Alpha particle sources for calibration purposes

ALPHA PARTICLE SOURCES FOR

CALIBRATION PURPOSES

by

KARLENE

CORBIT KLAGES

Submitted in Partial Fulfillment

of the Requirements for the

Degree of Bachelor of Science

at

the

MASSACHUSEI'TS

INSTITUTE OF TECHNOLOGY

June

1961

s

·

1.

Or

ftC

JUL 14

196

Signature of Author

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Signature redacted

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IJ:Ert.:::.9P

Ph¥ics,

1961

Signature redacted

Certified

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Signature redacted

_{. .}

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_{. .}

_{. . . . .}

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_.

Accepted

Five mil wires were coated with Po210 and Th228 in an

investi-gation of their properties as calibration sources for the charged

particle analyzer. In order to obtain good sources, the wires to be

used must be thoroughly cleaned and "dipped" for the shortest length

of time possible. For Po2 1 0, Ag wire produces peaks with the highes

The author is greatly indebted to her advisor Professor W. W.

Buechner and Mr. A. Sperduto for their constant aid and encouragement. Without their help this work would have been impossible.

K& <Qi.~j<~

INTRODUCTION page

THE CARGED PARTICLE ANALYZER....so... 1

METHOD OF CALIBRATING THE MACHI... 21

CHOICE OF RADIOACTIVE SOURCES USED FOR STUDY... 2

Po2 1 0

WIRESTRIED...

WIRE SZE...

SOLUTIONS USED FOR CLEANINGWIRES...

METHODS OF CLEANING WIRES AND THEIR EFFECT

UPON THE RESULTING PEAKS... 005 0~5 ... ... 0000 DISCUSSION OF TABLEI... DISCUSSION OF TABLE1...

REPRODUCIBILITY OF THE PEAK ENERGIES AND SHAPES

FOR VARIOUS CLEANING PRCESSES...

P021 0 CONCENTRATION...

AGE AND 'RESHNESS" OF THE DIPPING SOLUTION...

DIPPING PROCEEDURE...0 EXPOSURE PROCEEDURE...**... AGING OF SOURCES... CONCIUSIONS....00. 000... ... 0~0 OsO sos ...o .*... ... s.. ... 500 ... ... ... ... ... ... ...

23

APPENDIX I - VARIATIONS IN ENERGY FROM ZONE TO ZONE

FOR DIFFERENT PLATES AND THE ENERGY GAP BETWEEN

PLATES... ... 24

.3

.3

.3

.4

.

4

.7

.7

WAA3LL Q& COITh]Li~2~2S

(uOAYILNUJIi)

page

APPENDIX II - MEANS OF CORRECTING RESULTS FOR ENERGY GAP

AND ZONE DIFFERENCES•****••**•*•••••••••••...27

APPENDIX III - VARIATIONS IN THE CALIBRATION OF THE MACHINE

AND USE OF THE RESULTING CALIBRATION CURVES...29

APPENDIX IV - DESIRED ACTIVITY FOR CALIBRATION SOURCES AND

DIPPING TIME NECESSARY TO ACHIEVE SUCH ACTIVITY....32 APPENDIX V- DIPPING SOLUTIONS USED...34 APPENDIX VI- MERITS OF HYDRAZINE VS WATER AS

DIPPING SOLUTIONS...35

APPENDIX VII- MERITS OF THE SOAP DIPPING SOLUTION...37

APPEDIX VIII- METHOD OF DIPPING THE MIDDLE OF A WIRE WITH Po

APPENDIX IX - LENG OF THE WIRE SOJRCE...40 APPENDIX X - HEIGHT ADJUSTMENT ALPHA SLIT AND PRESSURE...42

APPENDIX XI- METHODS OF ANALYZING THE DATA... 43

APPENDIX XII- APPARATUS FOR COATING WIRES WITH Th228 ...

46

APPENDIX XIII- SUGGESTIONS FOR FUTURE WORK...49

INTRODUCTION4

THE CHARGED. *PMTICLE ANALYZER

The ONR-Generator group at M.I.T. uses a mass spectrometer to

analyze the reaction energies of various elements when they are

bom-barded with high energy protons or deuterons. The charged particles

upon entering the analyzer follow a curved path whose radius of

cur-vature is approximately proportional to the square root of the energr

of the particle divided by the magnetic field. The constant of

pro-portionality is 1 m/e and is different for different kinds of

parti-cles.

A set of three glass photographic plates is placed ina curval

holder which is then placed in the machine. The distance along the

plates is marked off in centimeters and each point along the plates

corresponds to a different radius of curvature with respect to the

paths followed.

METHOD OF CALIBRATING THE MACHINE

The distance along the plates is calibrated in terms of the

radius of curvature r by making numerous exposures of a calibration

source in one zone along the entire length of the three photographic

plates. _{This is done by varying the magnetic field, since a-tH = EC}

where Eo is a constant that is proportional to the energy of the radio-active source being used and H is the magnetic field. The method of producing such a source is the actual topic of the study, but it was

complicated by the fact that the calibration of the machine is

CHOICE OF RADIOACTIVE SOURCES USED FOR STUDY

Upon a study of nuclear decay chains it was found that the

only alpha-particle chains suitable for experimentation are those

in-volving Po2₁0_{, p20}6 _Th228 _{and Th}2 29_.

