General

Neutrons are electrically neutral particles. Because they interact only by the hadronic interaction with matter, neutron radiation is extremely penetrant. For detection neutrons have to be converted into charged particles. These particles produce common signals in radiation detectors. Neutrons are produced in nuclear reactions at accelerators or by nuclear fission. There are also neutron sources like Am-Be or Cf-252 sources.

Moderation

Some of the physical process, which convert neutrons into charge particles, take place only at low neutron energies. This is for instance true for the famous reaction n + He-3 -> H-3 + p which is used in He-3 counter tubes. To reduce higher neutron energies to thermal energies moderation has to be applied. Moderation makes use of energy transfer in collisions of neutron with light nuclei - usually on protons, deuterium or carbon. After several interactions in materials like water, polyethylene or graphite neutrons were thermalized. Neutron rem counters have large volumes of plastic, to moderate and detect incident neutrons.

Neutron Detection

Neutron detection is provided by proportional counter tubes filled with He-3 or BF-3 gas, by recoil proton counter tubes filled with hydrogen or methane, by scintillators which are dopped with neutron absorbers like Bor, or by plastic scintillators, where the recoil protons are detected. There are even more sophisticated detection techniques, like neutron activation analysis. 

Neutron Dose Rate

For the measurement of neutron doserate a neutron detector needs to be energy compensated with respect to neutron dose.  This is a filtering technique to tune the detector's response as a function of energy. As filtering reduces the efficiency it is difficult to design sensitive neutron dose rate meters. Berthold has designed the neutron dose rate probe LB6411 in cooperation with the research center Karlsruhe. This product has an excellent match to the new quantity ambient dose equivalent H*(10) over a wide energy range. 

Search for Neutron Emitters  

Neutron radiation occures only in nuclear facilities like reactors, accelerators or in the presence of radionuclides which emitt neutrons. These are mainly isotopes with spontaneous fission like Cf-252 or the some plutonium isotopes. As neutrons can not easily be shielded, neutron detection is an excellent tool to search for these materials. We offer the plutonium monitor LB6414 to search for illicit traficking plutonium at customs or at entrance doors of nuclear facilities. A significant neutron intensity level indicates in nearly all cases a dangereous situation.