Use of an Infrared Spectroscopic Method for Isotopic Analysis …
187
where: L is the physical cavity length (here = 100 mm), D is the beam displacement
within the cell (here = 18 mm), and N p is the number of passes through the cell (here
= 19). Other useful values are:
Cell Pathlength =
L ∗ N p
/cos(α)
(3)
Micro−mirror separation, MMS = 2D/N p
(4)
Micro−mirror distance from window center,
D k = (2k − 1) ∗ D/ N p − D/2
k|k = 1, 2, . . .
N p − 1
/2
(5)
The first and second micro-mirror windows are identical but oriented so the k =
1 mirror is the first reflector for window #2 and the k = (N p -1)/2 mirror is the first
reflector for window #1. The intensity of the sample beam exiting the sample cell is
measured by focusing the light onto a second mercury cadmium telluride detector
after passing through a 1 mm diameter aperture.
The cell has three welded gas ports (1/4
VCR, SwageLok). Two ports are available for connection to a gas manifold using convoluted metal tubing (CT Series,
SwageLok) and one port is connected to a pressure sensor (PX409-015AUSBH,
Omega). All plumbing connections and tubing are 304/316SS Swagelok VCR
fittings, and all o-ring seals are Kalrez for material compatibility with uranium
hexafluoride.
Uranium hexafluoride (UF 6 ) is a high vapor pressure solid at room temperature.
UF 6 vapor pressure near standard temperature and pressure can be estimated by the
equation:
VP UF6 ∼ 10
(10.7432−2593.48/T )
(6)
where: VP UF6 is the equilibrium vapor pressure (in mmHg) of UF 6 , and T is the
temperature in Kelvin [11].
At room temperature (293.15°K), the vapor pressure of UF 6 is approximately
79 torr. UF 6 is reactive in moist air, forming hydrofluoric acid (HF) and uranyl
fluoride (UO 2 F 2 ). Because of the radioactive nature of uranium and the chemical
hazards associated with hydrofluoric acid, UF 6 should be well contained to prevent
hydrolysis or radioactive material release. The described cell was designed with
materials unreactive to UF 6 and vacuum-sealed to prevent unintentional release.
The sample introduction system is designed to limit the total amount of UF 6 to
less than 25 mL (~6 mL in multipass cell) per sample of gas. A cold trap is available
as part of the gas manifold to allow for UF 6 purification by fractional sublimation.
Sample is introduced into the system by first closing P-10 valve-4 and evacuating
the cell, cold trap, and sample loop. When vacuum is achieved (<0.01 torr), the
sample loop is isolated by closing valves 1, 2, 3 and 5, then allowing UF 6 vapor
to fill the loop by opening valve 4. When there is sufficient pressure in the sample
187
where: L is the physical cavity length (here = 100 mm), D is the beam displacement
within the cell (here = 18 mm), and N p is the number of passes through the cell (here
= 19). Other useful values are:
Cell Pathlength =
L ∗ N p
/cos(α)
(3)
Micro−mirror separation, MMS = 2D/N p
(4)
Micro−mirror distance from window center,
D k = (2k − 1) ∗ D/ N p − D/2
k|k = 1, 2, . . .
N p − 1
/2
(5)
The first and second micro-mirror windows are identical but oriented so the k =
1 mirror is the first reflector for window #2 and the k = (N p -1)/2 mirror is the first
reflector for window #1. The intensity of the sample beam exiting the sample cell is
measured by focusing the light onto a second mercury cadmium telluride detector
after passing through a 1 mm diameter aperture.
The cell has three welded gas ports (1/4
VCR, SwageLok). Two ports are available for connection to a gas manifold using convoluted metal tubing (CT Series,
SwageLok) and one port is connected to a pressure sensor (PX409-015AUSBH,
Omega). All plumbing connections and tubing are 304/316SS Swagelok VCR
fittings, and all o-ring seals are Kalrez for material compatibility with uranium
hexafluoride.
Uranium hexafluoride (UF 6 ) is a high vapor pressure solid at room temperature.
UF 6 vapor pressure near standard temperature and pressure can be estimated by the
equation:
VP UF6 ∼ 10
(10.7432−2593.48/T )
(6)
where: VP UF6 is the equilibrium vapor pressure (in mmHg) of UF 6 , and T is the
temperature in Kelvin [11].
At room temperature (293.15°K), the vapor pressure of UF 6 is approximately
79 torr. UF 6 is reactive in moist air, forming hydrofluoric acid (HF) and uranyl
fluoride (UO 2 F 2 ). Because of the radioactive nature of uranium and the chemical
hazards associated with hydrofluoric acid, UF 6 should be well contained to prevent
hydrolysis or radioactive material release. The described cell was designed with
materials unreactive to UF 6 and vacuum-sealed to prevent unintentional release.
The sample introduction system is designed to limit the total amount of UF 6 to
less than 25 mL (~6 mL in multipass cell) per sample of gas. A cold trap is available
as part of the gas manifold to allow for UF 6 purification by fractional sublimation.
Sample is introduced into the system by first closing P-10 valve-4 and evacuating
the cell, cold trap, and sample loop. When vacuum is achieved (<0.01 torr), the
sample loop is isolated by closing valves 1, 2, 3 and 5, then allowing UF 6 vapor
to fill the loop by opening valve 4. When there is sufficient pressure in the sample