Alpha-particles pulse heights

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 particle calibration sources span energies from about 100 to 3,000 keV for proportional counters, and down to a few keV for liquid scintillation counters. In this experiment, a low-background, gas-flow, end-window proportional counter with automatic sample changer for alpha- and beta-particle counting is calibrated. Beta-particles sources are counted with pulse-height discrimination to eliminate interference from alpha particles the discriminator may be turned off when no alpha particles are present. 

Energy discrimination is based on the difference in pulse height produced by the two types of particles the alphas, being more energetic, produce higher pulses thus a simple discriminator at an appropriate level can reject the beta... 

Because alpha-particle spectra consist of characteristic, discrete energy peaks, they are quite useful for identification. Pulse-height analyzers (.Section I2B-S) permit the recording of alpha-particle spectra. 

Figure 2. Pulse height spectra from alpha particle detection by CdSe/ZnS core/shell and Yi gdCeojoO nanocrystals prepared by different methods.

Lao.9oCeo.ioP04 nanocrystals were surface modified with mixed surfactants a mixture of DDA and BEHP or a mixture of OA and BEHP. The surface modified nanocrystals were dispersed at SO wt % in polystyrene, forming translucent thick films on quartz discs. Pulse height spectra from alpha particle detection (Source Am) of nanocrystal samples superimposed with the result from a highly efficient plastic scintillator, BC-400 are presented in Figure 3. 

A more powerful technique involves the measurement of energy spectra with solid-state detectors. Alpha-particle spectra can be measured with an Au-Si surface barrier detector. For these measurements thin sources are required and both the source and the detector are placed in vacuum. Resolutions (full width at half maximum) of 10-30 keV are easily obtained and usual geometries are 5-30%. By measuring the a-particle spectrum, commonly known as a pulse-height... 

Figure 22 Pulse height spectra obtained with a BP-on-Si device with and without an "Am 5.5-MeV alpha particle source present. (From Ref. 73.)...

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