Technical Devices

Below you will find the technical specifications and capabilities of the instrumentation used to conduct experiments on the rare isotope beams created by the coupled cyclotron facility.Additionally, on the right side of the page you will find links to the different dedicated groups to each device as well as service level descriptions when applicable.

53-inch Chamber


Status: Operational
Location: S2 Vault
Contact Person: Dave Sanderson

Technical Detail

The vacuum vessel is a vertical cylinder with an inner diameter of 135.9 cm. The detector mounting platform is approx. 53 cm below the beam axis. The upper half of the chamber is fabricated from aluminum and is lifted off for access. The beamline connections are on this section, so the bellows will need to be disassembled before opening the chamber. The lower section is fabricated from stainless steel and includes the ISO-200 ports for the feedthroughs and the vacuum system.

The vacuum system consists of a 2000 l/s turbo pump with its associated forepump and a separate roughing pump. The turbo has a gate valve so it can be left running during venting of the chamber. Due to a lack of control rack space, all the vacuum gauges have readouts on the transducers with an interface to the laboratory’s control system.
One of the feedthrough ports is used for vacuum instrumentation and valves. The other eight are available for electrical and cooling feedthroughs. S800 style ISO-200 feedthrough plates and 92” Scattering Chamber style feedthrough plates with adapters can be installed.
The target mechanism incorporates an airlock for using chemically reactive targets, such as metallic calcium. The positioning of the targets is manual with a range of three 1.90 cm. high frames. The target frames are chosen by the experimenter. A second port for a target mechanism is located in the top lid, with an ISO-80 flange, upstream and centered on the beam axis.

The exit beamline quickly opens up to 30.5 cm ID to prevent any beam halo from interacting with the beamtube wall. Immediately before the faraday cup at the end is a diagnostic station with viewer and a turbo pumping system.

A large vertical slab of steel is immediately behind the faraday cup for shielding during tuning with primary beams. On the sides, water jugs are stacked to block neutrons from the faraday cup reaching the neutron walls.

The S2 vault has the normal complement of utilities, including clean power. A large jib crane has the reach to remove the top of the chamber during venting.

The following figure shows a CAD model of the chamber with its exit beamline.

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A1900 Fragment Separator

The A1900 is a third generation projectile fragment separator composed of 40 large diameter superconducting multipole magnets and four 45° dipoles with a maximum magnetic rigidity of 6 Tm. Its length is approximately 22 meters. The A1900 has a solid angle acceptance of 8 msr, a momentum acceptance of 5.5%, and can accept over 90% of a large range of projectile fragments produced at the NSCL.

The A1900 is instrumented with position and timing detectors at the intermediate dispersive image and at the final focal plane. The A1900 operation and fragment yields can be modeled with the code LISE using configuration and option files available on the A1900 group’s web page.

Although the A1900 is used mostly for transmitting separated isotopes to downstream experiments, it can also be used as a stand-alone experimental device or in conjunction with downstream devices for executing an experiment.

Status: Operational

Location: Transfer hall

Contact person: Tom Ginter

Device webpage

Service Level Description

References:

    Commissioning the A1900 Projectile Fragment Separator; D.J. Morrissey, B.M. Sherrill, M. Steiner, A. Stolz, and I. Wiedenhöver, EMIS14, Victoria, Canada, 6-10 May 2002, D'Auria (ed.), Nucl. Instrum. Meth. B 204 (2003) 90.
    doi: 10.1016/S0168-583X(02)01895-5

    A New High-resolution Separator for High Intensity Secondary Beams; D.J. Morrissey, and NSCL Staff, Nucl. Instrum. Meth. B 126 (1997) 316.
    doi: 10.1016/S0168-583X(96)01003-8

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Gamma-ray energy tracking array (GRETINA)

Atomic nuclei can emit light called gamma rays when they are excited. Gamma rays have a much higher energy than can be seen with our eyes. Special equipment called a gamma-ray spectrometer allows study of these rays and peering into the internal structure of the nucleus.

The NSCL has several detectors designed to "see" gamma rays. These include the NaI detector that uses sodium iodide to convert gamma rays into visible signals of light but has poor resolution, the Segmented Germanium Array (SeGA) that uses germanium to create a much clearer "picture" of where the gamma rays are traveling, and the scintillator array CAESAR (CAESium iodide ARray) that is optimized for high gamma-ray detection efficiency. The newest of these detectors is the Gamma-Ray Energy Tracking Array, GRETINA, which will arrive for its first science campaign at NSCL in early 2012.

Expanded Description

A collaboration of scientists from Lawrence Berkeley National Laboratory, Argonne National Laboratory, NSCL, Oak Ridge National Laboratory, and Washington University has designed and constructed a new type of gamma-ray detector to study the structure and properties of atomic nuclei. Construction started in June 2005 and was completed in March 2011. The detector is built from large crystals of hyper-pure germanium and will be the first detector to use the recently developed concept of gamma-ray energy tracking. GRETINA consists of 28 highly segmented coaxial germanium crystals. Each crystal is segmented into 36 electrically isolated elements and four crystals are combined in a single cryostat to form a quad-crystal module. There will be 7 modules in total. The modules are designed to fit a close-packed spherical geometry that will cover one quarter of a sphere. GRETINA is the first stage of the full Gamma-Ray Energy Tracking Array (GRETA).

