Counting systems with gas flow proportional detectors have some means of detecting the presence of P-10 counting gas. An adequate supply of P-10 is critical for proper operation of the detector, so the means of detecting the gas supply failures must be well thought out. Protean Instrument Corporation's Gas-PRO is the only fail-safe method in the industry. Only Gas-PRO protects you from under-reporting counting results.
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The problem: systems from other manufacturers
use a gas pressure sensor. P-10 flow can be blocked at any point
beyond the pressure sensor and the fault will not be detected.
More often, the detector window can be broken and the fault not
detected. The method of gas flow control does not matter. The
flow controller can be a manual flow meter or a digital gas conservation
system. Any of these systems will allow samples to be counted
even if there is a critical failure in the gas path!. Gas conservation systems do not halt
counting when there is a failure in the gas path!
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Is this really important? Yes!. Gas system
failures lead immediately to false negative results for alpha
counting. These graphs show the effect of a gas starved detector.
Within minutes alpha efficiency drops, beta efficiency increases
slightly, then drops. Unless check sources are run frequently,
you have no indication that the system has failed. Based on system calibrations, alpha activity
will be severely under reported as false negatives. |
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Every Protean system with a gas flow detector has Gas-PRO as a standard feature. Gas-PRO monitors the true P-10 flow rate through the entire system. ANY failure will be detected, and sample counting halted until the failure is corrected.Protean delivers FAIL-SAFE counting! |
What quality P-10 counting gas should be used?
Protean systems are built and tested using industrial grade P-10. We have found no performance advantage if high purity, ultrahigh purity, or research grade gas is used. This is a significant difference compared to other systems which require higher grades, since those grades are significantly more expensive and can be more difficult to obtain.
One potential problem with any P-10 supply is the presence of contamination. If you have confirmed that a tank of P-10 gas is contaminated, then try another tank first. If one is not immediately available then obtain one from a different supplier. We generally recommend trying a different supplier before trying a higher purity level.
How long will a tank of P-10 last?
Tank life depends on the usage pattern of the system. Worst case life for a standard 1A (220 cubic feet) tank on a system using an ultra-thin window is greater than 70 days. For a windowless detector system it is about 30 days. Worst case means the gas is left turned on and flowing at the factory set flow rate for 24 hours per day, 7 days per week. In practice tank life will exceed worst case by a considerable amount.
Gas flow detectors operate best with a continuous supply of P-10. If the supply is turned off, then atmospheric contamination can occur. It can be flushed out and the detector purged, but purging both a sample and guard detector can take several hours to complete. We recommend that if a Protean system is to be idle for some time then the secondary valve on the gas regulator be turned to nearly off. As long as the mechanical gas flow gauge on the instrument is showing any flow at all there is enough to keep the detector purged.
