Full text of "Transparencies Unit Unit 6 - The Nucleus: Project Physics"

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PROJECT PHYSICS

TRANSPARENCIES UNIT 6

Authorized Interim Version

HOLT, RINEHART & WINSTON, INC.

1 809250

Harvard Project Physics
Overhead Projection Transparencies

Unit 6
T40 Separation of Q, 0, y rays
T41 Rutherford's a -Particle "Mousetrap"
T42 Radioactive Disintegration Series
T43 Radioactive Decay Curve
T44 Radioactivity Displacement Rules
T45 Mass Spectrograph
T46 Chart of the Nuclides
T47 Nuclear Equations
T48 Binding Energy Curves

140

T40 Separation of a, /S, y Rays

T40

Separation of a , 3 , 7 Rays

With this transparency one may discuss the effect of a magnetic field on the emanations coming from a
radioactive source. The obsei-ved deflections are presented without identification to pennit the student
to apply his knowledge of the behavior of charged particles in a magnetic field, (see T32 Unit 4) .

Overlay T40-A Shows an electromagnet (with cuiTent off) surrounding a lead-shielded source of ra-
dio-activity. When no magnetic field is present only one path of radiation is observed.
Introduce overlay T40-B.

Overlay T40-B Shows the effect of a moderate magnetic field strength on the emanations. Since a de-
flection occurs, it must be true that this emanation possesses charge. Ask students to
apply the right hand and left hand rules to determine the charge on this ray. It will
be seen that the left hand rule is applicable since the force is upward and conse-
quently the charge is negative. It is, of course, the $ ray.
Note: Beta rays exhibit a continuous distribution of energies. We have indicated

betas of only one energy here for simplicity.
Remove overlay T40-B and introduce overlay T40-C.

Overlay T40-C Shows the effect of a more intense magnetic field on the radioactive emanations. A new
deflection is noted which necessarily is positive since it is opposite to the deflections
of the B rays. The degree of deflection shows that this positive ray, the G ray, has a
much larger momentum than tha t of the /S's. Point out that the decrease in the radius
of the $'s is a result of the increa sed B field. Additionally, have students comment on
the undeflected ray. Indicate that further increases in the magnetic field strength
will not affect this ray, although the other two would continue to be affected. This un-
deflected ray is, of course, the neutral y ray.

T-40

T-40—

Tt4So

T41

T41 Rutherford's 0 -Particle "Mousetrap"

T41 Rutherford's a-Particle "Mousetrap"

This transparency presents a simplified detail of the apparatus used by Rutherford and Royds in 1909
to show that the Q particle is a doubly-ionized helium atom, that is, the nucleus of a He atom.

Overlay T41-A Shows a thick-walled glass chamber leading to a discharge tube at the top. In the
lower portion is a thin-walled tube one hundreth of a millimeter thick containing ra-
don gas. The outer tube was evacuated and the apparatus was allowed to stand for a
week. As time passed, Cf particles from the radon gas traveled through the thin-
walled tube into the evacuated chamber. Here the " CI particle gas" was compressed
into the discharge tube by means of a mercury column not shown. A potential dif-
ference was maintained across the electrodes and an electric discharge was produced
in the "gas". The resulting light was examined with a spectroscope. Introduce over-
lay T41-B with a mask.

Overlay T41-B Illustrates more Q particles in the discharge tube and suggests light emanating from
the tube. The right side of the overlay provides the spectra which wei'e observed
as time went on. Reveal each spectrum separately by sliding an opaque mask down
the overlay. The final spectrum is a comparison spectrum of helium. Discuss the in-
tei-pretation of these results.

Note: You may wish to add the actual colors to the spectral lines. This can be done
with colored wax pencils, felt markers, or colored tapes. Refer to T39 Unit 4
for exact coloration.

1^-T

IM lAT

T42 Radioactive Disintegration Series
T42

T42

Radioactive Disintegration Series

This transparency will be useful in discussing the process of radioactive transmutation which elements
undergo by emitting G and $ particles. Four series are presented : Uranium-Radium ; Thorium ; Actin-
ium; Neptunium. It is intended that this transparency be completed by the teacher (with a wax pen-
cil) as students consult the Periodic Table and determine the complete symbol with A and Z for each
member of the series.

