Indian National Gamma Array

Indian National Gamma Array

About Indian National Gamma Array

The concept of a national facility for γ-spectroscopy took shape in early 2000 when a formal agreement between the various institutions (TIFR External website that opens in a new window, BARC External website that opens in a new window, SINP External website that opens in a new window, VECC External website that opens in a new window, UGC-DAE CSR and External website that opens in a new window IUAC External website that opens in a new window) was achieved for pooling the available resources. It was conceived that an Indian National Gamma Array consisting of Compton-suppressed Clover detectors with nearly 4π coverage would be set up as a national facility.

This facility would be rotated among the three accelerator laboratories in India with a minimum stay of one year at one place. Major funding for this project has been received from the Department of Science and Technology, Government of India. The Clover detectors that were available with the institutions were designed to be operated at a distance of ∼ 24 cm from the target with the accompanying anti-Compton shields subtending an angle of 30o at the target. As a result, a maximum of 24 Clover detectors could be accommodated in 4π geometry. The total coverage by Ge crystals is about 25% of 4π, corresponding to a total photopeak efficiency of ∼ 5%. Such a system would be optimized for collecting data at triples (γ-γ-γ) or at higher fold. Three campaigns with a smaller number of Clover detectors were carried out in 2001, 2003 and 2005 at TIFR, IUAC and VECC, respectively, with existing infrastructure.

Fabrication of the mechanical support structure at IUAC for holding 24 Clover detectors was taken up in early 2007 and completed by mid-2007. It was decided that the first campaign with the full INGA during 2007-2008 would take place at IUAC. Installation of the mechanical structure, cabling and electronic modules started by August 2007. The detectors and shields from all the collaborating institutions were received by January 2008. The first facility test to optimize the transport of beam at INGA beam line was carried out in February 2008. During March to June, 2008, the first cycle of experiments with the INGA facility was carried out.


Technical Details

  • INGA is an array of Compton-supressed Clover detectors with nearly 4π geometric coverage.
  • Individual shields subtend ∼ 30o at the target.
  • Maximum of 24 Clover detectors can be accommodated in the array.
  • Total photopeak efficiency of INGA is ∼ 5%.
  • The array is optimized for γ-γ-γ and higher fold data.
  • INGA can be used with auxiliary detectors like CsI-based charge particle detector array.


One of the major challenges in designing the beam line was the small clearance of ∼ 7.5 cm along beam axis between the collimators of the anti-Compton shields. A stainless steel beam tube of 6 cm diameter (top-left figure) has been used inside the array. The backward array can slide back on its guide rails without disturbing the beam line. The scattering chamber is made of 2″ diameter glass tube to minimize the attenuation of γ-rays in the chamber walls. Wilson seal couplings are used between the scattering chamber and beam tubes at both ends. The target is mounted on four rods inserted along the beam tube. The beam tube downstream of the target is mounted rigidly on the mechanical structure of the forward array.

Outside the array, 4″ diameter stainless steel tubes are used for transporting the beam. A Turbo-molecular pumping system backed by a rotary pump, with dedicated home-made control unit has been installed in the beam line. A removable collimator of 5 mm diameter with current readout is put at 1.5 m upstream of the target. In actual operation, the current intercepted by this collimator is minimized for centering the beam on target.


Automatic LN2 Filling System

A dedicated home-made controller with embedded PC has been developed to provide an automatic liquid nitrogen filling system (LN2) for the Clover detectors. The supply of LN2 is from a 1000 l dewar (INOX make) which can be periodically (once in 2 days) filled from a larger dewar (20,000 l), kept outside the beam hall. The distribution of LN2 is done with a four-column manifold catering to sixteen detectors of backward array and another two-column manifold catering to eight detectors of forward array.

Electrically operated cryogenic valves of Jefferson make (1/2″ diameter, normally closed), are employed for controlling the flow of LN2 to the detectors. These can be operated under software control by the program linserv working in linux operating system. The temperatures at the overflow ports of the Clover detectors and the filling manifolds are measured using platinum resistance thermometers (PT100) and the valves are closed under overfill condition. A graphical user interface (named, fill) enables the user to monitor the filling status of individual detectors. The detectors are filled automatically twice a day.

