The isotopes half life is 2 hours
Since given the following :
time = 8 hours × 3600s/hr = 28800 seconds
A₀ = 80 Bq as the first registration of detector counts per second
A = 5 Bq as the registration of detector counts per second eight hours later
Using the formula:
∴ A = A₀ e^-λt
∴ A/A₀ = e^-λt
∴ ln (A/A₀) = -λt
∴ λ = -ln (A/A₀) /t = ln2 / t_{1/2}
∴ t_{1/2} = -ln2 / ln(A/A₀) (t)
∴ t_{1/2} = -ln2 / ln(5/80) (8 hours) = 2 hours
Answer:
radio waves, microwaves, infrared, visible light, ultraviolet light, X-rays, gamma rays
Explanation:
Electromagnetic waves are oscillations of electric and magnetic fields in a direction perpendicular to the direction of motion of the wave (transverse waves). They are classified into 7 different types, according to their frequencies.
From lowest to highest frequency, we have:
Radio waves 
Microwaves 
Infrared 
Visible light 
Ultraviolet 
X-rays 
Gamma rays 