Neutron detector array for DESPEC (MONSTER) Kaushik Banerjee Variable Energy Cyclotron Centre Kolkata, India

For enough neutron rich nuclei S n lies below Q . If the decay proceeds to states above S n neutron emission dominates over  -ray de-excitation. Motivation: Measurement of beta-delayed neutron emission The accurate measurement of the half-lives, distribution of decay probabilities and particle emission probabilities provides essential data for the fields of nuclear structure, astrophysics and nuclear technology. Nuclear Structure: The measurement of beta decay with delayed neutrons and  - rays allows the study of the beta decay strengths to excited states and ground state of the daughter nuclide. Beta-delayed neutron time-of-fight spectroscopy has been utilized to study neutron unbound states. Particle bound states are studied by gamma-ray spectroscopy.

 Nuclear Astrophysics: In r-process very high neutron flux in a short time produces neutron rich nuclei, which then decays to stability. Systematic of experimental observable such as T 1/2 (half life), P n (branching ratio) and S n (neutron separation energy) values provide important input to r-process model calculations.  -delayed neutron emission probability N n  number of  decay going through neutron emission, N  number of beta decay A-1 Z+1 A Z+1 AZAZ A+1 Z (n,  )  nn The beta decay half life and the delayed neutron emission probability determine the speed of the process and conforms the abundance curve of stellar nucleosynthesis.

 Nuclear Technology: Some of the fission product undergo beta delayed neutron emission, which is essential to control the reactor (decay heat calculation). For neutron-rich nuclei the most general decay mode is β - - decay but in some cases if the neutron separation energy is low enough it may populate levels above S N. Such levels will then emit a neutron leading to a level in the nucleus which is an isotope with 1 neutron less. Comparison of prompt and delayed neutron spectra following neutron-induced fission of 235 U. Robert. C. Runkle et.al. NIMA 663, 75 (2012)

DESPEC (DEcay SPECtroscopy) experiment : The decay properties of very neutron rich nuclei will be studied.  -decay half-life T 1/2 and the delayed neutron-emission probability P n will be extracted by measuring n,  and  - rays. The selected nuclei from Super-FRS will be implanted in a sensitive detector at the focal plane, where the  -decays will take place. Properties of neutron rich nuclei will be investigated through complementary detection systems consisting of an implantation detector for the detection of the implanted ions and their  -decays, and neutron and  -ray detectors for the delayed neutrons and the  - -rays emitted along the entire de-excitation chain.

MONSTER will be used to determine the energy spectra and emission probabilities of  delayed neutrons with high resolution. Neutron energy will be measured by time of flight technique. Start signal from Si (implantation  detector). n -  will be achieved by pulse shape discrimination. Coincidence between  n and  -  -n for total and partial branching ratio. 200 detectors, 10cm radius 1 MeV TOF distance (m) Geometric efficiency 1ns 212.5%3.5% 35.6%2.5% Cylindrical cell of 20 x 5 cm filled with BC501A Reasonable intrinsic efficiency (  1MeV) Energy threshold ~ 30 keVee (E n  100 keV) Reasonable energy resolution < 10% up to 5 MeV: Good neutron timing ~1ns Reasonable flight path 2-3 m TOF Good total efficiency: 200 detectors Typical Neutron Energy range : 100 keV – 20 MeV A R Garcia et al, IOP Journal of Instrumentation 7C, (2012).

 As per the discussion in NUSTAR Neutron detector working group meeting at Lund University, October 2010, Indian participation will contribute 50 detectors.  Design and engineering drawing has been completed in collaboration with CIEMAT after detail discussion with neutron detector working group during NuSTAR meeting in GSI (March 2011) and in Bucharest (October 2011). Indian Activity for MONSTER

MONSTER cell assembly drawing Ø=20cm, L=5cm Light Guide Liquid Chamber Mu-metal shield Photo-multiplier tube Expansion chamber Quartz glass

Liquid Scintillator : BC501A Reflection coating = BC630 Optical Fibre : BCF 98MC PMT: Hamamatsu R4144, Voltage divider model: E1198 Light Guide : BC800 (thickness : 31mm) Liquid sealing: quartz glass (9.3 mm ) PTFE Teflon pipe capillary tube (Inner diameter = 1.9mm, Outer diameter = 2.5mm) to take care the thermal expansion of the liquid. Expansion volume ~6% Technical details

