Model 3450
Appendix A–7
Figure A–2. Effect of Distance on Exposure
Shielding
Shielding is any material used to reduce the radiation exposure rate
from a radioactive source. The 3450 gauge has some built-in
shielding, which reduces the exposure rate. When gauges are in
storage, additional shielding may be necessary to keep exposure to
personnel in adjacent areas below the dose limits for members of the
public.
The thickness of any material that reduces the incident radiation
intensity by one-half is known as the
half-value layer (HVL)
. The
HVL of a material varies with the type and energy of radiation. The
HVL values of certain common shielding materials are shown
below for gamma and fast neutron radiation.
Material
Cs-137 Gamma
Half-Value Layer
Am-241:Be Neutrons
Half-Value Layer
Concrete
1.9 inches
4.3 inches
Lead
0.3 inches
*
*
Lead does not provide any effective shielding of fast
neutrons.
A. R
AD
IA
TIO
N T
HE
OR
Y
Summary of Contents for RoadReader Plus 3450
Page 7: ...Model 3450 vii NOTES...
Page 13: ...xii NOTES...
Page 17: ...1 4 GAUGE PARTS AND ACCESSORIES Figure 1 1 Model 3450 Parts and Accessories...
Page 23: ...2 4 Figure 2 1 Effect of Moisture on Depth of Measurement...
Page 53: ...3 28 NOTES...
Page 169: ...Appendix E 2 STANDARD COUNT LOG Gauge Serial Number Date Moisture MS Density DS1 Density DS2...
Page 171: ...Appendix E 4 STANDARD COUNT LOG Gauge Serial Number Date Moisture MS Density DS1 Density DS2...
Page 173: ...Appendix E 6 STANDARD COUNT LOG Gauge Serial Number Date Moisture MS Density DS1 Density DS2...
Page 175: ...Appendix E 8 STANDARD COUNT LOG Gauge Serial Number Date Moisture MS Density DS1 Density DS2...
Page 181: ...Appendix G 4 NOTES...
Page 187: ...Appendix H 6 NOTES...
Page 199: ...Index 12 NOTES...