LUPIN, a new instrument for pulsed neutron fields

Abstract

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.

Comparison of the performance of different instruments in the stray neutron field around the CERN Proton Synchrotron

“…Table 1 shows that in location 1 (Route Goward) the results of the extended range rem counters, i.e. LINUS and LUPIN 3 He, are consistent within their uncertainties, while 2202D measures 40 % less. As expected, due to the relatively long and smoothed time structure of the beam losses, the results are not affected by dead-time losses.…”

“…The instruments employed were the following: two extended range rem counters (LINUS (2) and Thermo FHT 762 Wendi-2), an extended range prototype detector called LUPIN (3) , available in two versions ( 3 He and BF 3 ), specifically conceived for applications in pulsed neutron fields, three commercial rem counters (Studsvik 2202D, Berthold LB6411 and Thermo FHT 751 BIOREM) and two customised Centronic IG5 ionisation chambers [ pressurised Argon (A20) and Hydrogen type (H20)]. A detailed description of the detectors as well as of their response functions can be found in refs (4,5).…”

Instrument intercomparison in the high-energy mixed field at the CERN-EU reference field (CERF) facility

“…the LINUS used at CERN (4 -7) ; the Thermo Wendi-2, the Berthold LB6411 (8,9) ; the Thermo BIOREM FHT 752, whose response to highenergy neutrons can be enhanced by adding an external lead shell; the LUPIN prototype employed in its BF 3 version (10,11) ; (2) Other neutron detectors: the Thermo RadEye NL, employed with its small-size polyethylene moderator to increase the efficiency to fast neutrons (the main purpose of this instrument is to detect radiation sources more than estimating a neutron dose rate); the ABC 1260-1 neutron dosemeter, a bubble detector using an active counting system, whose response can be extended to several hundred MeV with the addition of a 1-cm thick cylindrical lead shell placed around the detector cap (12214) ; (3) Tissue-equivalent proportional counters (TEPCs):…”

Instrument intercomparison in the pulsed neutron fields at the CERN HiRadMat facility

“…In fact, as stated in ref. [4], two of the four requirements for an ideal detector to be used in PNF 1 are the capability to withstand very high instantaneous neutron fluxes with little or no saturation and, at the same time, to correctly measure the intensity of a single neutron burst. This makes the response linearity a fundamental parameter in determining the suitability of a detector for use in PNF, as it quantifies its ability to meet these two requirements.…”

“…Five detectors were employed: a novel rem counter specifically conceived for applications in PNF, called LUPIN (Long-Interval, Ultra-wide dynamic, PIle-up free Neutron rem counter) [4][5][6], two commercial rem counters (a Thermo Scientific FHT 762 Wendi-2 and a FHT 752 BIOREM) and two ionization chambers (pressurised Argon and Hydrogen type) employed in the Radiation Monitoring System for Environment and Safety (RAMSES) [7] at CERN. Since most of the monitoring stations at CERN usually deal with pulsed stray fields, this experiment was also conceived to verify the performance of the RAMSES detectors in extreme conditions.…”