Accelerator Mass Spectrometrys

Accelerator Mass Spectrometry

About Accelerator Mass Spectrometry

Accelerator Mass Spectrometry with 15UD Pelletron at IUAC is first AMS facility in India for the detection of 10Be and 26Al . This facility is now open for users to carry out 10Be and 26Al measurement work.

AMS is mass spectrometry using Accelerator. AMS is used to measure the very low concentration of trace elements. These trace elements generally are long lived radioisotopes and some times stable isotopes. Long lived radioisotopes serve as tracers and chronometers in many branches of science e.g. Geology, Archeology, Hydrology, Environmental Science, Biomedicine, Cosmo-Chemistry and Nuclear Physics etc. AMS is also used to determine stable isotopes at ultra trace levels in semiconductors, geological samples and other materials.

Features IUAC AMS Facility has Following Features

Multi-Cathode SNICS

Multi Cathode Source of Negative Ion by Cs Sputtering (MC-SNICS)
Multi Cathode Source of Negative Ion by Cs Sputtering (MC-SNICS)

Multi-Cathode Source of Negative Ion by Cs Sputtering (MC-SNICS) is capable of holding 40 cathodes. Cathode holder can be rotated in both ways from control room. Bidirectional motion and quick change of cathodes is necessary in AMS measurement for changing standard and AMS sample quickly to neglect accelerator parameter variation effect between different measurements.

Re-circulating Gas Stripper

Re-circulating turbo pumps for gas stripper
Re-circulating turbo pumps for gas stripper

IUAC Pelletron facility is equipped with foil stripper and gas stripper assembly. For AMS studies, transmission through the accelerator should be optimum. Gas stripper produces less divergence after stripping compared to foil stripper. Transmission also reduces by scattering of beam by gas molecules in accelerating tubes. So good vacuum should be maintained in these tubes. Therefore a new re-circulating turbo molecular pump - based pumping system has been designed and installed in the high - voltage terminal of the accelerator. This helps in improving beam transmission by maintaining good vacuum in the accelerating tubes while holding required gas pressures in the stripping area.

Off-Set Faraday Cup

Offset Faraday Cup situated after Analyser magnet ( Top View)
Offset Faraday Cup situated after Analyser magnet ( Top View)

Off-Set Faraday is installed after the analyser magnet. It is used to count stable isotopes which follows different trajectory after passing through analyser magnet in the case of simultaneous injection of both isotopes.

For example In the case of Be-10 measurement both 10Be17O- and 9Be17O- are injected simultaneously by selecting mass 26 in the injector magnet and that after acceleration17O5+ which is representative of 9Be current, is collected in the off-Set Faraday cup.

Off-Set Faraday cup is fitted with linear motion feed through and port aligner to make sure that all the stable ion beam should be collected in the Cup.

Wien Filter

Wien Filter
Wien Filter

Stripping can also happen at the places other than terminal by residual gas molecules inside the accelerating tube. These ions may not have the assumed value of kinetic energy T and accidentally can match the MT/q2 and can not be rejected by the analyser magnet. Stable isotope can also come by scattering off chamber walls of the magnet or residual gas molecules, because they are much more abundant. All these unwanted entities can be separated by the Wien filter (T/M selection).

In Wien filter electric field E and magnetic field B are oriented at right angle to each other and perpendicular to the direction of motion of the ions. Wien filter transmits only those ions having a particular velocity, which is tuned with electric and magnetic field inside the Wien filter given by v = E / B. All other unwanted ions are deflected from the central path which are later intercepted by the slit installed before the detector.

Detection Setup

Beam Hall 1 part of IUAC- AMS beam line
Beam Hall 1 part of IUAC- AMS beam line

AMS Chamber

AMS chamber is equipped with remote controlled ladder (containing solid state detector and quartz), insertable Faraday cup, and view ports.

Insertable Faraday Cup

Insertable Faraday cup is used for measuring the current of stable isotope. In case of AMS measurement of 14C, 36Cl, and 26Al, insertable Faraday cup will be used to measure the current produced by 12C/ 13C, 35Cl/ 37Cl and 27Al stable ions respectively.

Gas Cell Absorber

Gas cell Absorber is installed after the AMS Chamber and before the MAGIC detector. It is used for stopping 10B, the isobar of 10Be before detector. Gas cell absorber and AMS chamber is separated by 6 micro meter myler. For absorbing 40MeV 10B, 220 milli bar pressure of N2gas is required in gas cell absorber.

Multi-Anode Gas Ionization Chamber (MAGIC)

Multi - Anode Gas Ionization Detector is used to count rare isotopes after identification as having correct Z (atomic no.) and M (mass). IUAC MAGIC Detector system consists of 5 sections of anode(2cm, 5cm, 5cm, 5cm, 10.6 cm having 1 mm gap from each other), one cathode and frisch grid. The frisch grid is kept at ground potential. It is used to ensure that the size of the induced pulse on the anodes is independent of lateral position of ionization event inside the detector.All the feed through connections are taken on the back flange of the detector through LEMO sockets. On the front flange of detector, myler window of 6 micro meter thickness is present for holding the gas inside the detector and to slow down some impurities.

