Forest He-3 Tubes: Difference between revisions
No edit summary |
No edit summary |
||
| Line 14: | Line 14: | ||
The probability of neutron capture is measured in terms of a cross section. There is a nuclear data base for neutron capture located at [http://ie.lbl.gov/ng.html LBL]. The "free" neutron thermal cross section is about [http://ie.lbl.gov/ngdata/sig.htm <math>3.10 \pm 0.13</math>] barns ( 1 barn = <math>10^{- | The probability of neutron capture is measured in terms of a cross section. There is a nuclear data base for neutron capture located at [http://ie.lbl.gov/ng.html LBL]. The "free" neutron thermal cross section is about [http://ie.lbl.gov/ngdata/sig.htm <math>3.10 \pm 0.13</math>] barns ( 1 barn = <math>10^{-24} cm^2</math>). | ||
Revision as of 10:04, 6 June 2008
Thermal neutron capture of He-3 may be represented by the reaction below
[math]\displaystyle{ n + He^3 \rightarrow p + H^3 }[/math]
About 764 keV of energy is liberated in this nuclear reaction and distributed between the final products according to their masses. Because the proton is about a factor of 3 lighter than Tritium (H^3) , it will have more kinetic energy by about a factor of 3 (about 573 keV). This liberated proton can ionize other He-3 atoms via the reaction
[math]\displaystyle{ p+He^3 \rightarrow p + He^3(+) + e^- }[/math]
The same proton will ionize several He-3 atoms when dissipating the 573 keV kinetic energy.
The Tritium (H^3) can also ionize the gas but due to its higher mass it does not travel as far (shorter range) as the proton and makes a smaller contribution to the ionization signal.
reference: J. W. Leake, "Nuclear Instruments and Methods", Vol. 63, page 329, 1968).
The probability of neutron capture is measured in terms of a cross section. There is a nuclear data base for neutron capture located at LBL. The "free" neutron thermal cross section is about [math]\displaystyle{ 3.10 \pm 0.13 }[/math] barns ( 1 barn = [math]\displaystyle{ 10^{-24} cm^2 }[/math]).
File:He-3Tube DetectorDrawing.jpg
