1. VOXES: a detection system with eV resolution for X rays in keV range
Alessandro Scordo
Laboratori Nazionali di Frascati, INFN
Strange and non strange mesons induced processes studies at DAFNE, JPARC and RIKEN:present and future
Frascati, July 2017 1

2. Project’s goal
High resolution (few eV) measurements of the X rays (2-20 keV) emitted in various processes is strongly demanded in: particle and nuclear physics, fundamental science, astrophysics, biology, medical and industrial applications
Additionally, the realisation of such X-ray detector systems able to work in high background environments is badly needed.
Usually, X-rays of our interest don’t come from a point-like source; it is mandatory to explore the possibility to work with ‘extended’ (diffused) sources.
VOXES’s goal: to develop, test and qualify the first prototype
of ultra-high resolution and high efficiency X-ray spectrometer in
the range of energies keV using HAPG bent crystals
able to work in high background environments with ‘extended’ sources
High resolution von-Hamos X-Ray spectrometer using HAPG for Extended Sources in a broad energy range 2

3. K- mass is a fundamental quantity in physics
An example: the K- mass puzzle
K- mass is a fundamental quantity in physics
to reduce the electron screening effect
Needs precision below 0.1 eV! 3

4. Calculated efficiency ~ 400 times less than @ DAFNE
(6→5) kaonic nitrogen transition: 7560± 32 eV,
(7→6) kaonic nitrogen transition: 4589± 37 eV.
Exploratory test with DANE
Not yet performed
Calculated efficiency ~ 400 times less DAFNE
Un-efficient background reduction (statistics loss) 4

5. Presently, to achieve ~ 1 eV resolution, two options are available:
Commonly used detectors for X-rays in the range 1-20 keV are the Solid State Detectors (CCD, SDD, etc…)
However…
The solid state detectors have intrinsic resolution (FWHM ~ 120 eV at 6 keV) given by the electronic noise and the Fano Factor
Presently, to achieve ~ 1 eV resolution, two options are available:
Transition Edge Sensors (TES)
Crystals and position detectors (Bragg spectrometers) 5

6. TC ~ 50 mK !!! Transition Edge Sensors (TES).
Excellent energy resolution (few eV at 6 keV)
LIMITATIONS:
not optimised for E < 5 keV
very small active area
prohibitively high costs
rather laborious use (complex cryogenic system needed)
TC ~ 50 mK !!! 6

7. Limitation in efficiency
High resolution can be achieved depending on the quality of the crystal and the dimensions of the detectors
Geometry of the detector determines also the energy range of the spectrometer
nl = 2dsinqB
But….
Crystals response may not be uniform (shape, impurities, ecc.)
Lineshapes are difficult to be measured within few eV precision (surface scan)
In accelerator environments particles may hit the detector
Background reduction capability is mandatory
Typical d (Si) ≈ 5.5 Å
qB < 10° for E > 6 keV (forward & difficult)
Limitation in efficiency 7

8. Mosaic crystal consist in a large number of nearly perfect small crystallites.
Mosaicity makes it possible that even for a fixed incidence angle on the crystal surface, an energetic distribution of photons can be reflected
Increase of efficiency
(focusing) ~ 50
Loss in resolution
Pyrolitic Graphite mosaic crystals (d = Å):
Highly Oriented Pyroliltic Graphite (HOPG, Dq≈1°)
Highly Annealed Pyrolitic Graphite (HAPG, Dq≈0.05°)
flexible HAPG has twice higher spectral resolution, while flexible HOPG – approximately twice higher reflectivity 8

9. Already tested with 500 m slits
Bending does not influence resolution and intensity
Mosaic spread down to 0.05 degree
Integral reflectivity ~ 102 higher than for other crystals
Variable thickness (efficiency)
Excellent thermal and radiation stability
Already tested with 500 m slits
How much could one go further? Can we use it with diffused sources? 9

10. Von Hamos configuration
r = 206,7 mm
Cu (Ka1) = 8048 eV  qB = 13.28°
g path ≈ 180 cm
evH/eflat ~ rθ/a
radius of curvature angular aperture source size
PRO:
Focusing
Energy range given by the crystal
Distance from the source (background….)
Perfect (linear) Bragg spectrum
CON:
Absorption in air
‘Point-like’ source needed (low geom. eff.) 10

11. Johann configuration Rowland circle (r) Curved crystal with r = 2r
PRO:
Higher efficiency (geometrical, distance from source…)
No ‘point-like’ source needed
Less absorption in air
r = 206,7 mm
Cu (Ka1) = 8048 eV  qB = 13.28°
g path ≈ 10 cm
CON:
Non linear Bragg spectrum (unless using curved detectors….)
Near to source (background)
No vertical focusing (partially restore with spherical crystals)
Energy range fixed by the target 11

12. Designed & 3D-printed @ LNF
Starting VOXES: test Setup
Designed & LNF
Dectris Ltd
MYTHEN2 detector:
32 x 8 mm surface
640 channels  50 mm resolution
4-40 keV range
room temperature 12

13. Location for VOXES development13

14. first tests with HAPG crystals
Starting VOXES:
first tests with HAPG crystals
First stage measurements:
Ti, Cu, Br, Zr (activated with X-Ray tube)
X-ray detection with MYTHEN2 (Dectris Ltd, Zurich)
Different r crystals (10.6 mm & mm)
Different thickness (20,40,100 mm)
r = 10.6 mm
100 mm
r = mm
20 mm
r = mm
40 mm
r = mm
100 mm

15. MC simulations (running…)
Open questions:
Johann or Von Hamos?
which r ?
Which is the efficiency of the X-ray source?
Johann
Von Hamos 15

