New High Resolution Neutron Detector for the Studies of ...

1SSAP 2020 R. Grzywacz

New High Resolution Neutron Detector for the Studies of Exotic NucleiBeta-delayed Neutron Spectroscopy of Exotic Nuclei DOE DE-NA0003899

06/2019-06/2022

PI: Robert GrzywaczUniversity of Tennessee

Department of Physics and Astronomy

Neutron dEtector with xn Tracking(

Robert Grzywacz Lawrence HeilbronnMiguel MadurgaUniversity of TennesseeMustafa RajabaliTennessee Technological University

Supported:Dr. Cory Thornsberry (until October 2019)Dr. Kevin Siegl (from January 2020) Graduate students: Joe Heideman (NEXT) currentShree Neupane (NEXT) (until Sep 2019)Andrew Keeler (VANDLE) currentpresentations given at conferences and meetingsR. G. Erice/Mazurian Lakes/LECMNeupane (3)/Heideman (3)

DOE DE-NA000293406.2016-06.2019


New accomplishments: 2019-2020

● Proof of principle measurements at U. Kentucky with tritium target● Published NIM manuscript: proof of concept and the prototype performance ● Six prototype modules● Optimization of the detector manufacturing● Measurements at Ohio University with (d,n)

(efficiency, thin target)● More complete Monte Carlo (Geant4) model including

realistic timing algorithm, focus on array, UTK large scale computing infrastructure

● Measurement at ANL CARIBU (this week) with refractory βn-precursors ● J. Heideman dissertation nearly complete● A larger array of 40-50 detectors funded through NSF MRI


Beta-delayed neutron emissionComposite decay mode of neutron-rich nuclei

Far from stability decay energy Qβ increases and neutron separation energy Sn decreases. ● Delayed neutron emission becomes dominant decay mode ● Neutron energy carries the information about excited states in the emitter. Experimental challenge: reconstruct complete decay pattern with best possible resolution.

Delayed neutron spectroscopy – relatively unexplored field with vast discovery potential.Neutron array will be an essential part of FRIB Decay Station.

βn β2n β3+n

Exp. (NNDC)


Beta-delayed neutron emission

NEXT for direct reactions (α,n), (d,n):neutron energies and angular distributions.

R. Yokoyama et al. Phys. Rev. C 100, 031302(R) (2019).

Strong 1n emission from 2n unbound states observed in decays of N>50 gallium isotopes.Direct measurement of neutron and gamma-emission probabilities.


TOF-based neutron detectors What determines the energy resolution ?

Timing resolution

TΔT ~1 nsT~ 100 ns

DetectorThicknessΔTL~ 3 cm L~ 100 cm

Start

Stop

Stop

Efficiency ~ ΔTL

Efficiency and resolution are in conflict.Solution: localization of interaction in a thick detector !

(Δ EE )2

=(ΔTT )2

+( 2Δ LL )

2

ΔTL

Energy resolution:

L

VANDLE array


NEXT concept: tiled thin scintillator with the side light readout.

Start

StopStop

Neutron dEtector with Tracking (NEXT)

Neutron time-of-flight detector with good timing (~0.5 ns ) and neutron/gamma discrimination capabilities for decay and reactions studies.should measure100 keV to 10 MeV neutrons

● The interaction localization improves energy resolution● Ej276 plastic scintillator allows for neutron-gamma

discrimination.● Light readout with segmented photomultipliers

(or silicon photomultipliers)


E∼1

TOF2

TOF

Resolution improvements for NEXTTiming and tracking

Relative timing and position resolution have to be comparable

(ΔTT )∼( 2Δ LL )

133In

Design parameters(cost and technical feasibility)- reduce TOF length (L)- optimal segmentation - best timing resolution- electronic readout


Prototype of NEXT

Segmented scintillator with multianode PMT position sensitive light readout.