Overlay T42-A Shows the principal components in the Uranium Series. U-238 emits an 0 particle re-
sulting in an element possessing 90 protons and 234 nucleons. Element 90 is Tho-
rium. Therefore, the symbol yoTh^'^ is placed in the first blank circle. Th-234 then
emits a $ particle resulting in an element with 91 protons and 234 nucleons. Accord-
ing to the Periodic Table element 91 is Protactinium; therefore, ,„Pa-'' is placed in
the second circle. The procedure continues in a similar manner until the stable daugh-
ter is reached.

In this series some points are reached by a process called "branching"; a small
fi-action of atoms decay in a manner other than that shown. The branching in this
series is as follows:

.34 — B , p^234 — B_^ u"

Bi2w — g_^ rppio — §_

Pb-"' *^— Bi^

Remove overlay T42-A and introduce overlay T42-B.

Overlay T42-B Shows the scheme for the Thorium Series. Follow the same procedure as in overlay
T42-A. The bi'anching in this series is as follows:

AV-'

Po-'" -

Bi2.2 B , Po-M

^ Bi^

-^ Pb™«

Remove overlay T42-B and introduce overlay T42-C.

Overlay T42-C Shows the scheme for the Actinium Series, so-called because U-235 was once known
as Actinouranium. The branching in this series is as follows:

Ac^
Po^

Th^

-* At^

-i^ Ra=^

115 Q ^ Bi^^^ ■

Po^

-i-Pb^

Remove overlay T42-C and introduce overlay T42-D.
Overlay T42-D Shows the scheme for the Neptunium series. The branching is as follows:

Bi"^ Q , Tl^"-' ^-^ Pb^

T-42

238

Uranium Series

<^^^~^

^\ )^( )^\ )^.

stable

T-42

Neptunium Series

241

PuU

' - , ^

^\jO

(

stable

T43 Radioactive Decay Curve

T43

Radioactive Decay Curve

Use this transparency to aid in the discussion of the half-life concept in radioactive decay. A number
of overlays displaying sample data for a radioactive element and its accumulating "daughter" atoms
are presented for analysis.

Overlay T43-A

Overlay T43-B

Overlay T43-C

Overlay T43-D

to
Overlay T43-F

Shows the axes on which data for surviving and accumulating atoms will be plotted.
The vertical axis represents numbers of atoms, No being the original quantity. The
horizontal axis is in arbitrary time units. Introduce overlay T43-B.

Shows plotted data for the surviving parent atoms and the accumulating daughter
atoms for a short time interval. Point out that as radioactive decay occurs, the orig-
inal radioactive atoms transmute into new, in this case stable, atoms. The plot
shows this increasing number of daughter atoms along with the remaining num-
ber of parent atoms. Add overlay T43-C.

As time goes on, more parent atoms decay into new daughter atoms. This overlay
shows that the number of daughter atoms eventually becomes equal to the number of
remaining parent atoms. Add overlay T43-D.

As time progresses, the number of daughter atoms is seen to increase further while
the number of surviving parent atoms is shown decreasing. Continue with the re-
mainder of the overlays.

Now that you have presented the complete data for the graph you can indicate
the suggestion of Rutherford that it is possible to specify the time required for any
particular fraction of a radioactive substance to decay to one-half, one-third, or one-
fourth of the original quantity. The fraction 1/2 has been chosen for convenience
and the time T thus required is called the half-life. It is the time during which a ra-
dioactive material decays to one- half of its original amount.

Ask students to point out the half-life from the graph. It is 20 time units. Remove over-
lays T43-F-E-D and show that the number of atoms I'emaining after 20 time units have
elapsed is No/2. Return T43-D and show that at the end of another 20 units of time
(one half -life) the number of atoms remaining is y.^ the original [V2(No/2) = y^
No] . Return overlay T43-E and show that after another half-life (20 time units) the
number of atoms is V2 the original [1^ (14 No) = i/g No]. Finally show that overlay
T43-F illustrates another half -life [l/2*'(i/8No) = 1/16 No].

T-43

Time