Question

Q1 We have naturally occurring radioactive material with the chemical formula (Ce,La,Nd,Th)(PO4,SiO4). A sample of the ore is mined and is concentrated to 5%, 10%, 25% and 100% monazite So four samples are created in 5%, 10%, 25% and 100% of this monazite.

a. Calculate the activity of the samples. Thorium 232 with a known half life in literature should be used in activity calculations.

b. would activity be different if the samples with 10% and 25% were dissolved in acids or other minerals? assume same percentages.

show all steps for the question to be worth any marks the result should be given in Bq/gram thorium 232 half life is public information and it should be used in this case.

Answer 1

Th-232 T_1/2 = 1.4 e+10 yr

decay const. = 1.57 e-18 /s

The sample contains

1 Th-232 atom for 14 atoms or 1 molecule of the material

MW of the sample   P = 32 +

Th = 232 +

O = 16*8 +

Ce = 140 +

La = 139 +

Nd = 142 +

Si = 28   

= 841

841 gm of the sample contains N_A = 6.023e+23 atoms of Th-232

Th-232 atoms /gm of the sample = 6.023e +23/ 841

N = 7.162e+20

activity of the sample A = N = 7.162e+20 * 1.57 e-18

= 1124 Bq/gm

This activity is when the mineral contains only the radioactive material i.e. 100 % of the chemical as given above

if the sample contains 5% of the monazite

activity = 1124 *0.05 = 56.2 Bq/gm

for 10% concentration = 56.2 *2 = 112.4 Bq/gm

for 25% = 1124/4 = 281 Bq/gm

b) dissolving the sample in any other material will not effect the activity as long as the concentration levels are maintained. Radioactive decay is atomic level phenomena and does not depend on the chemical formula as long as the number of atoms remain same.

c)

c)