Panasonic PT-DZ12000U Operating Instructions Manual page 174

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
99
Tc
36
Cl
90
Sr/Y
238
U
9. Estimating beta energy using a paper shield
a) The density thickness of typical notepaper of 20 pound
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
beta particles such as C .
d) A single sheet of notepaper will reduce the count rate
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
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.
â max energy (KeV)
292
714
546 / 2270
Betas from short lived progeny
191 / 2290
99
32
2
14
163
Half-Value Thickness
7.5 mg / cm
15 mg / cm
150 mg / cm
130 mg / cm
2
2
2
2
2