GRETINA is a national resource that will move from laboratory to laboratory. It will be available at NSCL for experiments in the S3 vault for six months in 2012.

GRETINA Website
GRETINA Specs
Service Level Description

Simulation Program

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Segmented germanium array (SeGA) and CAESium iodide ARray (CAESAR)

Technical Detail on SeGA

The segmented germanium array (SeGA) allows “high-resolution” in-beam γ-ray spectroscopy of intermediate-energy beams from the Coupled Cyclotrons. Each of the eighteen detectors in the array is a single-crystal 75% relative-efficiency germanium counter with the outer surface electronically divided into 32 segments. By using the segment information, the interaction of the γ-ray can be localized within the detector, therefore reducing the uncertainty in the Doppler correction due to the finite opening angle of the detector. A detector frame is available and allows the detectors to be placed at several distances, so the experimentalist can decide on the compromise between efficiency and resolution for their particular needs. The standard configuration is 18 detectors at 20 cm, which gives an approximate 3% photo peak efficiency at 1.3 MeV with about 2% in-beam energy resolution. The detectors are also available for stopped beam experiments such as β-delayed γ-ray decay studies.

Status: Operational

Location: N2 vault, S2 vault, S3 vault

Contact person: Dirk Weisshaar

Service Level Description

Funding acknowledgement: The National Science Foundation through Major Research Initiative grant PHY-9724299 supported the acquisition of the SeGA array.

Reference:

    W. F. Mueller, J.A Church, T.Glasmacher, D. Gutknecht, G. Hackman, P.G Hansen, Z. Hu, K.L Miller, P. Quirin, Nucl. Instr. and Meth. A 466 (2001) 492.
    doi: 10.1016/S0168-9002(01)00257-1

Technical Detail on CAESAR

The scintillator array CAESAR (CAESium iodide ARray) is optimized for high gamma-ray detection efficiency. It consists of 192 CsI(Na) scintillation crystals of two geometries: 2"x 2"x 4" (144 pcs) and 3"x 3"x 3" (48 pcs). The intrinsic energy resolution of the detectors is better than 8% FWHM at 662 keV. The rectangular crystal shapes allow for a close-packed geometry around the target, yielding high solid angle coverage. A frame is currently being constructed for in-beam spectroscopy experiments in conjunction with the S800 spectrograph. The array will provide a full energy peak efficiency of 40% at 1 MeV. The intrinsic energy resolution of the detector units and the geometry of the array will result in an in-beam energy resolution of 10% (FWHM) at 1 MeV. The array was commissioned in May 2009.

Status: Operational

Location: S3 vault

Contact persons: Alexandra Gade and Dirk Weisshaar

Funding acknowledgement: The National Science Foundation through Major Research Initiative grant PHY-0722822.

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The Beta-Nuclear Magnetic Resonance Apparatus

The beta-NMR apparatus consists of a small electromagnet with a four-inch gap between pole faces. A foil is place at the center of the pole gap to catch the fast moving radioactive beam. Surrounding the foil is a pair of plastic scintillator telescopes used to detect beta particles emitted from the captured radioactive beam. The telescopes are placed on the north and south pole faces of the electromagnet. Small, multi-turn copper coils placed around the implantation foil are used to introduce radio-frequency waves into the sample.

A beta-NMR spectrum is obtained by determining the ratio of the counting rates in the north and south beta detectors as a function of the incoming frequency of the radio waves. At resonance, a deviation of this north/south counting ratio is observed. The frequency of the radio waves required to reach resonance is directly related to the magnetic strength of the radioactive nucleus.

Typically, large samples are required for conventional NMR and MRI experiments. However, by detecting the emitted beta particles from the radioactive sample, a sensitivity gain of over 14 orders of magnitude is realized by beta-NMR measurements over conventional NMR. Successful beta-NMR measurements at NSCL have been completed with sample sizes as small as a few hundred radioactive nuclei implanted per second.

Technical Detail

Status: Operational

Location: S2 vault, Stopped beam area

Contact person: Kei Minamisono

Funding acknowledgement: The beta-NMR station was constructed with support from the National Science Foundation.

Reference:

    P.F. Mantica et al., Nucl. Instrum. Meth. Phys. Res. A 422 (1999) 498.
    doi: 10.1016/S0168-9002(98)01073-0

    K. Minamisono et al., Nucl. Instrum. Meth. Phys. Res. A589 (2008) 185.
    doi: 10.1016/j.nima.2008.01.105

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Beta Counting System (BCS)

The central silicon implantation detector in the beta counting system is divided into 40 horizontal and 40 vertical strips, effectively providing 1600 independent silicon pixels. Each pixel is used to detect the incoming radioactive beam, and the location and time of the event is recorded. Subsequent beta radiations that occur when the nuclear isotopes undergo decay are correlated in software with previous implantations using the stored position and time information. Beta decay properties that can be deduced using this device include half-lives, branching ratios, and decay energies.

