NPI Rez Research Articles

Ion track etching in polyethylene-terephthalate studied by charge particle transmission technique

ABSTRACTIn the paper, thin films of polyethylene-terephthalate, pristine or irradiated with 170 MeV Xe+ ions to the fluence of 105 cm−2, were etched in the mild 1 M NaOH medium at 60°C for different times. The main aspects of the etching process (i.e. development of the pores, dependence of the foil thickness and transparency on the time of etching) were studied by the ion transmission technique (ion energy loss spectroscopy) that was previously introduced by the author’s team. It has been shown that the transmission method makes it possible to closely monitor the development of the polymeric porosity and to determine the important parameters of the etching process (e.g. etching rate along the latent tracks, bulk etching rate, radial etching rate, breakthrough, foil transparency). The measurement was carried out at the NPI Rez using the alpha particle microprobe on the Tandetron accelerator.

Neutron field study of p(35) + Be source reaction at the NPI Rez

The cyclotron-based fast neutron sources of the white- and quasi-monoenergetic spectra are operated at the NPI Rez Fast Neutron Facility utilizing the variable proton (up to 36 MeV) and deuteron (up to 20 MeV) beams delivered by the U-120M isochronous cyclotron and target stations with the Be(thick), D2O(thick), and Li(C) neutron production targets. The upgraded beryllium target station provides the high intensity neutron field of broad spectra up to 33 MeV with mean energy of 14 MeV. The energy range corresponds to the main energy part of IFMIF (International Fusion Material Irradiation Facility) neutron spectrum. This IFMIF-like source is appropriate for the radiation hardness tests of materials and electronics, validation of activation cross-section data within the fusion relevant research programs, and fast neutron activation analysis experiments. At the NPI CAS, the neutron field of p + Be source reaction was studied for proton beam energy of 35 MeV using the multi-foil activation technique. The modified version of SAND-II deconvolution tool was used for neutron spectrum reconstruction up to 33 MeV (i.e. energy region with a lack of experimental neutron spectral data).

Radiation hardness of Silicon Photomultipliers for CBM@FAIR, NA61@CERN and BM@N experiments

Results of radiation hardness study of Silicon Photomultipliers (SiPMs) to be used at forward hadron calorimeters, including designed Projectile Spectator Detector (PSD) of CBM, PSD of NA61 beyond 2020 upgrade and Zero Degree Calorimeter (ZDC) at BM@N are presented. High intensity beams at future heavy-ion accelerator facilities up to 106∕107 interactions/second will lead to high neutron fluence around calorimeters up to 3×1012 neq/cm2 accumulated during a year of the experiment operation. SiPMs produced by Ketek, Zecotek, Hamamatsu and Sensl manufacturers were irradiated at cyclotron of NPI Rez in a wide range of neutron fluences from 4×1010 up to 6×1012 n/cm2. Change of SiPM’s main parameters after irradiation including dark current, breakdown voltage, noise and signal response to LED was studied in the lab. Furthermore, several packs of irradiated SiPMs were installed at the currently operating NA61 PSD to study the cumulative radiation effect on the calorimeter performance. Beam scan with 20–80 GeV/c protons was performed to determine the dependency of detector energy resolution on beam energy before and after irradiation.

Neutron spectrum determination of d(20)+Be source reaction by the dosimetry foils method

The cyclotron-based fast neutron generator with the thick beryllium target operated at the NPI Rez Fast Neutron Facility is primarily designed for the fast neutron production in the p+Be source reaction at 35MeV. Besides the proton beam, the isochronous cyclotron U-120M at the NPI provides the deuterons in the energy range of 10–20MeV. The experiments for neutron field investigation from the deuteron bombardment of thick beryllium target at 20MeV were performed just recently. For the neutron spectrum measurement of the d(20)+Be source reaction, the dosimetry foils activation method was utilized. Neutron spectrum reconstruction from resulting reaction rates was performed using the SAND-II unfolding code and neutron cross-sections from the EAF-2010 nuclear data library. Obtained high-flux white neutron field from the d(20)+Be source is useful for the intensive irradiation experiments and cross-section data validation.

Neutron field of accelerator-driven p(35 MeV)+Be fast neutron source at NPI Rez

The accelerator driven fast neutron sources of the white- and quasi-monoenergetic spectra are operated at the NPI Rez Fast Neutron Facility utilizing the Be(thick), D2 O(thick), and 7 Li(C) target stations and the variable energy proton beam (up to 37 MeV) from the U-120M isochronous cyclotron. Recently, the design of beryllium target station was upgraded in order to provide the higher neutron flux at the modified positions of irradiated samples. Afterwards, the thick target neutron field of the p+Be source reaction was investigated for proton energy of 35 MeV. The spectral neutron flux for several target-to-sample distances was determined using the multi-foil activation technique. From measured reaction rates, new neutron spectra were reconstructed employing the SAND-II unfolding code and validated against the MCNPX predictions. The IFMIF-like (International Fusion Material Irradiation Facility) neutron field obtained from the p(35)+Be source is suitable for the neutron cross-sections validation within the IFMIF research program, radiation hardness tests of electronics, and neutron activation analysis experiments.

