feat: inner constructor for Particle

docs/src/api.md

@@ -11,7 +11,6 @@ Order = [:type]
 ## Constructors
 
 ```@docs
-Particle
 proton
 electron
 ```

docs/src/index.md

@@ -35,15 +35,15 @@ p = proton()         # proton
 α = Particle("alpha") # alpha particle
 
 # Create ions and isotopes
-fe3 = Particle("Fe3+")     # Iron(III) ion
-fe56 = Particle("Fe-56")   # Iron-56
+fe = Particle("Fe-56 3+")     # Iron(III) ion
+fe54 = Particle(:Fe, 3, 54)
 d = Particle("D+")         # Deuteron
 
 # Access properties
 println("Electron mass: ", mass(e))
 println("Alpha particle charge: ", charge(α))
-println("Iron charge: ", charge(fe3))
-println("Iron-56 mass number: ", mass_number(fe56))
+println("Iron(III) ion charge: ", charge(fe))
+println("Iron-54 mass number: ", mass_number(fe54))
 println("Deuteron mass: ", mass(d))
 ```
 

src/types.jl

@@ -18,7 +18,7 @@ Implementation type for charged particles.
 # Fields
 - `symbol::Symbol`: Chemical symbol or particle identifier (e.g., :Fe, :e, :μ)
 - `charge_number::Int`: Number of elementary charges (can be negative)
-- `mass_number::Int`: Total number of nucleons (protons + neutrons)
+- `mass_number::Int`: Total number of nucleons (protons + neutrons). If not provided, defaults to the most common isotope mass number
 
 # Notes
 - Mass number : For elementary particles like electrons and muons, `mass_number` is 0
@@ -35,7 +35,14 @@ struct Particle <: AbstractParticle
     symbol::Symbol
     charge_number::Int
     mass_number::Int
-
+    function Particle(symbol, charge_number, mass_number=nothing)
+        if isnothing(mass_number)
+            mass_number = elements[symbol].mass_number
+        else
+            mass_number >= 0 || throw(ArgumentError("Mass number must be non-negative, got $mass_number"))
+        end
+        new(symbol, charge_number, mass_number)
+    end
 end
 
 """

test/types.jl

@@ -1,6 +1,15 @@
 using Test, ChargedParticles, Unitful
+using ChargedParticles: is_electron, is_proton
 using Unitful: q
 
+@testset "Constructor" begin
+    # Test invalid mass numbers
+    @test_throws ArgumentError Particle(:He, 2, -1)
+
+    # Default mass number
+    @test mass_number(Particle(:He, 2)) == 4
+end
+
 @testset "String Constructor" begin
     # Test common aliases
     @test is_electron(Particle("electron"))