Most of the work was done with

P0210 because a supply of PoCl was readily available. Th228 was studied for similar reasons.

WIRES TRIED

Copper, chromel, alumel, paladium, tungsten,'gold, silver and platinum wires were all tried as bases on which to chemically plate

Po21 0 . Gold, tungsten, and alumel were rejected because Po2 1 0 will

not plate onto them.

WIRE SIZE

It was found that the size of the wire makes no difference in the position of the 1/3 height of the peak, but smaller diameter wires

do result in sharper peaks with smaller half widths. (Note: The

position of the 1/3 height of a peak is used to calculate the energy

of the particles that formed the peak during the exposure. The exit

-ence of the peak is the result of the fact that charged particles upon

hitting a photographic plate ionize the emulsion particles in their

path and thus expose the plate.) For this reason

5

used when available rather than 10 mil wires.

SOLUTIONS USED FOR CLEANING WIPES

Laboratory glass cleaner (Laf Soap) manufactured by the Finger

Lakes Chemical Corporation, Inc. and concentrated HCl was used to re-move dirt, grease and various oxides from the wires. A saturated

sh-tion of BaNO was used to remove oxide from the silver wires. Hydra-zine sulfate was used during the cleaning process to remove oxides and

sulfides, and it was used after dipping to prevent the later formation

of oxides or sulfides. Distilled water was used throughout the

cleaa-ing process as a rinse.

METHODS OF CLLAiZIWG WILES

AND THEIR EFFECT UPON TEE RESULTING PEAKS

Various methods of cleaning wires were tried, and these methods

are shown listed in Tables I and II along with the energies and

half-widths of the resulting peaks. In both tables, the processes are

listed in terms of decreasing energy of the water solution peak with

the exception of sources 1 and 2 in Table I. Table I is shown on page

5 and Table II is shown on page

6.

DISCUSSION OF TABLE I

The,:source dipped and cleaned according to method 2 has the

highest energy vjille the source dipped and cleaned according to method

3 has the next highest energy. All of the remaining methods produced

wires whose energy was at least .40 key less than the energy of the

wire produced by method:?. It is interesting to note that the peaks

of the water solution wires always have higher energy that similar hydrazine dipping solution peaks when the wires have been cleaned with either Lab Soap or hydrazine before dipping. The only exception to

this rule is the wire sources produced by methods 1 and 2. The

rea-son for this exception lies in the reproducibility of the cleaning

process. For those methods which neither clean the wires with Lab

Soap nor rinse them with hydrazine before dipping,the energy of

the-peaks resulting from the hydrazine dipping solution wires is in all cases greater than the energy of peaks resulting from similar water

dipping solution wires.

AG

TABLE

I

NUMBER

I

2

3

4

5

6

7

8

9

0

BANO3

S

S

0

0

0

0

0

0

CONC. HCL

0

0

0

0

0

0

0

0

HYDRAZINE

X

X

0

0

X

X

ACETONE

WATER

X

X

X

X

X

X

X

X

X

SOLUTION

H20

HYDRA.

H20

HYDRA.

H

0

HYDRA.

H20

HYDRA.-

H20

ENERGY

5299.30 5300.43 5299.71 5299.12 5299.04 5299.00 5298.31

5299.12

5299.00

1/2

WIDTH

3.04

3.60

3.60

3.65

5.13

4.56

5.19

4.60

3.33

NUMBER

10

11

12

13

14

15

16

17

LAB SOAP

0

0

0

0

CONC.

HCL

0

0

ACETONE

0

0

WATER

X

X

X

X

X

X

X

X

SOLUTION

HYDRA.

H20

HYDRA.

H20

HYDRA.

SOAP.

Hg20

HYDRA.

ENERGY

5298.75 5298.42 5299.21 5298.36 5298.33 5298.00 5297.76 5297.21

1/2

WIDTH

4.07

3.65

4.45

3.81

4.42

4.80

3.43

3.49

S=STORED O BEFORE DIPPING ONLY

ENERGY AND 1/2 WIDTH IN KEV

PT

TABLE

NUMBER

I

2

3

4

5

LAB SOAP

0

0

0

0

0

WATER

X

X

X

X

X

SOLUTION

SOAP

H20

HYDRA.

H20

HYDRA.

ENERGY

5299.85 5299.68 5299.17

5299.32 5299.06

WIDTH

3.76

2.84

3.38

3.21

3.18

0 BEFORE DIPPING ONLY X a BEFORE AND AFTER DIPPING

Method 1 produced the wire with the highest peak energy. The

second highest peak energy was produced by the wire that was cleaned and dipped according to method 2.' The peaks produced by these wires were both sharply defined but the wire that was dipped and cleaned

according to method 2 has the smaller half width.

