Bubble Detector Wanted

[Emma Black]

Does anybody know where I can get hold of some bubble detectors? I would like to experiment with some, but the two quotes I got from UK suppliers were crazy prices for just two. Thanks in advance.

[Richard Hull]

A crazy price of $400 U.S. for two is the norm now. BTI is not looking to sell to private individuals. They want to sell 30 or more to companies and 100 or more to government institutions. As they do not last long, (~6month to a year), they get to sell the same thing over and over again. They are nice, (were nice at $200 for 2 in 1999), but at $400 plus, with a minimum order for 2, they are out of the amateur's range for something that will go in the dustbin within 1 year.

Beware of buying one used as they will not work after their first birthday.

Richard Hull

[Emma Black]

Thanks Richard I knew they had a very short shelf life $100/150 for one would be fine however, I was quoted £495 plus tax each! and that was though a company email.

[Richard Hull]

Wow! that's $608.00 for one bubble dosimeter at the current exchange rate. I see what you mean about outrageous prices.

Richard Hull

[Matt_Gibson]

To me, that’s just unreasonable…

If it helps, I have the same Ludlum that you’re using and did a number of runs with a bubble detector. I found that my Ludlum reads (most of the time) needed to be multiplied by 7.5 if they were to agree with the bubble detector.

So if the Ludlum suggested a TIER of 500,000n/s, the bubble detector was suggesting 7.5 times that.

-Matt

[Richard Hull]

That clearly means on of two things.

1. the bubble dosimeter or the Ludlum are way off course.
2. The calc's in reducing the BTI to TEIR suffered some flaw in the chain of mathematical machinations.

Some critical work needs to be the arbiter. 7.5X error is approaching an order of magnitude. No sigma from any measurement to be found here.

Richard Hull

[Matt_Gibson]

Here is what I used for my bubble detector calculations:
https://www.gammaspectacular.com/fusion_calculator.html

[Richard Hull]

I plugged in some of my older values when I had my two BTI 33bub/mrem dosimeters two years apart and both my calcs and this nice little program were in agreement. So the point #2 is settled. No no errors in calculations.

It now falls back on the BTI and the Ludlum.

Richard Hull

[Richard Hull]

It is sad that all this data will be erased in very short order, disappearing forever.

Richard Hull

[Matt_Gibson]

I’d guess the Ludlum “hammer” that some of us are using isn’t as good at detecting fast neutrons, therefore reading much lower than the bubble detector? I’m pretty sure a few others (Finn Hammer for example) provided some similar results, or I might have just interpreted them wrong.

What is happening with the data being erased? We’re not losing the site again, are we?

-Matt

[Liam David]

Other than encouraging everyone to move this discussion to the Ludlum thread (viewtopic.php?t=14298), I'd like to point out that it's really important to have this detector in the far-field when making measurements and calculating n/s. I don't recall who has their detector where, but even with an assumed point source of neutrons, you can't put the hammer right next to the chamber and expect good results. The fusor isn't a point source which makes this even worse. I'd have to check the manual again and do the math, but the hammer might be calibrated assuming an isotropic and homogenous neutron field, so there could be funky corrections like taking solid angles into account. Regardless, I'd encourage everyone to move their hammers away from the chamber, something like 5-10x the size of the hammer or chamber. It would be good for everyone to log their data in the Ludlum thread (and I'll add mine later this month) and perhaps we can figure out what's going on. My initial data indicated a 2x discrepancy between a bubble detector and the Ludlum, not 7.5x, but the fact either discrepancy is more than a few tens of percent is concerning.

[Richard Hull]

I have said this many, many times over the years. Pile on the data and key information in the for sale or wanted portions of the forums and they will be erased when the material is sold or the need met. If the material isn't sold or the need met within 60 days, the entire thread is erased. Read the rules.

These areas are not archival. All threads are vapor in are vapor in 60 days.

Richard Hull

[Emma Black]

Liam, your post is pretty much why I wanted the detectors in the first place. Was planning on adding to the Ludlum thread, with a proper post.

Not for here, but my data from the hammer also gets strange when the probe was closer, it seems to miss counts making me question things. Its response is not the same for fast and thermal neutrons (see graphs in the manual).