nBHEAM 2025: Neutron Beams at High Energy: Applications and Metrology

7 Jul 2025, 09:00 → 8 Jul 2025, 17:30 Europe/Zurich

C-CR1 (IAEA Headquarter, Vienna)

The present workshop aims to bring together stakeholders with interests in high energy neutron fields, for example and not limited to, space and aviation applications, radiobiology, high energy accelerator facilities (both hadron therapy and research), fast and high energy neutron facilities, metrology, reference standards, dosimetry, and instrumentation.

High energy neutrons are of high relevance in many fields, as they are produced both naturally by galactic cosmic rays and solar particle events interacting with matter such as in spacecraft or the atmosphere, and also in and around man-made high energy accelerator facilities (for therapy and research). The neutron energy spectra in both cases show similar features: lower energy neutrons peaking around 1 MeV as evaporation products; and high energy neutrons peaking around 100 MeV originating as knock-on neutrons in peripheral collisions or in charge exchange reactions. Solar flares can produce neutrons with energies ranging up to several GeV.

Any reliable measurement of such fields requires instrumentation which has traceability to internationally recognised reference standards. There are quite a number of facilities worldwide suitable for fast neutron metrology and applications up to around 20 MeV, with well-established reference standards and procedures for metrology and dosimetry. Above 20 MeV only a few facilities exist, and metrology is more challenging as a consequence of both fundamental physics and technological complexity. Nevertheless, there is growing interest and expressed needs for high energy neutron metrology exceeding 100 MeV. This topic will be addressed during this meeting.

Meeting participants will be requested to contribute to discussions and recommendations. A meeting report will follow.

EVT2402522_Information Sheet-update.pdf

List of hotels in Vienna and information links to public transport

Monday 7 July

Welcome, Overview of the Meeting

Welcome
Appointment of Chairman and Rapporteur
Adoption of Agenda
Introduction to activities of CCRI(III)
Neutron related activities of IAEA

Aviation, Space and Radiobiology

1 Neutron radiobiology - The need to bridge experimental gaps for future space missions

Speaker: Charlot Vandevoorde (GSI)

2 Radiation exposure from neutrons in spaceflight and aviation

Secondary neutrons produced in the interactions of primary cosmic rays with matter are a relevant component of the radiation field in spaceflight and aviation and play a major role in radiation protection in these fields. On the International Space Station, the ORION spacecraft of the ARTEMIS program or any human-rated vehicle, neutrons are produced in the walls and other structures of the spacecraft. On planetary surfaces or at aviation altitudes, neutrons originate from the soil and regolith and from interactions with the constituents of the atmosphere. Energies of secondary neutrons from cosmic rays span many orders of magnitude from thermal energies up to tens of GeV and are relevant to the exposure in the range from approximately 100 keV to several GeV, depending on the shielding conditions and the primary particle spectra. Models predict that the build-up of the secondary neutron field leads to a maximum in the dose equivalent at altitudes in the Earth’s atmosphere of approximately 20 km above ground and an increase in the dose equivalent for aluminum shielding above approximately 10 cm in space, but little experimental validation for these predictions exist. Model calculations and measurements of neutrons and neutron dose in aviation and space flight will be presented.

Speaker: Daniel Matthiä (Institute of Aerospace Medicine, German Aerospace Center (DLR), Linder Höhe, Köln, Germany)

10:15 Coffee

Accelerator Facilities 1

3 Towards an ISO-accredited fast neutron beam facility at iThemba LABS

iThemba Laboratories for Accelerator Based Sciences (LABS) is a national facility and one of business units of the National Research Foundation (NRF) in the Republic of South Africa (RSA). It is a multidisciplinary research facility that is based on the development, operation and use of a number of particle accelerators and related research equipment. The largest accelerator at the facility, a K=200 separated sector cyclotron (SSC) powered by two solid-pole injector cyclotrons (SPCs) could accelerates protons to energies of up to 200 MeV and heavier particles to much higher energies.
Over the years, the iThemba LABS fast neutron beam facility has been developed to a unique status with respect to the production of nearly monoenergetic ns-pulsed neutron beams ranging between 30 MeV and 200 MeV. Other available neutron beam facilities with energy range similar to this facility are described in details by the EURADOS (European Radiation Dosimetry) Report [1]. With protons beams available from the SSC, quasi-monoenergetic neutron beams at iThemba LABS can be covered almost continuously via (p,n) reactions using $^7$Li and $^9$Be targets of varying thicknesses [2]. We are presently upgrading the facility with the aim of achieving ISO-accreditation as a fast neutron beam reference facility. This came about as a result of the facility being designated by the National Metrology Institute of South Africa (NMISA) as an entity responsible for providing traceability for the medium and high-energy neutron measurements in South Africa. The project of upgrading the facility is ongoing and is currently being realized by a formal collaboration between iThemba LABS, University of Cape Town (UCT), together with international partners Institut de Radioprotection et de Sûreté Nucléaire (IRSN in France), National Physical Laboratory (NPL in UK) and Physikalisch-Technische Bundesanstalt (PTB in Germany).
As part of the project, the iThemba LABS fast neutron beam facility has been redeveloped in an attempt to overcome some of the identified shortcomings, particularly associated with low energy neutron backgrounds and the stability of the proton beam on target. Once the upgrade and development project of the facility is completed, traceability of measurements shall be ensured by setting up a primary standard for neutron measurements in the energy range from 30 MeV to 200 MeV or by using a transfer device which is traceable to one of the primary standards. The ISO-accreditation status will also provide the facility with the ability to participate in international key-comparison studies in the area of neutron metrology for medium to high-energy neutrons. The upgraded facility is set to practically accommodate irradiations of a phantom of up to 30 x 30 cm$^2$ of beam size. For this contribution, we aim to discuss plans and activities using the fast neutron beam facility at iThemba LABS [3].