Traditional beta decay studies involved the collection of a bulk sample, whose overall decay was monitored as a function of time. By using a highly segmented silicon implantation detector, direct correlations can be made between individual radioactive isotopes and their emitted beta particles. When a beam particle implants into a pixel of the segmented silicon detector, information is recorded on a computer that helps identify the particle by mass and nuclear charge. In addition, the absolute time of the event is recorded. After some delay, a second event, corresponding to the beta decay of this particle, is detected in the same pixel. The energy of the beta particle and the absolute time of the event are recorded. The time difference between implant can be used to extract the beta decay half-life of the nuclear species.

The beta counting system is optimized to measure the short half-lives expected with nuclei with extreme numbers of protons or neutrons, where the shortest half-lives encountered are a few milliseconds. The high segmentation of the implant silicon detector reduces the probability for improper software correlations, which in turn greatly reduces background. Such background reduction permits the application of the system to the measurement of half-lives for nuclei that are produced at rates of only a few per day.

The beta counting system is typically supplemented with other detectors, for example, the MSU Segmented Germanium Array or the Neutron Emission Ratio Observer (NERO) to obtain additional information on the photons and neutrons, respectively, that may also be emitted by beta decay occurs.

Technical Detail

The Beta Counting System (BCS) is built around a double-sided silicon strip detector with 1600 pixels (40 strips in each of the horizontal and vertical directions). The detector has a thickness of 1 mm, which is sufficient to induce a detector response as the emitted beta particle traverses the detector. Radioactive species produced by fast fragmentation are implanted in this detector. Implantation events are correlated with subsequent beta decays on a pixel-by-pixel basis, allowing the identification of the species observed to decay and a direct measurement of the decay time. A stack of Si detectors and a Ge planar detector can be placed downstream of the BCS implantation detector to measure the total energy of emitted beta particles. The BCS can be used with other detector systems, such as the segmented germanium array (SeGA) or the neutron ratio emission observer (NERO), to study beta-delayed radiations. Readout of the detector signals from the BCS has recently been upgraded from more traditional analog electronics to an advanced digital signal processing system. Here a “snapshot” of each detector waveform is taken and translated by software into a useable data structure for subsequent analysis. The digital system offers a higher sensitivity for discriminating beta particles from background and does not introduce unwanted data loses encountered with analog electronics because of the latent data translation times.

Status: Operational

Location: S2 vault

Contact person: Sean Liddick

Funding acknowledgement: Supported in part by the National Science Foundation.

Reference:

    J.I. Prisciandaro, A.C. Morton, and P.F. Mantica, Nucl. Instrum. Meth. A505 (2002) 140.
    doi: 10.1016/S0168-9002(03)01037-4

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High Resolution Array Detector (HiRA)

HiRA consists of 20 telescopes. Each telescope consists of a stack of two silicon strip detectors, followed by a Cesium Iodide (CsI) detector. These detectors will each produce an electronic signal when a fragment enters the detector. By examining the electronic signals produced by a fragment that goes through the two silicon strip detectors and is stopped in the CsI-crystal, its mass, electrical charge and velocity can be determined. The silicon detectors have small strips, 0.079 inches in width, running vertically on one side of a detector and horizontally on another. This divides the area of each telescope into 1,024 square 0.079''x 0.079'' pixels, allowing us to determine where the fragment hits the detector and therefore its direction of motion with high resolution.

Technical Detail

The high resolution array (HiRA) is an array of 20 telescopes each of which contain a 65 µm thick Si-strip detector, a 1.5 mm thick silicon-strip detector and four 4 cm thick CsI(Tl) crystals. The silicon-strip detectors have an active area of 6.2 x 6.2 cm² which is divided into vertical 32 strips on the front. The 1.5 mm thick silicon-strip detector is double sided and has 32 vertical strips on the front-side and 32 horizontal strips on the back, providing an angular resolution of 0.15° at the nominal distance of 35 cm from the target. At this distance the 20 telescopes cover 70% of the solid angle between scattering angles of 5° and 30°. The telescopes are designed such that they can be independently placed, which allows optimizing the geometry for a specific experiment. The high resolution (about 30 keV) of the silicon-detectors will allow excellent isotopic resolution up to Z=16.

Status: Operational

Location: S2 and S3 vaults

Contact person: Bill Lynch

Device webpage

Funding acknowledgement: The high resolution array (HiRA) was funded by the National Science Foundation under Major Research Instrumentation grant PHY-9977707, NSCL at Michigan State University, the Indiana University Cyclotron Facility, Washington University in St. Louis, and the INFN Milano.

