32-Basic Radiation Detection: Detector lab 1


Well, howdy! We’ve now finished with the theory, and
we are now going to show you how the instrumentation works today. We’re going to start off with gas-filled
detectors, just like we started off in our lectures, and the first thing we’re going
to do—the first thing we’re going to play with—is the Geiger counter here. You can have them all hooked up with NIM-BINs,
like you see here, but this one is your basic hand-held Geiger counter, and it seems that
there is radiation in the room. Well, gosh, since we’re here to study uranium,
I have brought a source for us. This is Fiesta ware, and the nice orange color
that you see there actually comes from uranium, and, to give you an idea of how radioactive
it is, on a times 1 scale, I can make this go off-scale. Well, that sounds pretty scary, and, actually
I must be a brave man to sit here next to this radioactive plate, but, just between
you and me, your grandmother probably ate breakfast off plates like this, and they managed
to live a long and useful life, most of them. So, this is our second gas-filled instrument,
and this is an ion chamber. Inside here is a cylindrical chamber. It measures alpha, beta, gamma, and it has
readings in microR. Right now the radiation field is about 1microR,
or 1-5 microR per hour. And, if I set it on the plate, oh my gosh,
we’re up to 13-14-15 microR per hour. This gives you an idea of how sensitive the
Geiger counter is, that what is a small, small fraction of your annual dose that you get
from background radiation drives Geiger counters completely off-scale. The next gas-filled detector we are going
to talk about are BF3 tubes, and this unassuming tube right here is a boron trifluoride neutron
detector, as we talked about in class. This one is older than dirt; it was actually
calibrated in 1978, which I’m sure is older than most of you here. And, using this, we get a look at the other
parts of a NIM-BIN. The important parts are that we will hook
this to the pre-amplifier, which feeds the high voltage through it to the detector, does
shaping and uh. Okay, and so this detector is hooked up to
the preamp, and the preamp does a couple of things. You feed the high voltage through it to the
detector, and it provides shaping of the signal that comes back out and impedance matching,
so you get maximum signal returned along the cable. It’s fed into the amplifier, which is like
the volume control on your stereo. I can make the pulses larger or smaller, and
then from there we will feed it to the computer that acts as our MCA. Along the way, we have our friend the oscilloscope,
so that we can look at the pulses and debug what’s going wrong, because something will
always go wrong. So, let me hook up the source… let me go
hook up the detector, bring in the source, and we’ll go from there.

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