Iso-butane gas is used as counter medium. Gas input and output connections are taken through two KF-16 ports. Two similar ports are also present for By-Pass valve and Vacuum dial gauge. One rotary pump is used at the outlet port to take out the gas from the detector for maintain the pressure.

Clean Chemistry Laboratory

Clean Chemistry Laboratory
Clean Chemistry Laboratory

In AMS the isotope of interest is filtered (separated) from interfering isotopes at various levels. Chemical processing is the first filtering stage. During this stage the isotope of interest is separated from various elements present in the sample and converted in a suitable chemical form to produce high ion yield from the ion source. Chemical processing of sample also provide uniform matrix for analysis and reduces the mass of sample to be put in the ion source and thereby reduces the time needed to attain a given level of precision. Sometimes specific chemical form of the radionuclide reduces isobaric background.

A clean chemistry laboratory has been recently developed for sample processing. The laboratory is a metal free and equipped with all modern instruments. The lab has been designed to be kept at a positive pressure than the atmosphere with the clean air of about 6000 class. Laminar Flow stations of about 100 class air environment are being utilized for performing the column chemistry for samples processing.

Facilities Facilities available at IUAC for AMS measurement

10Be and 26Al AMS measurement faculties are available at IUAC. Clean chemistry laboratory is also available for the processing of geological samples. Once the user get the beam time allotted, can utilize the AMS facility. For beam time related queries Accelerator user committee can be contacted.

How and When to Apply for Beam Time at IUAC

To avail Pelletron Beam time, one must submit Beam time proposals by filling one of the Beam Time Request (BTR) Form (in prescribed formats, see below) with in the stipulated dates (May 31 for July AUC / November 10 for December AUC ) to the  AUC Convenor . If invited, they should present it before the Accelerator User Committee Members during the AUC Meeting on July 6-7 or December 17-18

  • BTR-1 : Beam Time Request for Fresh Proposals
  • BTR-2 : Beam Time Account (BTA) for Ph.D Students from Universities/Teaching Institutions
  • BTR-3 : Request of UFR Project (funding) and Beam Time
  • BTR-4 : Beam Time Request for Ongoing Proposal
Your plan What to submit How to defend in AUC meeting
If you are planning to get a beam time only, not funds Submit BTR1 form Presentation by the Principal Investigator / any collaborator / student
If you are planning to get both beam time and funds (Applicable for University Users only) Submit BTR3 form BTR3 should be forwarded by your University Registrar Presentation by the Principal Investigator / any collaborator (but not from IUAC) (student presentation not acceptable in case of sanction of funds)
If you are planning to get a subsequent run of an already availed run(s) of a sanctioned Project Submit BTR4 form Please submit all detailed reports and copies of published papers related to the run already availed Presentation is not required
For getting a complete Beam Time Account for a student Submit BTR2 form Submit detailed Thesis Proposal Presentation by the concerned student only (The guide may be present in the meeting)

Note : Simultaneous submission of BTR2 & BTR3 will not be entertained.

Accelerator User Committee (AUC)

  • The AUC evaluates the beamtime proposals / presentations in the AUC meetings on July 8 and December 19 of every year.
  • The decisions are thereby informed to the respective Principal Investigators.

Beam time scheduling

  • Beam time is scheduled by the Beam Time Scheduling Group of IUAC;following the sanctioned list of experiments and as per the requests made by corresponding users.
  • Corresponding users are informed about their beamtime ahead of the schedule.
  • One IUAC Personnel (LEC) is assigned to help the user during the experiment.
  • User Presentation is arranged at the end of the experiment to get the user feedback.

UFR Project

  • Similar procedure is being followed for funding User Facility for Research projects (UFR) as for beamtime.
  • A University project, if approved by AUC, gets standard funds for three years. Each year the corresponding funds are sent to the relevant University subject to submission of satisfactory academic report & audited utilization certificate of the project for the previous year.
  • At the end of 3 years , a project completion report is required alongwith the financial expenditure status.
  • For any UFR related queries, contact.

Beam available

The 15 UD Pelletron at IUAC is a vertical tandem electrostatic accelerator. Negative ions from the ion source are pre-accelerated, mass analyzed and injected at energy of 250 to 350 KeV into the accelerator. At the terminal they are stripped to various charge states (q) by foil or gas stripper. These positive ions then get repelled by the terminal to gain further energy which is then energy analyzed by an analyzer magnet (1.8 m radius) and can be delivered in seven beam lines by using a switching magnet.

The energy of the accelerated particle beam available depends on the charge state (q) of the ion and the terminal potential V (in MV)

E (MeV ) = ( q + 1) V + E(inj)

Accommodation

Hostel and Guest houses are available on the campus. Booking has to be done in advance for convenience and visit has to get approval before actual arrival. A canteen, TV room and other facilities are available.For accommodation booking, contact academic@iuac.res.in

AMS Group Members

Related Links

Future Plans 14C AMS Facility

AMS group of IUAC has been sanctioned and funded a project by Ministry of Earth Sciences to set up Radiocarbon AMS facility. A dedicated accelerator is planned to procure for this facility. For the sample processing prior to the 14C AMS measurement, a graphitization laboratory will also be developed.

Queries For Queries Related to Ams

Queries related to AMS can be sent to S Chopra at chopra@iuac.res.in OR P Kumar at pkb@iuac.res.in

List of Users

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