NEXT prototypes and manufacturing optimization

5x10 segments

Six prototypes: 5x Ej276 (n-γ) and 1xEj200:● Fabrication of Ej276 pixels a lot more challenging than Ej200 due

to mechanical properties of the material.● Better pixel separation when double reflector layer applied● Image distortions are caused by photocatode inhomogeneities

and some manufacturing inconsistencies

Ej200, single layer ESRpolished sides, adhesive

Ej276, double layer ESRun-polished sides, adhesive

Ej276, double layer ESRpolished sides, air gap

Ej276, double layer ESRpolished sides, adhesive

Ej276, single layer ESRpolished sides, adhesive

4x8 segments


Position and timing of mono-energetic neutrons should have alinear relationship.Test with mono-energetic neutrons ● University of Kentucky Accelerator Laboratory (UKAL) ● 3H(p,n) 3He reaction produces angular-dependent neutron energies● Collimated neutron beam

E.E. PetersA.P.D. RamirezS.W. Yates

Measurement at the University of Kentucky


J. Heideman et al. NIM A 946 (2019), 162528

1 MeV 1.4 MeV

Measurement at the University of Kentucky

n


NEXT model - neutron scattering

Multiple interaction of neutron in a detectorlead to distortion of the time and position response.(Geant 4 modelling, C. Thornsberry)


9Be( d,n) 27Al(d,n) at 7 and 7.5 MeV at 5 m TOFMultiple prototypes tested - reliable data down to 250 keV - efficiency for EJ200 (10”) and Ej276 (5”) compatible with GEANT 4 predictions with 20 keVee threshold- efficiency is lower for Ej276 (10”)

Ohio University measurement

OU participants: Tom Massey, Doug SolteszYenuel Alberty-Jones Joseph Derkin

Ej276

Ej200


Ohio U measurement with thin Al target (500 ug)

13 MeV~100 ns, ∆T ~1 ns

9Be( d,n) and 27Al(d,n) at 7 and 7.5 MeV @ 5 m TOF● High energy neutrons (5-13 MeV) with very short detector transit time (1- 2 ns)● Observed improvement in resolution after position correction● Effect limited by the start trigger time resolution (1 ns)

Joe HeidemanJosh HookerShree Neupane

Thick targetThin target


NEXT prototype array ( more modules in production to reach 12 total)

@ANL


RIBF RIKEN (11/2018)

Beta delayed neutron detection with VANDLE

Beta delayed neutron emitters beyond 78NiProduction: fission of relativistic 238U beamSearch for 1n emission from 2n unbound states.VANDLE (48 detector)+ HAGRID(12 detectors)

78Ni 84Ga


Prepare VANDLE for FDSi (improve efficiency)- construction of 30 new VANDLE modules- test performance of 160 cm-long bars (120 cm) - Geant4 model and optimization

- finalize the NEXT array (total of 12 modules)- merging VANDLE with the NEXT array - scaled up prototypes from Ej200

20”-long module (in production)3”x3” prototype (light guide design needed)

NSCL experiment in August 2020 (29F, island of inversion, Madurga et al. )Approved proposal at RIBF RIKEN in 60Ca region(Grzywacz et al.)

Proposals submitted to CARIBU with NEXT arrayREA6 proposals (reactions)FRIB Day-One experiments in 2022

Toward FRIB Decay Station Initiator (FDSi)


Understanding of the nβ neutron processShell-model and statistical modelCalculations use Hauser Feshbach model (Kawano coh3 code) combined with shell-model B(GT) with cross-shell excitation using (Brown, NushellX).Framework for the interpretation of the beta-n data (example: 83Ga decays).

Conclusions: neutron emission from the “compound” nucleus. Underlying mechanism:mismatch between wave functions in emitter and residual nucleus.

M. Alshudifat


Summary and plans

NEXT will provide improved energy resolution for fast neutrons, neutron detector for FDS.VANDLE - workhorse for beta delayed neutron emission studies(experiments at ORNL, NSCL, RIBF, CERN, ANL, ND), core neutron detector for the FDSi

NEXT prototype array constructed (50%) with H12700 PSPMT and new Anger logic boards● Finalized details of the construction of the NEXT module● Extensive characterization studies (sources, UKentucky, OhioU, ANL)● Proposed first experiments (ANL, NSCL) in collaboration with ORNL and LLNL● NIM published, two manuscripts in preparation (efficiency and scattering)● Construct and characterize 20” long and 3”x3” modules

VANDLE● Finalize the data analysis from the past experiments (Siegl, Keeler)● Prepare for beta-delayed neutron emission program at FRIB ● Construct 30 more VANDLE modules ● βn process modeling, collaborations with LANL

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