Rules Of Thumb For Alpha Particles - Panasonic PT-DZ12000U Operating Instructions Manual

RULES OF THUMB FOR ALPHA PARTICLES

1. An alpha particle of at least 7.5 MeV energy is needed to
penetrate the nominal protective layer of the skin
(7 mg / cm or 0.07 mm).
2. The alpha emissions and energies of the predominant
particles from 1 ìg of several common materials are:
238
Pu
239
Pu
240
Pu
242
Pu
a
Natural U
Oralloy (93%
b
Natural Th
D-38 (DU, tuballoy)
a 234
Includes
b 228
Includes
chemical separation,
disintegration rate lower than 0.5.
c.
With 2p (50%) geometry, the surface of a thick uranium metal
(tuballoy) source gives ~ 2400 alpha counts/min per cm .
Depleted uranium (D-38) gives ~ 800 alpha cpm/cm .
3. Alpha particles lose about 0.8 MeV per mg/cm density
thickness of the attenuating material.
4. Detector window thicknesses cause alpha particles to lose
energy at about 0.8 MeV per mg/cm of window thickness.
Therefore, a detector with a window thickness of 3 mg/cm
(such as sealed gas-proportional pancake alpha/beta
detectors and pancake GM detectors) will not detect alpha
emitters of less than 3 MeV.
2
DPM per ìg
39,000,000
140,000
500,000
8,700
1.5
235
U) 160
0.5
1
U in equilibrium.
Th in equilibrium. Depending upon the time since
228
Th can decrease to give a net
Alpha Energy (MeV)
5.50 (72%)
5.15 (72.5%)
5.16 (76%)
4.90 (76%)
4.20 (37%), 4.77 (36%)
4.39 (~ 80%)
4.01 (38%), 5.43 (36%)
4.20 (~ 60%)
2
2
2
2
2