Determination of Ca⁴⁸ by neutron activation

LIBR A

R

DETERMINATION OF Ca4 8 _{BY NEUTRON ACTIVATION} by

JAMES DUNN RUSSELL S.B., Massachusetts Institute of

( I 4q)

Technology

SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE

DEGREE OF MASTER OF SCIENCE

at the

MASSACHUSETTS INST ITUTE OF TECHNOLOGY

June, 1960

Signature of'Author... , . ... *... ... .... Departnient of Geology and Geophysics,

... ... . 0.

May 23, 1960

Certified by... 0.

Thesis Supervisor

Ac ce pted by. . . . .... . . . .

Chairman, Departmental Comittee on Graduate Students

ABSTRACT

Determination of Caloium48 by Aotivation Analysis

by James Dunn Russell

Submitted to the Department of Geology and Geophysios on May 23 in partial fulfillment of the requirements for the degree of Master of Scienoe.

The solid source mass spectrometer is not a sufficiently accurate device for measuring the abundance of the Ca4 8 _{isotope. Neutron} ac-tivation was used which produces 8.7 min. Ca4 9 which decays to 57 min. Se49. By determining the activity of Sc49 we have an indication of the amount of Ca4 8,

Lanthanum is used as an internal flux monitor and by initializing the ratio of lanthanum and calcium, and comparing the results of the radioactive substances, 57 min. Sc4 9 and 40.2 hr. La1 40 an indication of relative amounts of Ca4 8 is obtained. Analysis of radioactive detection methods indicates a theoretical accuracy of

o.1%.

The purpose of this thesis was to see if results are reproducible within the range of the theoretical accuracy. To obtain accuracy of

this amount, an accurate half life of the radioactive isotopes must be known. The half life of Lanthanum is known to sufficient accuracy and a new value for the principal component,57.3 + 0.4 min.,was ar-rived at by analyzing results from four cyclotron bombardments.

The next step was carrying out the procedure by using the M.I.T. Reactor. Contaminants were introduced making accurate measurements

possible, but valuable pointers were learned and suggestions were made on how to improve the accuracy, to the theoretical limit.

Thesis Supervisor: John W. Winchester Title: Assistant Professor of Geochemistry

ACDTNU7DGMENTS

The author wishes to express his deepest thanks to

Professor John W. Winchester for his assistance with all phases of this problem, particularly those pertaining to chemistry.

Also the author wishes to express his thanks to the

TABLE OF CONTENTS

Abstract.... . . . . . . . . . ...

Acknowledgemnents ... .... .. .. ... .

A Reinvestigation of the Problem of Ca"4 Variations...

Conclusions and Recommendations... . ...

Appendices

Appendix A Equipment.. ...

Appendix B Error Analysis... ....

Appendix C Cyclotron Bombardments

Determination of Sc49 half life...* Data from Cyclotron 3ombardment - 1... Data from Cyclotron Bombardment 2 ... Data froA Cyclotron Bombardment

4

4... Appendix D Dead Time Calculation...

Appendix E Reactor Irradiations...

Data from First Reactor Irradiation... Data from Second Reactor Irradiation...

Gamma Decay Date... ...

Appendix F Computer Analysis...4

Appendix G Decay Scheme Diagram Ca49-SO49--Ti 4 9.4...

Bibliography.. .... .. 4. ... ... ...--.... i i 1 3 12 15 17 27 38 47 56 61 65 87 93 98 101 104 106

TABLE OF GRAPHS Bombardment J 1 Beta Decay... Absorber DecayAnalysis... Absorber Curve... ... Feather Analyses ...

Ganna Energy Analysis...

Bombardment

#

2

Beta Decay...

Absorber Decay Analysis...

Absorber Curve ... Feather Analysis... Bombardment

#

4 Beta Decay... Beta Decay... Beta Decay... ****ee. 0.E . *000.0..*~ *.... . . ... #B ..

Dead Time Calculations...

