Bonner sphere

Fast neutron detection sometimes uses a hydrogenous moderator to slow down the neutrons and then employs a low-energy neutron detector as described above. One common fast neutron detector is a Bonner sphere. In this detector, a scintillator is placed in the center of a polyethylene sphere. Radiation transport calculations are used to produce efficiency curves that depend on the energy of the incident neutron. Another common fast neutron detector is a long counter. This detector uses a slow neutron detector (originally a BF3 chamber) at the center of a cylindrical moderator designed so that the detector is only sensitive to neutrons incident from one side. 

A different type of arrangement, using a LiI(Eu) scintillator to detect the neutrons after they are moderated, is the Bonner ball (or sphere). Using the Bonner ball, neutrons are detected by a LiI(Eu) scintillator, a BF3 tube, or an He counter placed at the center of polyethylene spheres with sizes ranging from 51 to 305 mm (2-12 in) in diameter. Using the Bonner sphere, the neutron energy is determined on the basis of the difference in moderating efficiency for the spheres of different sizes. Because the Bonner sphere is primarily used as a neutron dosimeter, it is discussed in more detail in Chap. 16. 

Rem ball Bonner sphere with BF3 n Measures neutron dose equivalent... 

The Bonner sphere, named after one of the first people to study its features and use it, is a neutron detector. It consists of a polyethylene sphere, at the center of which a neutron detector is placed (Lil scintillator or BF3 or He counter). With any one of these materials, the neutrons are detected through the reactions... 

Figure 16.13 Sensitivity of a 10-in (0.254 m) diameter Bonner sphere surrounding a 4 mm X 4 mm Lil scintillator. For comparison, the inverse of the response function RPG is also shown. The RPG gives dose rate, H, per unit neutron flux (Ref. 30).

Another advantage of the Bonner sphere, in addition to its convenient response function, is its complete insensitivity to gammas. This is the result of relying for neutron detection on charged-particle reactions with high Q value, thus making possible the complete rejection of pulses due to gammas with the use of a proper discriminator level. 

In the nuclear industry the Bonner sphere is known as the rem ball or rem meter. 

Figure 16.14 Calculated sensitivity of a 10-in (0.254 m) diameter Bonner sphere compared with the measured response (Ref. 30).

Observations made by Lewis et al. (75), Anderson and Bonner 6), and others (9B), for systems of the charge type -1-2, -fS, show that when substitution in the first sphere of coordination of the oxidizing agent is excluded, Cl does not exert its usual catalytic effect. Thus it seems likely that, in the Fe++ — Fe+ + + systems, activated complexes (a) and (c) can... 

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