Speaker: Zina Ndabeni (NRF-iThemba LABS)

4 Characterization of high energy neutron standard fields and study of calibration methods

The National Metrology Institute of Japan (NMIJ) has developed a 45-MeV quasi-monoenergetic high-energy neutron standard field using the cyclotron of the Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) facility of the Takasaki Institute for Advanced Quantum Science (TIAQ), National Institutes for Quantum Science and Technology (QST). The quasi-monoenergetic neutron field generated by the 7Li(p,n) reaction consists of a high-energy monoenergetic peak and continuum neutrons down to the low energy. Neutron fluence of the high-energy peak neutrons, which is essentially used for the detector calibration, was evaluated by a recoil proton telescope consisting of a polyethylene radiator and an organic liquid scintillator (E) with a Si(Li) detector (dE). The spectral fluence of the continuum neutrons at the calibration position, which are usually contaminants for the detector calibration, was evaluated by time-of-flight measurements using an organic liquid scintillator and a lithium glass scintillator, and the Bonner unfolding method. This information can be used for correction during the detector calibration.
We also studied the applicability of the two-angle differential method for detector calibration using 100-400 MeV quasi-monoenergetic neutrons generated by the 7Li(p,n) reaction at the cyclotron facility of the Research Center for Nuclear Physics (RCNP), Osaka University. In this facility, the neutrons generated in the target can be extracted at any angle by using a target swinger and a movable collimator wall. In this study, measurements were performed for quasi-monoenergetic neutrons generated in front of the target, i.e., in the 0 degree direction, and for continuum neutrons without the high-energy peak, generated diagonally forward, 25 degrees or 30 degrees, and the difference between them was used to attempt calibration only for the virtual high-energy peak neutrons. This method was tried out for multiple Bonner sphere detectors, which have various energy response characteristics depending on the spherical diameter and material of the moderator, and the applicability of the method was discussed.
We also introduce shielding experiments for quasi-monoenergetic neutrons at RCNP and white neutrons at CHARM of CERN that were conducted as application experiments for high-energy neutrons.

Speaker: Akihiko Masuda (National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology)

5 High energy mono-energetic and white neutron sources in RCNP, University of Osaka

High energy (above ~100 MeV) neutron beams offer unique opportunities to perform e
xperiments in the fields from fundamental physics such as nuclear physics and particle physics to applied science such as studying performances of detectors and shielding materials for high-energy neutrons, soft errors of semiconductor devices, and space engineering. Research Center for Nuclear Physics (RCNP) in University of Osaka provides two types of high-energy pulsed neutron beams, one is produced via the 7Li(p,n)7Be reaction and another generated via the spallation reaction with a tungsten target, both are driven by the primary proton beams provided by the K=400 RCNP ring-cyclotron. The monoenergetic neutron beam covers the energy range from ~5 MeV up to 390 MeV, and thanks to TOF (time-of-flight) tunnel with a 100 m-long flight path, the energy resolution is as good as 2.9MeV (FWHM) at the neutron energy of 387 MeV. The neutron intensity of the monoenergetic component is typically ~1010 neutrons/sr/C at 387 MeV [1]. The white neutron source has an energy distribution very similar to that of atmospheric neutrons produced by cosmic-rays [2] and is useful to test soft errors of semiconductor devices or highly integrated electric circuits due to cosmic neutrons. In this paper the specifications of those neutron sources and previous works with use of them will be presented. The recent results of the operation and information for users will be also mentioned.
References:
[1] Y. Iwamoto et al., Nuclear Instruments and Methods in Physics Research, A629, 43-49 (2011).
[2] Y. Iwamoto et al., Nuclear Technology, Vol.173, pp.210-217 (2011).

