System for measurement of low yield neutron pulses from D–D fusion reactions based upon a³He proportional counter

Abstract

A conventional neutron detection technique was adapted to measure low neutron yields from D-D fusion pulses. This method uses a 3 He proportional counter surrounded by a paraffin moderator. Electric signals generated in the 3 He tube are fed into a preamplifier. The output of the preamplifier is directly connected to a digital oscilloscope. The time-integrated signals represent the charge generated in the 3 He tube which is proportional to the total neutron yield. The integration time is determined by the preamplifier and moderator characteristics within some hundreds of microseconds. No meaningful neutron background was detected during this time window. The system, previously calibrated, was used to measure the neutron yield (<10 6 neutron/pulse) generated in a fast and very small plasma focus device designed to operate with energies of tens of Joules. Neutron yields as low as 10 3 neutrons per pulse were measured.

Dynamics and Density Measurements in a Small Plasma Focus of Tens-of-Joules-Emitting Neutrons

“…2(e)], around the moment of the pinch formation, measurements of the neutron yield and electri- Fig. 4), for this shot, gives evidence of a neutron yield of 1.6 × 10 4 neutrons/shot, which is in agreement with measurements in a similar electrode configuration reported in [5] and [6]. From the electrical diagnostics with time resolution (see Fig.…”

“…The neutron production was measured by using two moderated 3 He-filled proportional counters ( 3 He tubes) according to the technique reported by Moreno et al [6]. Both detectors were arranged symmetrically side-on at a distance of 23.5 cm from the anode axis.…”

“…More recent studies have demonstrated neutron production when operating with deuterium at 50 and 67 J of stored energy in the capacitor bank. Average yields of 1.2 ± 0.5 × 10 4 neutrons/shot at 6 mbar and 50 J and 3.6 ± 1.6 × 10 4 neutrons/shot at 9 mbar and 67 J have been measured [5] using a detection technique based on 3 He-filled proportional counters specially adapted for pulsed neutron sources of low production [6]. It has been observed that the energy of the fast neutrons has a mean value of 2.7 MeV with a standard deviation of 1.8 MeV, the latter obtained using the time-of-flight technique [5].…”

Influence of the Anode Length on the Neutron Emission of a 50 J Plasma Focus: Modeling and Experiment

“…The circuit current is obtained by numerical integration of the signal of the current derivative. The neutron yield diagnostics consisted in two detection systems based on 3He proportional counters tubes moderated by paraffin wax, one located on the axis and the other located radially [39]. The 3He detection systems were calibrated in efficiency only, using as reference a standard isotopic fast-neutron source ( 252 Cf).…”

“…The data is an extended set of results from the experimental study presented in [20] and [46], where a new technique was especially developed to measure neutron pulses of low intensity [39], [40]. The model is able to explain the dependence of the neutron yield with the pressure and anode length, and suggests a physical interpretation of the empirical scaling laws commonly used in PF design.…”