Detector cell for BC501A liquidLight Guide PMT Cover After light guide and Photomultiplier Tube coupling After assembly Proto-type detector fabricated at VECC

Threshold 150 KeVee n-  discrimination using zero cross over technique The detail characterization is under progress. Proto-type detector with photonis PMT XP4512B

Detectors: 30 detector cells supplied by St. Gobain + magnetic shielding PMT: 30 units model R4144 from Hamamatsu Situation: Initial problems with cell paint coating have been solved. The 30 cells where shipped to the factory and returned. Now 7 out of 30 cells show a yellowish color. They will be sent back to the USA. Status of the MONSTER at CIEMAT Spain

Detector Characterization Positioning system for detector and photo- cathode light collection characterization Software for automatic scanning with collimated radioactive sources. Detector and PMT XY scanning system Light collection efficiency as a function of the irradiation point. Homogeneity better than 6%.

Status: A lighter version has been designed and machined at CIEMAT workshops. The amount of Aluminium has been reduced both the housing and at the structure. Mechanical structure

Memory USB Data In Scale s FPGA DSP TDC ADC Clock s Power PCB updated to reduce the noise, modify the input ranges for analog signals improve the synchronization between boards, reduce the power consumption, add a 100 Mbytes/s transfer bus (besides the USB 2.0) Digitizer Board: A digitizer of 12bit resolution and 1Gsample/s sampling rate is being developed at CIEMAT. Input ranges: 100, 200, 500 mV & 1,2 V.

Summary The prototype detector for MONSTER has been fabrication at VECC. The detailed characterization of the proto-type is now under progress. The 30 cell of MONSTER are ready for real measurements by CIEMAT group. Funding has been obtained for building 20 additional cells. Two experiment has been planned for testing and characterisation of detector in 2013 at IGISOL and at PTB. TDR draft is under preparation.

Collaborators CIEMAT, Madrid, Spain IFIC,Valencia, Spain University of Jyvaskyla, Finland Variable Energy Cyclotron Centre, Kolkata, India Bhaba Atomic research Centre,Mumbai, India Panjab University, Chandigarh, India University of Uppsala,Sweden LPC – Caen, France

Thank You

Present Status MonteCarlo Simulations: Geant4 simulation for the modeling of light production and collection processes for finding the optimal cell design has been completed. Translator tool of cross section data format (ENDF, JEFF…) to GEANT4 has been done. First prototype detectors has been fabrication by Indian collaboration. The detailed characterization of the proto-type is under progress. Digital electronic developments: A digitizer of 12bit and 1GS/s is being developed at Ciemat. DESPEC prototypes (30 neutron detector) will be tested at JYFL facility for the validation of the technique. Flight path ~100 cm,  /  ~ 7.4%. Light guides made of poly-methyl methacrylate (PMMA)

Efficiency vs thickness and threshold Cell 10 cm radius 5cm thickness The intrinsic efficiency of the cell is strongly affected by the detector volume and by the detection threshold, because of the light yield response. Courtesy: D. Cano Ott Ciemat

Tentative Budget requirement for next one year( ): R&D + Prototype detectors development + electronics + lab development INR 70,00, Travel etc. (to attend meetings (National, International), participation in experiments (National, International) INR 30,00, Transportation of the detectors etc.) Total Budget requirement for the period INR 100,00,000.00

Neutron detector(cell + PMT) 50 cellsINR 2,00,00, Electronics and data acquisition 2. Power supply 3. Miscellaneous (cable, connector, computer detector stand etc.) 50 channels digitizer INR 1,05,00, INR 35,00, INR 25,00, Travel: Foreign Travel Local Travel 4 man month, 10 travel per year 4 man month, 10 travel for 5years Per year For 5 years Total cost of 4 man x 30 days = INR13, 80,000.0 Airfare for10 visit per year = INR 6,00,000.0 Travel cost for 5 years = INR 99,00, Local Travel cost for 5 years = INR 50,00, R&D, Lab setup Transportation of detector and electronics to the Experiment site: INR 50,00, Total estimated cost INR 6,14,00,000.00

1.Regulator for pumping: Swagelok 1/4in SS metering bellows-sealed valve, Part no SS-4BMW 2. Gloves: Nitrile Rubber 3. Mask: 3M 6001 ( Organic Vapor Cartridge)