Speaker: Tatsushi Shima (Research Center for Nuclear Physics, University of Osaka)

6 The neutron Time-of-Flight facility, n_TOF at CERN: Status and perspectives

n_TOF, at CERN, is the neutron time-of-flight facility dedicated to the study of neutron-induced reactions for fundamental and applied nuclear research. With high-precision neutron cross-section data, n_TOF plays a crucial role in addressing key questions in nuclear astrophysics and for innovation in advanced nuclear technologies. In nuclear astrophysics, experiments performed at n_TOF provide essential insights on the nucleosynthesis processes, such as the s-process responsible for the formation of chemical elements in stars. In nuclear technology, n_TOF contributes to the study of isotopes relevant for reactor design, nuclear waste transmutation, and radiation shielding. Furthermore, the facility investigates aspects linked to medical and space applications, including neutron therapy and radiation effects on electronics.

Established in 2001, n_TOF utilizes a high-intensity, pulsed neutron beam produced by spallation reactions, where 20 GeV/c protons from the CERN Proton Synchrotron (PS) impact on a lead target. The resulting neutron flux spans a wide energy spectrum, from thermal to GeV energies, enabling measurements with high accuracy and resolution over an extensive range. n_TOF is the only facility in which measurements from thermal up to few GeV are possible.

The facility features two areas suitable for time of flight measurements. EAR1, with a 185-meter flight-path, is optimized for high-resolution measurements. EAR2, with the 20-meter beam-line, is designed for high-flux applications, fundamental for low mass and short-lived radioactive samples or reactions with low cross sections. These complementary stations allow for different experimental conditions optimized for specific measurements, such as neutron capture, neutron-induced fission, elastic, inelastic and charged-particle emission reactions. NEAR is the novel experimental area, placed at about 3 meters from the spallation target, designed for spectral-averaged cross section measurements via activation, when a time-of-flight measurements are not possible.

Recent developments at n_TOF include upgrades of the spallation target to enhance neutron production efficiency, improvements in experimental techniques, and expanded research programs addressing emerging scientific challenges.
In this contribution, an overview of the status of the facility, the ongoing experimental activities and the planning of future projects will be presented with a focus on the activities induced by high energy neutrons.
In this contribution, an overview of the status of the facility, the ongoing physics program and the planning of future projects will be presented. The experimental activities at high energy will be the focus of this talk.

Speaker: Alice Manna (University of Bologna)

7 70 MeV~100 MeV Quasi-monoenergetic neutron reference fields in China

Based on the 100 MeV proton cyclotron at the China Institute of Atomic Energy (CIAE), we have established and investigated quasi-monoenergetic neutron reference radiation fields in the (70-100) MeV energy range. Quasi-monoenergetic neutrons were generated through proton bombardment on metallic Li targets with thicknesses of 3, 4, and 5 mm, followed by deflection magnets and a 3-meter-long collimator system. The neutron energy spectra were measured using the double-scintillator time-of-flight (TOF) method, while neutron fluence was determined through U-8 fission ionization chambers and recoil proton telescopes.
Over the past two years, systematic facility upgrades have been implemented:
1. Comprehensive concrete shielding was installed to fully enclose the neutron target chamber, effectively reducing scattered neutron background.
2. A beam-limiting aperture was added at the beam extraction port to confine the beam spot size to a minimum of 1×1 mm², ensuring complete proton bombardment on Li targets while minimizing parasitic neutron production from peripheral materials.
3. A pair of quadrupole lenses was incorporated upstream of the target chamber to enhance beam regulation and control capabilities.
4. Preliminary modifications for pulsed beam operation have been attempted at the cyclotron's extraction port, with this ongoing research currently underway.

Speaker: Tingyu Jiao (China Insititute of Atomic Energy)

12:00 Lunch

Accelerator Facilities 2

8 NEPIR (NEutron and Proton Irradiation) facility at INFN-LNL

The NEPIR (NEutron and Proton Irradiation) facility at the SPES (Selective Production of Exotic Species) project at LNL-INFN (Italy), is designed to serve as a unique fast neutron irradiation facility in Italy and a reference point for applied and basic science as well as industrial applications. Driven by the SPES cyclotron, which delivers 35-70 MeV protons at maximum currents of 500 μA, NEPIR will be developed in phases. Phase 0 will produce continuous energy (white spectrum) neutron beams with the possibility to mimic quasi monoenergetic neutron beams (we call it pseudo monochromatic). Phase 1 will provide not only a white spectrum but also true Quasi Mono-energetic Neutron (QMN) beams with controllable energy peaks in the 20-70 MeV range and a almost perfectly shaped atmospheric neutron spectra up to 70 MeV.
NEPIR represents a significant step toward addressing the growing demand for accessible, cost-effective neutron sources, filling the gap left by the declining availability of reactor-based neutron facilities, with the aim to advance the frontiers of neutron science by enabling the production of high-intensity neutron beams. It will support a wide range of scientific and industrial applications, from radiation shielding studies to developing advanced detectors and medical technologies. Even NEPIR phase zero, will allow studies like Single Event Effects (SEE) in electronics, relevant to numerous fields including nuclear energy, space, aviation, and automotive industries.
The modular approach of NEPIR and the strategic integration within the SPES infrastructure emphasizes cost-to-benefit efficiency establishing it as a crucial milestone in the advancement of Compact Accelerator-driven Neutron Sources (CANS) technology.
This talk will outline the overall details of the phases of NEPIR project and highlight the innovative features of the of the facility: the CoolGal target system and the ANEM (Atmospheric Neutron Emulator) presenting the results of the design as well as the advances in the prototype construction.

