July 29, 2016
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Xenon Xe 133 Gas

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Xenon Xe 133 Gas

XENON Xe 133 Gas

For Diagnostic Use

DRUG DESCRIPTION

XENON Xe 133 Gas is supplied in a mixture of xenon gas (5%) in carbon dioxide (95%). It is contained within septum sealed glass vials and is suitable for inhalation in the diagnostic evaluation of pulmonary function and imaging, as well as assessment of cerebral blood flow. Xenon Xe 133 Gas is reactorproduced as a by-product of Uranium U235 fission. Each vial contains the labeled amount of Xenon Xe 133 radioactivity at the time of calibration. The contents of the vial are in gaseous form, contain no preservatives, and are ready for use.

Xenon Xe 133 is chemically and physiologically related to elemental Xenon, a non-radioactive monoatomic gas which is physiologically inert except for anesthetic properties at high doses.

Physical Characteristics

Xenon Xe 133 decays by beta and gamma emissions with a half-life of 5.245 days1. Significant radiations which are emitted by the nuclide are listed in Table 1.

Table 1: Principal Radiation Emis s ion Data from Xenon-133

Radiation Mean Energy (KeV) Mean % per Disintegration
Beta-2 100.6 99.3
Ce-K-2 45.0 53.3
Ce-L-2 75.3 8.1
Ce-M-2 79.8 1.7
Gamma-2 81.0 36.5
Kα2X-ray 30.6 13.6
Kα1X-ray 31.0 25.3
KβX-ray 35.0 9.1

External Radiation

The specific gamma ray constant for Xenon Xe 133 is 3.6 microcoulombs/Kg-MBq-hr (0.51R/hr-mCi) at 1 cm. The first half value thickness of lead is 0.0035 cm. A range of values for the relative attenuation of the radiation emitted by this radionuclide that results from the interposition of various thicknesses of Pb is shown in Table 2. For example, the use of 0.20 cm of Pb will decrease the external radiation exposure by a factor of 1,000.

Table 2: Radiation Attenuation by Lead Shielding

cm of Pb Radiation Attenuation Factor
0.0035 0.5
0.037 10-1
0.12 10-2
0.20 10-3
0.29 10-4

To correct for physical decay of this radionuclide, the fractions that remain at selected time intervals after the time of calibration are shown in Table 3.

Table 3: Xenon Xe 133 Phys ical Decay Chart (Half Life 5.245 days )

Day Fraction Remaining Day Fraction Remaining
0* 1.000 8 .349
1 .877 9 .302
2 .768 10 .268
3 .674 11 .235
4 .591 12 .206
5 .518 13 .181
6 .452 14 .157
7 .398
* Calibration Day

REFERENCES

1 Kocher, David C., “Radioactive Decay Data Tables,” DOE/TIC-11026, p. 138,1981.

Last reviewed on RxList: 4/4/2016
This monograph has been modified to include the generic and brand name in many instances.

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