Power and Signal Cabling

The electronics for the various subsystems for INGA are mounted on 19″ instrumentation racks powered by UPS with surge protection circuitry. Two racks are used for mounting the LN2 control valves and two for housing the high voltage supplies for Clover detectors and anti-Compton shields. The energy and timing signals from the detectors are taken to the electronics cabin using RG58 signal cables. The cable ends in the electronics cabin are grouped into three patch panels. RG172 cables are used for the interconnection between the patch panels and the electronic modules.

Electronics and Data Acquisition System

NIM and CAMAC Modules Developed In-house

Home-made Clover modules are used for processing the energy signals from Clover detectors and anti-Compton shields. The timing logic for Compton-suppression along with the generation of required strobes for data collection and pile-up rejection were also incorporated in this module. The gain setting of the shaping amplifiers of Clover segments are kept at 4 MeV range. One NIM bin is used for powering four Clover modules. Eight detectors are grouped into one unit for creating multiplicity of γ-rays and for collecting data through one CAMAC crate. The combined multiplicity from all three crates is used for event selection.

New home-made LPCC CAMAC modules have been fabricated combining the List Processor (LP) and the Crate Controller (CC) which enables the data collection rates up to 1700 kilo bytes per second. Three CAMAC crates each having four 14 bit, 8 channel home-made AD814 ADCs, are used to collect data from all Compton-suppressed Clover detectors. The first CAMAC crate has the trigger generator which entertains the event trigger and transmits it to the other two CAMAC crates via trigger receiver modules of respective crates to maintain the synchronization of data between the three crates. The TDCss (PHILLIPS 7186) are used to create the hardware bit pattern in each CAMAC crate. The hardware bit pattern based data collection (CNAF list changes as per the bits raised for each event in TDC's of each crate) is also enabled to have more data collection due to zero suppression in data readout. The data collection software CANDLE is run in a dedicated PC with local data archival system. All the bias supplies, analogue processing modules and analogue to digital converters (except TDCs) have been fabricated in-house.

Trigger Logic

Data Rates

For multi-crate readout of ∼ 120 parameters, hardware supression is enabled, based on the hardware bit pattern readout of TDC. In the triples (γ-γ-γ) mode, on average the dead time is about 45 μs. Typical coincidence count rates were ∼ 12 kcs (γ-γ) doubles and 3-4 kcs (γ-γ-γ) triples for a total singles (γ) rate of 60-80 kcs. An oscilloscope trace of the multiplicity distribution is shown in the left figure.


Staff Telephone: +91 11 26893955, 26892601, 26892603 Telefax: +91 11 26893666


  • Pradip Datta

    Saha Institute of Nuclear Physics Kolkata, India

  • Ajay Deo

    Mumbai University, Mumbai, India

  • Dinesh Negi

    Inter University Accelerator Centre New Delhi, India

  • Tarkeshwar Trivedi

    Allahabad University, Allahabad, India

  • Anukul Dhal

    Banaras Hindu University Varanasi, India

  • Rishi Kumar Sinha

    Banaras Hindu University Varanasi, India

  • Santosh Roy

    Saha Institute of Nuclear Physics Kolkata, India

  • Rajarshi Raut

    Saha Institute of Nuclear Physics Kolkata, India

  • Ritwika Chakraborty

    UGC-DAE CSR, Kolkata Centre Kolkata, India

  • Samarjit Sihotra

    Punjab University, Chandigarh, India

  • Ritesh Kshetri

    Saha Institute of Nuclear Physics / Calcutta University, Kolkata, India

  • Tumpa Bhattacharya

    Variable Energy Cyclotron Centre Kolkata, India

  • Rajesh Kumar

    Punjab University, Chandigarh, India

  • Suresh Kumar

    Indian Institute of Technology Roorkee Roorkee, India

  • Krishichayan

    UGC-DAE, CSR, Kolkata Centre Kolkata, India

  • Anagha Chakraborty

    UGC-DAE, CSR, Kolkata Centre Kolkata, India


  • M. Kumar Raju

    Department of Nuclear Physics Andhra Uni., Visakhapatnam India

  • G. Jnaneshwari

    Department of Nuclear Physics Andhra Uni., Visakhapatnam India


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Contact us

Dr. S. Muralithar

Inter University Accelerator Centre Aruna Asaf Ali Marg, Post Box 10502 New Delhi 110067, India

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