Golang : Calculate half life decay example

My wife is a chemistry lecturer and she was showing her student how to calculate half-life decay of an element. For this tutorial, let's pretend that we are learning chemistry and learn how to calculate half-life decay of an element with a half-life of 25 years in Golang.

Solving half-life problems is focused on using several equations. The order in which you use them depends on the data given and what is being asked.

For our code example below, we are given:

-An element has a half-life of 25 years.

-The initial amount is 320 grams.

and asked :

-How many grams after 100 years ?

---

 package main

 import (
 "fmt"
 "math"
 "time"
 )

 func round(input float64) float64 {
 if input < 0 {
 return math.Ceil(input - 0.5)
 }
 return math.Floor(input + 0.5)
 }

 func halfLifeDecay(startValue int, startTime time.Time, endTime time.Time, halfLifeInSeconds int) float64 {
 timeSpan := endTime.Sub(startTime)

 x := 2.0
 y := timeSpan.Seconds() / float64(halfLifeInSeconds)

 value := float64(startValue) / math.Pow(x, y)

 // even if everything is gone(decayed)
 // the left over is still 1 mathematically and by physics law
 if value < 1 {
 value += 1
 }
 value = round(value)
 return value
 }

 func main() {

 // From http://www.chemteam.info/Radioactivity/Radioactivity-Half-Life.html

 fmt.Println("An element has a half-life of 25 years.")
 fmt.Println("The initial amount is 320 grams.")
 fmt.Println("How many grams after 100 years ? ")

 // Simulate 100 years later
 start := time.Date(2000, 11, 10, 20, 34, 58, 651387237, time.UTC)
 end := time.Date(2100, 11, 10, 20, 34, 58, 651387237, time.UTC)

 fmt.Println("-------------------------------------------------")

 // Confirm that we are using the proper start and end dates
 years := end.Year() - start.Year()
 fmt.Println("Total years : ", years)

 // we use 365 days, no leap or astronomical year
 halfLifeInSeconds := 25 * (365 * (24 * 3600))
 fmt.Println("Half Life in Seconds : ", halfLifeInSeconds)

 fmt.Printf("Grams left after %v years is : %v grams.\n", years, halfLifeDecay(320, start, end, halfLifeInSeconds))
 }

---

Output:

An element has a half-life of 25 years.

The initial amount is 320 grams.

How many grams after 100 years ?

Total years : 100

Half Life in Seconds : 788400000

Grams left after 100 years is : 20 grams.

---

If we change the years to 50 instead of 100:

An element has a half-life of 25 years.

The initial amount is 320 grams.

How many grams after 50 years ?

Total years : 50

Half Life in Seconds : 788400000

Grams left after 50 years is : 80 grams.

Happy decaying!

References:

https://www.socketloop.com/tutorials/golang-calculate-time-different

Formula from http://www.chemteam.info/Radioactivity/Radioactivity-Half-Life.html