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Sealed Source Radiation
Safety Training
Module 8: Working with the Americium-Beryllium Source
| Notice: You must complete this module if you will work with the americium-beryllium source or will spend time in rooms in which the source is used or stored. |
Researchers in the Physics Department use a 1 mCi americium-beryllium source for the calibration of detectors. Prof. Galbiati is the faculty member authorized to possess and use this source and is responsible for ensuring that the source is used in accordance with procedures approved by the Radiation Safety Committee.
Characteristics of the Americium-Beryllium Source
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Decay Scheme and Dose Rates
The decay scheme for Americium-241 is described below. A detailed fact
sheet is available upon request from EHS.
Radioisotope |
Half-Life |
Significant Radiations |
Comments |
Americium-241 |
432.7 yr |
5.6 MeV alpha; various alphas, betas and gammas from decay products |
Decays to long-lived Np-237, decaying in turn to Pa-233 and U-233. |
However, in addition to the radiations described above, an americium-beryllium source produces 4.5 MeV neutrons via a reaction in which the beryllium absorbs an alpha and emits a neutron (the 9Be(a,n)12C reaction).
Dose Rates
Radioisotope |
Gamma dose rate at 1 m from source
(millirem/hr per mCi) |
Neutron dose rate at 1 m from
source (mrem/hr per mCi) |
Americium-241 |
0.315 |
0.0074 |
The total dose rate at 5 cm from the source is 2 mrem/hour. In the interest of keeping doses as low as reasonably achievable, extended close contact with the source must be avoided.
Since the whole body dose limit is 5000 mrem, it would require 15,000 hours for a person standing one meter from the unshielded source to receive the annual allowable dose. While the source is in use, it will be shielded, so it is expected that persons working within the room will receive no measurable dose.
Source Design and Integrity
The drawing below shows a typical design of an americium-beryllium source
Fig.
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The americium oxide and beryllium powder are mixed together and compacted to form a pellet that is welded inside a stainless steel capsule. This inner capsule is then welded inside an outer stainless steel capsule.
The source meets the State of California definition of a sealed source (at least as stringent as the NRC's definition). The State of California concludes that “the source would be expected to maintain its containment integrity for normal conditions of use and accidental conditions which might occur during uses specified in this certificate.”
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Special Requirements (top)
In addition to the general requirements for sealed sources that are described in Module 7 (Working Safely with Sealed Sources), there are additional requirements for individuals who work with the americium-beryllium source or who work in a room in which the source is in use:
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In addition to this sealed source radiation safety training, every person who will handle the source must receive training in specific handling, storage and security procedures from Prof. Galbiati or from a person designated by Prof. Galbiati.
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Handling and storage of the source must be performed in accordance with procedures established by Prof. Galbiati.
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The source must not be handled directly with the hands and must be handled with remote handling tools such as tongs or forceps.
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All persons who handle the source must wear radiation monitoring badges with neutron detection capability.
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All persons who handle the source must wear radiation monitoring badges with neutron detection capability.
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The source must always be secured in accordance with procedures established by Prof. Galbiati or must be attended by a person authorized to use the source.
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All persons who work in a room in which source calibration operations are conducted or who handle the source must complete the Princeton University online Sealed Source Radiation Safety Modules and test.
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This is the end of the Working with the Americium-Beryllium Source
Module, which is the last of the eight Sealed Source Radiation Basics
modules. You may now go to the test or you may go to any of the previous
modules:
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