Pmax) radionuclide standard provides reasonable efficiency estimates except that the activity of a radionuclide that emits only low-energy beta particles will be underestimated. 

End-window proportional counters with thin windows that separate sample from detector have the alpha-particle counting efficiency shown in Table 8.1 for thin samples on planchets. The lesser counter efficiency relative to the internal detector is due to less than 27t geometry and attenuation in sample, air space, and window. 

Determination of the plutonium content of the sample by alpha-particle counting or other techniques (Brouns 1980). 

Alpha-particle counting is the most commonly used method for determining plutonium concentrations at low levels in biological samples, as well as in process waste streams, and in soil, water, and air filter samples (Brouns 1980). This method does not distinguish between the different alpha-particle emitters of plutonium (plutonium-236, plutonium-238, plutonium-239, plutonium-240, plutonium- 242), nor does it detect plutonium-241, a beta-particle emitter. 

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