Radiation hardness of semiconductor avalanche detectors for calorimeters in future HEP experiments

During the last years, semiconductor avalanche detectors are being widely used as the replacement of classical PMTs in calorimeters for many HEP experiments. In this report, basic selection criteria for replacement of PMTs by solid state devices and specific problems in the investigation of detectors radiation hardness are discussed. The design and performance of the hadron calorimeters developed for the future high energy nuclear physics experiments at FAIR, NICA, and CERN are discussed. The Projectile Spectator Detector (PSD) for the CBM experiment at the future FAIR facility, the Forward Calorimeter for the NA61 experiment at CERN and the Multi Purpose Detector at the future NICA facility are reviewed. Moreover, new methods of data analysis and results interpretation for radiation experiments are described. Specific problems of development of detectors control systems and possibilities of reliability improvement of multi-channel detectors systems are shortly overviewed. All experimental material is based on the investigation of SiPM and MPPC at the neutron source in NPI Rez.

Study of Neutron Induced Reactions on 7Be Using Large Angle Coincidence Spectroscopy

Neutron induced reactions on the radioactive nuclei 7Be represent a unique tool for study of the 8Be nuclear structure in the high-energy region. The interactions of thermal neutrons with 7Be is dominated by the strong 7Be(nth,p)7Li reactions. While 8Be in the ground state disintegrates rapidly into two α particles, the alpha decay from the 2− neutron capture state is prohibited because of the parity violation. The study of the 7Be(nth,α)4He reaction (with two 9496 keV α particles) is then a unique tool to study parity violation in strong interactions. The test was carried out on the collimated thermal neutron beam at NPI Rez using the large angle coincidence spectroscopy. The 7Be nuclei were prepared at the ISOLDE facility by implantation of the 60 keV 7Be ions into 5μm Al foil. The results showed that the ratio of the cross sections is σ(p1)/σ(p0) = (1.58 ± 0.06) x 10-2, and in the coincidence measurement simultaneous emission of two 8775 keV α particles is observed. This reaction channel corresponds to a two-stage process comprising transition from the neutron capture state (18991 keV) to an intermediate state by emission of γ photon that is followed by the decay into two alphas. The intermediate state in the highly excited 8Be nuclei is the level at 17640 keV (1+), which is in contrast to the previous reported data. In the experiment no α particles with the energy 9495 keV were observed.

In Situ Neutron Diffraction Studies of Phase Transformations in Si - Mn TRIP Steel

High strength and ductility of the TRIP steels is often attributed to the transformation induced plasticity effect resulting from the strain induced martensitic transformation of the retained austenite in the bainite microstructure. The present work reports results of in-situ neutron diffraction experiments focused on monitoring the phase evolution in two TRIP steel samples (two different thermomechanical treatments) subjected to tensile loading at room temperature. Comparison of the single lineprofile analysis of reactor data (TKSN-400 at NPI Rez) and multi lineprofile analysis of data obtained at spallation neutron source (diffractometer ENGIN-X at ISIS RAL Chilton) suggests that the former can be used in the first approximation for in-situ monitoring of the phase evolution in TRIP steels subjected to mechanical loads.

News and Reports

Allan Mackintosh Prize Awarded to a Neutron Scatterer, Bente Lebech Mott Medal and Prize Awarded, by Steve Lee NPL of NPI Rez Participates in Joint Access Program with NFL Studsvik, by Pavol Mikula SNS Core Vessel Installed, by Allen E. Ekkebus

Dispersion free measurements in neutron interferometry

Neutron interferometry is a method of high-accuracy determination of neutron scattering length b c. The phase shift acquired by a neutron wave that propagates through a sample inserted in one of the beams of an interferometer is proportional to the neutron wavelength. A knowledge of it precisely defines the accuracy of the determination of b c. As a solution of this problem, the non-dispersive sample geometry was proposed. In this case the phase shift is λ-independent but the very precise orientation of the sample relative to the crystal planes of the interferometer is required. To overcome this obstacle a new nondispersive phase difference method was developed which achieves an accuracy in the determination of b c of even better than 10 −4, i.e. at the level of 10 −5. This method was used for the high-accuracy measurement of the coherent scattering length of Si. Experiments carried out in HMI Berlin and NIST Gaithersburg and NPI Rez on different interferometric facilities at different neutron wavelengths proved that the coherent scattering lengths can be measured with a relative uncertainty of 0.002%.