Background Geiger counter/spectrometry

Background Geiger counter/spectrometry

  • iMetry is extreme sensitive device, that requires special attention for temperature during radiation measurement.
  • When you perform measurement, to avoid temperature drift and humidity drift, keep 25 degrees Celsius room temperature, steady low humidity, no direct sunlight,so far as possible. In other words, iMetry is basically temperature compensated system, but is vulnerable to temperature, especially during the temperature change, compensation circuit cannot keep track of it, by the temperature slope. So, before and during the measurement, try to keep the temperature as stable as possible.
  • Even with care, there is still inevitable drift with temperature, humidity, and time, so power-ON aging in constant temperature, following re-calibration, and measurement after follow-up observation might be effective.
  • To avoid non-linearity effect of iMetry, you may need to calibrate based on the targeted dose and background, not using attached simplified parameters.
  • When you measure background, please avoid walking around and surrounding iMetry, operator also should keep distance to get stable resuts, as radiation from K40 contained in a human body and shielding effect of a human body is not negligible.
  • Dose may be affected if something shields radiation, such as lead and car battery is around.
  • A possible element to raise the background radiation level is marble. Building which uses much marble may show background radiation over 0.1μSv/h higher than normal environment, so please be noted.

Background spectrometry

  • iMetry can continuously identify spectrum peaks derived from radioactive substances even in environmental background radiation (0.05μSv/h level).
  • Even in 0.01μSv/h level, iMetry may detect tiny spectrum peaks derived from radioactive substances with long measurement over 8 hours.
  • Before you measure your sample, you have to check and understand the background spectrum of the place of use with long enough (8hours, 24hours etc.) measurement.
    • To check the observed radiation is derived from Cs134/137, calibrate iMetry with Cs137 and Ba133, then if you observe a peak a bit higher than 600keV and lower than 661keV of Cs137, this can be basically identified. See also diagnosis, for strict measurement, please use precision measuring instrument.
  • Background radiation and radiation from floating dust must be distinguished, background environmental radiation is derived from radioactive substances attached to ground or buildings, radiation from floating dust, (nearby beta ray and gamma ray source), and cosmic gamma rays.

Control measurement

  • Even when you detect the spectrum of radioactive material from a sample, you have to remove the sample and take as long time as the measurement to perform background measurement, and make sure you did not false detect radiation from background.
    • In this case, be noted that the sample itself has shielding effect of the background radiation.
    • Thus, to perform more rigorous measurement, it is desirable to prepare a control sample (same amount of sample not including radioactive substances) and take the same time to perform background measurement.

Detection of a small amount of radioactive cesium

  • For detection of a small amount of Cs134/137, as entry being a spectrometer works fine in a low dose environment, it is more certain to measure in 5cm lead block shielding box, take some time, and identify with spectrum peaks around 600keV and 800keV than just identifying with a 3σ difference of radiation dose.
  • In a concrete room, peak around 600keV derived from Radon is easily observed, be careful not to mistake it to peak from Cesium.

  • 最終更新:2013-06-17 11:28:56