[1507.00607] Investigation of background in large-area neutron detectors due to alpha emission from impurities in aluminium

[ Authors ]
J. Birch, J.-C. Buffet, J.-F. Clergeau, P. van Esch, M. Ferraton, B. Guerard, R. Hall-Wilton, L. Hultman, C. Höglund, J. Jensen, A. Khaplanov, F. Piscitelli
[ Abstract ]
Thermal neutron detector based on films of $^{10}$B$_4$C have been developed as an alternative to $^3$He detectors. In particular, The Multi-Grid detector concept is considered for future large area detectors for ESS and ILL instruments. An excellent signal-to-background ratio is essential to attain expected scientific results. Aluminium is the most natural material for the mechanical structure of of the Multi-Grid detector and other similar concepts due to its mechanical and neutronic properties. Due to natural concentration of $\alpha$ emitters, however, the background from $\alpha$ particles misidentified as neutrons can be unacceptably high. We present our experience operating a detector prototype affected by this issue. Monte Carlo simulations have been used to confirm the background as $\alpha$ particles. The issues have been addressed in the more recent implementations of the Multi-Grid detector by the use of purified aluminium as well as Ni-plating of standard aluminium. The result is the reduction in background by two orders of magnitude. A new large-area prototype has been built incorporating these modifications.

Symptom, Dispute, Barreness, and Entropy: the Four Stable Boys of the Apocalypse!

“Their whole purpose is to push a potentially false apocalypse into the real thing.”

(from Xombi vol. 1, no. 3)

Comic book religion factoid!: The Four Horsemen of the Apocalypse first appear in the Book of Revelation in the Christian Bible (6:1-8). They are not named in the text, but they are often called Conquest (riding a white horse), War (red), Famine (black), and Death (pale green). However, most comic book representations of the Horsemen–here, as well as in the X-Men comics and Wonder Woman–change Conquest/white to Pestilence or Plague, who does not appear at all in the biblical texts. Presumably a disease-bearer makes for a better super-villain than Conquest, who, by definition, cannot lose.