If you are experiencing any problems with your scintillation detector, even if we didn’t manufacture it, don’t hesitate to contact us by email or by phone. We are eager to help you get your system back up and running. Even if we did not manufacture the detector, we offer a free evaluation service for most scintillation detectors. After the evaluation, we will provide a diagnosis of the problem and a quote to repair the detector. Here’s a table that shows some of the common symptoms, probable diagnosis and recommended solution for each problem. Another source of good information is our PDF library.
Basic Test Set Up
The basic set up for spectroscopy counting is shown in this figure.
This is the same set up that we use in our Final QC Test station. ASI uses state-of-the-art nuclear counting equipment to perform the final testing before each detector is shipped.
We use the following equipment:
- High Voltage: Ortec 556 High Voltage Power Supply
- Photomultiplier (if required): ASI in-house standard, size varies
- Voltage Divider (if required): ASI POB-14
- Pre Amp: Ortec Model 113 Pre Amplifier Linear Amp: Ortec 671
- Linear Amplifier MCA: Hardware-Ortec-Ametek Easy
- MCA. Software-Ortec Maestro.
ASI Final Quality Control Test Equipment Set Up
Scintillation Detector Troubleshooting Guide
The information provided here can be used to help in isolating any problem that you are observing with your detector. Diagnosing a problem with an open face or demountable detectors is sometimes easier because the detector can be inspected visually. When you return a detector to us for an evaluation, we perform both an electric test and a visual inspection. Sometimes we will need to disassemble the detector to complete the evaluation. We will ask for permission, before we begin disassembly.
Do not hesitate to contact us at any time if you would like us to assist by email or telephone. Also, please refer to our Evaluation and Repair Service information page for any units that need to be returned for service.
| FAULT | POSSIBLE CAUSES | CORRECTIVE ACTION |
| Poor Energy Resolution – Measured energy resolution does not agree with ASI Final QC TEST Data Sheet | Detector damaged during shipment. | If this is a new detector and it appears that some damage may have occurred during shipping, be sure to save all the packaging materials. Take photos and be prepared to file a claim with the carrier. |
| Demountable Detector: Poor optical coupling (e.g. voids) between the PMT and the optical window. (See example below.) | Remove the PMT and re-interface with a high-grade optical coupling grease. | |
| Open face type: poor optical coupling between optical window and crystal. (See example below.) | Return to ASI for evaluation and repair. | |
| Integral type: poor optical coupling between optical window and crystal. (See example below.) | Return to ASI for evaluation and repair. | |
| Hydrated crystal (yellow spots on the surface of the crystal). (See example below.) | Return to ASI for evaluation and repair. | |
| Poor ground. | Be sure that the detector housing and all other components in the system have good continuity. | |
| Drifting PMT/system drift. | Provide power to the detector for at least one hour then re-evaluate. Be sure that the system is operating properly. | |
| Defective PMT or improper operating voltage. | Confirm proper operating voltage. Replace PMT or return to ASI for evaluation and repair. | |
| Light leak – excessive count rate at low energies. | Confirm that the leak can be repaired by covering the leak with black tape or black felt. Contact ASI for more instructions. | |
| Pulse shape decay time constant set improperly for the crystal material. | Use the proper integrating shape time constant. | |
| “Double peak” | Fractured crystal. (See example below.) | Return to ASI for evaluation and crystal replacement. |
| No Signal | PMT failure | Return to ASI for evaluation and repair. |
| Check cables and other system components. | Repair or replace as necessary. | |
| Count Rate Too Low. | Excessive dead time. | Determine cause of excessive dead time (light leak, LLD setting, source positioning, etc.) and correct as necessary. |
| Verify source strength. | Correct as necessary. | |
| Crystal too small for energy of interest. | Contact ASI to review the problem. | |
| Excessive materials between the source and detector. | Remove materials to improve counting efficiency. | |
| Count Rate Too High. | Light leak. | See above. |
| LLD setting too low. | Correct as necessary. | |
| Excessive background. | Move detector to another location or shield as necessary. | |
| Signal Pulse Height Drift | Poor ground. | Be sure that the detector housing and all other components in the system have good continuity. |
| Drifting PMT/system drift. | Provide power to the detector for at least one hour then re-evaluate. Be sure that the system is operating properly. | |
| Defective PMT. | Replace PMT or return to ASI for evaluation and repair. | |
| Bent pin on base | Return to ASI for evaluation and repair. | |
| Unexplained Peaks in the Spectrum | Electronic system noise. | Isolate cause and repair as necessary. |
| Environmental background | Building materials, surrounding materials can all contribute to background in the spectrum. Shield as necessary. |
Detector Maintenance
These guidelines are provided to ensure that your scintillation detector provides many years of excellent performance. These recommendations apply to all detectors but are especially important for detectors that are designed to be used under normal laboratory conditions.
The most important advice is: Be sure to handle the detector carefully. Significant mechanical impacts that leave a dent in the housing will likely cause a fracture in the crystal material. Do not expose the detector to unnecessary vibration or rapid temperature change. Please be sure to read the ASI Limited Warranty Statement for more specific details.
When you receive a detector be sure to wait at least 24 hours in order to allow the detector to come into thermal equilibrium with the lab environment. Opening the package to soon will risk fracturing the crystal.
It is acceptable to clean the detector metal surfaces with a damp cloth. However, be careful that you do not remove the ASI label, it contains valuable information.
If it appears that the detector pins have collected dust that is difficult to remove with a light brush, it is acceptable to use a small paint brush with alcohol to brush the pins.
Opening Detector Shipments
When you receive a detector be sure to wait at least 24 hours in order to allow the detector to come into thermal equilibrium with the lab environment. Opening the package to soon will risk fracturing the crystal.