Reference:

    The High Resolution Array (HiRA) for Rare Isotope Beam Experiments, M.S. Wallace, M.A. Famiano, M.-J. van Goethem, A.M. Rogers, W.G. Lynch, J. Clifford, F. Delaunay, J. Lee, S. Labostov, M. Mocko, L. Morris, A. Moroni, B.E. Nett, D.J. Oostdyk, R. Krishnasamy, M.B. Tsang, R.T. de Souza, S. Hudan, L.G. Sobotka, R.J. Charity, J. Elson, and G.L. Engel, Nucl. Instrum. Meth. A 583 (2007) 302.
    doi: 10.1016/j.nima.2007.08.248

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Modular Neutron Array and Large Multi-Institutional Scintillator Array (MoNA-LISA)

This pair of detector arrays consists of a total of 288 bars of plastic scintillator. Each of these bars measures 10 cm by 10 cm and 2 m wide. The bars are typically stacked to form two walls that are each 2 m wide and 1.6 m high, but due to its modularity, the array can be configured in other ways as well. The ends of each detector bar are equipped with photo-multipliers that are able to detect the faint scintillation light and amplify it with a gain of 3×10E7. The detection efficiency for neutrons with energies up to 100 MeV is about 70%. These photo-multipliers also measure when the light arrives very precisely, so the position of the light emission along the bar can be determined within a few centimeters by measuring the time difference of the signals at the left and the right end. This time difference has to be known to within 250 picoseconds.

With the precise timing information, we also can calculate the velocity of the neutrons. We place a start detector before the reaction target—where the neutron is still part of the rare isotope—and use MoNA-LISA as a time-of-flight detector. The neutrons travel a distance of about 10 m in less than 100 nanoseconds. The sweeper magnet that is placed between the target and MoNA-LISA deflects all charged particles; otherwise they would interfere with the measurement of the neutrons.

The Modular Neutron Array and Large Multi-Institutional Scintillator Array (MoNA-LISA) is an efficient detector for high-energy neutrons. It is operated by a collaboration between Augustana College, MSU, Florida State University, Central Michigan University, Concordia College, Gettysburg College, Hope College, Indiana University at South Bend, Ohio Wesleyan University, Rhodes College, Wabash College, Western Michigan University, and Westmont College.

Technical Detail

Status: Operational

Location: N2 vault

Contact person: Thomas Baumann

Device webpage

Funding acknowledgement: The Modular Neutron Array and the Large Multi-Institutional Scintillator Array were each funded by the National Science Foundation through separate Major Research Instrumentation (MRI) grants to the participating institutions.

Reference:

    MoNA - The Modular Neutron Array; B. Luther, T. Baumann, M. Thoennessen, J. Brown, P. DeYoung, J. Finck, J. Hinnefeld, R. Howes, K. Kemper, P. Pancella, G. Peaslee, W. Rogers and S. Tabor, Nucl. Instr. and Methods A505 (2003) 33.
    doi: 10.1016/S0168-9002(03)01014-3

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Neutron Walls

In each wall there are 25 horizontal glass tubes attached to electronic units. The tubes are 79 inches long and 3 inches high, and an aluminum framework hangs them one above the other. They are filled with a special liquid which has a peculiar feature. When a neutron interacts with the liquid, it produces a small amount of visible light. The interaction is simply a collision of the incoming neutron with a proton in the liquid, as when billiard balls collide. This mechanism works very well for neutrons in the velocity range of 10–40 percent of the speed of light. There are small devices similar to photocells at both ends of the long glass tubes to register the very short light flashes from the collisions and convert them into electric signals.

The properties of the signals tell us what type of particle hit our device—a neutron or a gamma-ray. The Neutron Walls measure the time that elapsed since the neutron was produced in the experiment. Electric circuits used with the Neutron Walls can determine the time to 1 billionth of a second. The most important property of the detected neutrons is their energy which is deduced from this elapsed time. By measuring the difference in time between the two ends of the glass tube firing, experimenters can determine—with a resolution of 3 inches—how far to the left or right of center of the tube the neutron interacted.

Technical Detail

The neutron walls are two large-area (2 m x 2 m), high-efficiency, position-sensitive neutron detectors. Each wall consists of a stack of 25 glass cells filled with the scintillator liquid NE213, with which one can distinguish neutron from gamma-ray pulses by pulse shape analysis. Each cell is two meters long and has phototubes at its ends. Light from an interaction in the liquid reaches the phototubes via total internal reflection. Each wall has its own carriage and can be positioned independently of the other.

Status: Operational

Location: S2 vault

Contact person: Bill Lynch

Reference:

    A large-area, position-sensitive neutron detector with neutron/gamma-ray discrimination capabilities; P.D. Zecher, A. Galonsky, J.J. Kruse, S.J. Gaff, J. Ottarson, J. Wang, F. Deak, A. Horvath, A. Kiss, Z. Seres, K. Ieki, Y. Iwata, H. Schelin, Nucl. Instrum. and Meth. A 401 (1997) 329.

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Neutron Emission Ratio Observer (NERO)

Because neutrons are electrically neutral, it is very difficult to detect them. NERO uses about 400 pounds of plastic to slow the neutrons down. Once they have low velocities they enter tubes filled with gas that contains helium or boron. When a neutron strikes one of these gas nuclei, a charged particle is created—either a proton or an alpha particle. The charged particles knock electrons off the gas atoms, and these electrons are collected by high voltage electrodes that generate an electrical signal. This electrical signal is processed by a computer and tells us that there was a neutron around.