16. First spectrum with Cu Ka lines
First measurement conditions:
206,7 mm r, 100 mm thickness, 9.6 cm2 surface
XZ opening angle : Dq = 0.2°
Beam on HAPG is 3 mm (X spread)
qB = 13.28° (Ka1 line = 8047,78 eV)
‘semi’ Von Hamos configuration Z X
1 hour
data taking
X spread ≈ 60 channels
( 60 x 50 mm = 3 mm) 16

17. First spectrum with Cu Ka lines
Very preliminary
12 hours (X-ray tube off)
12 hours (X-ray tube on)
Amp (Ka1) ≈ 0.5 Amp (Ka2)
∫ Ka1 ≈ 1740
∫ Ka2 ≈ 875 17

18. Von Hamos configuration
‘’semi’’ -Von Hamos config. r
In order to compare the results all measurements have been rescaled to 12 hours DAQ

19. Alignement & optimization

20. Angular spread and attenuation
S(q) = S(0°) / cosq q

21. Angular spread and attenuation

22. Angular spread and attenuation
S(q=78°) = S(0°) / cos(78°) q

23. Angular spread and attenuationq
Incindent (VH) angle q ≈ 10°
450 mm thickness
(optimized for 6-8 keV)

24. VH vs ‘semi’-VH configuration
DAQ time scan (rescaled)
“semi-VH” VH
“semi-VH” VH
“semi-VH” VH
“semi-VH” VH
“semi-VH” VH
“semi-VH” VH
“semi-VH” VH
“semi-VH” VH
“semi-VH” VH

25. VH vs ‘semi’-VH configuration
30 m DAQ

26. VH vs ‘semi’-VH configuration
30 m DAQ

27. Larger slits spectra (30 m DAQ)
Even larger value for the first slit lead to possible Ka1 and Ka2 separation
These spectra could be further improved when using HAPG thicnkess of 40 & 15 mm

28. Quality check measurement @ PSI
T. van EGIDY and H. P. POVEL
Nuclear Physics A232 (1974) ;
pM1 Line
Low momentum p,m
(≈ 100 MeV/c)
Possible calibration lines 28

29. X O E S FAIR (exotic atoms) JPARC (K-atoms) PSI (-atoms) DANE
Medical Applications
(Mammography)
FAIR
(exotic atoms)
HAPG technology development
JPARC
(K-atoms) X
PSI
(-atoms) O E S
Particle and Nuclear Physics
X-ray spectroscopy (DANE-Luce)
DANE
(K-atoms)
LNGS
(PEP)
Industry, art and Safety: Elemental Mapping
Foundations:Quantum Mechanics 29

30. Thank you for the attention
Next steps…
Measurement of the pionic atoms transitions at PSI
Fast & triggerable position detectors  Linearly Graded SiPM (FBK)
Parallel measurement of energy & position to improve background reduction
& conclusions
The VOXES project aims to investigate the possibility to use Bragg
spectrometers with diffused sources and in high background environments
HAPG crystals are ideal candidates for this porpouse and can be used in different geometrical configurations (Von Hamos, Johann, ecc…)
Such a spectrometer may have a strong impact in several fields like nuclear and fundamental physics, medical, elemental mapping, astrophysics
Thank you for the attention 30

31. SPARE

37. New measurements are needed
Kaonic helium is formed when a K- is captured in the electron orbit
It down cascades toward the lowes levels emitting X-rays
To test the influence of the strong interaction the energy a precise measurement of the line shift and width of the 3d->2p transition is needed
The discrepancies between different theoretical models and approaches could be eliminated with ~ 1eV precision measurement
Best measurements (SIDDHARTA):
 
4He +5 ±3 (stat.) ±4 (syst.) ±8 (stat.) ± 5 (syst.)
3He −2 ±2 (stat.) ±4 (syst.) ±6 (stat.) ±7 (syst.)
New measurements are needed 37

38. 38

39. PG - artificial graphite
Production
Thermo cracking of CH4
on heated substrate at T=2100oC
Pyrocarbon d002=3,44Å, mosaicity 30o
Annealing under pressure
at T>2800oC
Pyrographite:
HOPG d002=3,356-3,358Å, mosaicity <1o
HAPG d002=3,354-3,356Å, mosaicity <0.1o 39

40. Already tested with 500 m slits
Bending does not influence resolution and intensity
Mosaic spread down to 0.05 degree
Integral reflectivity ~ 102 higher than for other crystals
Variable thickness (efficiency)
Excellent thermal and radiation stability
Already tested with 500 m slits
How much could one go further? Can we use it with diffused sources? 40

42. Specific features of HAPG: Peak reflectivity at different reflection orders

43. Specific features of HAPG: Peak reflectivity for different crystal thickness

44. Specific features of HAPG: Mosaic spread

45. H. Legall, H. Stiel, I. Grigorieva, A. Antonov et al. (unpublished)‏
Comparison of HOPG and HAPG in (004)-reflection
F = 400 mm in (004)-reflection
Ge (111)‏
Ge (111)‏
H. Legall, H. Stiel, I. Grigorieva, A. Antonov et al. (unpublished)‏ 45

46. Comparison of HOPG and HAPG
(004) reflection at distance F=400 mm
E/∆E=4100 (CuKα)‏
E/∆E=3500 (CuKα)‏
The highest resolution of E/∆E=7000 for (004) reflection
at 15 µm HAPG film at distance 1500 mm was achieved
H. Legall, H. Stiel, I. Grigorieva, A. Antonov et al., FEL Proc. 2006 46