Flux and neutron spectrum measurements in fast neutron irradiation experiments

Transcription

1 Flux and neutron spectrum measurements in fast neutron irradiation experiments G.Gorini WORKSHOP A neutron irradiation facility for space applications Rome, 8th June 2015

2 OUTLINE ChipIr and SEE: New ISIS Instrumentation for ChipIR DIAMOND DETECTORS PROTON RECOIL TELESCOPE GEM DETECTORS 2

3 ISIS neutron source Protons are accelerated by a synchrotron up to 800 MeV. Protons are produced into two bunches 70 ns wide and 322 ns apart. Protons produce neutrons via spallation reactions on a target. ISIS (RAL, Didcot, U.K.):spallation neutron source (800 MeV). 1 0,5 Proton signal 3 0-0, Time of flight [ns] F 10 6 n/cm 2 /s above 10 MeV

4 ChipIR Irradiation of electronic components to simulate the disruptive effects (Single Event Effects, SEE) of atmospheric neutrons on micro-electronics. Typically SEE per hour on VESUVIO.. x100 on ChipIR. ChipIR is designed to mimic the atmospheric spectrum. ChipIR built at ISIS with contributions from CNR. Reference spectrum of atmospheric neutrons 4

5 Fast neutron measurements on ChipIR Development of fast neutron detectors (contribution from Milano UNIMIB-IFP) Diamond detectors Moderate spectroscopy information, Flux, Beam Monitoring, Map Proton Recoil Telescope Energy Spectrum (up to >100 MeV), Flux GEM detectors 2D Map 5

6 6 Diamond Detectors

7 7 Diamonds in a Neutron Field

8 Diamond Detectors + - Gold or Aluminium Multi-layer contact Diamond Multi-layer contact Gold or Aluminium Signal Read-out Charge amplifier: Integrates the current pulse = measures the deposited charge in the detector. With a given amplification (10 mv/fc for α-spectroscopy with diamonds). Diamond features Radiation hardness. High mobility of free charges ( fast response, comparable to Si, Ge). Room temperature operation (Eg=5.5 ev) No Cooling. Compact volume solid state detector. 8

9 PHS measured on different beamlines in TS1 Prisma has more fast neutrons: it is closer to the source (8m) 9

10 M. Rebai - 18 December 2014 Event density plot at ISIS-VESUVIO E n >6 MeV Flight path: 12.5 m Peak Rate: 1 MHz. Prompt g Events due to the interaction of 3.5 MeV neutron which release energy via elastic recoil on the 12 C nucleus. 10 M. Rebai et al., JINST 7 C05015 (2012).

11 Stability achieved at ISIS If a V bias (HV) polarity inversion is performed the detector is stabilized 11

12 Telescope Proton Recoil spectrometer 12

13 Telescope Proton Recoil spectrometer 1. A prototype has been tested in A TPR has been designed for Chipir Pulsed nature of the source implies large instantaneous count rate NEED FAST SIGNALS Schematics of a TPR spectrometer Large Background from spallation target NEED coincidence measurements Ep = En cos 2 θ

14 Thin YAP and LaBr3 crystals YAP LaBr3 Example pulses LaBr 3 YAP Density (g/cm 3 ) Scintillation time (ns) Refractive index Max emission wavelenght Light Yield (photons/kev)

15 TPR prototype: Experimental setup at ISIS (VESUVIO) 1 YAP detector 500 um Si detector Target= 2mm CH2 Neutrons C2 cividec preamp for Si detector

16 Coincidence Measurement Pulse example Example of coincidence E-ΔE matrix using coincidence at ISIS typical of protons in transmission

17 Spectrum measured with TPR prototype on VESUVIO Monte Carlo simulations of the VESUVIO beam line are used for analysis of the experimental data. The neutron flux for E n > 10MeV was found to be (8.8 ± 0.8) 10 4 cm -2 s -1 at 180 µa proton current. MCNP simulation of the proton recoil counting efficiency for a CH 2 target in air, compared with the contribution of a hypothetic target of pure Hydrogen in vacuum. Proton recoil spectrum measured by the TPR compared to Monte Carlo simulation of the VESUVIO beam-line. Linear scale is on the top, log scale on the bottom.

18 Design of a TPR for ChipIr Aim: Spectroscopic Measurements of neutrons from 10 MeV to 800 MeV. This energy range is too broad for a single Telescope. Three Telescopes are designed to cover the whole range and fulfil the following criterions 1. Efficiency of each Telescope must be in the order Energy Resolution must be better than 20%. 18 Schematics of the TPR system for Chipir (not to scale). The system is composed by three telescopes (A, B and C).

19 TPR for ChipIr design (2) Telescope A Telescope B Telescope C Energy Range MeV MeV MeV Efficiency Energy Resolution 20% - 10% 20% -15% Not defined Angle 20 deg 30 deg 45 deg Target thickness 0.2 mm 1 mm 2 mm Target radius 2 cm 2 cm 2 mm E detector 2 mm YAP 1 inch YAP 4 x plastics 5mm Delta E detector Silicon 0.3 mm Silicon 0.5 mm Plastic 5 mm distance 22 cm 22 cm 22 cm Detectors diameter 1 inch 1 inch Square 2.25 x2.25 cm Table summarizes the most important parameters and choices for the three telescopes that compose the system. 19

20 MCNP calculation of response function for Telescope A (10-30MeV) 20

21 MCNP calculation of response function for Telescope B ( MeV) Above 80 MeV contribution of inelastic reactions on Carbon becomes important At low energies only Elastic Scattering on H 21

22 Telescope C: High energies ( MeV) Ch1 Ch2 Ch3 Ch4 22 A different design to go to high energies: a stack of plastic scintillators and Iron slabs. A moderate spectroscopic information: this configuration corresponds to 4 energy channels. Figure shows proton energy distributions. Dashed vertical lines represents the 4 channels of Telescope C.

23 23 ngem Detectors

24 Principle 50 μm Pictures of bi-conical channels Schematics of electric fields Schematics of triple-gem 24 A hydrogenated converter is used to convert neutrons into charged particles A Gas Electron Multiplier (F.Sauli, NIM A ) is made by 50 μm thick kapton foil, copper clad ( 5 μm thick) on each side and perforated by an high surface-density of bi-conical channels; Applying a potential difference (tipycally between 300 and 500 volts) between the two copper cladding, an high intesity electric field is produced inside the holes ( kv/cm). GEM is used as a proportional amplifier of the ionization charge released in a gas detector.

25 20 cm ngem large area prototypes GEM Foil HV Test Cathode Stretching and Framing GEM Stretching and Framing 35 cm 25 Assembly 256 Pads At the moment it is the largest area GEMbased fast neutron detector

26 ngem Detectors at ISIS Prototypes have been tested in Measurements on different ISIS beam-lines Large area detector suited to measure beam with variable collimation 2D Map of the neutron beam Good stability 26

27 Real-time 2D beam map measurements Monitor for a fast neutron beam with energies ranging from a few mev to 800 MeV neutrons Tested at neutron beam of the Vesuvio facility at RAL- ISIS ngem-s-2 2D Beam profiles and intensity in real time 27 Neutron beam monitorig

28 Conclusions Diamond detectors Measurements performed at ISIS on TS1 beam-lines. They give time resolved bi-parametric information (Pulse Height and Time of Flight) Technical issues beinge addressed for ChipIr: polarization and pileup effects TPR spectrometer Measurements performed with a prototype on VESUVIO Design of a TPR suite for ChipIr in progress. GEM detectors Measurements performed with a large area ngem Will be used to map the ChipIr beam 28

29 29 END