simple nuclear experiments with a license-free alpha source carl willis, heas 2011
DESCRIPTION
Simple Nuclear Experiments With A License-Free Alpha Source Carl Willis, HEAS 2011. Introduci ng the NRD “ Nuclespot ”. 5-millicurie Po-210 static eliminator in aluminium holder Obtain from Larry at www.amstat.com 1-year lease is $147.50 No NRC license required!. - PowerPoint PPT PresentationTRANSCRIPT
19/28/2011
Simple Nuclear Experiments WithA License-Free Alpha Source
Carl Willis, HEAS 2011
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Introducing the NRD “Nuclespot”
• 5-millicurie Po-210 static eliminator in aluminium holder• Obtain from Larry at www.amstat.com• 1-year lease is $147.50• No NRC license required!
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Chapter 1: The Na-23(a,p)Mg-26 ReactionThis reaction often leaves the Mg-26 nucleus in a short-lived excited state from which it decays by emitting gamma rays. It is an important source of gamma radiation in salt wastes from plutonium processing.
Procedure• Table salt is poured into the Nuclespot’s grill and retained with a piece of
packing tape.• The arrangement is counted on an HPGe detector for ~7 hours, with the
source facing the detector.• A “background” is collected from the Nuclespot without salt.
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Mg-26 Excited StatesTwo excited states are expected, both having half-lives on the order of 200 fs.
(This and subsequent nuclear energy level diagrams taken from the National Nuclear Data Center: www.nndc.bnl.gov.)
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Restoring an HPGe Detector• HPGe detector originally from Taylor Wilson• Required replacement of FET, replacement of can insulator sheet, and
restoration of Dewar vacuum• FET replacement: 2 (in parallel) or single 2SK152 (a $2 transistor)• Can insulator replaced with a transparent book-binding sheet from OfficeMax• Dewar drilled for continuous-pumping by a high-vacuum system • RESULT: 1.5 keV FWHM @ 662 keV—close to new specs
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Lab Area (i.e. Bedroom)HPGe detector is surrounded by 500 lb of lead bricks. Consumes 30 liters LN2 every week (most lost to filling process). Detector Dewar must be fed every 8 hours. NIM electronics controlled by homebrew LabVIEW interface.
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Gamma spectrum from plutonium salt waste(Sher and Untermeyer, 1984)
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Chapter 2: The F-19(a,p)Ne-22 ReactionThis reaction has a very high cross-section, and a peak from the Ne-22 signature gamma rays can be discerned almost immediately.
Procedure• Sodium fluoride (NaF) is poured into the Nuclespot’s grill and retained with a
piece of packing tape.• The arrangement is counted on an HPGe detector for ~5 hours, with the
source facing the detector.• A “background” is collected from the Nuclespot without NaF.
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Ne-22 Energy LevelsA single energy level is accessible with the Po-210 alpha.
Half-life is 3.6 ps.
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Chapter 3: The B-10(a,p)C-13 ReactionThis reaction results in a complex spectrum of high-energy gamma rays from multiple excited states in the C-13 nucleus.
Procedure• Elemental boron powder is poured into the Nuclespot’s grill and retained
with a piece of packing tape (this stuff is messy, so be careful). • The arrangement is counted on an HPGe detector for ~5 hours, with the
source facing the detector.• A “background” is collected from the Nuclespot without boron.
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Kinematics of the B-10(a,p)C-13 Reaction
Linear momentum is conserved: Energy is conserved: Combined equation:
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Kinematics of the B-10(a,p)C-13 Reaction
• The maximum C-13 energy occurs when
C-13 Nuclear State (keV)
C-13 Maximum KE (keV)
C-13 Max. Velocity (m/s)
0 (ground state) 3745 7.45E+063089.4 3131 6.82E+063684.5 2999 6.67E+063853.8 2960 6.63E+06
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Doppler effects after the
B-10(a,p)C-13 reaction
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(This curve generated from SRIM data)
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Lifetime of C-13 excited states
The two lowest excited states have half-lives in the range of 1 fs, very brief compared to the slowing-down time of ~500 fs for the fastest C-13 nuclei. Significant Doppler broadening / shift is expected from the gamma peaks corresponding to these states.
The 3854-keV state has a much longer half-life of 8.6 ps. Little Doppler broadening is expected in this gamma peak.
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Conclusions
• Radioactive sources available to the public at modest cost without licensing CAN be used to perform nuclear transmutation reactions at detectable levels.
• Potential areas of further study : Nuclear energy levels, selection rules, reaction kinematics, decay rates, non-destructive sample analysis