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Front View of the Assistant |
The “ Assistant”
- 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
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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. |
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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.
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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 ACCOMMODATIONS
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 |
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| APPLICATIONS Potential applications for the Changer
Lab's Assistant, Gamma Sample Changer: 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
- 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
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