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GM tubes demonstrate good energy response to X-rays - Gamma rays, but at the very low photon energy range between approximately 40 KEV to 100 KEV they typically demonstrate an increase in response, due to the Compton effect (at these low energies electrons are knocked from the gas in the tube as well as the metal wall of the tube). The smaller the tube, the more pronounced the increase in response to these low energy photons.
It so happens that Tin (Sn) metal selectively absorbs photons at these low energies. By surrounding the GM tube with a shield of specially machined Tin, one can provide a GM tube with flat response to photons (X-rays and Gamma rays) with energies from 50 KEV to 1.5 MEV +-15%. Below 50 KEV the Tin absorbs even more of the photons so a Tin shielded GM tube energy response drops very rapidly as the energy of the photon flux drops below 50 KEV. However, it is possible to provide a small "window" in the Tin shield which allows detection of 30 KEV to 50 KEV photons as well as the greater than 50 KEV photons.
Aware's line of Energy Compensated detectors include both "windowed" and "non- windowed" Tin shielded GM tubes. The other variable is the size of the GM tube. The smaller the size, the less sensitive the tube and therefore the better the tube is for measuring very high radiation levels. The sensitivity of the standard RM-60 is 18 CPS / milliR /hr. standardized to Cesium 137, that is it generates 18 counts per second when exposed to one milliR per hour gamma flux with energy of 660 KEV (Cesium 137 energy). With that response, the standard software can display maximum radiation levels of approx. 190,000 microR per hr. (190 milliR / hr.) Our RM-71632 Energy Compensated monitor generates 0.26 CPS / milliR / hr. This is 69 times less sensitive as compared to the RM-60 and therefore the standard software can display flux levels as high as 14 Roentgen per hr. (14,000 milliR / hr. or 14,000,000 microR / hr.)
Following is a list of Aware's line of Energy Compensated X-ray Gamma ray monitors:
RM-EC7 with low energy window in Tin shield:
(Energy Response: 40 kev to 1.5 mev +5% to -15%) (See graphs below)
(Flux Response: 7.9 CPS / milliR / hr.)
$289
RM-71416-W with low energy window in Tin shield:
(Energy Response: 30 kev to 1.5 mev +25% to -5%)
(Flux Response: 1.37 CPS / milliR / hr.)
$299
RM-7149 with Tin shield no window:
(Energy Response: 50 kev to 1.5 mev +- 15%)
(Flux Response: 1.37 CPS / milliR / hr.)
$299
RM-71611 with Tin shield no window:
(Energy Response: 50 kev to 1.5 mev +- 15%)
(Flux Response: 0.46 CPS / milliR / hr.)
$299
RM-71632 with Tin shield no window:
(Energy Response: 50 kev to 1.5 mev +- 15%)
(Flux Response: 0.26 CPS / milliR / hr.)
$299
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