1. OSCAR: a modular low-threshold hodoscope
GDS Topical Meeting 2017
Istituto Nazionale
di Fisica Nucleare
OSCAR: a modular low-threshold hodoscope
for low energy nuclear reactions
I. Lombardo, D. Dell’Aquila, M. Miranda, M. Vigilante
and the NUCL-EX Collaboration
Dip. di Fisica, Università di Napoli Federico II
& INFN – Sez. di Napoli
Univ. Napoli Federico II and INFN – Napoli
Legnaro, 25/01/2017

2. 3α C3N6H6 α d Important: Hodo with particle identification
Application fields of low-threshold hodoscopes
Hodoscope  wall of detectors with good energy and angular resolution MS
Coupling with magnetic spectrometers: angular correlation studies  spectroscopy of particle-emitting states.
Example: X(6Li,d)Ya+Z
Hodo
Univ. Napoli Federico II and INFN – Napoli d 3α α
C3N6H6
Coupling with «tagging» detectors: complete kinematic reconstruction  branching ratios of decay in unbound excited states
Example: 14N(d,a)12C*3a
Hodo
Important: Hodo with particle identification

3. Development of new hodoscopes
Application fields of low-threshold hodoscopes
Hodoscope  wall of detectors with good energy and angular resolution
Coupling with active gas target:
Improvement in energy recostruction
of high energy ejectiles
Example: 2H(X,Y)p and similar, at high energy
Hodo
Univ. Napoli Federico II and INFN – Napoli
Coupling with MF detectors:
QT physics
Isospin diffusion
QT Multi-BU
IMNS
Example: HI+HIX+12C*3a
Hodo
Multi-detector
array
Development of new hodoscopes

4. Test and Characterization at LNS - INFN
A new versatile hodoscope: OSCAR
OSCAR: hOdoscope of Silicons for Correlations and Analysis of Reactions
Silicon pads, 300 mm (HAM.)
Charge PRE  22mV/MeV
Two boards  plug and play
Strip Si 20 mm (nominal!)  Micron Std.
SSSSD  16 strip , 3 mm wide; mm interstrip
Charge PRE, 16 ch. NET Inst. (45, 90 mV/MeV)
Univ. Napoli Federico II and INFN – Napoli
Front-End  Analogic Digital one
Test and Characterization at LNS - INFN

5. Nice granularities  30-40 cm
Geometries and MC simulations
TEST of OSCAR at LNS: 40,48Ca+40,48Ca at 35 A MeV
OSCAR was placed at 102 cm from the target, qlab = 52o
Univ. Napoli Federico II and INFN – Napoli
4 strip in one pad  geometrical overlap
Exp. data  fragment AD in LAB
Solid angles  MC simulations
+ cross check with Rutherford
scattering
Nice granularities  cm

6. Calculated with the real thickness of SSSSD
Isotopic resolution and energy thresholds
TEST of OSCAR at LNS: 40,48Ca+40,48Ca at 35 A MeV
Isotopic identification up to Li
Very low thresholds
(≈ 1.2 A MeV)
Univ. Napoli Federico II and INFN – Napoli
Thin dead layer (0.3mm)
Negligible effect of electronics on the identification threshold
Cross talk levels under control
Calculated with the real thickness of SSSSD

7. Very good  nuclear spectroscopy
Energy resolution
TEST of OSCAR at LNS: 40,48Ca+40,48Ca at 35 A MeV and a - source
Ca+Ca
a source
Univ. Napoli Federico II and INFN – Napoli
Pu-Am-Cm source in DE-E
dE ≈ 70 keV FWHM
Very good  nuclear spectroscopy

8. Worsening of I.R. going towards the RD corner
A critical point: the SSSSD thickness uniformity
Map of the SSSSD thickness  new LNS facility
a Source 241Am
2 mm collimator
mobile support
SSSSD
Si + electronics a
Univ. Napoli Federico II and INFN – Napoli
High non-uniformity (with this peculiar pattern) silicon wafer cut (20 mm!)
FUNDAMENTAL aspect  influence isotopic resolution
Worsening of I.R. going towards the RD corner

9. … does the channeling play a role?
A critical point: the SSSSD thickness uniformity
Map of the SSSSD thickness  new LNS facility
We can investigate how the thickness gradient of the large surface SSSSD influence the I. R.
Mass spectra  from the DE-E line with an analytical method  Bethe-Bloch formula
N. Le Neindre et al, NIM A 490 (2002) 251
Univ. Napoli Federico II and INFN – Napoli
t/y
Good mass resolution sA only if t/y < 0.3 mm/mm.
Mandatory requirement!
Energy loss effect, but …
… does the channeling play a role?