Speakers: Pierfrancesco Mastinu (INFN-LNL), Dr Luca Silvestrin (Dipartimento di Fisica, Università degli studi di Padova)

9 Introduction of a new test area for neutron detection instruments with a dominant high energy neutron component at PSI

Neutron radiation fields around high-energy particle accelerator facilities or at high altitudes often have a broad energy distribution with significant component of neutrons with energies greater than 20 MeV. Reference fields with comparable conditions are desirable for the calibration of monitoring instruments and dosemeters to be used in these environments. In the present study, a suitable area for this purpose is investigated.
The PSI High Intensity Proton Accelerator facility (HIPA) is a cascade of three accelerators that delivers a proton beam with a final energy of 590 MeV and, at present, a maximal current of 2.2 mA. The beam passes through two graphite targets, and it is used to produce intense beams of secondary particles feeding experimental areas for research in multiple disciplines. A collimation system ensures a reproducible position of the beam spot on the targets.
The experimental areas are heavily shielded by layers of concrete and iron. This setup outside the shielding above the targets provides a steady neutron field with a broad spectral neutron distribution and dominant high-energy component, which can be used as test area for survey instruments and dosimeters. The area is accessible from May to December with mean availability of 95%, considering normal operation of HIPA.
The neutron spectral distribution of this area is characterized at two positions by measurements with an extended range Bonner Sphere spectrometer (ERBSS). The results are compared to Monte Carlo simulations using the multi-purpose particle transport code FLUKA. Three commercially available extended range survey instruments sensitive to neutron radiation constantly monitor the field intensity in addition to a proton current monitor positioned upstream the target. Long term investigations of the reading of these instruments in addition to measurements of the intensity gradient of the neutron field showed that it can be considered as a reference workplace field with a dominant high-energy neutron component.

Speaker: Sabine Mayer (Department of Radiation Safety and Security, Paul Scherrer Institute)

10 n_ACT@BDF: A high intensity & high energy neutron activation station at the CERN Beam Dump Facility

The Beam Dump Facility (BDF) at CERN is a new, general-purpose intensity-frontier experimental facility operating in beam-dump mode at the CERN SPS accelerator. It is designed to search for feebly interacting GeV-scale particles and to perform measurements in neutrino physics, serving the Search for Hidden Particles (SHiP) experiment (SPSC-P-369).

The high-energy (400 GeV/c), high-intensity (350 kW) proton beam from the SPS, impacting BDF’s tungsten production target, generates a unique particle spectrum, fluences, and radiation dose in the region surrounding the target. This presents an opportunity to create synergies to exploit the target complex for additional purposes, without perturbing the main physics goals of BDF and SHiP.

A Letter of Intent has been submitted by the n_TOF Collaboration for a parasitic Neutron Activation Station (n_ACT, CERN-SPSC-2024-027) to utilize the copious neutrons produced in the spallation target. Due to the high-energy and intensity proton beam, a wide-energy neutron spectrum is generated, including a large quantity of high-energy neutrons, extending up to few GeVs, which could be exploited for physics research.

This contribution will detail the scientific case, feasibility considerations, as well as the plan for a complete scientific and technical proposal by the end of 2025, aiming for a staged start-up from 2031, with full implementation by 2035.

Speaker: Michael Bacak

Materials and Instrumentation

11 Evaluation of spectrum and fluxes of the ChipIr facility for atmospheric neutron testing of electronics

The ChipIr beamline at the Rutherford Appleton Laboratory, UK, is a facility dedicated to fast neutron testing, particularly aimed at evaluating single-event effects (SEEs) on microelectronics. SEEs, induced by energetic particles such as high-energy atmospheric neutrons, pose significant reliability threats to electronic devices utilized in safety-critical applications including avionics, automotive, aerospace, and medical applications. With advancements in microelectronic miniaturization and complexity, rigorous SEE testing has become increasingly critical, demanding precise neutron environments that accurately reflect atmospheric energy distribution. ChipIr extracts fast neutrons from an 800 MeV proton beam impinging on a tungsten target. This specialized setup includes filters and collimators enabling flexible configuration options for researchers. To comprehensively characterize ChipIr’s neutron beam, two principal measurement techniques have
been employed: activation foil with threshold reactions and silicon diode detectors. Activation foils, composed of diverse materials including gold, bismuth, and cobalt, serve as a passive method enabling determination of neutron flux across a broad energy spectrum. (n,xn) reactions are identified as an important tool for high-energy neutron measurements. Post-irradiation, gamma-rayspectroscopy with high-purity germanium detectors quantifies the activation rates, from which neutron flux spectra are derived through Bayesian unfolding methods. Results indicate that the ChipIr neutron spectrum, spanning from thermal energies up to 800 MeV, mimics the terrestrial atmospheric neutron spectrum, with a flux (E > 10 MeV) of 5.9E6 s-1 cm-2.
Active measurement approaches utilize silicon detectors, enabling real-time monitoring and mapping of beam profiles. Such detectors are sensitive to neutrons with energies greater than 10 MeV, aligning with the established standards for SEE evaluation. Extensive spatial profiling across multiple beam configurations has demonstrated excellent beam uniformity for smaller beam apertures, essential for precise device-level testing, and a defined gradient suitable for larger system-level evaluations. Furthermore, the facility provides a flux reduction capability via steel and polyethylene attenuators, maintaining spectral integrity sufficiently close to atmospheric conditions, albeit with slight hardening of the neutron spectrum.
The results detailed in this characterization highlight ChipIr’s suitability for industry and academic users needing to test the susceptibility of electronics to SEEs in a field that replicate terrestrial conditions.

