# 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

Unit 6
T40 Separation of Q, 0, y rays
T41 Rutherford's a -Particle "Mousetrap"
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 -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-

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

V

T42

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 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:

Th

.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:

B

AV-'

Po-'" -

Bi2.2 B , Po-M

a

^ 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^

B

Th^

-* At^

a

-i^ Ra=^

115 Q ^ Bi^^^ ■

Po^

a

-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

92

cc

238

\

Uranium Series

ct

/

/

<^^^~^

^\ )^( )^\ )^.

stable

T-42

A

T-42

T-42

Neptunium Series

CL

CL

241

y

PuU

' - , ^

\

^\jO

(

y

stable

T43

T43

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

Number of Surviving
Parent Atoms

Number of Accumulating
Stable Daughter Atoms

T-43

Time

Number of Surviving
Parent Atoms

//Number of Accumulating
Stable Daughter Atoms

T43

A

B
C

Time

T4I

Number of Surviving
Parent Atoms

/^Number of Accumulating
Stable Daughter Atoms

f«

Time

Number of Surviving
Parent Atoms

/'^^Number of Accumulating

Stable Daughter Atoms

\^

A

6

C

ID
E

Time

Number of Surviving
Parent Atoms

9

/^Number of Accumulating
Stable Daughter Atoms

Time

Number of Surviving
Parent Atoms

/^Number of Accumulating
Stable Daughter Atoms

1F4I1

Time

Number of Surviving
Parent Atoms

T^

A

B
C
D
E

Time

Number of Surviving
Parent Atoms

Number of Accumulating
Stable Daughter Atoms

T4S

Time

T44

T44

This transparency will be useful in leading a teacher-directed discussion of the Displacement Rules of
Radioactivity. Space is provided to write in more examples of each type of decay: alpha decay, beta-
decay, and beta+ decay.

Overlay T44-A Shows the first rule in a visualized "before-after" diagram. Before the a particle is
ejected, the radioactive nucleus contains A nucleons, Z of which are protons. After
the a is emitted, the nucleus possesses 4 less nucleons, 2 of which are protons. The
nucleus is now a new element of atomic number Z-2. Introduce T44-B with a mask.

Overlay T44-B Shows the Cf decay displacement rule in the fonn of a general equation. Below is a
specific example. Mask the Th-234 and ask students to present the result. Space is
provided for writing-in further examples:

ggRa"-' ►seRn^^" + ,He'

8331^1^ ^8,T12«« + ,He^

Remove overlays T44-A and B. Introduce overlay T44-C.

Overlay T44-C Shows the second rule in a visualized "before-after"diagram. Before the \$~ particle is
ejected, the radioactive nucleus contains A nucleons, Z of which are protons. After the
B~ is emitted, the nucleus retains its original mass number but increases its atomic
number by one unit. An antineutrino V is also given off but it does not affect A to Z.

Overlay T44-D Shows the B~ decay displacement rule in the form of a general equation. Below is a
specific example. Mask the Pa-234 and ask students to present the result. Space is
provided for writing in further examples:

sBi"^-
.Pu"'

-^84Po"^ + _ie» + V

■^ 95Am-" + -ie° -f V

Remove overlays T44-C and D. Introduce overlay T44-E.

Overlay T44-E Shows the third rule in a visualized "before-after" diagram. Before the positron is
ejected, the radioactive nucleus contains A nucleons, Z of which are protons. After the
j5+ is emitted, the nucleus retains its original mass number but decreases its atomic
number by one unit. A neutrino V is also given off but it does not affect A or Z. In-

Overlay T44-F Shows the /S"'" decay displacement rule in the fonn of a general equation. Below is a
specific example. Mask the Si-30 and ask students to present the result. Space is pro-
vided for writing-in further examples:

rN'

— eC" -f ^eo -f V

9F" -«0i« _|- ,e° -f V

T-44

BEFORE

CL

DECAY

AFTER

T44

BEFORE

CL

DECAY

AFTER

92

u

238

»

Jh'''+He

T-44

BEFORE

ft

DECAY

AFTER

T^44

DECAY

AFTER

Y'+,e°+i)

Jh

234

*.,PaV,e°+i)

T-44

DECAY

TF44W

BEFORE

ft-

DECAY

AFTER

15

P

30

S*^*^ I I

T45 Mass Spectrograph

T45

T45

Mass Spectrograph

A schematic diagram of the apparatus known as the mass spectrograph is presented in this transpar-
ency. Overlays ilkistrate the operation of the velocity selector and the mass-determining section of the
spectrograph.

