To demonstrate deflection of radiation by EM fields
1. Set up a source that will emit radiation through electrically charged plates (Fig. 31.16).
2. You will observe that the alpha will be attracted towards the negative plate and repelled from the positive plate.
3. The beta will behave in an opposite manner, being attracted to the positive plate. 4. The gamma will be unaffected as it holds no charge.
lead block beta
gamma alpha
radioactive substance FIG. 31.16
electrically charged plates
fluorescent screen
radioactive compound N beta gammaalpha S
photographic plate
FIG. 31.17 Deflection of alpha, beta and gamma radiation in a magnetic field
1600 y 3.82 d 3.05 m 26.8 m
Ra-226 Rn-222 Po-218
Pb-214
Po-214 0.16 ms
Bi-214 19.7 m
Po-210 138 d
Bi-210 5.0 d
Pb-210 22 y
Pb-206 stable
FIG. 31.18 The decay chain of radium 226 showing decay times in years (y), days (d) and minutes (m)
lead block Decay products
In the Leaving Certificate Physics exam, you can be asked to work out what product will result from a radioactive emission. As we learned earlier, alpha, beta and gamma all have different effects on the parent nucleus in order to convert it to the daughter nucleus. A convenient example is given in Fig. 31.18:
• Alpha – subtract 4 from mass/subtract 2 from atomic number. • Beta – no mass change/add 1 to atomic number. • Gamma – no mass change/no atomic number change.
For deflection in a magnetic field, you should remember Fleming’s left-hand rule. Fig. 31.17 shows the possible directional effect from magnetic deflection of each particle. Note how gamma is unaffected as it does not have a charge.
