One suggestion: You could see the approach used by Ferrarini et al (2010), based on a logarithmic amplifier.

FERRARINI, M.; VAROLI, V; FAVALLI, A.; CARESANA, M.; PEDERSEN, B. A wide dynamics neutron monitor with BF3 and logarithmic amplifier based front-end electronics Nuclear Instruments and Methods in Physics Research, Section A, n. 613-2, pp. 272-276, 2010.

What is the purpose of the measurement? Is the purpose for radiation protection or radiation physics. By online are you asking to specify detection for the source? Also, what is the expected ratio of the neutron to gamma fields? You also need to specify the min and max rate that you expect to encounter. Finally, what is the pulse structure. You have to answer all of these questions in order to specify the detection system. For operational Health Physics, when the AGS at BNL was a proton machine, we used tissue equivalent proportional counters, a predetermined quality factor from neutron spectra from periodic measurements, and used them in a integrate mode. This was needed to specify the dose equivalent rate. Other facilities used Anderson-Braun style moderated detectors where the moderator was designed to provide a dose-equivalent responding instrument.

At the moment we are setting up two different neutron detectors for n-TOF at CERN. Moreover, we are setting up a few neutron detection panels in collaboration with JRC Ispra. We also have a patent pending for a neutron detection technique. All this without 3He, we use 6Li.

If you provide more details I might be able to give you some (useful?) suggestion.

You can check our approach at http://www.calmanm.es/start

Hope it heps!

The best are the scintillator 6Li detectors with gamma discrimination.

Thank you for the replies. I am not looking for a detector to be used for a specific application. On the contrary, I would like to sum up the categories of detector available of the state of the art for measuring in pulsed neutron fields.

The purpose of the measurements would be radiation protection, as well as machine protection and beam diagnostics. I am thinking at pulsed fields generated by the interaction of important beam losses with the structure surrounding particle accelerators, but also at the normal radiation protection monitoring around these facilities, where you may deal with pulsed fields.

@ Joseph: AB detectors usually show important underestimations due to the dead time losses.

@ Paolo: Are you actually dealing with pulsed fields in n-TOF? If so, which is the approach you used to deal with them?

@ Sebastian: As far as I understand you want to measure radiation level on the ground, so a radiation field which is everything but not pulsed...

For example, one of the options I considered are activation detectors based on silver activation. In this case you do not suffer of saturation issues, but you have a response delayed in time (tens of seconds of half-life of the produced isotopes). Other activation detectors exist, based on the activation of 12-C, but in this case you are limited by the energy threshold needed for the impinging neutrons to initiate the reaction (about 14 MeV).

Other ideas?

You can have a look at this paper. Another one, exploiting a similar technique with scintillators, is in preparation. As for the patent, unfortunately at the moment I cannot disclose its content.

Thermal neutron detection using a silicon pad detector and 6LiF removable converters

Massimo Barbagallo, Luigi Cosentino, Vittorio Forcina, Carmelo Marchetta, Alfio Pappalardo, Paolo Peerani, Carlotta Scirè, Sergio Scirè, Maria Schillaci, Stefano Vaccaro, Gianfranco Vecchio, Paolo Finocchiaro

Review of Scientific Instruments 03/2013; 84(3). DOI:10.1063/1.4794768

ABSTRACT A semiconductor detector coupled with a neutron converter is a good candidate for neutron detection, especially for its compactness and reliability if compared with other devices, such as 3He tubes, even though its intrinsic efficiency is rather lower. In this paper we show a neutron detector design consisting of a 3 cm × 3 cm silicon pad detector coupled with one or two external 6LiF layers, enriched in 6Li at 95%, placed in contact with the Si active surfaces. This prototype, first characterized and tested at INFN Laboratori Nazionali del Sud and then at JRC Ispra, was successfully shown to detect thermal neutrons with the expected efficiency and an outstanding gamma rejection capability.

fission chambers are well suited for gamma/neutron mixed fields ; you can do TOF spectrometry with them.

Consider the use of neutron fluence monitoring with neutron sensitive SRAM devices.

See for example the article: "The application of a SRAM chip as a novel neutron detector" from B. Mukherjee, D. Makowski et al, and other related articles from these authors. About monitoring pulsed neutron fields generated in X-FEL at DASY.

See also for example the article: " A new active method for the measurement of slow-neutron fluence in modern radiotherapy treatment rooms" from F. Gómez, A. Iglesias et al, and other related articles from these authors. About monitoring pulsed neutron fields generated in a medical linac.

Good results in the detection of pulsed neutron fields have been obtained with diamond detectors coupled with fast current amplifiers: see "Diamond detectors for fast neutron measurements at pulsed spallation sources" (M.Rebai et al 2012 JINST 7 C05015).

Also, beam diagnostics and real time monitoring could be possible: at the moment, only results with X-rays and UV light are available in the literature: see “Diamond detectors for UV and X-ray source imaging” (M. Girolami et al IEEE Electron Device Letters, Vol. 33, No. 2, pp. 224-226).

Diamond detectors do not suffer from saturation problems, ensure a very fast response (in the ns regime) and show very high radiation hardness. The basic operating principle of the detectors, as well as their technology, is very simple, acting mainly as photoresistance or Schottky photodiodes: you do not need for scintillators, attenuators or other additional items in your detecting system.

Right! Indeed we have obtained wonderful results with slow neeutrons, in collaboration with an austrian company (CIVIDEC). A neutron converter we produce was applied to a diamond detector and exposed to a neutron field from a reactor. The n-gamma discrimination was perfect. CIVIDEC is going to market these detectors quite soon.

You may read our publication on on-line measurement of pulsed neutrons. Though silver activation gives delayed signal, using good algorithm one can enhance the measurement time. We have recently developed a high sensitivity, versatile pulsed neutron detector which is under calibration. The publication details are as follows:"Pulsed Neutron Monitoring at High Energy Electron Accelerators with Silver Lined Proportional Counter" P. M. Dighe et al AIP Conf. Proc. 879, 1105 (2007); http://dx.doi.org/10.1063/1.2436256

Dear P.Dighe, could you please present a private copy of your interesting paper, I´ve no access to the journal?

Thanks Hanno

...please consider that, if a start pulse signal is available and the source distance is known, our detection scheme with converter+solid state detector also allows to determine the neutron energy (time-of-flight measurement).

Thanks for the ideas.

@ P. Dighe: You mention a good sensitivity, but usually the sensitivity in terms of nSv per count is pretty low... Can you please send me a copy of the reference [2] cited in your paper?

@ Paolo & Marco: Thanks for the suggestions.

Helium filled gas detectors can be used for on-line detection, they are even cheaper and efficient

Ion chamber detectors have the slow response and the activation counters have the low efficiency so they're not a good selection for pulsed neutron detection. Special plastic scintillator is the best choice .I made it.