Department of Radiation Transport Physics NZ61

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.

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
A block diagram of electronics
Enery spectrum of Californium 252 isotope source.

Institute of Nuclear Physics 

Polish Academy of Sciences

ul. Radzikowskiego 152

31-342 Kraków, Polska

Department of Radiation Transport Physics




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