Full fledged shielded box for Geiger Counter

Lead shielding box with 5cm thickness lead blocks


5cm thickness lead blocks are suitable for very good low radiation environment. Cs137 spectrum from outside can be dropped to 1/100 level. Still, as lead itself emits some gamma ray derived mainly from Pb212, and characteristic X-ray is emitted when gamma ray hits lead, it won't drop to zero.
By blocking characteristic X-ray with 1mm copper inner shielding, radiation can slightly be dropped. (No need to do this if you are to just detect radioactive cesium spectrum)

    • With 5cm thickness lead blocks and pulse detection threshold 100, 0.0023μSv/h level environment can be achieved.
    • If you add 1mm thickness copper inner shielding to the 5cm blocks, 0.0017μSv/h level environment can be achieved.

For minimizing the cost,
    • 5cmx10cmx10cm lead block * 2
    • 5cmx10cmx20cm lead block * 6

Prepare and build them up to get shielding space with 1L capacity. These blocks may weigh up to 80kg.
iMetry take some space, but with a ziplock, you may still push 1L content in the space, more than enough for DIY basic measurement.
If you are building 2L space, you may need 10 lead blocks in 5cmx10cmx20cm, the total weight will be 114kg.

50mm鉛箱.png

You may need to contact by FAX or Email, but Sanko-Metal is recommended for providing high quality lead blocks quite cheaper than those who present prices on the internet. Price of lead is always changing by factors like Chinese construction industry, up to the quotation. In our case, took around 40000 yen including shipment.
This full fledged shielding environment costs a bit more than simplified one, but it's rather easier to build as it consists of blocks not plates, and yet performs much better, so highly recommended. Please also note that lead is generally recycled, such generally available lead is relatively cheaper, but not designed for strict radiation shielding. When you get lead blocks, first check if they have high radiation points, with iMetry Moving Average Window set to 1 minute. (There won't be any problem in most cases, but also for practice of iMetry handling. iMetry can be used for such basic survey purpose. Don't forget to wear gloves and put iMetry in a plastic bag.)


Before you build up the shielding box, carve a V shaped groove for cables with a carving knife. This should be V shaped, to block radiation coming through the groove. Groove might be V shaped carved with a carving knife. Each block is accurately machined, so it is desirable to build them against each other tightly without gaps. Except ones touching other blocks, better cover surfaces with packing tape and use gloves when handling to avoid direct touch to lead.

V字溝.jpg

Check pulses in very low radiation environment with simplified oscilloscope function accessed from Pulse Detection Parameter menu.

When operated in 50mm lead + 1mm copper shielding and pulse detection threshold=100, iMetry detects pulses around 7cpm. You can check pulses in very low radiation environment with simplified oscilloscope function accessed from Pulse Detection Parameter menu. You may observe relatively high energy pulses.
In 50mm lead block shielding, environmental radiation in low energy area is blocked to 1/1000 level, remaining pulses in low energy area might be derived from characteristic X-ray and stochastic overlap of many noise pulses derived from semiconductor noise, but most of the 7cpm pulses are high energy pulses.

The example of measurement when 50mm lead + 1mmcopper shielding, pulse detection threshold=100

5mmleadbox_with_copperBG.PNG

  • 最終更新:2013-06-18 15:49:39

このWIKIを編集するにはパスワード入力が必要です

認証パスワード