Delayed neutrons [english]

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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 10⁷n/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.

Two photos of the experimental system for measurements of delayed neutrons. Big, cubical block of poliethylene visible

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.

CAD drawing of the experimental system for delayed neutrons measurement

Enery spectrum of Californium 252 isotope source.