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HeNeutron detection Pulsed field Linac Proportional counter Logarithmic amplifier a b s t r a c t A number of studies focused in the last decades on the development of survey meters to be used in pulsed radiation fields. This is a topic attracting widespread interest for applications such as radiation protection and beam diagnostics in accelerators. This paper describes a new instrument specifically conceived for applications in pulsed neutron fields (PNF). The detector, called LUPIN, is a rem counter type instrument consisting of a 3 He proportional counter placed inside a spherical moderator. It works in current mode with a front-end electronics consisting of a current-voltage logarithmic amplifier, whose output signal is acquired with an ADC and processed on a PC. This alternative signal processing allows the instrument to be used in PNF without being affected by saturation effects. Moreover, it has a measurement capability ranging over many orders of burst intensity. Despite the fact that it works in current mode, it can measure a single neutron interaction. The LUPIN was first calibrated in CERN's calibration laboratory with a PuBe source. Measurements were carried out under various experimental conditions at the Helmholtz-Zentrum in Berlin, in the stray field at various locations of the CERN Proton Synchrotron complex and around a radiotherapy linear accelerator at the S. Raffaele hospital in Milan. The detector can withstand single bursts with values of Hn(10) up to 16 nSv/burst without showing any saturation effect. It efficiently works in pulsed stray fields, where a conventional rem-counter underestimates by a factor of 2. It is also able to reject the very intense and pulsed photon contribution that often accompanies the neutron field with good reliability.

Activation of thin Al foils is a well-established technique for measuring the intensity of high-energy proton beams via the 27 Al(p,3pn) 24 Na reaction. The aim of this work was to investigate the various factors that influence the reliability of the results: the cross sections, the competing production of 24 Na by secondary neutrons generated in the foil and spallation processes that can cause loss of the produced nuclei from the foil. The technique was applied for the calibration of an ionization chamber used as beam monitor for a 280 GeV/c mixed proton/pion beam at CERN. The calibration factor obtained experimentally was compared with the theoretical value deduced by Monte Carlo simulations. An additional experiment was conducted employing the alternative reaction nat Cu(p,x) 24 Na, whose cross section is known with low uncertainty over a wide energy range.