Technical Detail

The neutron emission ratio observer (NERO) is a low-energy neutron detector consisting of three concentric rings of 3He and BF3 proportional counters embedded in a 60 x 60 x 80 cm³ polyethylene matrix and centered around a 22.4 cm diameter beam line opening. NERO detects neutrons ranging in energy from 1 keV to 5 MeV with an efficiency of approximately 30%–40%. A rough estimate of the neutron energy distribution can be obtained from ratios of counts within the three rings. Layers of boron carbide and water can be placed around the detector to minimize neutron background.

Status: Operational

Website

Location: N2 vault

Contact person: Fernando Montes

Funding acknowledgement: The neutron emission ratio observer (NERO) is funded by the National Science Foundation and the Alfred P. Sloan Foundation.

Illustrations:

 

 

Schematic drawing of NERO indicating the sizes of the various detector rings and the beam line hole.
(gif 18.2 kByte eps 872 kByte)
Photograph of the full setup of NERO including electronics and shielding as seen from the back of NERO.
(jpg 800 2048 px wide)

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S800 Spectrograph

The S800 is equipped with sensitive detectors that measure the positions and angles of particles deflected by the magnetic fields. Sophisticated software is then used to deduce the characteristics of the particles before and after the reaction. Various types of experiments are performed using this technique, sometimes in combination with other types of detectors located around the target to get a more complete picture of each reaction. For example, strange modes of vibration of nuclei can be studied, as well as exchange of nucleons (protons or neutrons) during the split moment of a nuclear reaction between an accelerated nucleus and a target nucleus.

Technical Detail

The S800 spectrograph combines both high resolution and high acceptance in a single device and is specially designed for reaction studies with radioactive beams. Its large acceptances both in solid angle (20 msr) and momentum (5%) are well adapted to the large emittances of secondary beams produced by projectile fragmentation. The high resolution is achieved via an analytical reconstruction method in which aberrations are calculated a priori from the magnetic field maps and used directly to correct the raw data. The spectrograph is installed vertically on a carriage that can rotate from 0° to 60°. Its maximum rigidity is limited to 4 Teslameter (Tm). The S800 is preceded by an analysis line that allows for different optical modes of operations, either focussing or dispersion matched. The maximum rigidity of the analysis line is limited to 4.9 Tm.

Status: Operational

Location: S3 vault

Contact person: Daniel Bazin

Device webpage

Service Level Description

S800 Map Server

Funding acknowledgement: The S800 construction was initiated under the NSCL Phase II construction project (NSF PHY-8215585) and completed under the NSCL Cooperative Operative Agreement (NSF PHY-9214992).

References:

    The S800 spectrograph; D. Bazin, J. A. Caggiano, B.M. Sherrill, J. Yurkon, A. Zeller, EMIS-14 conference proceedings, Victoria, BC, Canada, May 6-10, 2002, Nucl. Instr. Meth. B 204 (2003) 629.
    doi: 10.1016/S0168-583X(02)02142-0

    Focal plane detector for the S800 high-resolution spectrometer; J. Yurkon*, D. Bazin, W. Benenson, D.J. Morrissey, B.M. Sherrill, D. Swan, R. Swanson, Nucl. Instr. Meth. A 422 (1999) 291.
    doi: 10.1016/S0168-9002(98)00960-7

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Low Energy Beam and Ion Trap (LEBIT)

The low energy beam and ion trap (LEBIT) takes the fast rare isotope beams delivered by the A1900 fragment separator and carefully slows the isotopes down to low velocities. The rare isotopes can even be brought to rest and captured in special traps for ions.

The ions delivered by the A 1900 fragment separator are sent through a massive piece of matter, called a degrader, to absorb most of their energy. Through a thin window they enter a chamber filled with 1 atm Helium. Here, they lose their remaining energy and come practically to rest. They remain charged which allows them to be guided by electric fields to a very thin nozzle where the gas flow takes them into a vacuum chamber. Radio-frequency devices called ion guides are used for a loss-free low-velocity transport of the ions into ultrahigh vacuum. There they are modestly accelerated for their further transport. The ions receive their last treatment in a gas filled ion trap (the so-called “Paul trap”) where they are captured, cooled and finally released as short, high-quality ion bunches.

Status: Operational

Location: Room 173

Contact Person: Georg Bollen

Device webpage

Funding Acknowledgement: The construction of LEBIT (downstream of the gas cell) was funded by Michigan State University, and the gas cell was funded by DOE under Contract DEFG02-00ER41144.

References:

    The low-energy-beam and ion-trap facility at NSCL/MSU; S. Schwarz, G. Bollen, D. Lawton, P. Lofy, D. J. Morrissey, J. Ottarson, R. Ringle, P. Schury, T. Sun, V. Varentsov, and L. Weissman, EMIS-14 conference proceedings, Victoria, BC, Canada,May 6-10, 2002, Nucl. Instrum. Meth. B 204 (2003) 507.
    doi: 10.1016/S0168-583X(02)02122-5

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Sweeper Magnet

The sweeper magnet separates the neutrons and the remnants of a collision so that they can be detected in the S800, MoNA and Neutron Walls. The magnet generates a strong magnetic field using superconducting coils. As neutral particles, the neutrons are not affected by the magnetic field and fly straight after the reaction. However, the charged remnants are “swept” away in a different direction towards, for example, the S800 or another detection system. The sweeper thus acts as an auxiliary device that serves the actual detectors.
The sweeper magnet weighs about 50,000 pounds and generates a magnetic field of 40,000 Gauss which is about 400 times stronger than a typical refrigerator magnet. The superconducting wire is held at a temperature of –452 °F and can carry a current of 500 Amperes.

