Tellurium-121

Properties and data of the isotope ¹²¹Te.

Content

Tellurium-121 is a radioisotope of the chemical element tellurium which, in addition to the element-specific 52 protons, has 69 neutrons in the atomic nucleus, resulting in the mass number 121. The very short-lived, only artificially producible, unstable and therefore radioactive nuclide has no practical significance; dealing with ¹²¹Te is for academic purposes only.

The isotope is one of the few atomic nuclei in which some metastable nuclear isomers have longer half-lives.

General data

Name of the isotope:Tellurium-121; Te-121Symbol:¹²¹Te or 12152TeMass number A:121 (= number of nucleons)Atomic number Z:52 (= number of protons)Neutrons N:69Isotopic mass:120.904945(28) u (atomic weight of Tellurium-121)Nuclide mass:120.8764206 u (calculated nuclear mass without electrons)Mass excess:-88.54316 MeVMass defect:1.099835868 u (per nucleus)Nuclear binding energy:1024.49051203 MeV (per nucleus)
8.46686374 MeV (average binding energy per nucleon)Separation energy:S_N = 7.252(26) MeV (first neutron)
S_P = 7.415(27) MeV (first proton)Half-life:19.17(4) dDecay constant λ:4.184943563920 × 10^-7 s^-1Specific activity α:2.100193302734 × 10⁺¹⁵ Bq g^-1
56761.981154995 Ci g^-1Spin and parity:
(nuclear angular momentum)1/2+Year of discovery:1939

Radioactive Decay

Half-life T_½ = 19.17(4) d respectively 1.656288 × 10⁶ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
EE/β⁺	¹²¹Sb	100 %	1.056(26) MeV	0.573139(11) MeV 80.4(22) %

Parent Nuclides

Direct parent isotope is: ¹²¹I.

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
^121mTe	293.974(22) keV	164.2(8) d	11/2-

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 69) and isobaric (same nucleon number A = 121) with Tellurium-121. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 69	Isobar A = 121
38	¹⁰⁷Sr
39	¹⁰⁸Y
40	¹⁰⁹Zr
41	¹¹⁰Nb
42	¹¹¹Mo
43	¹¹²Tc	¹²¹Tc
44	¹¹³Ru	¹²¹Ru
45	¹¹⁴Rh	¹²¹Rh
46	¹¹⁵Pd	¹²¹Pd
47	¹¹⁶Ag	¹²¹Ag
48	¹¹⁷Cd	¹²¹Cd
49	¹¹⁸In	¹²¹In
50	¹¹⁹Sn	¹²¹Sn
51	¹²⁰Sb	¹²¹Sb
52	¹²¹Te	¹²¹Te
53	¹²²I	¹²¹I
54	¹²³Xe	¹²¹Xe
55	¹²⁴Cs	¹²¹Cs
56	¹²⁵Ba	¹²¹Ba
57	¹²⁶La	¹²¹La
58	¹²⁷Ce	¹²¹Ce
59	¹²⁸Pr	¹²¹Pr
60	¹²⁹Nd
61	¹³⁰Pm
62	¹³¹Sm
63	¹³²Eu