Speaker: Carlo Cazzaniga (UKRI-STFC)

12 Detector response functions for in situ high energy neutron spectrometry

Fast and high energy neutron fields are produced through the interaction of energetic charged particles with matter, which is a concern for aviation, space exploration, radiotherapy and accelerator environments. To improve radiation risk models for exposed individuals it is necessary to fully characterise the different components of the mixed radiation fields at the point of exposure. In situ measurements of neutron fluence spectra can be achieved through spectrum unfolding, where the incident neutron energy distribution is deconvolved from the measured signature(s) using a library of energy-dependent response functions and mathematical or computational techniques. The detector response functions must span the full energy range for the application and account for non-linearities associated with the whole system, including the detector, electronics and acquisition. For neutrons with energies below 20 MeV, detector response functions can reliably be simulated subject to appropriate scaling to experimental data. However, for neutrons with energies above 20 MeV the availability and quality of reaction cross section data and models are insufficient for the simulation of detector response functions, requiring direct measurement at high energy neutron facilities providing ns-pulsed beams.

The experimental and analytical procedures to derive detector response functions for unfolding are presented for the example of organic scintillators. Detector response functions are simulated with Geant4 between 1-20 MeV and validated against measurements at fast neutron reference facilities AMANDE (Autorité de Sûreté Nucléaire et de Radioprotection, France), and PIAF (Physikalisch-Technische Bundesanstalt, Germany). For applications where neutrons exceeding 20 MeV are expected, nearly mono-energetic detector response functions are measured at the iThemba LABS (South Africa) neutron facility using time-of-flight techniques. The spectroscopic capabilities of modern (EJ-276) and traditional (BC-501A) detector systems are demonstrated through the unfolding of known neutron fields with MAXED, using simulated and measured detector response functions.

Speaker: Tanya Hutton (University of Cape Town)

13 Development of a portable monitor for cosmic ray neutron observations

Andy Buffler1, Marco Caresana2, Andrea Cirillo2, Massimiliano Clemenza3 and Luna Pellegri4,5
1Metrological and Applied Sciences University Research Unit (MeASURe),
Department of Physics, University of Cape Town, South Africa, 7700
2Department of Energy, Politecnico di Milano”, Via Lambruschini 4, 20156 Milan, Italy
3INFN sezione di Milano Bicocca, Piazza della Scienza 3, 20126 Milan, Italy
4School of Physics, University of the Witwatersrand, Johannesburg 2050, South Africa
5 iThemba Laboratory for Accelerator Based Sciences, Somerset West 7129, South Africa

Measurements of high-energy cosmic-ray neutrons are typically carried out using neutron monitors located around the world. These measurements have a wide range of applications, including space weather observation, solar cycle analysis, and radiation protection at flight altitudes. The flux of cosmic-ray neutrons is also responsible for inelastic reactions that produce isotopes such as ²⁶Al in rocks—used to date the age of rocks and minerals that have been exposed to these neutrons over extended periods.
However, several aspects of cosmic-ray neutron measurements remain under investigation, including the spatial heterogeneity of the particle flux across the Earth and its relationship with other secondary cosmic-ray particles, such as muons. On the one hand, studies in this field would greatly benefit from widespread measurements of secondary cosmic rays at the Earth’s surface; on the other hand, neutron monitors are generally heavy, non-portable systems. Additionally, environmental factors such as snow cover can significantly affect neutron flux intensity at ground level, especially for low-energy neutrons (below 10 MeV). As a result, cosmic-ray observations typically achieve high sensitivity only for neutron energies above 20 MeV.
For these reasons, Politecnico di Milano and INFN are developing a portable neutron monitor for ground-level cosmic-ray neutron measurements. The system is based on a commercial thermal neutron counter with high sensitivity, housed within a modular moderator made of polyethylene and lead. This work presents the characterization of the neutron detector in a mixed neutron/gamma radiation field and the Monte Carlo simulations used to determine the optimal moderator dimensions. These efforts are preparatory steps toward the device's calibration in quasi-monoenergetic neutron fields at iThemba LABS.
Calibration of moderator-based detectors is typically performed using the shadow-cone technique in monoenergetic fields to suppress the background from scattered neutrons. According to ISO 8529, this technique is a standard for neutron energies up to 20 MeV; however, its application becomes more complex at higher neutron energies. That said, the low sensitivity of neutron monitors to neutrons below 10 MeV may allow for a relaxation of the stringent requirements for background suppression. This work includes Monte Carlo simulations evaluating the effectiveness of the shadow-cone technique for high-energy neutron measurements.

