Polonium-221

Properties and data of the isotope ²²¹Po.

Contents

Polonium-221 is a radioisotope of the chemical element polonium, which has 137 neutrons in its atomic nucleus in addition to the element-specific 84 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 221. The very short-lived, only artificially produced, unstable and thus radioactive nuclide has no practical significance; the study of ²²¹Po is exclusively for academic purposes and scientific research.

In 2010, the previously unknown isotope polonium-221 was reported for the first time. In the experiment described, a 670-MeV/u uranium-238 beam impinged on a beryllium target, producing projectile fragments that were subsequently selected with the FRS fragment separator. The identification was achieved by time-resolved Schottky mass spectrometry in the ESR storage ring [1].

See also: List of individual Polonium isotopes (and general data sources).

General data

Name of the isotope:Polonium-221; Po-221Symbol:²²¹Po or 22184PoMass number A:221 (= number of nucleons)Atomic number Z:84 (= number of protons)Neutrons N:137Nucleon pairing (Z - N):even - oddNuclear ratio (N/Z ratio):1.6309523809524 (= neutron-proton ratio)Neutron excess (N-Z):53Isotopic mass:221.021228(21) u (atomic weight of Polonium-221)Nuclide mass:220.9751527 u (calculated nuclear mass without electrons)Mass excess:19.77375 MeVMass defect:1.82316818 u (per nucleus)Nuclear binding energy:1698.27022066 MeV (per nucleus)
7.68448064 MeV (average binding energy per nucleon)Separation energy:S_N = 3.561(26) MeV (first neutron)
S_P = 8.475(301) MeV (first proton)Half-life:2.2 minDecay constant λ:0.005251115004242 s^-1Specific activity α:1.430902906211 × 10⁺¹⁹ Bq g^-1
386730515.19227 Ci g^-1Spin and parity:
(nuclear angular momentum)(9/2+)Year of discovery:2010

Radioactive Decay

Half-life T_½ = 2.2 min respectively 1.32 × 10² seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β^-	²²¹At	100 %	2.991(24) MeV

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 137) and isobaric (same nucleon number A = 221) with Polonium-221. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 137	Isobar A = 221
82	²¹⁹Pb
83	²²⁰Bi	²²¹Bi
84	²²¹Po	²²¹Po
85	²²²At	²²¹At
86	²²³Rn	²²¹Rn
87	²²⁴Fr	²²¹Fr
88	²²⁵Ra	²²¹Ra
89	²²⁶Ac	²²¹Ac
90	²²⁷Th	²²¹Th
91	²²⁸Pa	²²¹Pa
92	²²⁹U	²²¹U
93	²³⁰Np	²²¹Np
94	²³¹Pu
95	²³²Am
96	²³³Cm
97	²³⁴Bk