Berkelium-235

Properties and data of the isotope ²³⁵Bk.

Contents

Berkelium-235 is a radioisotope of the chemical element berkelium, which has 138 neutrons in its atomic nucleus in addition to the element-specific 97 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 235. The very short-lived, only artificially produced, unstable and thus radioactive nuclide has no practical significance; the study of ²³⁵Bk is exclusively for academic purposes.

The report on the discovery of berkelium-235 appeared in 2026 [1]; according to it, the nuclide was produced by irradiating a gold-197 target with argon-40 ions at various energies (182.4 and 187.5 MeV, respectively) and identified by measuring the radioactive decay chains: ¹⁹⁷Au(⁴⁰Ar,2n)²³⁵Bk.

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

General data

Name of the isotope:Berkelium-235; Bk-235Symbol:²³⁵Bk or 23597BkMass number A:235 (= number of nucleons)Atomic number Z:97 (= number of protons)Neutrons N:138Nucleon pairing (Z - N):odd - evenNuclear ratio (N/Z ratio):1.4226804123711 (= neutron-proton ratio)Neutron excess (N-Z):41Isotopic mass:235.05665(43) u (atomic weight of Berkelium-235)Nuclide mass:235.0034453 u (calculated nuclear mass without electrons)Mass excess:52.76914 MeVMass defect:1.898136512 u (per nucleus)Nuclear binding energy:1768.10277211 MeV (per nucleus)
7.52384158 MeV (average binding energy per nucleon)Separation energy:S_N = 8.697(429) MeV (first neutron)Half-life:ca. 1 minDecay constant λ:0.011552453009332 s^-1Specific activity α:2.959733244963 × 10⁺¹⁹ Bq g^-1
799927904.0443 Ci g^-1Spin and parity:
(nuclear angular momentum)(3/2-)Year of discovery:2026

Radioactive Decay

Half-life T_½ = ca. 1 min respectively 6 × 10¹ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²³¹Am	?100 %	7.764(17) MeV
EC β⁺	²³⁵Cm	?	4.417(128) MeV

Radioactive decay scheme of the isotope berkelium-235

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 138) and isobaric (same nucleon number A = 235) with Berkelium-235. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 138	Isobar A = 235
82	²²⁰Pb
83	²²¹Bi
84	²²²Po
85	²²³At
86	²²⁴Rn
87	²²⁵Fr
88	²²⁶Ra
89	²²⁷Ac	²³⁵Ac
90	²²⁸Th	²³⁵Th
91	²²⁹Pa	²³⁵Pa
92	²³⁰U	²³⁵U
93	²³¹Np	²³⁵Np
94	²³²Pu	²³⁵Pu
95	²³³Am	²³⁵Am
96	²³⁴Cm	²³⁵Cm
97	²³⁵Bk	²³⁵Bk

External data and identifiers

Adopted Levels, Gammas:NuDat 235Bk

Literature and References

[1] - J. G. Wang, Z. C. Li, Z. Y. Zhang et al.:
Decay properties of new isotopes ²³⁵Bk and ²³¹Am.
In: Physics Letters B, 875, 140365, (2026), DOI 10.1016/j.physletb.2026.140365.