Tabletop Fusion Revisited
I do not think that it is possible for R. P. Taleyarkhan et al. (“Evidence for nuclear emissions during acoustic cavitation,” Research Articles, 8 March, p. [1868][1]) to have observed 2.5-MeV neutrons for the simple reason that the pulse-height threshold used in their experiment is greater than
Response function of NE213 scintillator for 0.5-6 MeV neutrons measured by an improved pulse shape discrimination
Abstract Using the pulse shape discrimination method combined with the time of flight technique, we have obtained the response function of a 2″ diameter × 2″ thick NE213 scintillator by measuring directly the proton recoil energy spectrum of 0.5–6 MeV prompt neutrons from a 252 Cf source. Three parameters, time of flight (TOF), pulse shape discrimination (PSD) and recoil energy (RE), were recorded in an event-by-event mode with a TOF gate. We attempted to improve the determination of maximum proton recoil energies equal to incident neutron energies by employing two analysis methods. First, we attempted to separate better neutrons from coexisting gamma rays in the PSD spectrum by projecting neutron channels of the PSD spectrum onto both TOF and RE spectra in a cubic matrix constructed by the three-parameter data. The resulting two-dimensional matrix composed of TOF and RE channels was free from gamma rays and corresponding Compton-recoiled electrons, and then projected with neutron energy bins of 0.05 MeV wide determined by TOF. Finally, to determine the maximum proton recoil energies from each RE spectrum with a realistic function, accounting for the nonlinear response of the NE213 scintillator due to the quenching effect, we performed a least-squares fit to the RE spectrum using the four-parameter function. The response function obtained in the present work agrees well with previous experimental results obtained by Gul et al. (Nucl. Instr. and Meth. A 278 (1989) 470) and a Monte Carlo study by Cecil et al. (Nucl. Instr. and Meth. 161 (1979) 439).
AXIOMATISABILITY OF WEAKLY FLAT, FLAT, AND PROJECTIVE S-ACTS
ABSTRACT This paper gives necessary and sufficient conditions on a monoid S that the class of flat left S-acts be (first order) axiomatisable. It presents also a streamlined version of the result of Stepanova that the class of projective left S-acts is axiomatisable if and only if the strongly flat left S-acts are axiomatisable and S is left perfect.