Speaker: Andrea Cirillo

14 Challenges and requirements for neutron dosimetry at laser-driven accelerators

Over the past 40 years, laser wakefield acceleration (LWFA) has been developing at a dramatic rate, from a conceptual notion into a concrete reality. Many petawatt (PW) and multi-PW facilities are operating or under-construction worldwide presenting a novel and exiting alternative to conventional accelerators. In fact, with current technology, the expected particle energies are up to 100 GeV for electrons and at the GeV order for protons. While beam intensities can be as high as 10$^9$ - 10$^{10}$ electrons and 10$^{10}$ - 10$^{12}$ protons per laser shot. In these conditions, fast and high-energy neutrons are generated as secondary particles. Furthermore, by optimizing experimental setups, laser-driven neutron sources are subsequently produced.

Neutron dose measurements at laser-driven accelerators are pivotal and concurrently arduous. Indeed, the generated primary and secondary radiation fields are mixed and non-monochromatic. They exhibit a challenging time structure as they follow the laser pulses which are typically in the sub-picosecond regime. This poses severe limitation on any measurement device and complicates the correct interpretation of the collected data. Additionally, there is a lack of well-established reference standards and procedures for metrology and dosimetry of neutrons at laser facilities.

In this contribution, we present the difficulties associated with neutron dose measurements at laser-driven accelerators. We, as well, highlight the needs both for adequate detection systems as well as for traceability to internationally recognised reference standards. We present the use case of multi-PW laser-driven ELI Beamlines facility as a concrete example.

Speaker: Anna Cimmino

15 A new GEANT4 fission physics model for simulation of high energy neutron detection and measurements

Nuclear fission is a subatomic physical phenomenon in which a nucleus divides into two parts, emitting several light particles and releasing substantial energy. It may occur spontaneously or be induced by incident particles, such as photons and neutrons. Neutrons in a wide energy range can be detected by exploiting nuclear fission, as neutrons may induce fission for neutron energies from thermal to high-energy regions above 20 MeV, depending on nuclides. A fission counter for neutron detection, commonly made of gas ionization counters embedded with fissile nuclides, detects incident neutrons by counting energetic fission fragments. Therefore, considering the dynamics of fission fragments and secondary particles is important in characterizing a fission counter, as the secondary particles may affect the overall detector performance. GEANT4, a simulation toolkit for the passage of particles through matter, has physics models for nuclear fission; however, none of them provides fission observables as detailed as FREYA (Fission Reaction Event Yield Algorithm) or GEF (General description of Fission process) code can describe. A new fission physics model has been developed based on the high-precision particle physics model, and it invokes evaluated nuclear data files (ENDF) and some GEF calculation results for modeling nuclear fission for fissionable and fissile nuclides under the GEANT4 framework. This presentation will introduce the newly developed GEANT4 fission model in detail.

Speaker: Pilsoo Lee (Korea Atomic Energy Research Institute)

15:15 Coffee

Nuclear Data

16 Experiment for double-differential cross section measurement with the emission of light charged particles from high energy neutrons on carbon at n_TOF

In hadron therapy for cancer treatment, secondary neutrons with energies up to about 200 MeV are produced by beam interaction with tumor cells and other surrounding materials. The risk assessment of secondary tumors induced by these neutrons requires double-differential cross sections (DDX) data for the emission of light charged particles (p, d, t, 3He and α). Experimental DDX data for tissue constituents are still rather scarce for neutron energies above 20 MeV and mostly measured for discrete neutron energies at mono-energetic neutron beam facilities. There are only very few DDX data available for discrete neutron energies close to and above 100 MeV for carbon.

Therefore, a proof-of-principle measurement of DDX on carbon at continuous neutron energies from 20 MeV to 250 MeV was carried out between September and October 2024 at the neutron time-of-flight facility n_TOF at CERN. This facility offers a white neutron spectrum up to several GeV which is unique in Europe. Two carbon targets were irradiated inside a new dedicated vacuum chamber, and the ΔE-E technique was used to identify secondary particles emitted at several measurement angles with combinations of silicon transmission detector (ΔE) and organic/inorganic scintillators as stop detector (E). Furthermore, the time-of-flight technique was exploited for the determination of the neutron incident energy on the target.

Preliminary results have shown our valid experimental approach for some combinations of ΔE-E telescopes. Some experimental inconsistencies with theoretical expectations still emerged and have provided useful insights for optimisations of the experimental setup. An analysis of the overall performance including first results will be presented. In the end, DDX data with uncertainties comparable to data from mono-energetic neutron sources are expected for the final validation of this proof-of-principle experiment with continuous energy coverage, which can then be extended in future experiments to tissue elements beyond carbon.

