NEPIR (Neutron and Proton Irradiation facility) is the project of a new irradiation facility at INFN Legnaro National Laboratories (LNL). The facility will exploit the LNL 35-70 MeV high current proton cyclotron of the SPES complex, to feed two different compact neutron sources in order to generate high flux neutron beams with different energy spectra: quasi-monoenergetic neutron beams and atmospheric-like neutrons. This contribution focuses on the first stage of the construction of the facility: the NEPIR Phase 0, financed and in an advanced design phase. It will use a Be neutron production target capable of delivering up to ∼ 2 × 106 n cm−2 s −1

Bisello, D.

Esposito, J.

Mastinu, P.

Prete, G.

Silvestrin, L.

Wyss, J.

IRIS Unicas (Università degli Studi di Cassino e del Lazio Meridionale)

The Phase 0 of the NEPIR project at LNL

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DOI 10.1393/ncc/i2019-19072-3Colloquia: EuNPC 2018IL NUOVO CIMENTO 42 C (2019) 72The Phase 0 of the NEPIR project at LNLD. Bisello(1), J. Esposito(3), P. Mastinu(3), G. Prete(3), L. Silvestrin(2)and J. Wyss(1)(4)(1) INFN, Sezione di Padova - Padova, Italy(2) Department of Physics and Astronomy, University of Padova - Padova, Italy(3) INFN, Sezione di Legnaro - Legnaro (PD), Italy(4) DICeM, University of Cassino and Southern Lazio - Cassino (FR), Italyreceived 5 February 2019Summary. — NEPIR (Neutron and Proton Irradiation facility) is the project of anew irradiation facility at INFN Legnaro National Laboratories (LNL). The facilitywill exploit the LNL 35-70 MeV high current proton cyclotron of the SPES com-plex, to feed two different compact neutron sources in order to generate high fluxneutron beams with different energy spectra: quasi-monoenergetic neutron beamsand atmospheric-like neutrons. This contribution focuses on the first stage of theconstruction of the facility: the NEPIR Phase 0, financed and in an advanced de-sign phase. It will use a Be neutron production target capable of delivering up to∼ 2 × 106 n cm−2 s−1.1. – IntroductionNEPIR is a new proposed multipurpose neutron irradiation facility [1]. It was orig-inally conceived to study the Single Event Effects (SEE) induced by solar protons andatmospheric neutrons in microelectronic devices and systems. A neutron-induced SEEoccurs when a strongly ionizing secondary particle causes a current spike. In digitaldevices, these spikes can alter data and lead to errors; in analogue devices, the spikesmay even lead to device destruction. To study neutron induced SEE effects, the NEPIRfacility will deliver both Quasi Mono-energetic Neutron (QMN) beams, and a complemen-tary continuous energy spectrum beam similar to that of fast neutrons (En > 1 MeV),generated by energetic cosmic rays naturally present at sea level (atmospheric neutrons).Because of limited funds, the completion of the NEPIR facility is a long-term goal.In this work, we will focus only on a simple initial Phase-0 stage, as it is funded. It willbe constructed in 2019 and opened to academic and industrial users in 2021. The directproton irradiation beam line will be completed in the near future with additional funds.Creative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 D. BISELLO et al.2. – The neutrons of NEPIRNEPIR will exploit the SPES variable energy (35-70 MeV) proton cyclotron to delivertwo different types of fast (En > 1 MeV) neutron beams: Quasi Mono-energetic Neutrons(QMN) [2] and atmospheric-like neutrons with a continuous energy spectrum.By varying the accelerator energy, thin lithium targets will produce QMN beamswith energy peaks in the 35-70 MeV range. By using a carbon energy degrader, theminimum energy may be lowered to 20 MeV. Protons that pass through the thin targetsare deflected magnetically towards a beam dump. The neutron energy spectrum in theforward direction (0◦) is not purely mono-energetic: besides a high-energy peak closeto the energy of the incoming proton, there is also broad distribution at lower energiescoming from nuclear breakup. Each of these two components contain about half of thetotal neutron intensity, however the fraction of high-energy neutrons in the peak decreasesrapidly with angle while the energy tail changes much less. Hence, by taking data atlarger angles, one can correct the measure of the flux of neutrons in the energy peak.For a current I = 10 μ A of 70 MeV protons, the calculated maximum flux of neutronsin the energy peak at the closest test point (3 m) will be ∼ 2.7 × 105 n cm−2 s−1.Variable energy QMN facilities are of multidisciplinary interest as they allow, in gen-eral, the study of energy-dependent effects of neutrons in matter.The Atmospheric Neutron EMulator (ANEM) [3] production target is a specializedtool. Energetic neutrons produced in cosmic-ray air showers (atmospheric neutrons)are indeed a great and growing concern to the electronics industry. ANEM will produceneutrons with a energy distribution similar to that of atmospheric neutrons at sea level inthe 1-65 MeV energy range, that comprises 65% of fast atmospheric neutrons, which canhave energies up to GeV values. ANEM will allow flexible studies and tests for unexpectedsensitivity to low energy neutrons, very useful before performing measurements at high-energy facilities. For a current of 10μA of 70 MeV protons, the calculated integral flux inthe 1–65 MeV energy range at the closest test point (4 m), will be ∼ 7 × 106 n cm−2 s−1which is ∼ 2×109 times higher than the natural one in the same energy range at sea level.Additional moderator panels can be used to further shape the fast neutron spectrum toresemble that of other environments (eg. the surface of Mars).3. – NEPIR Phase 0NEPIR has been partially funded within the italian SPARE (Space Radiation Shield-ing) project. Health risks due to cosmic radiation are a major showstopper for safe colo-nization. Shielding is the only practical countermeasure, but it is poorly effective againstvery high energy nuclei from galactic sources, and exposure to secondary neutrons re-mains even if the charged particles are stopped. New, highly hydrogenated materialsare under development for the shielding of spacecraft. Active shielding using high tem-perature superconductor magnets are a promising alternative and arguably the ultimatesolution of the problem, but they also have to be tested. SPARE consists in a test cam-paign of active and passive materials using high energy protons and QMN neutrons atthe complementary accelerator facilities in Trento (TIFPA) and LNL (NEPIR).However the available funds from SPARE are insufficient to complete the constructionof NEPIR. In order to produce neutrons as soon as possible, we are designing a low costbut still useful phase-0 version.Figure 1 shows the layout of the NEPIR facility during Phase 0. In this stage, nobunker will be built in the experimental hall. Only one neutron production target, aTHE PHASE 0 OF THE NEPIR PROJECT AT LNL 3Fig. 1. – Layout of the NEPIR Phase 0 facility: the cyclotron feeds the target, located insidethe conduit from the cyclotron hall to Hall A9. The second beamline entering hall A9 will beused for future direct protons irradiationsthick Be target, will be available and it will be placed inside the conduit (diameter 30 cm)through the 3 m thick wall that separates the cyclotron hall from the experimental hall(A9). High density polyethylene pellets will fill the gap between the conduit surface anda 10 cm diameter aluminum beam pipe. This structure acts as a collimator and definesthe neutron beam (shown in cyan) towards the test point in A9. Only minimal additionalshielding will be provided.4. – The thick Be targetThe phase-0 Be target under study will produce neutrons with a continuous energyspectrum. The 70 MeV proton current will be less than 1μ A (maximum power of 70 W)to limit radioprotection issues. The chosen material is Be, for the abundant productionof high energy neutrons and the high melting point (much higher than the alternative Li).The low power proton beam will be extracted in air through a thin (50μ m) Ti windowand imping on 30 mm thick beam stopping Be target. The first 2 mm will be solid Beplate, followed by Be under the form of pellets or granules, for an additional effectivethickness of 28 mm. These will be enclosed in an aluminum canister to prevent thedispersion of the toxic metal eventually pulverized by defoliation and blistering causedby hydrogen accumulation in the material. The solid Be slab will seal the canister. The20 MeV minimum energy used at the facility guarantees that the impinging protons willpass through the initial Be plate and stop in the pellets; the energy deposition in theinitial plate is minimum. A closed circuit fluxing inert gas through the pellets would beused for cooling and for venting any hydrogen. The simulated (MCNPX) neutron energyspectrum in the forward direction (inside a 3◦ semi-aperture cone) generated by a thickBe target is shown in fig. 2(left), for different energies of the impinging proton beam. Itis characterized by a relatively flat energy distribution up to a sharp cutoff value that can4 D. BISELLO et al.Fig. 2. – (Left) Neutron yield in the forward direction for different energy of the impinging protonbeam on a thick Be target. (Right) Lin-lin plot of the effective neutron spectrum obtained bysubtraction of neutron spectra generated by 60 MeV (renormalized) and 70 MeV proton beams.The integral yield in the 52-69 energy interval is ∼2.8×105 n cm-2 s-1.be adjusted by changing the energy of the proton beam (the time required for a changeis 10–15 minutes). The maximum neutron flux with a 70 MeV, 1μ A proton beam is∼ 2 × 106 n cm−2s−1 at a test point distance of 3 m.By exposing a microelectronic device under test (DUT) to two such neutron beams,one can measure the SEE sensitivity to the neutrons in the energy interval defined by thetwo cutoff values. Figure 2(right) shows the 60 MeV spectrum (solid red) renormalizedto match the 70 MeV spectrum (blue) in the 10-50 MeV energy region. The difference(purple) approximates a box-like energy distribution in the 58-68 energy region. Bysampling this way different energy intervals with a width of few MeV, one may preciselyreconstruct the energy dependence of the cross section of the DUT to neutron-inducedSEE. This technique gives the phase-0 facility QMN-like capabilities, making it a veryattractive general purpose tool.5. – ConclusionsThe basic design of the NEPIR facility, its beam-optics, the beam dump and theANEM target is defined. We expect minor adjustments before we can completely fix theQMN system, especially in the design of the collimator. An ANEM prototype exists andwill undergo thermal tests by the end of 2018.To produce neutrons as soon as possible, we are designing a Phase 0 version of thefacility with the available limited funds. Construction will begin in 2019. We plan tocharacterize the NEPIR Phase 0 neutron beam by the end of 2020, and open it upto academic and industrial users by 2021. This new neutron activity at the LegnaroLaboratories will then lead up to the building of the final NEPIR facility.REFERENCES[1] Bisello D. et al., J. Phys.: Conf. Ser., 1021 (2018) 012010.[2] Pomp S. et al., EURADOS Report 2013-02, Braunschweig, May 2013.[3] Acosta Urdaneta G. C. et al., Int. J. Mod. Phys.: Conf. Ser., 44 (2016) 1660207.

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The Phase 0 of the NEPIR project at LNL

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