CESIUM 111
4. CHEMICAL, PHYSICAL, and RADIOLOGICAL INFORMATION
4.1
CHEMICAL IDENTITY
Information regarding the chemical identity of cesium is located in Table 4-1.
4.2
PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES
Information regarding the physical and chemical properties of cesium is located in Table 4-2.
Cesium is a silvery white, soft, ductile metal with only one oxidation state (+1). At slightly above room
temperature, cesium exists in the liquid state. Compared to the other stable alkali metals, cesium has the
lowest boiling point and melting point, highest vapor pressure, highest density, and lowest ionization
potential. These properties make cesium far more reactive than the other members of the alkali metal
group. When exposed to air, cesium metal ignites, producing a reddish violet flame, and forms a mixture
of cesium oxides. Pure cesium reacts violently with water to form cesium hydroxide, the strongest base
known, as well as hydrogen gas. The burning cesium can ignite the liberated hydrogen gas and produce
an explosion. Cesium salts and most cesium compounds are generally very water soluble, with the
exception of cesium alkyl and aryl compounds, which have low water solubility.
There are several radioactive isotopes of cesium ranging from
114
Cs to
145
Cs (Helmers 1996). The
radioactive isotopes have a wide range of half-lives ranging from about 0.57 seconds (
114
Cs) to about
3x10
6
years (
135
Cs) (Helmers 1996). The radioactive isotopes
137
Cs and
134
Cs are significant fission
products because of their high fission yield, and their relatively long half-lives. The fission yield of
137
Cs
in nuclear reactions is relatively high; about 6 atoms of
137
Cs are produced per 100 fission events (WHO
1983).
137
Cs has a radioactive half-life of about 30 years and decays by beta decay either to stable
137
Ba
or a meta-stable form of barium (
137m
Ba). The meta-stable isotope (
137m
Ba) is rapidly converted to stable
137
Ba (half-life of about 2 minutes) accompanied by gamma ray emission whose energy is 0.662 MeV
(ICRP 1983). Figure 4-1 illustrates this decay scheme. The first beta decay mode that forms
137m
Ba
accounts for roughly 95% of the total intensity, while the second mode accounts for about 5% (WHO
1983). Radioactive
134
Cs primarily decays to stable
134
Ba by beta decay accompanied by gamma ray
emissions or less frequently to stable
134
Xe by electron capture (EC) accompanied by a single gamma ray
CESIUM 112
4. CHEMICAL, PHYSICAL, and RADIOLOGICAL INFORMATION
Table 4-1. Chemical Identity of Cesium and Compounds
Characteristic
Cesium
(metal)
Cesium
chloride
Cesium
carbonate
Cesium
hydroxide
Cesium
oxide
Cesium
nitrate
Synonym(s) Caesium Cesium
monochloride
Dicesium salt Cesium
hydrate
Registered trade
name(s)
No data No data No data No data No data No data
Chemical formula Cs CsCl Cs
2
CO
3
CsOH Cs
2
O CsNO
3
Chemical
structure
Cs
Cs Cl
Cs
+
O
O
O
Cs
+
Cs OH
O
CsCs
N
+
O
-O
-O
Cs
+
Identification
numbers:
CAS registry 7440-46-2 7647-17-8 534-17-8 21351-79-1 20281-00-9 7789-18-6
NIOSH RTECS FK9225000 FK9625000 FK9400000 FK9800000 No data
EPA hazardous
waste
No data No data No data No data No data No data
OHM/TADS No data No data No data No data No data No data
DOT/UN/NA/
IMCO shipping
No data No data No data No data No data No data
HSDB No data No data No data No data No data No data
