Promethium-138m

Properties and data of the isotope ¹³⁸Pm.

Content

General data

Name of the isotope:Promethium-138m; Pm-138mSymbol:¹³⁸Pm or 13861PmMass number A:138 (= number of nucleons)Atomic number Z:61 (= number of protons)Neutrons N:77Isotopic mass:137.91955(3) u (atomic weight of Promethium-138m)
Excitation energy: +x keVNuclide mass:137.8860892 u (calculated nuclear mass without electrons)Mass excess:-74.93869 MeVMass defect:1.224975484 u (per nucleus)Nuclear binding energy:1141.05731349 MeV (per nucleus)
8.26853126 MeV (average binding energy per nucleon)Half-life:3.24(5) minDecay constant λ:0.0035655719164606 s^-1Specific activity α:1.567326739208 × 10⁺¹⁹ Bq g^-1
423601821.40778 Ci g^-1Spin and parity:
(nuclear angular momentum)(5-)

Radioactive Decay

Half-life T_½ = 3.24(5) min (minutes) respectively 1.944 × 10² seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
EE/β⁺	¹³⁸Nd	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
¹³⁸Pm		10(2) s	(1+)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 77) and isobaric (same nucleon number A = 138) with Promethium-138m. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 77	Isobar A = 138
43	¹²⁰Tc
44	¹²¹Ru
45	¹²²Rh
46	¹²³Pd
47	¹²⁴Ag
48	¹²⁵Cd
49	¹²⁶In
50	¹²⁷Sn	¹³⁸Sn
51	¹²⁸Sb	¹³⁸Sb
52	¹²⁹Te	¹³⁸Te
53	¹³⁰I	¹³⁸I
54	¹³¹Xe	¹³⁸Xe
55	¹³²Cs	¹³⁸Cs
56	¹³³Ba	¹³⁸Ba
57	¹³⁴La	¹³⁸La
58	¹³⁵Ce	¹³⁸Ce
59	¹³⁶Pr	¹³⁸Pr
60	¹³⁷Nd	¹³⁸Nd
61	¹³⁸Pm	¹³⁸Pm
62	¹³⁹Sm	¹³⁸Sm
63	¹⁴⁰Eu	¹³⁸Eu
64	¹⁴¹Gd	¹³⁸Gd
65	¹⁴²Tb	¹³⁸Tb
66	¹⁴³Dy	¹³⁸Dy
67	¹⁴⁴Ho
68	¹⁴⁵Er
69	¹⁴⁶Tm