Measurements of Delayed Neutrons

In our department an experimental setup for measurements of neutron fluxes has been designed and constructed. Th e measurement is based on detecting of delayed neutrons emitted from activated probes of fissile materials. The device is used to measure high fluxes of fast neutrons, above 10⁷ n/cm²s, generated in high-temperature plasma (deuterium or deuterium-tritium) of fusion devices. The activation method is based on the use of samples containing isotopes of fissile materials such as ²³²Th, ²³⁸U and ²³⁵U.

Proportional helium counters He-3 are used for delayed neutrons detection.

For the construction of the experimental setup the following materials and components have been used:
• borated polyethylene (C₂H₄ + 25% B),
• cadmium,
• boron carbide (B₄C),
• polyethylene (C₂H₄),
• bismuth,
Figure below shows the a cross-sectional drawing of the experimental setup.

Below, a scheme of the measurement system for recording and data acquisition is presented. Delayed neutrons are registered using proportional helium counters He-3 and signals are recorded with multi-channel amplitude analyzer (MCA). An example of the spectrum of acquired pulses in helium detectors on a MCA  is shown below. A neutron ²⁵²Cf californium source has been used for tests and calibration measurements.

Within a part of the project, doctoral thesis was completed: “Detection of delayed neutrons from fissionable samples – Monte Carlo modeling and physical assumptions for a design of the DET-12 device.”, which included a detailed description of the device construction and contained results of the necessary calculations to build a prototype of the measurement station.”

A.Kurowski at all, Metoda pomiaru strumieni neutronów z reakcji syntezy w reaktorach termojądrowych poprzez detekcję neutronów opóźnionych z aktywacji materiałów rozszczepialnych. Projekt i budowa systemu pomiarowego
https://rifj.ifj.edu.pl/handle/item/288