NCI No data No data No data No data No data No data
CAS = Chemical Abstracts Services; DOT/UN/NA/IMCO = Department of Transportation/United Nations/North
America/International Maritime Dangerous Goods Code; EPA = Environmental Protection Agency;
HSDB = Hazardous Substances Data Bank; NCI = National Cancer Institute; NIOSH = National Institute for
Occupational Safety and Health; OHM/TADS = Oil and Hazardous Materials/Technical Assistance Data System;
RTECS = Registry of Toxic Effects of Chemical Substances
CESIUM 113
4. CHEMICAL, PHYSICAL, and RADIOLOGICAL INFORMATION
Table 4-2. Physical and Chemical Properties of Cesium and Compounds
Property
Cesium
(metal)
Cesium
chloride
Cesium
carbonate
Cesium
hydroxide
Cesium oxide
Cesium
nitrate
Molecular
weight
132.906 168.36 325.82 149.91 281.81 194.91
b
Color Silvery-white White White Colorless Golden-yellow White
b
Physical state Solid (liquid
slightly above
room
temperature)
Solid Solid Solid Solid Solid
b
Melting point 29 °C 646 °C 610 °C 272 °C 490 °C 414 °C
b
Boiling point 685 °C 1290 °C No data No data No data No Data
Density, g/cm
3
1.93 (20 °C)
b
3.988 (20 °C)
b
4.24 (20 °C)
b
3.68 (20 °C)
b
4.65 (20 °C)
b
3.66 (20 °C)
b
Odor No data No data No data No data No data No data
Odor threshold:
Water No data No data No data No data No data No data
Air No data No data No data No data No data No data
Solubility:
Water Reacts
violently with
water
1.87 kg/L
(20 °C)
2.1 kg/L 4 kg/L
(15 °C)
Very soluble in
water
b
Soluble
b
Organic-
solvent(s)
Soluble in
ethanol
b
Soluble in
ethanol and
ether
b
Soluble in
ethanol
b
Partition
coefficients:
Log K
ow
N/A N/A N/A N/A N/A N/A
Log K
oc
N/A N/A N/A N/A N/A N/A
Vapor pressure 0.0075 mmHg
at 144.5 °C
No data No data No data No data No data
Henry’s Law
constant
N/A N/A N/A N/A N/A N/A
Autoignition
temperature
No data No data No data No data No data
Flashpoint No data No data No data No data No data No data
Flammability
limits
No data No data No data No data No data No data
Conversion
factors
No data No data No data No data No data No data
Explosive limits No data No data No data No data No data No data
a
Data from Burt 1993 unless otherwise specified.
b
Lide 1998
N/A = not applicable
CESIUM 114
4. CHEMICAL, PHYSICAL, and RADIOLOGICAL INFORMATION
Figure 4-1. The Decay Scheme of
137
Cs
β = beta decay; γ= γ -ray emission
137
Cs
β
1
-
β
2
-
137
Ba (Stable)
γ
CESIUM 115
4. CHEMICAL, PHYSICAL, and RADIOLOGICAL INFORMATION
emission as depicted in Figure 4-2. The energy of the various gamma rays are in the range of 0.24–
1.4 MeV. The half-life average energy of the beta transitions and intensity of the transitions for both
134
Cs and
137
Cs are summarized in Table 4-3.
CESIUM 116
4. CHEMICAL, PHYSICAL, and RADIOLOGICAL INFORMATION
Table 4-3. Decay Properties of the Radioactive Isotopes of Cesium
Isotope Half-life (years) Decay mode Intensity percent Beta particle energy (MeV)
134
Cs 2.062 β
1
-
27 0.02309
β
2
-
2.5 0.1234
β
3
-
70 0.2101
137
Cs 30 β
1
-
94.6 0.1734
β
2
-
5.4 0.4246
a
ICRP 1983
b
The
134
Xe daughter yield from the electron capture decay of
134
Cs is approximately 3x10
-6
.
CESIUM 117
4. CHEMICAL, PHYSICAL, and RADIOLOGICAL INFORMATION
Figure 4-2. The Decay Scheme of
134
Cs
EC = electron capture; β = beta decay; γ = gamma-ray emission
134
Cs
β
1
-
β
2
-
β
3
-
EC
134
Ba (Stable)
134
Xe (Stable)
γ
1
γ
2
γ
3
γ
4
γ
5
γ
6
γ
7
γ
8
γ
10
γ
11