It is interesting to note once again that the peak energies of water dipping solution wires are again higher than the peak energies of the corresponding hydrazine dipping solution wires. In all cases,

the wires were cleaned with Lab Soap.

REPRODUCIBILITY -OF THE PEAK ENERGIES AND SHAPES

FOR VARIOUS CLEANING PROCESSES

Two tables are given that illustrate the reproducibility of several of the cleaning methods shown in Tables I and II. (Note:.

Reproducibility means the ability of a given cleaning and dipping

pro-cess to result in peaks of the same energy.) Table TIT indicates the

reproducibility of processes for cleaning and dipping silver wireand

Table IV indicates the repr'oducibility of cleaning and dipping processes

for platinum wire. The numbers in Tables III and IV refer to the

cor-responding cleaning and dipping processes listed in Tables I and II

respectively. Table III is shown on page 8 and Table IV on page.9.

These wires were all run after they were a day old in order to give them time to reach equilibrium.

A G

TABLE

lII

NUMBER

3

2

9

E N ER GY

5299.57 4.42 5299.28 7.13 5299.28 3.33

1/2 WIDTH

5299.82 4.31 5298.30 5.49 5299.68 5.04

IN K EV

5300.59 3.01 5298.94 9.31 5298.94 3.26

N5300.10 3.80 5301.27 4.75 5299.47 4.56

AVE. ENERGY

j5300.02±

.59 5299.44±1.83 5299.16± .92

AVE. 1/2 WIDTH

3.88

6.67

4.05

cO

PT

TABLE

NUMBER

2

3

5

ENERGY

&

5299.18

2.51 5299.17

3.38 5299.19

3.04

1/2 WIDTH

5299.94 2.89 5300.18 3.35 5298.95 3.21

IN KEV

5299.68 2.84 5299.00 3.30

AVE. ENERGY

5299.60t.42 5299.45*i.73 5299.07*.

2

AVE. 1/2 WIDTH

2.75

3.34

3.12

It is interesting to note that although Ag method 2 yielded

the highest energy for a peak during the cleaning process run, the

reproducibility of such sources is poor. That is, any given wire made according to this method may produce peaks whose energy ranges from

5301.27 key to 5298.30 key, which is an energy variation of 3.66 key.

Such a source is useless for calibration purposes since the energy of

sources to be used for calibration purposes must be known to a high degree of accuracy without having to actually measure the energy of

each source. Hence, the variation in energy from source to source must be as small as possible. In this respect, a source dipped and cleaned

according to Pt method 2 is the most reproducible since its variation

in energy is only +.42 key. The next most reproducible dipping and

cleaning method is Ag

3

the average by

:.

method Ag3 produces better sources than method Pt 2.

P0210~ CONCENTRATION

If two silver wires are-dipped in solutions containing .5 mc/cc

of Po2 1 0 and 1.5 mc/cc of Po2 1 0 respectively for the same length of

time, the first wire is not only less active, but results in a peak

whose energy is always less than the corresponding peak energy of the

second wire. This is true regardless of how long a time interval is

taken, or the kind of dipping solution that is used (hydrazine or water).

This includes the possibility of using a hydrazine dipping solution

In addition, it was found that theIonger a wire is dipped, the

lower the resulting peak energy is. This process may have some lower limit; but before that point is reached, the sources have such a-Jow

order of activity that they are no'longer useable as calibration sources.

This statement is true regardless of the Po21 0 concentration.

AGE AND "FRESIESS" OF THE DIPPING SOLUTION

Age refers to the length of time that has passed since the

solu-tion was originally prepared. "Freshness" of a solution refers to the

number of times the solution has been used for dipping sources. The

fewer wires that have been dipped in a solution the "fresher" it is.

Age-is of no importance what-so ever, but "freshness" is very

important. The reasons why a dipping solution should be "fresh" are

as follows. First of all, wires dipped in fresh solutions never form

sulfides or oxides, whereas wires that are dipped in "old" solutions

do. The greater number of times a solution has been used, the greater

is the probability that oxides or sulfides will form. Second,the

fresher the solution, ib othe:higherethecenerg f-the resnltirgpeaks

will become and the better the peak shape will become'. Third, Po21 0

plates unto a platinum wire more readily from an unused solution than

from a used solution. In addition, there appears to be an upper limit

on the amount of Po21 0 that will plate unto a platinum wire from any

given solution;-and the more times a solution has been used, the lower

this upper limit becomes.

DLL~.L~Ii~~G rI~OCLAJ9U.LI

After cleaning, the wires were coated with a thin film of Po21 0

by placing them in a' slightly acid solution of PoCl. Normally the

activity of a finished wire is approximately proportional to the lengthe

of the dipping time. However, if the wire is left in the solution too

long, the amount of Po2 1 0 coating it reaches a maximum and then starts

to decrease until a stable activity is reached.

EXPOSURE PROCEEDURE

The wires were placed in a wire holder after dipping. The wire

holder was then placed in the target chamber of the charged particle analyzer. The wire was adjusted to the correct height by mechanical

means; and, aier the chamber was properly evacuated, the exposure was

made by opening the valve into the charged particle analyzer.

