Pa
Actinide
Protactinium
Z 91A 231mass 231.04
Slow-motion stage
Protactinium-231
proton
neutron
alpha particle (2p + 2n)
Parent nucleus · 231 nucleons
91 protons (coral) and 140 neutrons (blue) are packed together and held by the strong force.
A real decay takes about 10⁻²¹ s. At ⅓× this stage stretches it across eleven seconds.
Choose a reaction
Reaction
23191Pa22789Ac+42He
Two protons and two neutrons leave together as one helium nucleus.
Z
9189
-2
A
231227
-4
n⁰
140138
-2
Energy released
5.20MeVtypical value
Alpha particle5.110 MeV
Mass convertedE = Δm c²0.00558 u
In joules8.33 × 10-13 J
Compared with a bonda C–C bond is 3.6 eV≈ 1,444,444 ×
Measured alpha energies fall between 4 and 9 MeV.
The particle
- Charge
- +2
- Mass
- 4 u
- Speed
- About 5% of the speed of light
- Ionising power
- Very high
- Stopped by
- Stopped by a sheet of paper or dead skin