# 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

#### See also : Golang : Calculations using complex numbers example

Tags : golang half-life-decay power-of math-pow round

##### By Adam Ng

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