Overlay T45-A

Overlay T45-B

Shows the arrangement of magnetic and electric fields used to select ions of a certain
Sliced. The electric and magnetic forces on ions in the beam are in opposite direc-
tions. The magnitude of the magnetic force increases with the speed of the ions. Only
those ions on which the magnitude of the magnetic force equals the magnitude of the
electric force will be undeflected and pass through the slit. Three beams are shown,
one of ions moving too slowly, one of ions moving too rapidly, and one of ions moving
at just the right speed to pass through the slit. For these ions F mag = F elect, that
is, qvB - qE. So the speed of ions going through the sUt is v = E/B. Introduce overlay
T45-B.

Shows an undeflected beam passing through the slits and entering a second magnetic
field B' produced by a separate magnet. The beam is now acted on only by this mag-
netic field which will cause it to follow a circular path. The centripetal force is sup-
plied by the magnetic force qvB' = mv-/R- The mass can now be determined by solv-
ing for m and substituting v = E/B into the equation. Thus

m = qBB'R
E

The radius of curvature R can be measured with the aid of the film pack. The values
B, B' and E are determined from the design of the apparatus, and measurements of
magnet current and plate voltage.

T-45

T45

T46

T46 Chart of the Nuclides

T46

Chart of the Nuclides

This transparency is based upon the "Chart of the Nuchdes" pubHshed by the Knolls Atomic Power Lab-
oratory, Schenectady, New York. It represents a plot of stable and unstable radioisotopes with other
pertinent nuclear information.

Overlay T46-A Shows a g-rid with a vertical axis indicating the number of protons or the atomic
number and the horizontal axis giving the number of neutrons or A-Z. Add overlay
T46-B.

Overlay T46-B Shows the positions of the 265 stable nuclides. Add overlay T46-C.

Overlay T46-C Shows the positions of those radioactive nuclides which occur naturally. Add over-
lay T46-D.

Overlay T46-D Shows the positions of the 265 stable and approximately 1130 radioactive isotopes.

Overlay T46-E Shows a line plotting nuclides which contain equal numbers of protons and neutrons.
Those nuclides with small atomic numbers lie on this line while those of higher
atomic number possess more neutrons than protons. Add overlay T46-F.

Overlay T46-F Shows those nuclides with nuclei possessing 2, 8, 20, 50, or 82 protons, or 2, 8, 20, 50,
82 or 126 neutrons. These nuclides are unusually stable. The numbers are referred to
as "magic numbers". Remove overlays T46-F-E-D-C and introduce overlay T46-G.

Overlay T46-G Shows a simplified detail of the chart indicating stable nuchdes (large numbers) and
those radioactive nuclides which experience positron decay and k -capture.

J-A6

NUMBER OF NEUTRONS (A-Z)

-rT4fB

A
B

NUMBER OF NEUTRONS (A-Z)

-MB

NUMBER OF NEUTRONS (A-Z)

nw

< 40

Nuclides

^ " f

k*

mm*ma

^'

r

Stable Nu:lides

■

'^'

J-

1 ■

Nuclides

^

■^^'

m

/

V

NUMBER OF NEUTRONS (A-Z)

^^^^

120
100

^^^

32

31

Ge

1

66

(^a

e+

e+

«7l

oa

64

65

.jjr

30

Zn

60

61

kfi+
62

k/s^
63

64

r^ii

/s+

e+

/S+

/s+k

e+

^5.