AGING OF SOURCES

A time study was made of copper, paladium,silver, platinum,

and chrome. This time study indicated that paladium and copper are

both unsuitable as calibration sources.

The paladium source yielded a triple peak that degenerated into

a double peak over the course of seven days.

The copper source yielded a double peak composed of a

high,ex-tremely sharp peak with a smaller peak immediately behind it. Over

the course of seven days the two peaks merged into one rather wide

peak with a double tip.

The Pt wire maintained a sharp -ront edge and a narrow

half-width throughout the entire time study in addition to maintaining its

or-ginal height. On the other hand both Ag and Chromel lost their

peak shape although Chromel maintained a sharp front edge whereas Ag's

front edge gradually took on a gentler slope. Both Ag and Chromel

decreased in height by 40% and 30% respectively.

The plates also indicated that Pt and Ag have a sharp dip

fol-lowed by a rise in energy during the latter part of the first day with

the rise occuring over a longer time period for Pt than for Ag. This

indication was then verified by additional time runs on Ag and Pt.

The graphs for these time runs are shown on pages 14 through 19.

The plates were calibrated with the sources on which the time study was

being made. In each case this calibration was made right after the

sources were dipped and it was later discovered that, the energy of the

sources used for the calibrations changed in an unknown manner during

the calibration. The only thing known concerning this change in energy

is the magnitude and direction of the net change. For this reason,

three different calibrations were used to analyze the data. The

un-corrected calibration curves assumed that the energy of the calibration

sources remained constant during the calibration (as we know it did

not). The corrected calibration curves were made by assuming that the

energy of the calibration sources decreased linearly with time (this

is not very likely but it is a possibility). The third graph for both Ag and Pt was made by assuming that the calibration curve of plate

3905 is universal since the energy of the calibration source in this

case was constant.

ENERGY IN KEV 2 I

I

CHANGE OF

AG WITH

TIME USING

UNCORRECTED

CALIBRATION

CURVE 3860

5302.00t 5301.00t H I 5300.001\0 I

ENERGY IN KEY 5302.00 10 5301.00 o 5300.00 I I p p 2 3 4 5 6 7 I TIME IN DAYS

CHANGE OF

AG WITH TIME

CORRECTED CALIBRATION

CURVE 3860

p

USING

ENERGY IN KEV 1: I 1 4 5 TIME IN DAYS

CHANGE OF

AG WITH TIME

CORRECTED CALIBRATION CURVE3

5303.00 t 5502.00

I

USING

3905

ENERGY IN KEV 5306.001 5305.00+ 5304.00+ 5303.00 5302.00-j 5301.00+ 0 TIME IN DAYS

CHANGE OF

UNCORRECTED

PT

WITH TIME

USING

CALIBRATION CURVE 3901

I

I

I

ENERGY IN KEV 5306.001

8

0

0

CHANGE OF

I\

PT WITH TIME USING

CORRECTED

CALIBRATION CURVE

3901

I

ENERGY IN KEV 5307.00t 5306.00+ 5305.001.0 5304.00 5303.00 fA

.

I

I

CHANGE

OF

PT

WITH

TIME

CORRECTED

CALIBRATION

CURVE 3905

I

I

USING

I

I`-

l

Since the exact manner in which the energy of the caiibration

sources changed is unknown, none of the three curves is exact but

they do make good approximations. However, the relationship between

all pairs of points that are connect by a straight line is the

cor-rect relationship, since it is independent of the calibration. By

means of these connected points it becomes evident that there is a

dip fobwed by a rise in energy during the latter part of the first

day for both Ag and Pt with the rise for Pt occuring over-alonger

period of time than that for Ag.

The energy of the Ag wire was measured again four weeks later

and found to have decreased by7ketj'or it decreased at arate of

2key per week. In addition, the peak shape degenerated completely.

When new, the peak had a steep slope in front and a half-width of

3.30 key which increased to 4.33 key over the course of six days.

Four weeks later it had increased to greater than 14.25 key, and -the

front slope was at approximately 450 angle to the vertical.

The Pt wire held up much better. One week after the last day

of the time study, the wire was run again and its energy had decreased

by only .75 key. In additionto maintaining its sharp front edge, the width of the peak changed very little. When new the

half-width was 3.60 key. Seven days later it was 3.92 key and seven days

after that is was only 4.10 key. The net change in the peak's half-width was only .50 key and most of that occurred during the first six

days of the time run.

COiCLUS:Oi

For conviences sake, the conclusions will be listed numerically

as follows.

1. Five mil., wire is suggested for dipping purposes since

smaller diameter wires produce better peak shapes than larger diameter wires without lowering peak energy.

2. Ag wires should be cleaned by washing with Lab Soap and

then dipping them in a saturated BaNO3 solution followed by

concentrated HCl and hydrazine. The wire should be thoroughly rinsed with distilled water between each of these solutions and just before being placed in the dipping solution. A slightly acid solution of PoCl should be used for dipping the

wire after which the wire should be throughly rinsed with dis-tilled water.

