Note when you perform radiation measurement

Note when you perform radiation measurement

  • iMetry is a measurement equipment capable of detecting very low radiation, so sensitive that a few things need to be noted to avoid mishandling. Precautions at official iMetry page has many of these precautions, each one of them are simple or obvious, but it is recommended to take a look.

Measurement of low amount radiation


Lead shield is needed for low amount radiation measurement

  • When you measure bulky sample with low amount of radioactive substances, please be noted that the observed dose may appear lower, due to the shielding effect of the sample itself.
  • When you measure low radiation sample, as the dose rate follows a Poisson distribution, you need to take long time and measure in a Full fledged radiation shielding box. When you perform a measurement of precise radiation dose, keep distance from human body to avoid shielding effect. And be careful not to walk around the system, during measurement. Also, when you perform measurement more than once, to keep the human body effect constant, operator should stay in a certain position or keep distance during measurement.
    • (Reference)In a environment with 0.0716μSv/h background radiation, when the system is surrounded by seven people with 1m distance, iMetry showed 0.0674μSv/h. This may be due to radiation shielding effect by human body. In that case, a person in 1m distance has approximately 0.0007μSv/h of radiation shielding effect.
  • If you block background radiation with 50mm thick lead plate and take certain time for measurement, this may rely on the environmental background radiation, in a environment for example 0.06μSv/h background radiation, this accuracy is relative, but in the 50mm lead box, it may be also possible to take out a significant figure for a relative comparison of three orders of magnitude after the decimal point.
    • These significant digits can be effectively used if you perform measurement repeatedly comparing with and without sample at the sampe place, environment, and the same time (Consider aging drift of the detector).
  • Unlike other survey meters, iMetry can detect spectrum even in low radiation dose with sufficient shielding, so better take time and check spectrum, than just relying on the 3σ dosage difference.

Pulse height analysis

  • Depending on the background dose, but at the time of 0.05μSv / h, in the lead-shielded environment, the spectrum of radiation by Cs134/137 much 0.0015μSv / h, if you take the time for about 24 hours, the background dose 600keV vicinity it is possible to detect the peak of.
  • From the limit of the scintillator performance of iMetry, you can not disassemble the peak of 661keV of Cs137 and 604keV of Cs134. In addition, in case of Cs134 and Cs137 mixture, you can screen Cs134 and Cs137 from 795.9keV peak of Cs134.
  • With the exception of cosmic rays, due to K40, one of marble from, or which of radon origin, I131, the stable after radiation that can be detected by simple spectrometry in the environment in general, Cs134 in the accident early in the polluted environment due to accident / synthetic spectrum of 137 is detected in general. Time and the fuel has been used, the mixing ratio of Cs134/137 will continue to change slowly in response to the elapsed time after the accident.
    • Other radioactive substances are hard to identify in the preparation is quite reality. Novice error look at the various spectrum. In most cases, and Kaminoyama, or mountain, of 800keV per be detected It is a pile of 1450keV vicinity of K40 than 600keV of Cs134/137.
    • In addition, you need to be careful if the mountain stands only 600keV, party may be possible that a look at the spectrum bismuth, of Bi214 609keV. Let's be careful.
      To the person who starts the radioactivity inspection now:5.View of the spectrum (In Japanese)
  • Please be careful not mistaken seen as characteristic spectrum of γ-ray, the Compton scattering. Using the example in the spectrum of test nuclides Cs137, in addition to the peak of the spectrum of 661keV, Compton edge by Compton scattering is seen at the bottom. Please be careful not mistaken seen as radiation spectrum due to various other this.
    compton.png

Upon radiation measuring very small amount, airplane mode is desirable

Aluminum shield has been made ​​in housing iMetry, but not want to be contacted during the measurement equipment that emits WiFi, and equipment that emits radio waves inside performing therefore the measurement of ultra-low energy. In addition, separation of a certain distance from the device that emits radio waves is required.

Verified diagnosis

  • There can also be a simple instrument only, calibration of the device is shifted to iMetry. If you suspect the spectrum can be seen, sensitivity even lower, you need to decide on the detailed analysis using specialized equipment obtained the spectrum sharper.

  • The definitive diagnosis of radionuclides, that misjudge the backscatter, There can determine the error due to calibration drift. There are also problems of resolution, it is not intended to either use larger the volume of the scintillator sensor, improved incidence efficiency using the Wave Guide to the measurement device using a (tl) scintillator CsI, nuclide definitive diagnosis of is difficult. In addition, the definitive diagnosis of species, further, or germanium semiconductor, definitive diagnosis by the device using a CdZnTe is also required.
  • On the other hand, in spectrometry using a semiconductor, GR-1 with the UK Cromek Inc., a CdZnTe is expensive instrument with Ge as not something very, high resolution is out, clear I will give a sharp spectrum.
    粉体並びに液体試料用現場型放射能測定器の開発(in Japanese)

Geiger Counter Energy Calibration

The iMetry, software does not correspond to the energy correction at this time. After calibrated with cesium in a simple way as a work-around, as 70%, the background dose to come out correctly, we are together by performing a simple energy correction.
Therefore In terms of cesium 137, iMetry is the be 30% underestimate the radiation dose at this time.
Is not a problem with the hardware, energy correction is a matter of software. To correspond to the energy correction, you do not need to Kaikaeru fatal hardware.
iMetry is intended simple screening, but will be addressed in future versions of the software iMetry (Official site)。

Energy correction, that the energy response characteristics of the scintillator of γ-ray, an error occurs because of characteristics of the scintillator radiation dose by the energy of the γ-ray dose measurements by detection efficiency of the count is changed by the energy of the γ-ray mainly it is said that (which can not be accurately corrected necessarily Compton scattering because the used radiation meter) roughly to correct the algorithm of the table or the like.

Surface contamination survey

It is necessary to work in a plastic bag etc., covering a sensor so that an iMetry detector may not be polluted on the occasion of a surface contamination inspection.

  • 最終更新:2013-05-21 15:03:10

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