The magnet is placed immediately behind a target where the exotic neutron-rich nuclei react and break up into a charged nuclear fragment and one, two or more neutrons. The charged fragments typically have velocities of about 40 percent of the speed of light, or 55 million miles per hour. The magnetic field is strong enough to bend these particles by 40° over a distance of only 1 meter.

Alternatively, the sweeper also has its own lower-resolution detection system. This system can determine all the detailed properties of the fragments following the breakup—the charge, mass, angle, velocity, momentum and energy. By combining this information with the corresponding information about the neutrons, it is possible to reconstruct the properties of the original neutron-rich exotic nucleus.

Technical Detail

The sweeper magnet was built at the National High Magnetic Field Laboratory (NHMFL) at Florida State University. It is a superconducting dipole magnet with a maximum field of 4 T. The bend radius is 1 m with a bend angle of 400. It has a vertical gap of 14 cm which allows for neutron coincidence experiments (with the neutron walls or MoNA) covering about ±70. The total weight of the magnet is more than 50,000 lbs.

Status: Operational

Location: N2 vault

Contact person: Michael Thoennessen

Service Level Description

Funding acknowledgement: The construction of the sweeper magnet was funded by the National Science Foundation through Major Research Instrumentation grant PHY-9871462.

References:

    A Compact Sweeper Magnet for Nuclear Physics. A. F. Zeller, J. C. DeKamp, M. Thoennessen, B. M. Sherrill, P. G. Hansen, M. Bird, Y. Eyassa, S. W. Van Sciver, and K. W. Kemper, Advances in Cryogenic Engineering 45 (2000) 643.

    Structral Design and Analysis of Compact Sweeper Magnet for Nuclear Physics; S. Prestemon, M. D. Bird, D. G. Crook, Y. M. Eyssa, J. C. DeKamp, L. Morris, M. Thoennessen, and A. F. Zeller, IEEE Transactions on Applied Superconductivity 11 (2001) 1721.

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RF Fragment Separator

This figure illustrates the selection provided by the RFFS. The top panel shows a typical particle identification plot of energy loss versus time of flight, for fragments produced from a 112Sn beam. The bottom panel shows the vertical position at the slit location versus the same time of flight, each group corresponding to one of the time of flight lines shown in the top panel. The vertical position of the groups can be tuned by adjusting the phase of the RFFS, while the vertical slits can be closed to any position to perform the actual filtering.

The RFFS relies on the difference in the arrival times among the various isotopes selected by the fragment separator due to their different velocities and the micro-structure in time of the beam. A uniform RF electric field is applied transverse to the beam direction in the RFFS such that the ions are deflected to a greater or lesser extent depending on the phase of the applied RF during the time that they traverse the device. The phase of the RF is tuned such that a set of slits placed downstream from the RFFS blocks the bulk of the contaminants.

The figure shows an example of the effect of the RFFS, which is equivalent to that of a velocity filter, albeit modulo the period of the cyclotron RF. The data shown was taken with a reduced momentum acceptance of 0.5%, for which the time of flight lines are clearly separated. As the momentum acceptance of the A1900 is increased, these lines overlap and the separation provided by the RFFS degrades. The filtering quality of the RFFS depends on the following factors: i) the RF voltage applied between the plates, ii) the time of flight difference between the fragment of interest and the contaminants, and iii) the momentum acceptance used in producing the radioactive beam. It should be noted that this device cannot rid of contaminants that have time of flights which matches full 2π rotations of the RF phase. The program LISE++ can be used to simulate the RFFS for planning experiments.

Technical Detail

The RFFS is composed of an RF cavity coupled to an RF system which provides the power, followed by a diagnostic box equipped with a set of continuously moveable vertical slits, where the actual filtering occurs. This box is also equipped with a pair of Parallel Plate Avalanche Counters (PPAC) to track particles at the slit location, a plastic scintillator for time-of-flight measurements, and a configurable stack of Silicon detectors for particle identification and implantation. A re-entry can located next to the Silicon stack can be used to insert a high-efficiency Germanium detector next to the implantation site for isomer tagging.
The horizontal plates of the RF cavity are 1.5 meter long and 5 cm apart. The maximum field so far has been achieved with a peak voltage of 100 kV at a frequency of 21.315 MHz. The maximum field is a function of the frequency because the quality factor (Q) of the cavity varies. The figure shows a technical drawing of the RF cavity, with its two symmetric coarse tuner drives at the top and bottom, the RF coupler on the right-hand side, and the fine tuner at the bottom left.

Status: Operational

Location: S2 vault

Contact person: Daniel Bazin

Service Level Description

Funding acknowledgement: The construction of the RFFS was funded by the National Science Foundation through Major Research Instrumentation grant PHY-0520930.

