Here is a spectrum I collected of an old Americium source which was filtered with 1.5mm of 99.97% pure cadmium. Even without graphing the data in log scale, the higher energy peaks are apparent thanks to the significant reduction of 59 keV gamma rays. the count rate with out attenuation was ~300 cps while the attenuated count rate was ~25 cps.
Spectrum of 241Am attenuated with Cd
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Geoff
- Posts: 141
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Spectrum of 241Am attenuated with Cd
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Sesselmann
- Posts: 1392
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Re: Spectrum of 241Am attenuated with Cd
Geoff,
Nice experiment, so the cadmium is selectively attenuating the low energy noise which in turn makes the low intensity peaks stand out. Was there a particular reason for choosing cadmium?
Steven
Nice experiment, so the cadmium is selectively attenuating the low energy noise which in turn makes the low intensity peaks stand out. Was there a particular reason for choosing cadmium?
Steven
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Geoff
- Posts: 141
- Joined: 01 May 2015, 12:21
Re: Spectrum of 241Am attenuated with Cd
I used it based on what I read in the paper Gamma-Ray Interactions with Matter by G. Nelson and D. Reilly
Filtering is usually employed in the measurement of plutonium gamma-ray spectra. Except immediately after chemical separation of americium, all plutonium samples have significant levels of 241Am, which emits a very intense gamma ray at 60 keV. In most samples, this gamma ray is the most intense gamma ray in the spectrum and must be attenuated so that the plutonium gamma rays can be accurately measured.
A thin sheet of cadmium is commonly used to attenuate the 241Am activity. Table 2-1 shows the effect of a cadmium filter on the spectrum from a 2g disk of plutonium metal. In the absence of the filter, the 60-keV gamma ray dominates the spectrum and may even paralyze the detector. A 1 to 2mm cadmium filter drastically attenuates the 60-keV activity but only slightly attenuates the higher energy plutonium lines. The plutonium spectrum below 250 keV is usually measured with a cadmium filter.
When only the 239Pu 414-keV gamma ray is of interest, lead may be used as the filter material because it will attenuate gamma rays in the 100-to 200-keV region and will stop most of the 60-keV gamma rays. It is interesting to note that at 60 keV the mass attenuation coefficients of lead and cadmium are essentially equal, in spite of the higher Z of lead (82) relative to cadmium (48). This is because the K edge of lead appears at 88 keV, as discussed in Section 2.3.1.
Filtering is usually employed in the measurement of plutonium gamma-ray spectra. Except immediately after chemical separation of americium, all plutonium samples have significant levels of 241Am, which emits a very intense gamma ray at 60 keV. In most samples, this gamma ray is the most intense gamma ray in the spectrum and must be attenuated so that the plutonium gamma rays can be accurately measured.
A thin sheet of cadmium is commonly used to attenuate the 241Am activity. Table 2-1 shows the effect of a cadmium filter on the spectrum from a 2g disk of plutonium metal. In the absence of the filter, the 60-keV gamma ray dominates the spectrum and may even paralyze the detector. A 1 to 2mm cadmium filter drastically attenuates the 60-keV activity but only slightly attenuates the higher energy plutonium lines. The plutonium spectrum below 250 keV is usually measured with a cadmium filter.
When only the 239Pu 414-keV gamma ray is of interest, lead may be used as the filter material because it will attenuate gamma rays in the 100-to 200-keV region and will stop most of the 60-keV gamma rays. It is interesting to note that at 60 keV the mass attenuation coefficients of lead and cadmium are essentially equal, in spite of the higher Z of lead (82) relative to cadmium (48). This is because the K edge of lead appears at 88 keV, as discussed in Section 2.3.1.
