Bonner Spheres Spectrometer

Bonner Spheres Spectrometer

The Bonner sphere spectrometer consists in an array of thermal neutron detectors (He-3 proportional counters), each housed in a spherical polyethylene moderator of different diameters.


Upon request, the moderators can be designed to host a different type of thermal neutron detector.

Through the comparison between the counts detected by each sphere, it is possible to determine the incident neutron energies. These data must be processed by an unfolding code to calculate the neutron spectrum.

An accessory set is available upon request to extend the energy range up to 10 GeV.

The proportional counter is connected to a compact electronic module, housed in 2.5 cm diameter aluminum cylinder with a length of 7.6 cm, having the following main characteristics:

  • Precision wide band charge sensitive pre-amplifier followed by an amplifier
  • Twelve-turn trim pot to finely tune the amplifier sensitivity to the desired level to obtain a good high voltage plateau
  • Discriminator circuit that produces, when a charged event is detected, a TTL pulse (width adjustable from 40 to 500 ns)
  • Threshold control trim pot allowing to control the discriminator level
  • Analog monitoring test point allowing direct monitoring of amplified charged events using an oscilloscope
  • High performance high voltage generator, adjustable over a range of 0-2200 V
  • Test point to measure and adjust the high voltage setting

The central acquisition box is based on 8-CH TTL hi speed DIO modules, a real-time processor and a reconfigurable field-programmable gate array. The central box is connected to a PC through an Ethernet cable, and is programmed to continuously acquire the counts coming from the detectors, also when the acquisition PC is off.

A user-friendly dedicated acquisition software is installed on the PC; it allows to start and stop the measurements, to modify the parameters and to visualize the saved data.

Additional information

Main features:

Compact and high-performance system
Worldwide standard
Fully customizable (moderator diameters, material and number)
Detectors: He-3 proportional counters
Moderators: HD polyethylene, spherical, from Ø 3” to Ø 18”
Accessory set for energy range extension up to 10 GeV
Exportable archived data (ASCII files)
Optional special electronics for use in pulsed fields