References:

    J. Stoker et al., "Commissioning Report on the NSCL RF Fragment Separator", Proceedings of the 234th ACS National Meeting, Boston, MA, USA, August 19-23, 2007

    M. Doléans et al., "Status report on the NSCL RF Fragment Separator", Proceedings of the 22nd Particle Accelerator Conference (PAC2007), Albuquerque, NM, USA, June 25-29, 2007

    D. Gorelov et al., "RF-Kicker System for Secondary Beams at NSCL/MSU", Proceedings of the 2005 Particle Accelerator Conference (PAC2005), Knoxville, TN, USA, May 16-20, 2005

    K. Yamada et al., Nucl. Phys. A 746 (2004) 156c-160c
    doi: 10.1016/j.nuclphysa.2004.09.064

Technical drawing of the RF cavity of the RFFS. The horizontal plates in between which the RF electric field is generated are the top and bottom of the two wedge-shaped electrodes, each attached to a side of the cylinder tank end caps.

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Beam Cooler and Laser spectroscopy (BECOLA) endstation

The BEam COoler and LAser spectroscopy (BECOLA) endstation is being developed for laser spectroscopy and beta-NMR experiments with low energy radioactive ion beams at NSCL.

Expanded Description

The BECOLA endstation will include a cooler/buncher and switchyard followed by two collinear laser beamlines and is designed to operate at maximum beam energy of 60 keV. The cooler/buncher, which operates near 77 K, will capture and cool low energy ion beams from the NSCL gas stopper and release ion beams as short ion bunches with low emittance. Simulations by SIMION 8.0 gives transverse and longitudinal emittances of typically 1 pi mm-mrad and 1.5 eV-micro second, respectively. The bunched or continuous beam will be transported to one of two laser beamlines.

One of the laser beamlines will be used for laser polarization (polarizer). The rare-isotope ions may be neutralized by charge exchange reactions with alkali vapor, and will be optically pumped with circularly polarized laser light. The Beta-NMR technique will be applied for the polarized beam. The BECOLA beam line is instrumented for the photon counting technique (laser spectroscopy). The bunched beam from the cooler/buncher will be exposed to fixed-frequency laser light and the de-exciting photons will be measured as a function of atom/ion velocity to determine the hyperfine structure. The construction of the BECOLA beam line will be completed by the end of 2012.

A laser system for BECOLA beamline has been installed. The 700-1000 nm light from a titanium-sapphire ring laser (Matisse TS, Spectra Physics) pumped by a 15 W solid-state CW laser (Millennia Pro, Spectra Physics) is frequency doubled and the 350-500 nm light is generated (WaveTrain, Spectra Physics) for experiments. The titanium-sapphire ring laser is locked on a precision wave length meter (WSU-30, TOPTICA) for long term stability. The laser light is transported to the BECOLA beam line via optical fiber, enters through a window on the side of switchyard, and is then collinearly overlapped with the ion/atom beams.

The BECOLA project is funded by the NSF. More details of the project are posted at the BECOLA webpage.

Status: Under construction; expected completion date: October 2012

Location: Room 173

Contact person: Kei Minamisono

Design of BECOLA endstation: bunched or continuous ion beams from the cooler/buncher will be transported to one of two experimental legs. One is for production of polarization for Beta-NMR experiments and laser spectroscopy. The other leg is open for other experiments.

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Triple plunger for exotic beams (TRIPLEX)

The TRIPLEX plunger device allows precision level lifetime measurements of exotic nuclei. A new feature of the TRIPLEX is that it has two degraders at different distances to the target, which enables advanced techniques, such as the measurements of two different lifetimes in a single setup. The device holds three thin foils and is able to separate the foils by very precise distances. A nuclear excited state is produced in the first foil (the target) and decays in flight while traveling a distance that is related to its lifetime. If the decay occurs after the nucleus passes through the second or third foil (the degrader), the nucleus will be traveling significantly slower. The gamma rays emitted during the decay are detected by the segmented Germanium array. The energies of the gamma rays are Doppler-shifted according to the velocity of the nuclei and the lifetime can be obtained from measurements with different target-degrader distances.

A target (or degrader) of dimension 50 mm x 50 mm can be mounted in the plunger, and the foil separation is controllable between 0 to 30mm with a precision of 1 micrometer. The standard application allows lifetime measurements in the range from 1 ps to several hundred ps.

Status: Operational

Location: S3 vault

Contact Person: Hiro Iwasaki

Funding acknowledgement: The TRIPLEX plunger was constructed with support from the National Science Foundation.

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Summing NaI detector (SuN)


16x16 inch NaI(Tl) with a 45 mm borehole along its axis

SuN is a γ-Total Absorption Spectrometer. It is a cylindrical shape NaI(Tl) detector, 16-inch in diameter and 16-inch in height. It is segmented in 8 optically separated segments, which are positioned above and below the beam axis as shown in the figures. Each segment is being read by three photomultiplier tubes resulting in a total of 24 signals coming out of the detector. The signals from the PMTs are gain-matched using potentiometers located on the PMTs themselves as well as by appropriate high-voltage adjustment. The signals are then fed into the NSCL Digital Data Acquisition System (DDAS).