3. Pt wires should be cleaned by washing them with Lab Soap

and the dipping them in Concentrated HCl. The wire should be rinsed with distilled water before and after using the concentrated HCl. After cleaning, the wire should be dipped

in a slightly acid solution of PoCl and then thoroughly rinsed

with distilled water.

4. Neither Pt nor Ag wires should be used for calibration

purposes until they are at least one day old.. However,

over-aged sources are just as bad as under-aged sources,

particu-larily Ag, since the peak energy decreases with time and the

peak shape degenerate. In this respect, Pt is much better

than Ag for calibration purposes, but Ag wires do ted -to

yield peaks with a higher initial energy than silmiliar Pt

wires. However, this difference may rest entirely upon the positions of the wires relative to the rise in energy that

occurs during the latter part of the first day since the wires

are slightly less than one day old.

5. Slightly acid PoCl solutions should be used for dipping

purposes. The age of the solution is dnimportant, but each

solution should be used one time only. The concentration of

P0210 in the solution should be as-great as possible (there may be an upper limit to this statement but it is greater

than 2.5 me/cc of P0 2 1 0) and the dipping time as short as

possible.

Th" -"

The source presently in use was made by the Radioactivity Center of M.I.T. by using the method designed by A.C.Wahl and W.R.Danieles for the preparation of an emanating uranium source. The source was formed

by percipitating barium stearate containing 2 mc of Th228 and 2 mc of Ra228. This source has approximately 100% emanation. The resulting

radioactive gas is pumped through a closed system and attracted to the

desired target by electrical means. A 100 microcurie source can be prepared in two or three hours dipping time.

Only one Th228 wire was actually tested, but the results of the

test indicate that Th228 would make extremely good calibration sources. Even though the source was very active (1/16 mc), the peaks were sharp

and narrow. The 1/2 width of the 8 Mev peak was 4.5 key and the half=

width of the other two peaks were on the order of 3.0 key. This is

extraordinary because the more active a source of a given radioactive

element is, the more its peak shape degenerates and the lower its peak energy becomes due to the increased thichess of the radioactive coating. The ideal source thickness is one atom thick and this parti-cular source was at least 200,000 atoms thick.

In addition to the narrow half-width, the peaks have little or

no energy tails on either side of the peaks.

Two runs seperated by a period of eight and one half hours were

made using this (L.urce. During this time lag there was no apparent drop in the energy of any of the three peaks involved.

±PLAIX I

VARIATIONS IN ENERGY FROM ZONE TO ZONE

FOR DIFFERENT PLATES AND THE ENERGY GAP BETWEEN PLATES

Each plate is approximately 27 cm. long and 5 cm. wide. The

plates are exposed in three stripts that are 8 mm. wide and tun the

full length of the set of plates. These strips are denoted as zones

30, 40, and 50. If a constant energy source is used to expose all three strips, the resulting peaks should fall at the same distance along the plates for each zone. In actual practice, this not only

does not occur, but the variation in distance is different for each

set of plates

used.

dif-ferences for a number of plates in the graph on page 25. The plates

with sucessive numbers are part of a set and should be viewed as a

whole.

In addition to-the above variation, the meeting point of any

two plates in a set of three represents an abrupt jump in th radius

of curvature at that point because one plate tends to be higher than the other. This height differential is different for each zone; and

hence, the jump in the radius of curvature is different for each zone.

This difference in height was measured by means of a micrometer and

then expressen in terms of a step function in energy by calculating

the change in the' radius of curvature at that point and then converting

this change into key. This gap was largest for zone 30 and varied

from .016 cm. which represents an energy differential of 1.43 key to

.025 cm. which represents a change in energy of 2.20 key. The size

& DISTANCE PLATE 3856 77 3858 77 3860 77 3861 36 3901 3902 37 3905 .77 ZONES ZONES 0 0 50 30 40 50 0 t-40 50 30 40 30 40 50 0 0 0 30 40 50 ZONES 0 50 ZONES 0 0 0 30 40 50 ZONES ENERGY IN KEV 5300.00 5302.00

ENERGY

VARIATIONS

BETWEEN ZONES 8 PLATES

0 30 0 30 0-4 0 5040 40 50 ZONES ZONES ZONES 0 30 400 3906 37 5296.00 5298.00

of the gap Lor any particularset o p was coputec by measuring

the gap a number of times and calculating the average.(Note: Between

each measurement, the plates were removed from the plate holder and then replaced.) The variations from this average were on the order of

+.002 cm or +.10 key.

APPIlDIX II

MEANS OF CORRECTING RESULTS FOR ENERGY GAP

AND ZONE DIFFERENCES

The means of adjusting the results for these differences is shown in the graph on page 28. The small circles represent energy differences between ones at the upper part of plate 3901 and the lower part of plate 3902. This was accomplished by exposing all three zones

using the same source with everything else held constant. The

dot-ted lines represent the correction that would be used if there was no height differential between the two plates. The solid lines represent the corrections to be used asuming that the variation along any given plate is linear and that the plates are displaced equally on either

side of the proper position at the position there rthe twoplates meet.

