Question

Polonium, one of two elements discovered (in 1902) by Marie Curie in pitchblende and named after her native country (Poland), has an intensely radioactive isotope with a half-life of 103 years. What is the decay rate in disintegrations (counts) per second for a freshly prepared 0.0010 gram sample of this isotope, 209Po?

Answer 1

Polonium, one of two elements discovered (in 1902) by Marie Curie in pitchblende and named after her native country (Poland), has an intensely radioactive isotope with a half-life of 103 years. What is the decay rate in disintegrations (counts) per second for a freshly prepared 0.0010 gram sample of this isotope, 209Po?

First, define desintegration per second --> atoms per / second

atoms = via mass/moles/avgrado

mol of sampe = mass/MW = 0.0010 /209 = 0.00000478468 mol

atoms of sample = mol*Na = (0.00000478468)(6.022*10^23) = 2.88133*10^18 atoms

Now, get rate

Half life = ln(2)/k

k = ln(2)/HL

k = ln(2) /(103 yeas) = 0.00672958427 1/y

change to seconds

1 year = 31536000 s

k = 0.00672958427 1/y * ( y / 212248.43 s )= 3.1705*10^-8 1/s

now

Activity = desintegrations / second = ( 2.88133*10^18 atoms ) *  (3.1705*10^-8) 1/s

ACtivity = 9.1*10^10 atoms / s

Activity = 9.1*10^10 Bq