!^ so

— ^^
28

i^U

58

5\$

60

61

62

DD

■■■ ■

Stable Nuclides

LU

Ni

k

56

57

58

k

59

60

61

■

■
■ ■ ■

^

. jrr-

H H ■ M

z 60

o

I

r

■

■ ■ H
■ ■ HM

*

J-

■ ■

< 40

M

r

20

/

r^-

NUMBER OF NEUTRONS (A-Z)

T47

T47 Nuclear Equations

T47

Nuclear Equations

This transparency will be useful in presenting the nuclear equations associated with certain major
events in the history of nuclear physics: the first artificial transmutation; the discovery of the neu-
tron; and the mass-energy relation.

Overlay T47-A

Overlay T47-B

Overlay T47-C

Overlay T47-D

Shows visualizations for two nuclear reactions: the upper one represents the first
artificial transmutation of an atom of one chemical element into an atom of another
chemical element; the lower one represents the nuclear reaction for the discovery
of the neutron. Mask that segment which is not being discussed at the moment. This
overlay is essentially for visualizing the capture of the Q particle by the target nu-
cleus and its subsequent transmutation and release of one of its nucleons. It will also
serve to emphasize the conservation of charge and mass number. Introduce overlay
T47-B.

Shows the nuclear equations for these reactions along with black spheres to distin-
guish protons from neutrons in the nucleus. The "compound intermediate" 9F'* is in-
cluded to emphasize the capture of the fl particle by the N-14 nucleus. Remove over-
lays T47-A and B. Introduce overlay T47-C.

Shows the nucleons involved in a nuclear reaction exhibiting a loss of rest mass. Add
overlay T47-D.

Shows the nuclear equation for the reaction and indicates which nucleons are pro-
tons. In addition, the rest mass of each nucleus is presented in ATOMIC MASS UNITS.
Space is provided to compute the mass defect from which the mass-energy relation
may be discussed.

T-47

T-47

12

T-47

I-

T-47 T-47

H' + ir-CBe)-He+,He

1.007825 7.016005

4.002603 4.002603

T48 Binding Energy Curves
T48

T48

Binding- Energy Curves

This transparency presents plots for the total binding energy of nuclei and the average binding energy
per nucleon.

Overlay T48-A Shows a grid with the number of nucleons in the nucleus plotted along the horizon-
tal axis. The vei'tical axis will be determined by the subsequent overlays. Introduce
overlay T48-B.

Overlay T48-B Shows a plot of the total binding energy for 47 nuclides. The total binding energy is de-
fined as the difference between the sum of the rest masses of the protons and neutrons
in the free state and the rest mass of the nucleus containing the same number of nu-
cleons. The values run from 2.2 MeV for H-2 to 1803 MeV for U-238. The value for
Sn-120 is 1020 MeV; for He-4 it is 28.3 MeV. Remove this overlay and introduce
T48-C.

Overlay T48-C Shows a plot of the average binding energy per nucleon for the same 47 nuclides. To
compute the binding energy per nucleon simply divide the previously determined total
binding energy by the number of particles in the nucleus. The binding energy per nu-
cleon is seen to be highest for the middle elements — the most stable nuclei. The
average binding energy per nucleon curve is useful in predicting energy releases in
nuclear reactions. When the products of a nuclear reaction lie higher on the binding
energy curve than do the reactants, they have more binding energy per particle and
release energy equal to the increase in the total binding energy.

) 120 160 200

NUMBER OF NUCLEONS IN NUCLEUS (A)

Total
Binding
Energy

in
MeV

isoa
i6oa
i4oa
ooa
looa
8oa
6oa

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300

u-

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•

•
•

•

•

•

•

Sn'^°

•

•

•

•

. . 4

•

•
•
•

1

He..

•

•

^^Q^H^E

so no 160 200 240
NUMBER OF NUCLEONS IN NUCLEUS (A)

Binding
Energy

Per

Nucleon

in

MeV

10

f

i

I
I

\i /I

c

f

•

• •

• •

•

%

•••

•

^,234

He..

••

•

•

•

y2:J8

•Li^

.He^

.H^

,h'

y 120 160 200

NUMBER OF NUCLEONS IN NUCLEUS (A)

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