This graph is used in the foffowing manner. Given the energy

of a peak in zone 30 at the distance of 60 cm., its energy can be

compared to the energy of another peak in zone 50 by adding 2.19 key

to its measured energy. 2.19 key is just the energy difference be,

tween the solid line for zone 30 and the solid line for zone 50 at the

distance of 60 cm.

DISTANCE ALONG PLATES IN CM ZONES 30 40 50 76. 72-68 64 56

52-481

CORRECTIONS

FOR DIFFERENCES IN ZONE ENERGIES

FOR PLATES 3901-02

APPENDIX III

VARIATIONS IN THE CALIBRATION OF THE MACHINE

AND USE OF THE RESULTING CALIBRATION CURVES

The vaiiation in calibration is illustrated by the graphs shown

on pages 30 and 31. The uncorrected calibration curves show the

ap-parent energy of an assumed constant energy source as the position

along the plate is varied. These energies are found by assuming that the p

the present calibration of the machine is correct. This calibration is obviously no longer valid, for if it were, the points would fall

along a vertical line of constant energy.

Actually the energy of the calibrating source in the cases of plates 3901 and 3860 was not constant but changed by 1.88 key and

.87

cor-rected calibration curves-show the apparent energy vs position assuming

that the energies of the sources used to calibrate plates 390 and 3860

decreased linearly with time.

This variation in calibration from plate to plate was further

verfied by attempts to use the calibration curve of plate 3905 as a

universal curve and also by similar results found by other laboratory

personnel.

DISTANCE ALONG PLATES IN CM 76+ 72+ x N-i

xx

/

/

I

I

UNCORRECTED

CALIBRATION

CURVES

30

-

PLATE 3905

PLATE 3901

---

PLATE 3860

N%)

/

/

DISTANCE ALONG PLATES IN CM 76 f

_-PLATE

--

PLATE

-- PLATE

/

II

II

II

I'

4?

I,

CORRECTED

CALIBRATION

CURVES

31

N)

K

3905

3901

3860

I

APPENDIX IV

DESIRED ACTIVITY FOR CALIBRATION SOURCES AND

DIPPING TIM NECESSARY TO ACHIEVE SUCH ACTIVITY

When a radioactive wire is used for calibration purposes the

resulting peaks should have a maximum height of 250 to 300 counts.

Since peaks are counted under a microscope in strips that are 8 mm. x

.5

square millimeter. This particular figure was chosen because it is

large enough to make the error due to statistical variations small and small enough to prevent counting difficulties.

The height of a peak is determined by the activity of the wire used and the exposure time. Since an exposure time of greater than

five minutes is undesirable, the activity of the wires to be used

must be on the order of 530,000 particles per minat a distance of

2.25 cm. from the activity meter when viewed through a 2 mm. hole. The short exposure time is necessary tin order that the magnetic

field does not have enough time to drift very far.

The dipping times for two kinds of wires and for two different

concentrations of Po2lO is shown in Table 0 on page

33.

TABLE

₀

WIRE

SIZE

CONG. OF P0

_TIME

PT

5 MIL

1.5

33 MIN.

AG

5 MIL

2.5

c

10

MIN.

DIPPING SOLUTIONS USED

Three different kinds of P0210 dipping solutions were used; a

"water" solution, a hydrazine solution, and a "soap" solution.

The "water" solution is composed of PoCl dissolved in a .3N HCl

solution. It is the solution that had been used in the lab previous

to this study. However, it _{appeared to have two defects. First of all,}

Ag wires dipped in this solution often became coated with silver

sul-fide or silver oxide, and such a coating increases peak half-width

and shifts the thi±d height towards a lower energy. Second, Pt wires

would barely collect Po

The hydrazine solution was designed to solve both of these

pro-blems. It is composed of PoCl in a 1.5N HCl solution that is saturated

with hydrazine sulfate _{( NH2NH2_ 2SO4}

₎

The "soap" dipping solution was created when it was found that

the use of Lab Soap in the cleaning process shifts the third height

of the resulting peaks towards a higher energy. This soap solution is

composed of a standard water solution with a small amonnt of Lab Soap

added to it.

APPENDIX VI

MRITS OF HXDRAZINE VS WATER AS DIPPING SOLUTIONS

Although hydrazine was developed for two express reasons it was found to'be unnecessary for the solution of the first problem

and a defect rather than an asset in the solution of the second.

The first problem was one of the formation of sulfides and oxides on Ag wire during and after it was being dipped. It was discovered that although hydrazine prevents the formation of oxides or sulfides during the dipping process, the wires still tended to form oxides and sulfices after dipping. It was found that the

pro-blem of the formation of sulfides and oxides arises only after a

dip-ping solution has been used a large number of times. If the solution

has been used relatively few times, neither sulfides nor oxides will form on Agwire either during or after the dipping process, regardless of the kind of dipping solution used.