Irradiation

#

1 Beta Decey

Sample # 1s... Extrapolation l1... Sample j lb... Extrapolation-4 lb... Sample

#

ic... Extrapolation 1o... Sample - 1d... Extrapolation

#

ld... Sample - 2...I..-...7.. Extrapolation 2 Sample

#

. . . Extrapolation ' 3... Sample # 4... Extrapolation

#

4 ... Sample

#

5... Extrapolation

#

5... Sample 6 Extrapolation

#

6... Irradiation

#

2 Beta Decay Beta Decay Gross Gamma Gross Gamma No absorber. Absorber.... Decay Curve. Decay Curve. ... O .. . . .... , a * ~0~* *0* .*e* .. ~0* .S ~ 0~~*~ ~ S *e.eeee.~e. .5~~ *45 *~ 0~ *0e ... 590 500 .50.0. * S ~5 * 0 *.*5~~ . S.... ~ . . ... ... S ~ ... . ~0~~~*~~ 0~~~~~*~ . ~ S 5*. .. ~*. ... ... ... ~ .. ~. .. 05* 0*405 S.~ .. 0 ... ... ... 0 . .. .

OBJECT

The purpose of this thesis is to find if neutron activation is a reliable method in accurately determining the relative abundancy of the Ca48 /C&- ratio.

This was shown to be theoretically possible, the results from the irradiations not definitely proving the accuracy.

If variations can be found to exist then some reason for these variations will produce results of geologic importance. Oxygen iso-tope variations have been used to determine temperature of formation of carbonates, sulfur isotope variations may suggest biogenic origin.

The calcium variations might be attributed to either of these methods. Correlations would be necessary after variations are found to exist.

Also, in the calcium method, there are a wealth of samples to be tested. All limestones, carbonate shells, and bone materiels contain a large amount of calcius, so the importance of this method could equal or excel that of any other isotopic variation method.

A REINVESTIGATION OF THE

In recent years variations in isotopic abundances have played an important role in the field of geology. Originally, the belief was that the values for isotopic abundances were invariants. Theories were later formulated that there should be slight variations from equilibrium ex-change reactions of the type:

2H2 018

C0216

4=2' 2H2016 +

002

18

As analytical techniques became better, slight variations were found. We expect the fractionation effects which produce the varia-tions in isotopic composition to be the greatest between the elements showing the largest relative mass differences. Indeed this must be true since slight fractionation effects have been established up to the mass range of about 80, and not for those of much higher mass.

The ratio of masses of the two stable isotopes of hydrogen is 1 : 2 so we would expect variations to be the largest for this element.

Variations of as much as 25% variation in the ratios of these isotopes have been reported.

Oxygen isotopic ratios have been found to vary in a very useful way. The equilibrium constant for the exchange reaction:

212018 4

Co

21 6 - 2016 I 00218

varies with the temperature, so the paleotemperature method was devised with which, in a carbonate, one can ascertain the temperature of forma-tion by measuring the 018/016 ratio. The equaforma-tion is:

t

=

14.80 - 5.41

where t is the formation temperature in degrees centigrade and

Oi

The maximum variation of4J in ocean water is .17% which represents a variation of about 100C.

Nitrogen is known to fractionate. For the reaction:

N4H₄+ + N1 5 HZ --- N15 H4 + N1 4H4Z

fractionations of the order of 10% have been found to take place in the N14/N15 ratio. Biologic fractionation is also believed to occur

in Nitrogen.

Sulfur isotopic variations are also known. Ranges of the 832/S34 ratio are 21.60 --- h23.O0 The variations of the S32/836

are twice that of the S32/34 variations.

Calcium has been studied but significant variations have not yet been found. Except for hydrogen and helium, calcium exhibits the largest relative mass difference (20%). The isotopic effect should be larger than that of any other element except hydrogen if the fractionation is due to mass difference.

Calcium has six isotopes,

Isotope Abundance COO0 96.9 % Ca4 2 0.64 -Ca43 0.14 % Ca4 4 2.1 % Ca4 6 0.0032 % Ca4 8 _{0.18 %}

Between the Ca4 8 and normal calcium (Ca4 0) variations could go as high as 10 % comparing with other isotope variations. The usual method

of determining isotopic variations is the gas source mass spectrometer which in some cases is as accurate as 0.01%. Unfortunately calcium cannot be obtained in gaseous form so the solid source mss spectrometer must be used providing an accuracy of 31 or even greater.

The method of activation analysis was chosen with the hope of deter-mining the relative abundance of Ca4 8 to the nearest 0.1%. By acti-vating, or bombarding calcium, with nuclear particles, different nuolides are formed and then can be identified by some radioactive counting technique. Neutrons were chosen as the bombarding particles. The products formed by thermal neutrons from (At.,x) (neutron in, gamma out) reactions are:

Ca

(i,Y)

1.1 - Ids

.

Ca'

-C,(.,Y )o

&

my

c/4

--

+ _Sc"

d

k7.,

O

)

-4.7 VRY

CMP

-

.Ma

'"

~*T".

