Gilson and Voss - Voss Associates

32
7. The bremsstrahlung from a 1 Ci P aqueous solution in a
glass bottle is ~ 3 mrad/h (30 ìGy/h) at 1 m.
8. Half-value thickness vs beta energy
Isotope â max energy (KeV) Half-Value Thickness
99
Tc 292
2
7.5 mg / cm
36
Cl 714
2
15 mg / cm
90
Sr/Y 546 / 2270
2
150 mg / cm
238
U
Betas from short lived progeny
191 / 2290 130 mg / cm 2
9. Estimating beta energy using a paper shield
a) The density thickness of typical notepaper of 20 pound
2
weight is 7.5 mg/cm .
b) Take a reading with your beta detector of the surface
contamination you wish to estimate the energy of.
c) A single sheet of notepaper will stop all but the most
energetic of alpha particles, will have virtually no effect
on gamma radiation, and will only stop very low energy
14
beta particles such as C .
d) A single sheet of notepaper will reduce the count rate
99
from Tc by ½.
e) Continue adding more sheet of notepaper until the net
count rate is less than ½ the unshielded count rate.
f) Multiply the number of sheet of notepaper necessary to
2
reduce the count rate to ½ by 7.5 mg/cm . That density
thickness is your half-value layer and you can compare
the required density thickness with the table in step 8 or
some other reference.
32
7. The bremsstrahlung from a 1 Ci P aqueous solution in a
glass bottle is ~ 3 mrad/h (30 ìGy/h) at 1 m.
8. Half-value thickness vs beta energy
Isotope â max energy (KeV) Half-Value Thickness
99
Tc 292
2
7.5 mg / cm
36
Cl 714
2
15 mg / cm
90
Sr/Y 546 / 2270
2
150 mg / cm
238
U
Betas from short lived progeny
191 / 2290 130 mg / cm 2
9. Estimating beta energy using a paper shield
a) The density thickness of typical notepaper of 20 pound
2
weight is 7.5 mg/cm .
b) Take a reading with your beta detector of the surface
contamination you wish to estimate the energy of.
c) A single sheet of notepaper will stop all but the most
energetic of alpha particles, will have virtually no effect
on gamma radiation, and will only stop very low energy
14
beta particles such as C .
d) A single sheet of notepaper will reduce the count rate
99
from Tc by ½.
e) Continue adding more sheet of notepaper until the net
count rate is less than ½ the unshielded count rate.
f) Multiply the number of sheet of notepaper necessary to
2
reduce the count rate to ½ by 7.5 mg/cm . That density
thickness is your half-value layer and you can compare
the required density thickness with the table in step 8 or
some other reference.
Page 127
Page 127
32
7. The bremsstrahlung from a 1 Ci P aqueous solution in a
glass bottle is ~ 3 mrad/h (30 ìGy/h) at 1 m.
8. Half-value thickness vs beta energy
Isotope â max energy (KeV) Half-Value Thickness
99
Tc 292
2
7.5 mg / cm
36
Cl 714
2
15 mg / cm
90
Sr/Y 546 / 2270
2
150 mg / cm
238
U
Betas from short lived progeny
191 / 2290 130 mg / cm 2
9. Estimating beta energy using a paper shield
a) The density thickness of typical notepaper of 20 pound
2
weight is 7.5 mg/cm .
b) Take a reading with your beta detector of the surface
contamination you wish to estimate the energy of.
c) A single sheet of notepaper will stop all but the most
energetic of alpha particles, will have virtually no effect
on gamma radiation, and will only stop very low energy
14
beta particles such as C .
d) A single sheet of notepaper will reduce the count rate
99
from Tc by ½.
e) Continue adding more sheet of notepaper until the net
count rate is less than ½ the unshielded count rate.
f) Multiply the number of sheet of notepaper necessary to
2
reduce the count rate to ½ by 7.5 mg/cm . That density
thickness is your half-value layer and you can compare
the required density thickness with the table in step 8 or
some other reference.
32
7. The bremsstrahlung from a 1 Ci P aqueous solution in a
glass bottle is ~ 3 mrad/h (30 ìGy/h) at 1 m.
8. Half-value thickness vs beta energy
Isotope â max energy (KeV) Half-Value Thickness
99
Tc 292
2
7.5 mg / cm
36
Cl 714
2
15 mg / cm
90
Sr/Y 546 / 2270
2
150 mg / cm
238
U
Betas from short lived progeny
191 / 2290 130 mg / cm 2
9. Estimating beta energy using a paper shield
a) The density thickness of typical notepaper of 20 pound
2
weight is 7.5 mg/cm .
b) Take a reading with your beta detector of the surface
contamination you wish to estimate the energy of.
c) A single sheet of notepaper will stop all but the most
energetic of alpha particles, will have virtually no effect
on gamma radiation, and will only stop very low energy
14
beta particles such as C .
d) A single sheet of notepaper will reduce the count rate
99
from Tc by ½.
e) Continue adding more sheet of notepaper until the net
count rate is less than ½ the unshielded count rate.
f) Multiply the number of sheet of notepaper necessary to
2
reduce the count rate to ½ by 7.5 mg/cm . That density
thickness is your half-value layer and you can compare
the required density thickness with the table in step 8 or
some other reference.
Page 127
Page 127