High-Resolution Neutron Imaging with Timepix-based Modular System at PSI

1. Additional input of IEAP CTU in Prague on high resolution neutron imaging to MS25 BrightnESSreport Tomas Slavicek, Stanislav Pospisil and Jan Zemlicka on behalf of BrightnESS team Of the Czech Technical University in Prague

2. High-resolution neutron imaging with Timepix-based modular system at PSI (ICON) • Cold neutron beam at PSI used (ICON) • Gadolinium Siemens Star patter (1.7 mm from the sensor and 7.8 from the last beamline aperture) • L/D = 760 • Sensor: silicon 300 um thick with very thin 6LiF convertor layer • Counting / ToT mode, Bias 50 V • Acquisition time per frame: 1 ms • Total lifetime ~ 2000 s Additional input of IEAP to MS25 BrightnESS report

3. 100mm 50mm Spatial resolution in counting mode Gd calibrator: Siemens star => Resolution ~ 65 mm Spatial resolution beyond this limit (for micrometer-size features) remains a challenge. Additional input of IEAP to MS25 BrightnESS report

4. Ultra high-resolution neutron imaging • Tritons were rejected to improve resolution (based on energy information) • In total ~107 alphas processed for final image formation • Each alpha tracks fitted to find exact impact point • Each pixel virtually oversampled to submatrix 20 × 20  effective pixel pitch ~ 2.5 m • 256 × 256 pixel device effectively works as a 26 MPixel device 10m Tritons 50 m Suppressed background 100 m alphas 200 m 300 m 400 m 500 m Additional input of IEAP to MS25 BrightnESS report

5. Silicon 6LiF FWHM 3H- UCN PSF a Bragg curve Range of a Insensitive Si layer Range of 3H- Absorption Monte-Carlo simulations • Simulations performed using MCNP, SRIM and Matlab • Aim: To estimate detection efficiency and spatial resolution Expected UCNs velocity: 500 cm/s. For such neutrons the cross section of 6Li increases to 0.34 Mbarn. The cross section of 10B reaches 1.67 Mbarn. 50% of such UCNs are fully absorbed in 6LiF layer of 85 ug/cm2 (~ 320 nm thickness). For 10B it is layer of 7 ug/cm2 (~ 30 nm thickness). Used 6LiF density of 2.65 g/cm3 and 10B density of 2.35 g/cm3. Geometry used in simulations Additional input of IEAP to MS25 BrightnESS report

6. Spectroscopy of 10B(n,alpha)7Li products applied for thermal neutron high resolution imaging with high S/N ratio in mixed n-gamma radiation fields Pixel detector response to every charged article (alpha and 7Li) in a form of 3D-cluster with a shape corresponding to convolution of Gaussian and individual pixel responses Amplitude spectrum of Timepix neutron detector with 10BCconverterof1.8 ug/cm2 (~ 36 nm) thickness as measuredby integration of alpha and 7Li cluster volumes. By fittingof7Li*clusters, theimpact point of neutron to thedetectorisdeterminedwithprecisionof 3 micrometers! Additional input of IEAP to MS25 BrightnESS report

7. Operation in Event-by-event modeMicrometer spatial resolution 10m 50 m • Smallest pattern features (10 µm) clearly recognized • 2.5 µm effective pixel pitch • Cold neutron beam at PSI used (ICON) • Gadolinium Siemens Star patter Additional input of IEAP to MS25 BrightnESS report

8. Neutron micro radiography and tomography • Horizontal channel of the LVR-15 nuclear research reactor at NPI AS CR • “Neutra” tomographic facility at PSI have been also used Blank cartridge X-ray radiography 2D a 3D neutron radiography Neutron tomography of Lemo connector Neutron radiography of fishing line on Al plate Additional input of IEAP to MS25 BrightnESS report

9. Cold neutron radiography performed at PSIWrist watch Additional input of IEAP to MS25 BrightnESS report

10. Glue raised through capillary attraction Glued Al pieces(measured at NPI Rez) Additional input of IEAP to MS25 BrightnESS report

11. Conlusion • We demonstrate only resolution for neutron radiography and tomography. • The high resolution which is below 60 µm can be applied in diffraction experiments to move the detectors closers to the investigated object. Additional input of IEAP to MS25 BrightnESS report