Technical Details

The efficiency of SuN for a Cs-137 source (Eγ = 661 keV) is 85%. For the summing of the two sequential γ-rays from the decay of Co-60 the sum-peak efficiency is 65%. The summing efficiency of SuN highly depends on the multiplicity of the γ-cascade being detected; the higher the multiplicity the lower the efficiency. The hit-pattern from the eight segments of SuN can be used to estimate the average multiplicity of a given sum peak. SuN has been simulated in GEANT4 and for a given γ-decay scheme the detection efficiency can be estimated using this simulation tool.

Status: Operational

Location: ReA3 experimental hall

Contact Person: Artemis Spyrou

Website

SuN renderings

Left: Schematic view of the SuN detector
Right: SuN segmentation

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Low-Energy Neutron Detector Array (LENDA)

LENDA is a low-energy neutron (0.15-10 MeV) detector array that consists of 24 scintillator bars, each with dimensions of 300(height)x45(width)x25(depth)mm. High-gain Hamamatsu-phototubes assemblies (H6410) are attached at the both ends of each bar. The scintillators are wrapped in nitrocellulose membrane filter paper, surrounded by aluminum foil and a layer of insulating tape to ensure efficient light collection. Two frames that each can hold up to 12 bars (vertically mounted) are available. The frames are designed to place the center of the bars at a distance of 1 m from the target location and the total solid angle coverage is 0.16 sr. Neutron energies can be determined via a time-of-flight measurement (an external time reference must be provided). The resolution that can be achieved is approximately 420 ps (corresponding to about 5% in neutron energy, almost independent of the energy, if the bars are placed 1 m from the target). The position along the bar can be determined through a measurement of the time difference between signals arriving at each end of the bar, with a resolution of about 6 cm. The current DAQ system used for LENDA is based on the usage of CAEN VME TDC’s and QDC’s. A VME-based JTEC XLM72V FPGA module is used to implement the logic of the array.

People interested in using LENDA for experiments at NSCL should collaborate with the charge-exchange group led by Remco Zegers.

Status: Operational

Location: Can be placed at various locations

Contact Person: Remco Zegers

Reference: http://arxiv.org/pdf/1111.4011v1 and to be published.

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Ursinus College Liquid Hydrogen Target

The Ursinus Liquid Hydrogen Target has a target cell that maintains liquid Hydrogen at about 18 K. The target cell can be operated in 3 standard configurations:
1. Cell thickness of ~30 mm (~200 mg/cm2) and a diameter of 38 mm
2. Cell thickness of ~8.5 mm (~60 mg/cm2) and a diameter of 30 mm
3. Cell thickness of ~19.3 mm (~130 mg/cm2) and a diameter of 30 mm
Cell windows are currently made of Kapton foil of ~125 micrometer thick. Use of thinner foils or other materials will require further development. Instead of Liquid Hydrogen, the target system can also be used for Liquid Deuterium.

The available Liquid Hydrogen Target infrastructure includes a dedicated gas handling system, cryo-cooler, and beam line interconnections. At present, the Liquid Hydrogen Target is only available for use in experiments at the target position in front of the S800 spectrograph (in the S3 vault). Usage of the target in other vaults would require implementation of safety features and procedures.

People interested in using the Liquid Hydrogen Target for experiments at NSCL should collaborate with Lew Riley (Ursinus College) and Remco Zegers (NSCL).

Status: Operational

Location: S3 vault

Contact Person: Remco Zegers

Funding acknowledgement: The construction of the Liquid Hydrogen Target was funded by the National Science Foundation through Major Research Instrumentation grant PHY-0922615.

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Single Event Effects Test Facility (SEETF)

The Single Event Effects (SEE) Test Facility at NSCL is a dedicated in-air irradiation station with complete diagnostic equipment and controls, located in the S2 experimental vault. While it has been tailored to measure the response of electronic components to energetic heavy ions available at the Coupled Cyclotron Facility (to simulate the environment in space), it can be adapted for doing other in-air irradiation measurements. At the conclusion of an experiment, the experimenters will have all the information they need on operation conditions (beam energy, current, spot size, etc.) in an easily interpreted form.

The maximum beam energies achievable with the SEE Test Facility are set by the requirement that beams must be degraded by approximately 15% in energy to get adequate spatial uniformity. A limit on the minimum beam energies is the requirement that beam from the A1900 fragment separator (located upstream of SEETF) must have a rigidity of at least 1.5 Tm; beams at the SEETF target position with energies lower than this limit are possible by using degraders in the SEETF setup, but come at the expense of a lower beam purity and a wider energy distribution.

Status: Operational

Location: S2 vault

Contact Person: Thomas Baumann

Device manual: Click here

Reference: Performance of the High-Energy Single-Event Effects Test Facility (SEETF) at Michigan State University’s National Superconducting Cyclotron Laboratory (NSCL); R. Ladbury, R. A. Reed, P. Marshall, K. A. LaBel, N. Anantaraman, R. Fox, D. P. Sanderson, A. Stolz, J. Yurkon, A. F. Zeller, and J. W. Stetson, IEEE Trans. Nucl. Sci. 51 (2004) 3664.
doi: 10.1109/TNS.2004.839300

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