1. X O E S New X-ray detector systems for future VIP-like experiments
INFN-CSN5
Young Researcher Grant 2015, n /2015. O E S
Alessandro Scordo
Laboratori Nazionali di Frascati, INFN
FQT2018 LNF, Frascati, 02/07/2018 1 1

2. New measurements are needed
The discrepancies between different theoretical models and approaches could be eliminated with ~ 1eV precision measurement
Best measurements (SIDDHARTA):
Target  
4He +5 ±3 (stat.) ±4 (syst.) ±8 (stat.) ± 5 (syst.)
3He −2 ±2 (stat.) ±4 (syst.) ±6 (stat.) ±7 (syst.)
New measurements are needed 2

3. K- mass is a fundamental quantity in physics
A possible application: 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 3

4. 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, for some applications (like exotic atoms measurements) X-ray detector systems have to be operated in high background environment.
These X-rays not always are produced by a point-like source; it is mandatory to develop detectors working 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 with ‘extended’ sources
High resolution von-Hamos X-Ray spectrometer using HAPG for Extended Sources in a broad energy range 4 4

5. Presently, to achieve ~ 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 ~ eV resolution, two options are available:
Transition Edge Sensors (TES)
Crystals and position detectors (Bragg spectrometers) 5 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 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 7

8. H. Legall, H. Stiel, I. Grigorieva, A. Antonov et al.,
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
E/∆E=4100 (CuKα)‏
Pyrolitic Graphite mosaic crystals (d = Å):
Highly Oriented Pyroliltic Graphite (HOPG, Dq≈1°)
Highly Annealed Pyrolitic Graphite (HAPG, Dq≈0.07°)
E/∆E=3500 (CuKα)‏
flexible HAPG has twice higher spectral resolution, while flexible HOPG – approximately twice higher reflectivity
H. Legall, H. Stiel, I. Grigorieva, A. Antonov et al.,
FEL Proc. 2006 8 8

9. 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 9 9

10. Von Hamos configuration
Designed & LNF
For a given X-ray energy the Bragg angle (θB ) and the curvature radius of the crystal (ρc ) completely determine the position of the source, the crystal and the position detector
Designed & SMI
Dectris Ltd
MYTHEN2 detector 10 10

11. The source size problem What has been done so far?
This means:
Point-like sources
High yields (no need to increase them)
1 eV (Si, Mica, etc) or 2-3 eV (HAPG) resolution is very easily achievable
Bragg spectroscopy is usually exploited by XAS, XES, synchrotron light users, etc…
But what if we really need wider sources for higher statistics?
Or what if our photons come from a diffused isotropic source? 11 11

12. The source size problem
X ray source
Slits
HAPG
Signal photons
Background (?)
Is it all? Are the red lines really (only) background?
With this configuration you are limited to few tens of microns sources and very compact spectrometers…. 12 12

13. Horizontal spread For each ∆θ’ , S0’ pair, the
2 values of the slits can be
found; first, we
define the position of the intersection point zf :
Then, the 2 slits aperture are defined by:
and the vertical illuminated portion of the HAPG is 13 13

14. The vertical spread of the beam on the target (A0) and on the HAPG
The vertical spread of the X-ray beam is fixed by the slits positions (z1,z2) and their frame size (As), together with the hole in the front panel of the setup box (zh,Ah).
The vertical spread of the beam on the target (A0) and on the HAPG
crystal (Ac) are then:
We first define the position of the intersection point zf and the f angle : 14 14

15. Characterization @ 6 keV
Line (eV)
Line (A)
sinq q L1 L2
Fe Ka1
6403,84
1,94
0,29
16,77
716,58
686,09
Fe Ka2
6390,84
16,81
715,13
684,57
Fe Kb
7057,98
1,76
0,26
15,18
789,78
762,22
In the limit of a background free pure gaussian peak, the precision is related to the resolution via:
S0’ = 500 mm
Dq’ = 0,2 °
r = 103,4 mm
𝛿𝐸= 𝜎𝐸 𝑁
4, =0,052 𝑒𝑉 15 15

16. Characterization @ 6 keV16 16

17. Characterization @ 8 keV
Line (eV)
Line (A)
sinq q L1 L2
Cu Ka1
8047,78
1,54
0,23
13,28
900,54
876,47
Cu Ka2
8027,83
13,31
898,31
874,18
Cu Kb
8905,29
1,39
0,21
11,98
996,49
974,80
In the limit of a background free pure gaussian peak, the precision is related to the resolution via:
S0’ = 600 mm
Dq’ = 0,26 °
r = 103,4 mm
𝛿𝐸= 𝜎𝐸 𝑁
6, =0,036 𝑒𝑉 17 17

18. Best results and efficiencies
Crystal & Line
e ( 10-5)
s (eV)
dE (eV)
Cu (8 keV)
r = 77,5 mm
2,7
6,8
0,07
r = 103,4 mm
2,8
4,8
0,04
r = 206,7 mm
1,1
3,6
Fe (6 keV)
4,5
4,2
0,1
1,6 4
0,09
0,8
NEW Al BOX
2,2
3,5 18 18

19. Higher energies and wider ranges: Mo + Nb
Line (eV)
Line (A)
sinq q L1 L2
Mo Ka1
17479,34
0,71
0,11
6,07
733,35
729,24
Mo Ka2
17374,30
6,11
728,94
724,81
Nb Kb
18622,50
0,67
0,10
5,70
781,31
777,46
S0’ = 1900 mm
Dq’ = 0,7 °
r = 77,5 mm
Nb Kb
Mo Ka1
Mo Ka2

20. Quality check measurement @ PSI
pM1 Line
Low momentum p,m
(≈ 100 MeV/c)
(Low) estimated precision:
4, (𝑒𝑥𝑝𝑒𝑐𝑡𝑒𝑑) =0,06 𝑒𝑉 20 20

21. K mass determination

22. What about the VIP Cu spectrum?
VIP spectrum WITH current ON
How much could one gain with a ≈ 100 times better resolution?
Estimations including efficiency and MC to optimize a possible setup are needed (and planned…)
VOXES spectrum

23. 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 23

24. Hints for possible measurements?

25. Thanks for your attention