The second problem was that of the reluctance of a coating of

Po2lO to form of the surface of a Pt wire. In this case it was found

that hydrazine actually decreased the amonnt sof radioactivity achieved

in any given time interval by a factor of 9 over 4.

In terms of an increase in peak energy for any given method of

preparation or dipping, the value of using hydrazine is variable. For

Pt wires, the hydrazine solution always produced lower energy peaks

than similarily cleaned water solution peaks. For Ag wires the re-sults appear to depend upon the method of cleaning the wire to be

dip-ped and the concentration of Po2 1 0 in the dipping solution.

fore, that the hydrazine solution gives higher energy peaks than the

corresponding water solution when the Ag wires are neither cleaned

with Lab Soap nor rinsed with hydrazine. On the other hand, wires

that are cleaned with either Lab Soap or hydrazine yield higher energy

peaks when dipped in the water dipping solution rather than in the

hydrazine dipping solution, the only exception being cleaning and

dip-ping methods

1

and 2.

It was also found that for wires cleaned

ac-cording to processes

5

or

6,

the best dipping solution depends upon

the concentration of Po210 in the dipping solution. If the

concen-tration of Po

is on the order of

.5

mc/cc, then the hydrazine

dipping solution yields peaks whose energy is slightly greater than

the energy of the-corresponding water dipping solution peaks.

How-ever, when'the concentration of Po

_{is on the-order of}

1.5

mc/c,

the water dipping solution produces the higher energy peaks.

APPENDIX VII

MERITS OF THE SOAP DIPPING SOLUTION

Investigation of Table I on page 5 shows that the use of the

soap dipping solution for dipping Ag wires is definitely detrimental

to the production of a high energy peak. On the other hand, the Pt

wdire that produced the highest energy peak in Table II (page 6) was

dipped in the soap dipping solution. Since only one wire of the type

was dipped, the reproducibility of this method of dipping is unknown, and it may be that that particular wire was a statistical freak.

APPENDIX VIII

METHOD OF DIPPING THE MIDDLE OF A WIPE WITH Po210

Figure 3 on page 39 shows the wire holder. The wire is placed in the holder as shown after being threaded through a 2mm long capil-lary tube. _{The holder is then clamped in the dipping stand} ( figure 2)

by means of the spring pin. The capillary tube is then centered in

the middle of the wire by centering it in the capillary tube support

and clamping the support shut. The capillary tube is then filled

with a highly concentrated solution of PoCl by capillary action.

After dipping the tube is emptied in the same manner and both tube and wire are rinsed with distilled water.

The wire holder is than placed in the wire holder stand

(fig-ure 1) for exposure. During the exposure the capillary tube can either be pushed to one side or removed from the wire by breakage.

WIRE

HOLDEF

SPRING PIN

R

STAND

NOTE: WIRE HOLDER PLACED IN STAND SUCH THAT WIRE IS IN

EXACT CENTER OF THE STAND

FIG. I

o-2 MM LONG CAPILLARY TUBE

AND CAPILLARY TUBE SUPPORT

SPRING PIN

DIPPING

STAND

GROOVE & HOLES FOR WIRE 0

WIRE

HOLDER

PIG.

3

FIG.

2

39

AP PEiNDIX IX

LENGTH OF THE WIRE SOURCE

The wires that result from the normal dipping process are

radioactive for a distance of approximately 1.5 cm. from one end. A

wire source that is used for calibration purposes should be no longer then 2mm. For the single gap spectrograph, this requirement presents

no problems because the wire holder is designed to shield all but 2 mm.

of the wire source from being exposed. However, the multi-gap

spec-trograph t'designed to view the target or wire source over a range

of 1800. A wire holder of the type used in the single gap

spectro-graph will not work. There are three methods by which this problem can be solved.

The first solution is to dip a wire only 2 mm. from the end.

This is the method that is presently in use, but it has many drawbacks, some of which are listed below. First, surface tension no only makes

it impossible to dip exactly 2 mm. of wire but it also makes it

im-possible for the radioactive material to be evenly distributed along the wire. Sedondly, the end of the wires are always flat and ragged

from cutting which tends to assist the uneven plating of Po2 1 0 onto

the wire at that point and hence to distort the peak shape and position. Thirdly, it is difficult to make sure that the wire is perfectly hori-zontal during the exposure since it can be supported at one end only.

The second solution involves using the wire holder discussed

in Appeidix XII -for holding Th2 wires. By using this holder the

wire can be dipped an arbitrary length sinde all but 2 mm. of the wire

is shielded. This solution has one drawback. The wore holder will

necessarily become contaminated and Po210 has a tendency to spread.

shown in Appendix VIII to dip a2 mm. strip in the middle of a wire.

This solution has no apparent drawbacks and it has the advantage of

using the dipping solution only once without having to throw out a

large quantity of PoCl eacn time a wire is dipped.

