La
Lanthanide
Lanthanum
Z 57A 139mass 138.91
Slow-motion stage
Lanthanum-139
proton
neutron
alpha particle (2p + 2n)
Parent nucleus · 139 nucleons
57 protons (coral) and 82 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
13957La13555Cs+42He
Two protons and two neutrons leave together as one helium nucleus.
Z
5755
-2
A
139135
-4
n⁰
8280
-2
Energy released
5.20MeVtypical value
Alpha particle5.050 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