Neptunium-235

Properties and data of the isotope ²³⁵Np.

Contents

Neptunium-235 is a radioisotope of the chemical element neptunium, which has 142 neutrons in its atomic nucleus in addition to the element-specific 93 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 ²³⁵Np is exclusively for academic purposes.

In 1950 a report appeared in which the short-lived isotope neptunium-235 was described for the first time. In the experiments presented there, 16-MeV deuterons (hydrogen-2 nuclei) from a cyclotron struck natural uranium and uranium-235 targets, forming the nuclide by the reaction

²³⁵U(d,2n)²³⁵Np

. Subsequent X-ray, gamma-ray, and alpha-particle measurements following chemical separation allowed the identification of characteristic signatures that were clearly assigned to neptunium-235 [James et al.: Products of helium-ion and deuteron bombardment of U²³⁵ and U²³⁸. The Transuranium Elements: Research Papers, Paper 22.8, p. 1604, (1949)].

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

General data

Name of the isotope:Neptunium-235; Np-235Symbol:²³⁵Np or 23593NpMass number A:235 (= number of nucleons)Atomic number Z:93 (= number of protons)Neutrons N:142Nucleon pairing (Z - N):odd - evenNuclear ratio (N/Z ratio):1.5268817204301 (= neutron-proton ratio)Neutron excess (N-Z):49Isotopic mass:235.0440615(15) u (atomic weight of Neptunium-235)Nuclide mass:234.9930504 u (calculated nuclear mass without electrons)Mass excess:41.04302 MeVMass defect:1.914084548 u (per nucleus)Nuclear binding energy:1782.95827195 MeV (per nucleus)
7.58705648 MeV (average binding energy per nucleon)Separation energy:S_N = 6.983(8) MeV (first neutron)
S_P = 4.3909(9) MeV (first proton)Half-life:396.1(12) dDecay constant λ:2.025381674333 × 10^-8 s^-1Specific activity α:51902696757332 Bq g^-1
1402.775588036 Ci g^-1Spin and parity:
(nuclear angular momentum)5/2+Year of discovery:1949

Radioactive Decay

Half-life T_½ = 396.1(12) d respectively 3.4223040 × 10⁷ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²³¹Pa	0.00260(13) %	5.1938(15) MeV
EC	²³⁵U	99.99740(13) %	0.1243(18) MeV

Parent Nuclides

Direct parent isotopes are: ²³⁹Am, ²³⁵Pu.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 142) and isobaric (same nucleon number A = 235) with Neptunium-235. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 142	Isobar A = 235
84	²²⁶Po
85	²²⁷At
86	²²⁸Rn
87	²²⁹Fr
88	²³⁰Ra
89	²³¹Ac	²³⁵Ac
90	²³²Th	²³⁵Th
91	²³³Pa	²³⁵Pa
92	²³⁴U	²³⁵U
93	²³⁵Np	²³⁵Np
94	²³⁶Pu	²³⁵Pu
95	²³⁷Am	²³⁵Am
96	²³⁸Cm	²³⁵Cm
97	²³⁹Bk	²³⁵Bk
98	²⁴⁰Cf
99	²⁴¹Es
100	²⁴²Fm