APPENDIX X

HEIGHT ADJUSTMENT4, ALPHA SLIT AND PRESSURE

Having the wire at the correct height is very important sinde

a change in height of .001 cm. results in a shift in peak energy of

.21 key. However, a check was made to find out the magnitude of the

error due to variations in the heights of the wires from the correct

position. It was found that the maximum variation caused an energy

shift of only .14 key from the average energy, and the average varia-tion was +.10 key from the average energy.

The size of the opening into the analyzer was varied from4

to _{8 and had little or no effedt upon the peak width or energy. Simian}

larly pressure has no effect as long as it is less than 10-2 mm. of Hg.

METHODS OF ANALYZING THE DATA

Those plates which included a zone and a distance calibration were analyzed using only the considerations mentioned in Appendixes

II and III. This includes all of thePt wires, all of the dipping

and cleaning reproduction wires, and the final time study runs of Ag

and Pt.

The plates concerning the various methods of cleaning Ag wires were calibrated by _{zone but not by distance along the plate. Hence,}

in order to analyze the plates the following assumptions were made

using the energy of the peak which resulted from a wire being dipped

according to the 6th cleaning and dipping method as the base energy. (See Table I page 5.)

1. Assume that the zone calibration is correct. This

immedi-ately gives the relative energies of peaks resulting from

pro-cesses 1,r2. and 6;3, 4 and 5; 7, 8 and 14; 11, 12, and 13 and

10, 16, and 17.

2. Assume that the energy difference between wires produced by

methods 5 and 6 favors 5 by .04 key. This assumption rests on

the fact that type 5 sources have slightly greater energy than

type6 sources when averaged over a number of such sources. This

assumption relates the energies of peaks resulting from processes 1, 2 and 5 to 3, 4 and 6.

3.

Gh~at, inere canL Ae ui erence Co ueweei a wire jinsed with

hydrazine and then dipped in a hydrazine _{dipping solution and}

a wire that is metely dipped in the hydrazine dipping solution

without a previous rinse. This assumption relates the energies

of types 1 through 6 to sources of types 7, 8 and 14.

4. Assume that at most the energy of the type 13 source equals

that of the type 14 source. This assumption is based on the fact that for similarily prepared sources, the hydrazine

dip-ping solution source always has a higher energy than that of

the corresponding water dipping solution source. Hence, it

is extremely unlikely that the energy of the type 13 source would be greater than that of the type 14 source. On the

con-trary, the reverse is most likely to be true. By this means

the energies of source types 1 through

8

source types 11, _{12 and 13.}

5. Assume that the energy difference between the type

3

and the type

9

such types as listed in Table III (page'18). This relates the

type _{9 source to the other known sources.}

6. Assume that the energy of the type

9

than that of the type 10 source by .25 key. This assumption

is based on the fact that for similarly prepared sources the energy differential is more on the order of .50 key in favor of type

9

dif-ference in energy between type

9

would be any smaller or would favor the type 10 source.

The plates involving dipping time and solution concentration were not calibrated. However, the relationship between water dipping solution peaks and hydrazine dipping solution peaks irrespective of which is in which zone indicates not only the proper relationship

between the hydrazine dipping soliktion peaks and the water solution peaks but also an approximate zone calibration. This calibration

in turn with the'above Irelationship yields the remaining results.

The remaining.plates were analyzed qualitatively only and hence no quantitative calibration assumptions were necessary.

APPARATUS FOR COATING WIRES WITH Th

Figure 1 ohopage 47 shows the thorium dipping chamber. This

chamber is placed in the closed radioactive gas system mentioned in

the section or Th228 ( page 23). The wire is introduced into and

removed from the dipping chamber by pushing-the long rod on the left hand side of the figure through the chamber until its end extends out

thecther side. The actual dipping is accomplished by applying 900

volts DC to the push rod after the chamber has been connected to the gas system.

Since the dipping process makes the entire length of the wire

radioactive, a wire holder of the type shown in figure 2 is needed

to shield all but 2 mm. of the wire during the exposure.

Insulator

Gas

inlet

Apply DC

Voltage

Wire

Lucite

_/Brass

Gas

Outlet

X1111

THORIUM DIPPING CHAMBER

Fig. I

0

o

0

0

oQo

0

,,DlA.

Wire Clamped between moving

jaw,and stationary jaw in

scratched groove

Clamp Adjustment

EIII0

WIRE HOLDER

Fig.

2

- - I

A __.

SUGGESTION FOR FUTURE WORK

1. Investigate the soap dipping solution using Pt and Chromel wires.

2. Investigate the properties of Chromel wire.

3. Investigate the energy dip and rise that occurs for Po2 1 0 sources

that are coated on Pt or Ag wire.

4. Check the problems of calibration by running calibration runs in

all three zones for at least three sets of plates. If the calibrations

are not sonsistent, each individual plate should be calibrated across the top and bottom for zone variations and along one zone for distance variations.

5. Th228 should be investigated more closely as a calibration source using Pt and Chromel wires.

Wahl, A. C., and Danieles, W. R. "Emanating Power of Barium

.Stearate for .9-Second Actinon (Rn2g9)." Journal of

Inorganic and Nuclear Chemistry Vol. 6, No. T .p 273

195b.