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[Phys-L] Re: Survey Meters

Still do.

Because of its much greater electron density an iodide is more sens to
gamma rays. If it's "window is thin it may also be used for X-rays and
betas, not from tritium tho!

Because most betas have a high cross section with the normal filling gas
they are about as efficient as an iodide is for gammas. If an alpha
gets in, its efficiency is ~ 100%.

I'm rather certain student scalars are still sold w/ both G-M and xtal
detectors.
All one must do is adj. the HV appropriately (after plugging in).



Yes, I think stand alones are no longer mfg'd. [Canberra and Tracor
Northern most popular.] E, G, & G gobbled up Ortek that made the pro
ones (PCI slot?) . Some info from a quick search:

bc, who has a Tracor Northern stand alone (in Tek. bin.) and a microAce.


http://www.amptek.com/gamma8k.html


Ludwik Kowalski wrote:

Old GM counters, even those designed for beta rays, often had thin
enough windows to detect alpha particles. The NaI mounted on the PMT is
for gamma rays. The NaI crystal, the PMT and its power supply (usually
not portable) are likely to be much more expensive than a GM tube and
its simple battery-operated HV unit (as in yellow civil defense
dosimeters).
Ludwik Kowalski
Let the perfect not be the enemy of the good.

On Oct 17, 2005, at 9:52 PM, Brian Whatcott wrote:



Thanks for the check on unit comparisons.
In browsing for meter schematics, I noticed that an iodide scintillator
into a PMT seems to be the preferred way of achieving a sensitive
detector.
And I was piqued to notice a nuclear spectrum analyzer. Not quite sure
of its
operational modus: pulse height binning?

Brian W

At 12:30 PM 10/17/2005, you wrote:


If FS (Plessey) most sensitive scale is one cGy/hr then my calc.
result
is the old analog would be 500 times more sensitive. Like photometry
a
proliferation of unites makes conversion difficult.

cGy ~= cSv one Sv = 100 rem [is r on meter rem or rads?]


note air dose ~= 0.7 tissue.

so (if no error) no surprise.

bc


Brian Whatcott wrote:


Remembering that several years ago, I sampled the decay of
radio active dist wiped from the terminal screen
(a thread of Luwik's as I recall) I bought a Plessey PDRM 82
survey meter as a replacement for the Victoreen OCD: CDV-700

The Victoreen was a yellow tin box with an analog meter,
an earphone and a tube on a lead. It had a check source stuck
on the side of the can.
The Plessey is an orange high impact plastic case with a
digital display.
The Victoreen was scaled 0.5mr/hr and 300 counts/min
with a X100 X10 X1 sensitivity switch.

The Plessey scale is marked cGy/h (IN AIR) - and it turns out,
the sensitivity is way lower than the Victoreen, so I don't get
a reading from screen dust. Pity - it looks SO cool!


Brian Whatcott Altus OK Eureka!