Speaker: Mirco Dietz (Physikalisch-Technische Bundesanstalt (PTB))

17 Measurement of high energy neutrons penetrating shields from GeV protons on a thick copper target

Secondary neutrons are a significant concern in high-energy and high-intensity hadron accelerator facilities (e.g., J-PARC, CERN, SNS, ESS). The neutrons with energies from thermal to maximum energy contribute to external doses behind the shields and activate materials around the beamlines. For neutrons below 20 MeV, several techniques to measure their energy spectra and its reference field has been established. For neutrons above 20 MeV, only a few techniques and fields are available [1]. Thus, Monte Carlo codes (e.g., PHITS, FLUKA, MCNP) employing nuclear physics models and cross-section data are mainly used to obtain the energy spectra through particle production and transport. However, discrepancies among calculated results have been observed across different codes, particularly as the primary beam energy above GeV. Therefore, technique to measure neutron energy spectra above 20 MeV at facilities with incident energy exceeding 1 GeV is desired to obtain experimental data that enable us to validate the calculated results.

To obtain neutron spectrum above 20 MeV, a few detection techniques can be used behind the shields, including NE213 liquid scintillator, Bonner spheres, and activation foils. Recently, shielding experiments have been conducted employing these techniques for neutrons generated by 24 GeV/c protons and 50 cm long copper target at the CERN High-energy Accelerator Mixed-field (CHARM) facility in the East Hall of the CERN Proton Synchrotron (PS) [1-7]. Using an unfolding method with data obtained from NE213 scintillator, neutron energy spectra were derived. The spectra indicated high-energy neutron components (>100 MeV) [1]. The NE213 scintillator, however, has limited sensitivity to neutrons above 100 MeV, and thus, the shape of the neutron response matrix is less dependent on its energy, which may lead to uncertainty in the unfolding process.

To address this limitation, alternative detection methods are being studied. CsI(Tl) scintillator, known for its pulse shape discrimination (PSD) capability and high light yield, is one of the candidates for extending the measurable neutron energy range beyond 100 MeV [8-10]. However, several challenges, such as determining detector response characterization, energy calibration, and background suppression, must be overcome before actual application in the high-energy neutron field vicinity of high energy accelerator. Thus, this study aims to investigate the feasibility of using CsI(Tl) scintillators. In this presentation, we will introduce (1) the results of neutron energy spectra measurement using the NE213 scintillator at CHRAM facility and (2) the test results obtained with the CsI(Tl) scintillators under the same condition as that of the NE213 scintillator. For (2), we acquired waveforms for PSD to distinguish neutron events from gamma-rays and obtained cosmic-ray muon events for energy calibration. We will discuss how these measurements improve neutron detection above 100 MeV.
[1] E. Lee, et al., NIMA 998:165189 (2021).
[2] E. Iliopoulou, et al., NIMA 855: 79–85 (2018).
[3] N. Nakao, et al., JNST 57 (9) 1022–1034 (2020).
[4] N. Nakao, et al., JNST 61 (4) 429–447 (2024).
[5] T. Kajimoto, et al., NIMB 429:27–33 (2018).
[6] T. Kajimoto, et al., NIMA 906:141–149 (2018).
[7] T. Matsumoto, et al., JNST 61(1) 98–110 (2024).
[8] C.M. Bartle, et al., NIMA 422:54–58 (1999).
[9] Y. Ashida, et al., Prog. Theor. Exp. Phys., 043H01 (2018).
[10] S. Longo, et al., JINST 13, P03018 (2018).

Speaker: Eunji Lee (High Energy Accelerator Research Organization)

18 EURADOS task on improving the description of nuclear reactions between nucleons and light nuclei, notably 12C, 14N and 16O

The European Radiation Dosimetry Group (EURADOS) has identified a weakness in nuclear models describing the interactions between nucleons with energies from 20 to 200 MeV and light nuclei, mainly carbon, nitrogen and oxygen. This type of interaction is fundamental to a proper description of radiation transport for nucleons in the environment and in the human body.
This contribution will present the actions underway within EURADOS, the nuclear data community with the JEFF meeting and within the High Priority Request List (HPRL) of the Nuclear Energy Agency (NEA).

Speaker: Michaël Petit (ASNR)

Discussion/Summary

Tuesday 8 July

Summary of Day 1

Neutron Metrology: Why and how?

19 Neutron metrology: Why and how?

This talk will give an overview of the importance of neutron metrology to a range of sectors such as nuclear power, defence, healthcare and aviation. The current framework of National Metrology Institutes, key comparison exercises and transfer standards that underpins traceable neutron measurements worldwide up to neutron energies of 20 MeV will be discussed.

