NESCOFI @ BTF

NESCOFI@BTF stands for NEutron Spectrometry in COmples Fields. BTF refers to the Beam Test facility of the INFN-LNF, where a photoneutron beam can be produced and is used from the project for detector testing.

Index

1. Project Goal

NESCOFI@BTF started in 2011 with the aim of developing innovative neutron sensitive instruments for the spectrometric and dosimetric characterization of neutron fields, intentionally produced or present as parasitic effects, in particle accelerators used in industry, research and medical fields. Neutron spectra in these fields range from thermal (1E-8 MeV) to tens or hundreds MeV, thus spanning over more than 10 decades in energy.

To date, the multi-sphere spectrometer (or Bonner Sphere spectrometer) is the only existing device having the capability to simultaneously determine all energy components over such a large energy interval. The main disadvantage of this spectrometer is the need to sequentially expose a considerable number (usually more than 10) of detector+moderator configurations, thus leading to time-consuming irradiation sessions.

The idea behind NESCOFI is to provide real-time spectrometers able to simultaneously provide all energy components in a single irradiation. These could be employed for:

The final users of the NESCOFI products will be a variety of facilities interested to monitor not only the intensity of a neutron beam, but also Ðand simultaneously- its energy and/or direction distribution (chip-irradiation, material science neutron beam-lines, reference neutron fields, research and cancer therapy facilities).

The basic idea behind the project is to exploit the moderation of neutrons in hydrogenated materials, as extensively done in Bonner Sphere spectrometers, but new designs and computational methods have been introduced. Particularly, instead of estimating the neutron energy distribution by exposing different detector+moderator configurations, this project aims at a single moderator embedding several "direct reading" thermal neutron detectors at different positions. The energy or angle distribution of the neutron field will be obtained using unfolding algorithms relying on the device response matrix and on the reading of the different detectors. This "unfolding" problem has a number of analogies with the spectrum reconstruction with Bonner Sphere spectrometers, for which a special code called FRUIT (FRascati Unfolding Interactive Tools) was developed at LNF.

The NESCOFI project planned to be completed in three years (2011-2013), organized as follows: 2011:

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2. Physics Activities

2.1 - Year 2011

2.1.1 Achievements of the first year (2011)

Identifying, measuring and establishing suitable neutron fields for the future testing needs of the NESCOFI@BTF project purposes during 2012 and 2013:

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2.1.2 Study and optimization of the geometry of the prototype spectrometers [10, 11, 12]

A simulation campaign was done to identify the appropriate moderator dimension and internal distribution of the thermal neutron detectors. The resulting design, called SP^2 (SPherical SPectrometer), has spherical shape and embeds 37 or 31 (according to the version, low-Energy or High-Energy respectively) thermal neutron detectors. The detector positions are symmetrically positioned along the three perpendicular axes.

Because this stage has the purpose of optimizing the geometry, the prototypes were equipped with well-established passive detectors (Dysprosium activation foils). Active thermal neutron detectors, under development during the current year 2012, will replace the passive detectors in the final spectrometer.

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2.1.3 Testing the experimental prototype spectrometers

These tests were aimed at experimentally confirming the device response matrix, previously determined with Monte Carlo codes.

The prototype Low-Energy SP^2 [10, 11], equipped with Dy activation foils, was tested neutron fields previously characterized by a well-known Bonner Sphere spectrometers.

These fields are: 2.5 MeV and 14 MeV mono-chromatic neutrons (available at FNG, ENEA Frascati) and a photo-neutron field produced in a 15 MV medical Linac.

The experimental results confirm that:

The prototype High-Energy SP^2 [12], equipped with Dy activation foils, was tested in calibration neutron fields at:

The analysis of these data are currently under elaboration, but preliminary results show that the experimental and the calculated responses generally differ by less than 5% for all energies.

The PTB and TSL experiments have been partially supported by EU FP7 ERINDA 2011 program (PAC 1/3 and PAC 1/8).

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2.2 - Year 2012

3. Collaboration Tasks and External Funds

3.1 - Year 2011

3.2 - Year 2012

3.3 - Year 2013

....

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4. Innovation

The activity performed during 2011 allowed developing an innovative design for neutron spectrometers, consisting in a single moderating sphere embedding a number of thermal neutron detectors symmetrically located along the three orthogonal axes. The sphere can be made of polyethylene (30 cm diameter, 37 measurement positions) or polyethylene + lead (25 cm diameter, 31 measurement positions), according to the energy interval to be measured. See Section 2, "Physics activities".

This design has the capability of simultaneously determine all energy components of the neutron field (as the well-known Bonner Sphere spectrometer), BUT in a single exposure.

In 2013 the passive detectors will be replaced by active thermal neutron detectors (active detectors are under study in current year 2012). The resulting instrument will be a real-time spectrometer able to simultaneously provide all energy components in a single irradiation. This is an absolute innovation in neutron measurements.

The final users of the NESCOFI products will be a variety of facilities interested to monitor not only the intensity of a neutron beam, but also and simultaneously- its energy and/or direction distribution (chip-irradiation, material science neutron beam-lines, reference neutron fields, research and cancer therapy facilities).

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5. Publications

Year 2011

Year 2012

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6. Talks

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7. Final User

Because the project aims at developing a real-time neutron spectrometers able to simultaneously provide all energy components from thermal up to 1 GeV (12 decades in energy) in a single irradiation, the potential final users of the NESCOFI products will be a variety of facilities interested to monitor not only the intensity of a neutron beam, but also and simultaneously- its energy and/or direction distribution. The field of applications will be: research particle accelerators, chip irradiation and material science neutron facilities (spallation sources: ISIS, TSL, SNS), nuclear reactors and fuel processing/fabrication plants, radiotherapy medical facilities.

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8. Meetings

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9. International Review Pannel

Prof. Carles Domingo, Profesor Titular of the Universitat Autonoma de Barcelona, UAB Head of the Neutron Measurement group of the UAB carles.domingo@uab.cat

Prof. Francisco Sanchez Doblado, Profesor Catedratico of the Universidad de Sevilla, Head of the Physiology Department. paco@us.es

Download the 2012 mid Year Report of the International Review Panel Link to files Review1 & Review2

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10. INFN Review Pannel

2011 funding report L'esperimento si propone di sviluppare rivelatori neutronici sensibili anche all'energia e di interessante concezione. Incidono purtroppo sui costi dell'esperimento il costo di utilizzo di fasci presso altri laboratori, per cui in attesa di soluzioni piu' generali, temporaneamente si finanzia un set di misure delle due richieste nel 2011.

2012 funding report L'esperimento si propone di realizzare rivelatori di neutroni sensibili anche all'energia e di interessante concezione e procede secondo i programmi. La tematica e' di estremo interesse e pertinenza e si apprezza l'attivita' finora svolta. Si finanzia l'esperimento in sostanziale continuita' col precedente anno

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Reference

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