2.1 PF-6 device

This machine (Figure 2a) has been described in a number of papers (see e.g., [1, 10–12]). Its battery charged to 12–20 kV contains up to 6 kJ of energy. Typical range of initial pressures of pure deuterium in the device in this configuration was in the range from 2 to 8 Torr. Amplitude of a discharge current of the device measured by a Rogowski coil reaches 0.7 MA. The definition of the device as a neutron source (its major parameters that were measured many times) is as follows:


Taxonomy of Big Nuclear Fusion Chambers Provided by Means of Nanosecond Neutron Pulses DOI: http://dx.doi.org/10.5772/intechopen.89364

• Pulse duration is in the range 15–20 ns, that is, a "thickness" of a quasispherical neutron "sheath" (Figure 1a) spreading into a space from the source has its value of about 10 cm. In other words, 10 cm is the length of the neutron packet coming to a detector from the neutron source. Thus, the DPF source irradiates an ns neutron pulse to a detector as a neutron bunch with a size much smaller than the characteristic dimensions of the elements and systems of a NFC.

A DPF is an ecologically more acceptable radiation-producing device in comparison with another neutron sources like the accelerators, fission reactors, and isotope-based sources because:


In Figure 3, the oscilloscope trace of the current derivative of a typical "shot" (discharge) of the device is presented. Chambers that have been used in this device were of two types (small and large) designed and manufactured at the VNIIA. With the last one, it may be sealed, obeying a gas generator with deuterium-tritium mixture and produce the 14-MeV neutrons with the yield up to 10<sup>11</sup> neutrons of 15–20 ns time duration.

### 2.2 Activation methodology

A silver activation counter—SAC [1] (in fact two of them—SAC-1 and SAC-2) is the main tool in this technique of measurements of the absolute neutron yield Yn. It is based on silver as activated material. The whole detector is composed of a Geiger-Muller (G-M) counter wrapped with a silver foil and placed within a hydrogenreach moderator. Fast neutrons (2.5 MeV) emitted from a DPF source are slowed

Figure 3. Oscillogram of the current derivative for a typical "shot" of the PF-6 device.

down in the moderator. Indirect products of two reactions of decelerated neutrons with Ag are β� emitters. This type of neutron detectors is a wide-spread tool in the DPF community, in particular because of the short (ns) neutron pulses generated by a DPF that is much shorter compared with the half-life of the reactions (see Table 1). We used these detectors with and without cadmium foil enveloping our moderators of SACs. With this foil, the effective "threshold" of neutrons' energy registered by the counter is 500 keV. In this case, slow neutrons coming to the detector after scattering in the surroundings are not registered. SACs that were used since many years as the Yn monitor for the PF-6 device were calibrated many times by special isotope-based neutron sources placed inside the device's chamber. The calibration of SACs has been combined with MCNP calculation [14].

The SAC method has a number of limitations. It can be better operational if it will be used in a combination with other methods of Yn monitoring. So other elements [14–18] (In, Be, and Y) were exploited for a so-called cross-calibration technique with SACs. In a Table 1, one may see the most important nuclear data regarding the nuclear reactions that were engaged in the PF-6 neutron activation monitors. Here,T1/2 is the half-life time of particular radionuclides.

The elements have been chosen because of their specific advantages. Thus, a cross-section for the reaction with Be (the BNAC detector) has an effective threshold near 1 MeV, so undesirable multiple-scattered neutrons do not undergo this reaction and, therefore, are not measured. The inelastic scattering reaction with In has such a threshold equal to 340 keV. Fusion neutron yttrium monitor (FNYM) does not need any neutron moderator to allow neutrons detection.

A large area gas sealed proportional detector SP-126C (Canberra made) has been chosen in these techniques as a β� particle counter. Its calibration includes the following procedures: use of calibration sources of β� and neutron radiations with a parallel set of various Monte Carlo calculations for β� particle and neutron transport. We applied the MCNP5 [16] Monte Carlo code with MCNP5DATA [17] cross section library that have been used for the above-mentioned calculations.

In some of the above-mentioned activation techniques, the gamma spectrometry system based on the high purity germanium (HPGe) detector equipped with multichannel analyzer (MCA) was used. The detector is supplied by the


#### Table 1.

Nuclear data relating to the nuclear reactions that are engaged in neutron activation techniques.

manufacturer with its numerical characterization and software for mathematical calibration of the system (ISOCS/LABSOCS). Specific features of the abovementioned activation methods, calibration procedures, and their MCNP support calculations one may find in the work [18].