Speaker: Neil Roberts (NPL)

10:05 Coffee

HE Neutron Fields: Broad Energy, Workplace, etc

20 Challenges and developments in neutron metrology for high energy workplace radiation fields

Neutron spectra found in typical workplace environments, especially in the high-energy (>20 MeV) domain, of particle accelerators, accelerator-driven spallation sources, and at cruising altitudes onboard aircraft, often differ significantly from those produced by standard radioactive sources defined in the ISO 8529 series. This discrepancy poses a substantial challenge in neutron metrology, as the energy-dependent response of dosimeters and survey instruments can lead to inaccurate measurements if they are calibrated using reference fields that do not reflect actual workplace conditions. In addition, above 20 MeV, neutron interaction cross-sections are derived from theoretical models with limited experimental verification. This introduces significant uncertainties and complicates the validation of detector response functions in high-energy fields. ISO 12789 highlights the need for well-characterized and application-specific radiation fields to ensure meaningful calibration and performance evaluation of radiation protection instruments.
This presentation will provide an overview of representative workplace radiation fields and their critical role in advancing neutron metrology, particularly for radiation protection applications. It will illustrate the unique challenges involved in establishing and characterizing reference workplace fields in the high-energy radiation environments. These include the need to replicate complex, mixed radiation fields with broad energy spectra, and the difficulty in accurately modeling and measuring neutron fluence and energy distributions.
An emerging aspect with significant implications is the introduction of the new operational quantities – ambient dose and personal dose – as recommended by the ICRU and the ICRP. These quantities are intended to provide a more meaningful link to protection quantities across a broader energy range, particularly at high energies where traditional quantities such as H*(10) and Hp(10) may not remain conservative. Their adoption will likely require the redefinition of reference fields and recalibration procedures, particularly for workplace environments, to ensure consistent and accurate dose assessments.
To progress in this respect, several essential advancements are required: the development of standards how to characterise different high-energy reference fields, improved physics models that are benchmarked against experimental data, advanced spectrometric techniques for real-time field characterization, and internationally coordinated efforts to update and expand the ISO framework (including ISO 12789). These efforts seem essential to improve the traceability and reliability, and relevance of neutron measurements in the complex radiation environments.

Speaker: Fabio Pozzi (CERN)

HE Neutron Fields: Quasi-monoenergetic

21 Quasi-monoenergetic high energy neutron fields: present status and future prospects

I provide a review of the status and features of facilities presently offering quasi-monoenergetic neutron fields above 20 MeV, and discuss the physical and technological challenges associated with providing such fields to a metrological standard. I present perspectives on facilities which might mature or emerge in the next few years.

Speaker: Andy Buffler (University of Cape Town)

Discussion

12:15 Lunch

Reference Standards: Instrumentation

22 Instruments for the characterization of high energy neutron beams

Despite the increasing importance of simulation tools for the development of detectors and dosemeters for high-energy neutron radiation, measurements in neutron reference beams are still indispensable for the verification of calculated detector responses. Beams with a continuous energy distribution can be used if the instrument under test allows the selection of the neutron energy using the time-of-flight technique, but quasi-monoenergetic beams are required for dosemeters integrated over the neutron energy distribution. Thus, the characterization of these reference beams must basically cover the energy range from thermal neutrons to the maximum energy, which can be several hundred MeV. In most cases, this task can only be accomplished by combining measurements with several different reference detectors traceable to the primary standards of the neutron fluence. The talk will give an overview of the most important types of reference detectors for the fluence of high-energy neutrons. In addition, detectors for measuring the spatial neutron fluence distribution, i.e. the beam profile, and monitor detectors for correlating measurements at different fluence rate levels will be discussed.

Speaker: Ralf Nolte (PTB (retired))

Discussion

Reference Standards: Cross sections

23 Nuclear reference data for high energy applications

High-quality nuclear data is the most fundamental underpinning for all neutron metrology applications.
A review of recommended evaluated nuclear data for high-energy dosimetry applications will be presented,
focusing on IAEA Neutron Data Standards (nds.iaea.org/standards) and the International Reactor Dosimetry and Fusion File (IRDFF-II).

Neutron data standards include evaluated fission cross sections on H, U-235, and U-238 targets that extend up to at least 150 MeV.
Reference neutron spectra, like the Cf-252(sf) spectrum, are also included, serving for the validation of evaluated dosimetry cross-section
data as well as to define the efficiency of multiple neutron detectors.

The International Reactor Dosimetry and Fusion File (IRDFF-II) contains a consistent set of nuclear data for fission and fusion neutron
metrology applications up to 60 MeV neutron energy. The IRDFF-II library includes 119 metrology reactions and five metrology metrics
used by the neutron dosimetry community. The recommended decay data, particle emission energies, and probabilities for 68 activation
products are also listed, together with 29 neutron benchmark fields (including some high-energy fields) for the validation of the
library contents. The IRDFF-II library and comprehensive documentation are available online at nds.iaea.org/IRDFF/.

Speaker: Roberto Mario Capote Noy (IAEA NAPC-NDS)

24 Uncertainties of MC calculations

Speaker: Jason Hirtz (CEA)

Discussion

15:35 Coffee

Discussion and Recommendations