| T O P I C R E V I E W |
| Zugstar |
Posted - 04/16/2022 : 18:19:53
I have a approx 13 cm diameter x 5cm deep vintage Fiestaware bowl (red). It is quite active. These are the measurements I made with a 600+ GC:
Bowl propped up almost vertical on its rim, facing the GC for maximum surface area exposure. I reset the GC for each measurement to avoid averaging carryover from prior measurement, and then a new average captured for about 5 minutes.
Data:
36CPM, .09 uSv/h, Distance about 3m away from bowl, away to the side...background reference.
450 CPM, 1.07 uSv/h, D=50cm (QC directly in front, tube facing the bowl)
1570 CPM, 3.65 uSv/h, D=25cm
24200 CPM, 57.8 uSv/h, D=0.5cm
20900 CPM, 49.8 uSv/h, D=0.5cm, Sheet of paper in front of QG
58 CPM, 0.144 uSv/h, D=0.7cm, 3mm thick plastic Sheet and 3mm thick aluminum sheet in front of QG
=>The testing reveals emission is principally Beta.
I wonder if folks suffered heath consequences from Fiestaware back when it was used as daily dishware?
=>The bowl is in pristine condition w/o any gouges or scratches in the glaze, so risk of shedding particulate matter into the air is negligible, but I'll definitely store the bowl in a metal case.
=>Is it safe to contact it directly with the fingers though to momentarily handle it? People, of course, handled the dishware frequently in the past, e.g. eating from it and then later washing it in the sink, etc. |
| 1 L A T E S T R E P L I E S (Newest First) |
| ullix |
Posted - 04/16/2022 : 23:51:46
You have well established that your Fiestaware is basically a beta-only emitter; with the plastic+alu sheets you are down to almost background.
For one thing this has the consequence that all uSv values are meaningless!
A conversion factor from dose-rate in in counts-per-time to dose-rate in uSv/h -- aka "calibration" or "Sensitivity" -- is valid ONLY for the setup used for establishing it!
Such a setup usually involves a well characterized pure-gamma emitter, like Cs-137, Co-60, or Ra-226 in a casing which prevents the emission of betas. To emphasize, it is PURE GAMMA!
To my knowledge, such an experiment has never been done for M4011 and J305 tubes - their calibration/sensitivity factors were taken from a bit of hand-waving - but for the LND7317 tube we have the manufacturers spec of:quote:
GAMMA SENSITIVITY CO60 (CPS/mR/HR) 58
which translates to 348 CPM/(uSv/h). For unknown reason GQ is using 379 CPM/(uSv/h) in the 600 counter. Why they claim the tube to be more sensitive than even the manufacturer says is their secret.
But anyway, this factor is established for a gamma(!) spectrum like that from Co-60. For the SBM20 tube two factors are given, one for Ra226 and one for Co60, and they differ by some 30%. This is a result of different gamma spectra, and the gamma-energy dependent sensitivity of a Geiger tube.
As your environment will never be like any of those setups, it is always the experimenter's INTERPRETATION of which factor is appropriate to use.
The only thing certain is that with beta emitters all those factors are invalid!
I tried to summarize these issues in the GeigerLog manual, chapter "Appendix G – Calibration".
Health concerns:
I don't think you are anywhere near a health problem. It begins by defining what a problem level is. See e.g. in the GL manual chapter "Occupational Radiation Limits". Why is there a more than 5 fold difference between US and Germany in the regulatory limits? If there were any real facts on the matter, such discrepancies would not happen.
And is there a problem at all with very low levels of radiation, or perhaps even an advantage? Google for LNT (Linear No Threshold) theories, for this is a much debated topic.
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