Ne-22 how many neutrons


Uranium-235 is the isotope of the chemical element uranium, whose atomic nucleus consists of 143 neutrons and the 92 protons characteristic of this element; this results in the mass number 235.

Uranium-235 was discovered in 1935 by Arthur Jeffrey Dempster - a Canadian-American physicist. It is the only fissile isotope that occurs naturally as a (primordial) primordial nuclide. The cross section for slow thermal neutrons is about 584.3 ± 1 barn; for fast neutrons this is of the order of a barn. The fission of a uranium-235 atom sets 202.5 MeV or 3.24 × 10 in the nuclear reactor-11 J, which corresponds to 19.54 TJ / mol or 83.14 TJ / kg. Another 8.8 MeV escape as anti-neutrinos.

Bombarding U-235 nuclides with neutrons triggers many different fission reactions - such as:

10n + 23592U → 14156Ba + 9236Kr + 3 10n.

See also: Overview of the uranium isotopes.


General data


Radioactive decay

Uranium-235 is the starting nuclide of the so-called uranium-actinium series - (4n + 3) series - which in English-speaking countries is often referred to as the actinium series or actinium cascade and which ends in the stable lead isotope Pb-207 Has.

Half-life half-life = 7,04(1) × 108 Years or. 2,2201344 × 1016 Seconds s.

Decayproductproportion ofDecay energyγ energy
α to231Thapprox. 100%4.6780 (7) MeV


Uranium-235 gamma emissions

E.γI.γDose (MeV / Bq-s)
143.76 (2) keV10,96(14) %0,01576(20)
163.356 (3) keV5,08(6) %0,00830(11)
185.715 (5) keV57,0(6) %0,1059(12)
205.316 (10) keV5,02(6) %0,01031(12)

Interfering nuclides in the gamma spectrometric determination: Ra-223 (Eγ = 144.27 keV; I.γ = 3.36%); Ra-226 (E.γ = 186.21 keV; I.γ = 3,56 %).

Among the large number of gamma lines caused by the U-235 in the gamma spectrum, the table only lists those whose intensities Iγ are greater than 5 percent.


The figure shows the natural decay scheme (uranium-235 decay series) for the nuclide uranium-235 - also called uranium-actinium decay series - whose end point is the stable lead nuclide Pb-207.


Starting nuclides

Direct mother nuclides are: 239Pooh, 235Np, 235Pa.


Natural occurrence

Comparison of the natural uranium isotopes including isotope frequency (proportion of the isotope mixture):


Atomic mass Arproportion ofHalf-lifeSpin
Isotope mixture
238.02891 u100 %
isotope 234U234.04095 (2) et al0,0054(5) %2,455(6) × 105 Years0+
isotope 235U235.04393 (2) and0,7204(6) %7,04(1) × 108 Years7/2-
isotope 238U238.05079 (2) et al99,2742(10) %4,468(6) × 109 Years0+


NMR data

235U is one of the NMR-active nuclides.


Radiation protection

The Radiation Protection Ordinance (StrlSchV) lists the following exemption limits, clearance values ​​and other values ​​as a radioactive or highly radioactive radiation source for the isotope uranium-235 (further data, explanations: see there):


Core isomers

Nuclear isomeric nuclides or excited states with the activation energy related to the ground state in keV.

descriptionExcitation energyHalf-lifeNuclear spin
235mU0.0760 (4) keVapprox. 26 minutes1/2+
235m2U2500 (300) keV3.6 (19) ms


Isotonic and isobaric nuclei

The following table shows isotonic (same number of neutrons N = 143) and isobaric (same number of nucleons A = 235) atomic nuclei for the nuclide uranium-235. Naturally occurring isotopes are marked in green; light green = radionuclides.


OZIsotons N = 143Isobar A = 235
95238At the235At the


External data and identifiers


last changes at 15.03.2021.


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