Cesium-135m

Properties and data of the isotope ¹³⁵Cs.

Content

General data

Name of the isotope:Cesium-135m; Cs-135mSymbol:¹³⁵Cs or 13555CsMass number A:135 (= number of nucleons)Atomic number Z:55 (= number of protons)Neutrons N:80Isotopic mass:134.9059772(11) u (atomic weight of Cesium-135m)
Excitation energy: 1632.9(15) keVNuclide mass:134.8758073 u (calculated nuclear mass without electrons)Mass excess:-87.58167 MeVMass defect:1.21759284 u (per nucleus)Nuclear binding energy:1134.1804249 MeV (per nucleus)
8.40133648 MeV (average binding energy per nucleon)Half-life:53(2) minDecay constant λ:0.00021797081149684 s^-1Specific activity α:9.795902464094 × 10⁺¹⁷ Bq g^-1
26475412.065121 Ci g^-1Spin and parity:
(nuclear angular momentum)19/2-Magnetic dipole moment:μ(μ_N) = + 2.18(1)Quadrupole moment Q:+0.89(7) barn (100 fm²)Nuclear g-factor:g_l = 0.22947368421053

Radioactive Decay

Half-life T_½ = 53(2) min (minutes) respectively 3.180 × 10³ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
Iso	¹³⁵Cs	100 %

Nuclear Isomers

Nuclear isomers or excited states with the activation energy in keV related to the ground state.

Nuclear Isomer	Excitation Energy	Half-life	Spin
¹³⁵Cs		2.3(3) × 10⁶ a	7/2+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 80) and isobaric (same nucleon number A = 135) with Cesium-135m. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 80	Isobar A = 135
44	¹²⁴Ru
45	¹²⁵Rh
46	¹²⁶Pd
47	¹²⁷Ag
48	¹²⁸Cd
49	¹²⁹In	¹³⁵In
50	¹³⁰Sn	¹³⁵Sn
51	¹³¹Sb	¹³⁵Sb
52	¹³²Te	¹³⁵Te
53	¹³³I	¹³⁵I
54	¹³⁴Xe	¹³⁵Xe
55	¹³⁵Cs	¹³⁵Cs
56	¹³⁶Ba	¹³⁵Ba
57	¹³⁷La	¹³⁵La
58	¹³⁸Ce	¹³⁵Ce
59	¹³⁹Pr	¹³⁵Pr
60	¹⁴⁰Nd	¹³⁵Nd
61	¹⁴¹Pm	¹³⁵Pm
62	¹⁴²Sm	¹³⁵Sm
63	¹⁴³Eu	¹³⁵Eu
64	¹⁴⁴Gd	¹³⁵Gd
65	¹⁴⁵Tb	¹³⁵Tb
66	¹⁴⁶Dy
67	¹⁴⁷Ho
68	¹⁴⁸Er
69	¹⁴⁹Tm
70	¹⁵⁰Yb
71	¹⁵¹Lu