Changer Labs Inc. (located in Oak Ridge, Tennessee, USA) designs and manufactures roboticaly controlled, very reliable, sample changers that handle a large number (up to 200) small samples for gamma counting and spectroscopy.

SAMPLE CHANGERS

The "Assistant"

The Assistant from Changer Labs has been designed to fill the need for an easily customized gamma sample changer that can handle the smaller samples of applications such as NAA or the environmental samples now possible with the new larger Germanium detectors. The Assistant's design is highly flexible so that the sample staging area and shielding can be scaled up or down to tailor the system to the sample size and number needed. The Assistant is equally adept at placing a sample in a well detector or placing the sample on the end cap of a coaxial detector. NaI detectors can be accommodated in either the floor mount configuration or a table top version. The system software adapts to multiple sample trays where the size and spacing of samples is independently defined for each tray.

People doing gamma spectroscopy in bioassay, radiochemistry, waste characterization, sediment analysis or environmental radiation monitoring with either germanium or sodium iodide detectors can often benefit from a gamma sample changer that automates routine counting procedures.
Front View of the "Assistant"

Applications

Potential applications for the Changer Lab's "Assistant", Gamma Sample Changer:
  • Neutron Activation Analysis (NAA)
  • Waste characterization
  • Bio-Assay analysis
  • Food Stuff monitoring
  • Ra-228 in drinking water by HPGe gamma spectroscopy
  • Environmental gamma monitoring
  • Automated well detector spectroscopy (HPGe or NaI)
  • Health Physics applications with large numbers of small samples
  • Air filters and swipes for isotope specific analysis
  • Sediment and Oceanography samples with limited volumes and moderate count times
  • Basically any gamma spectroscopy application with significant numbers of samples can benefit if the samples are relatively small and the detector is either HPGe germanium or NaI with solid or well type detectors

Features and Benefits

  • Compatible with all popular MCAs
  • Accommodates all streamlined cryostats
  • Handles samples from <¼ to 3 in diameter
  • High Capacity, up to 200 samples, with 20 mL LSC vials
  • Suitable for well or coaxial Germanium or NaI detectors
  • Table top configuration available for NaI
  • Highly flexible design easy to scale up or down
  • Small foot print for efficient space utilization
  • Power lid option for 4 pi shielding
  • Automated pull back for dead time control in NAA
  • Stainless Steel drip pan for easy clean up
  • Removable sample trays
  • Safe shutdown in the event of power loss
  • Complete systems available including detector, electronics, and PC-based MCA

Watch the "Assistant"

Watch the "Assistant" in action; sample loading and unloading.
Sample Loading
Sample Unloading

  • System Size

    The Assistant's structural components are standard industrial extrusions and linear motion bearings. They are available in a wide variety of lengths so that the width, depth, and height of the cabinet and the length of the vertical travel can be customized to optimize sample capacity and shield requirements for any application.

  • Sample Container Size

    Sample containers from 10 mm test tubes to 3 inch diameter wide mouth jars can be accommodated. The samples are loaded into a removable sample tray that is positioned over a stainless steel drip pan for easy decontamination. Sample container size determines minimum spacing between samples in the tray which determines the maximum number of samples for the system. High sample density in the tray helps to minimize floor space requirements. The sample positions in the tray are defined in software for maximum flexibility

  • Shield

    The system shield can range from a simple insertion shield with no lid, to a full 4 pi shield with an automatic top as shown below. There are several standard shields available that are designed to fit the sample size that will be utilized. Most shields use lead bricks stacked into a steel shell and lined with either copper/cadmium (Cu/Cd) or copper/tin (Cu/Sn). Standard wall thickness is 4 inches but 6 inches is available. Extra shielding can be added between the sample storage area and the counting cavity via an optional separate 4 inch wall on the sample storage area side.
    Keeping the counting cavity small minimizes the total shield weight. The system design leaves ONLY the detector and the sample inside the cavity during counting. This helps maintain the lowest background possible.

  • The Hand

    A self-centering, four point hand is used to provide a wide tolerance for variations in the sample container’s dimensions, weight, and positioning. The hand features a positive close and grasp design, so that an unexpected power loss will not cause the sample to drop. The hand senses the absence of a sample when the hand fully closes and a sample is supposed to be present. This condition is treated as a fault condition by the software and results in a safe system shut down.

  • Operating Modes

    The system has three operating modes: Master, Slave, and Local. Slave mode is the most typical the whole sample changer is controlled as a peripheral device with high level commands such as load#1, loadnext, reset, unload. Control of the spectral acquisition is through the MCA’s native script/batch/job language. Responsibility for defining the sample queue and taking control of the MCA system rest with a Changer Lab Windows program that runs on the MCA computer system. In the Master mode the Assistant's software is in control of the sample queue and runs the MCA system through MCA batch commands. Local control allows the user to control all axis movements with easily accessible switches for set up without a computer.

  • Sample Wall

    With a significant number of samples loaded into a changer tray there is always the possibility of a hot sample interfering with the background of a low level sample. This may require more shielding between the samples in the tray and the sample in the counting position than is required in the counting shield in general. In this situation the system can be supplied with an additional shield wall between the sample tray and the counting shield.

  • Detector Accomidations

    The system can be configured for either NaI (Tl) or Germanium detector systems. Any standard detector cryostat can be accommodated. Vertical dipstick Germanium detectors have the dewar located underneath the shield inside the system cabinet, while horizontal dipsticks can have the end cap penetrate the shield side wall. An "in-line" type cryostat simplifies the installation and removal of the detector. Well detectors do not represent any special problems as long as the container is longer than the well depth so that there is a place for the hand to grab the sample.
    Using two detectors at the same time is possible, as is a split spectrum with low energy and high energy spectra accumulated simultaneously from a single detector

ALTERNATE CONFIGURATIONS

Since every facility is different and has their own needs, there can be a need to customize a system. The nice part about the Changer Lab's design is that it can be easily modified to accommodate your special needs. Check out some of our alternate configurations below.
  • Dual tray "wide" configuration - 200 samples (20 mL LSC vials) with full 4" shield, auto lid, and an extra wall. Advantages: Maximum sample capacity, near 4pi shielding, NaI or Ge detectors on the end cap or in a well.
  • Dual tray "wide" configuration - 200 samples 20 mL LSC vials) with full 4" shield and an extra wall. This system does NOT have the automatic lid as it is used for production NAA work that implements the automatic pull back feature to limit detector dead time. If the sample activity is sufficient that dead time is a issue the extra shielding provided by closing the lid is not necessary. Advantages: Maximum sample capacity, faster cycle time for load/unload operations configuration.
  • Single tray configuration - 100 samples (20 mL LSC vials) 6 leg system, with full 4" shield, auto lid, and an extra wall. Advantages: Near 4 pi shielding, NaI or Ge detectors on the end cap or in a well.
  • Single tray - 100 sample (20 mL LSC vial), 4 leg system with small round shield. This system is NaI but the frame would easily accommodate a vertical Germanium dewar with LN2 or mechanical cooling. Advantages: Space, weight, cost. NaI or Ge detectors on the end cap or in a well.
  • Single tray - 64 sample (50 mL centrifuge tube), 4 leg system with square shield and auto-lid. This system is Ge but the frame would easily accommodate a NaI.
  • Desktop system for a side well NaI and minimal shielding Advantages: Cost, space, and easy to add more shielding.
  • Highly customized machine designed to insert known isotope samples with significant activity into a very deep (~10 inches). A re-entrant ion chamber for activity determination. The automation of this measurement saves labor time, dose due to handling and simplifies time delayed recounts.