10. Tilt is needed! Channeling effects on ultra-thin detectors
In the literature  very few studies on channeling effects in ultra- thin Si detectors  important to prevent loss of energy resolution
G. Thungstrom et al, NIM A 546 (2005)
Channeling
(higher
residual energy)
Si 14.5 mm
a 241Am
From the difference with respect to a purely gaussian trend:
 channeled component
about 15%
Our SSSSD,
21 mm thick «pixel»
Non channeled
(gaussian)
Univ. Napoli Federico II and INFN – Napoli
Tilt is needed!

11. Further investigations
Channeling effects on ultra-thin detectors
Estimate of the channeling effect in the SSSSD:
1) By subtraction of the gaussian component (quantitative, but difficulties  Bragg region)
2) By using the skewness g of residual energy spectra (qualitative)
Some dependence on the thickness:
> thickness  > channeling
But at very low thicknesses???
Quasi – flat behaviour?
preliminary
Univ. Napoli Federico II and INFN – Napoli
G. Thungstrom et al, NIM A 546 (2005)
Further investigations

12. QT investigation (barriers, N/Z, etc.)
40,48Ca+40,48Ca at 35 A.MeV results
Low energy part of LCP and fragment spectra isotopically resolved (H, He, Li, Be)
Univ. Napoli Federico II and INFN – Napoli
QT investigation (barriers, N/Z, etc.) 12

13. Signals of isospin diffusion
40,48Ca+40,48Ca at 35 A.MeV results
Low energy part of LCP and fragment spectra  QT emission
48Ca+48Ca
48Ca+40Ca
Univ. Napoli Federico II and INFN – Napoli
40Ca+40Ca
N/Z1
N/Z2
N/ZQP
N/ZQT
N/ZMV
Signals of isospin diffusion 13

14. Good correlator for LCP
Unbound fragment emission: correlations
Use of OSCAR for correlations  complex fragment emission
Projectile
Target
Pre-equilibrium, stopping, compression
Flow, expansion
Fragmentation
Secondary decays
Univ. Napoli Federico II and INFN – Napoli
4He+4He correlation
LCP correlations possible
Due to the limited statistics  4He+4He correlation (8Be)
Very nice peak at 92 keV (8Begs)
Erel resolution: ≈ 50 keV FWHM
Good correlator for LCP 14

15. Thank you for your attention!
Summary and Conclusions
Hodoscopes  good candidates to be used as powerful ancillary detectors in a large variety of experiments
OSCAR: a new low-threshold and high granularity, modular, hodoscope
20 mm mm Si Strip – Si pad detector, 5×5 cm2 area
Test of the detector performances: mass and energy resolution
Problems: gradient of thickness, channeling in ultra-thin detectors
Results on QT emission in Ca+Ca collisions at 35 A.MeV
4He+4He correlations with OSCAR  powerful correlator properties
Univ. Napoli Federico II and INFN – Napoli
Thank you for your attention! 15

16. Further Slides
Univ. Napoli Federico II and INFN – Napoli

17. Applicazioni a SPES@LNL
Alcuni risultati di Fisica – 2
Rapporti isotopici per il QT (selezioni in vpar)  isospin diffusion
ISOBARIC RATIO
40Ca+40Ca
48Ca+40Ca
48Ca+48Ca
Univ. Napoli Federico II and INFN – Napoli
S. Albergo, S. Costa, E. Costanzo, A. Rubbino, Nuovo Cim A 89 (1985)
Applicazioni a 17

18. Tests e caratterizzazioni ai LNS - INFN
Overview di OSCAR
OSCAR: Odoscopio di Silici per le Correlazioni e le Analisi di Reazioni
Pads di Silici da 300 mm (Ham.)
Preamplificatori di Carica 22mV/MeV
Due schede  plug and play
Strip Si da 20 mm (nominali!)  Micron sct.
SSSSD  16 strip da 3 mm; mm interstrip
Pre di carica a 16 vie NET Inst. (45, 90 mV/MeV)
a source spectrum – 300 mm
Univ. Napoli Federico II and INFN – Napoli
Elettronica Front-End  analogica (per adesso)
Tests e caratterizzazioni ai LNS - INFN