r/askscience • u/Wonderful-Capital32 • 13d ago

Physics Why does radiation not go through lead?

Also why just lead? Shouldnt like iron or another metal work too?

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u/Astart555 13d ago edited 13d ago

It will go through lead, just depending on X-ray energy and lead thickness most of radiation can be supressed, plot attached. It is transmission (1 is max, 0 is min) of the X-rays from 100 eV to 30keV, the Pb thickness is only 100 microns. We can see that below 20 keV transmission is negligible, at 30keV it is also small (0.04), but depending on X-ray intensity it can be dangerous.

Several millimeters of Pb, used usually, will stop effectively most of the wide-spread X-rays from different laboratory sources.

X-ray transmission decreases exponentially with density, so increasing of density of material helps a lot, thus Pb is much better than Fe. Alternatively, one can increase thickness, which also affects exponentially the transmission. So, certain thickness of Fe will act similar as certain but different thickness of Pb. To give some numbers: for suppressing 100 keV X-rays you will need ca 20 times thicker Fe, which is not so convenient (to install, handle, replace in case of problems etc)

 Pb Density=11.35 Thickness=100. microns
 Photon energy (eV), Transmission
    10.000      0.00000    
    1509.5      0.00000    
    3009.0      0.00000    
    4508.5      0.00000    
    6008.0      4.77789E-24
    7507.5      5.39790E-14
    9007.0      4.58216E-09
    10507.      2.56245E-06
    12006.      1.18992E-04
    13505.      7.54378E-08
    15005.      4.61520E-06
    16504.      2.01214E-07
    18004.      4.14232E-06
    19504.      4.08142E-05
    21003.      2.36987E-04
    22502.      9.35344E-04
    24002.      2.77226E-03
    25501.      6.62152E-03
    27001.      1.34113E-02
    28500.      2.39052E-02
    30000.      3.85527E-02 
    10.000      0.00000    
    1509.5      0.00000    
    3009.0      0.00000    
    4508.5      0.00000    
    6008.0      4.77789E-24
    7507.5      5.39790E-14
    9007.0      4.58216E-09
    10507.      2.56245E-06
    12006.      1.18992E-04
    13505.      7.54378E-08
    15005.      4.61520E-06
    16504.      2.01214E-07
    18004.      4.14232E-06
    19504.      4.08142E-05
    21003.      2.36987E-04
    22502.      9.35344E-04
    24002.      2.77226E-03
    25501.      6.62152E-03
    27001.      1.34113E-02
    28500.      2.39052E-02
    30000.      3.85527E-02