C.* S7 mmN9a -+T

Activity from the 57 min ccsqnox+aA will be the most abundant and easily traced product for short times (up to several hours) after ir-radiation. For a 1 hour irradiation and a 2 hour decay, the abundances of activities relative to Sc 9 will be approximately:

...- 4 -

3 o,ooW

ScSO

49

showing So49 being by far the most prcminent. Furthermore the slight Ca4 5 _{activity can be eliminated by counting through an aluminum}

ab-sorber of proper thickness.

The easiest method of preparing samples would be to dry weigh samples of pure CaCO₃ before irradiation and compare the ratios of So49 activity to weight of CaCO₃. Variance of this ratio would indi.-cate variances in Ca4 8. The production of 57 min. Sc49 is proportional to the neutron flux. The flux may very easily vary within .1% at a different position in the irradiation tube, appearing as a Ca4 8 variation.

To solve this problem, a fixed ratio of some stable element was added to the CaCO3 before irradiation. After irradiation the ratio of So49 activity and the activity from the added substance was compared for each sample. This provides a flux monitor since the change in neutron flux should affect both quantities proportionally. Naturally the half life of the irradiated element that was added should be either much greater or much less than that of So49 for purposes of resolution. Lanthanum was chosen, the production reactions are:

99 .% LaAx, j o.au$W.i 1 "

--.09%

2-16" Ye.La'"

()&

₃

'

the addition of the tracer be done quantitatively, can the counting be done with required accuracy, can the data be resolved to the desired accuracy, and will neutron energy variations affect the results.

If there are impurities in the CaCO3, they will be activated and will obscure some of the results. If purification techniques are per-formed on the material, then care must be taken so that further isotopic fractionation does not occur, changing the Ca4 8/Ca ratio.

The problem in adding the tracer is to add it quantitatively (at least within the

.1%

accuracy required). If trace amounts are added, then a solid weighing will not be permissible because of weighing

in-accuracies. If a solution mixture is used then when the CaCO3 and tracer are precipitated, the precipitation must be quantitative.

The accuracy of counting data is partly governed by procedure and partly by statistical mechanics. However, the accuracy of the statis-tical deviations can be kept below

t

.1%.

Resolution of the data into components is the most difficult of the problems. Impurities in the CaCO3 will add components to the decay curves, making accurate resolution less likely.

It is difficult to express the accuracy of graphically analyzing the data but certainly on two cycle semi-logarithm paper each point can easily be plotted to the nearest .5% so the accuracy resulting from 25 such points should be 0.1%. If we assume the human eye can make a good least squares analysis a line drawn through these points

should be very accurate. With care an intercept can be read off the line to about .2 % accuracy. Resolution of two components will be roughly half as accurate if the half lives are widely separated and

much less accurate if they are not. To obtain more accuracy a method of analysis should be programmed to run on a high speed digital computer. With this technique, data could be analyzed to the utmost in accuracy,

even with several components. However, even the computer cannot resolve half lives that are very near to each other accurately.

The variation of neutron flux can create another problem. The cross-sections (probability of registering a hit) are dependent on the incoming energy of the particle.

If the cross section of Ca4 8 and that of Lal39 vary with respect to different energy relationships, then a wide variation of energies with respect to position in the irradiation tube will cause variations in Sc4 9/La140 ratios. We oannot determine the effects of this theoreti-cally, but if we set up our samples in this manner:

Us tan d ar3 neutrons

lsamDle )

I $amp.L

3

then we can makD extrapolations between standards to ccnpare with each sample.

This compilation of work was started to find out if this application of neutron activation is feasible as a method of determining Ca4 8. The first step was to find an accurate determination of the half life of So 9. An accurate half life is a great aid in analysis of radioactive components. Calcium Carbonate and Calcium metal were bombarded with 15.0 MEV deuterons in the MIT cyclotron to produce So49 by the reaction

Ca (49 , ) .7

r

au Ca PS'N SC -+ T _4_

'When CaCO3 was used, 112 min. F1 8 was produced by the reactions

01 8(d,2n)F1 8 and 017(d,n)F18.

The 112 min. component was difficult to separate from 57 min.

Sc49 so several methods of reducing the F1 8 activity were used. One was to get rid of the F1 8 producing oxygen before bombardment by using

calcium metal instead of calcium carbonate. Improvements were made in the separation procedures. After three bombardments, the fourth re-sulted in a very good value for the half life. The half life without an impurity correction was 57.7

t

0.2 minutes. After correction the value chosen was 57.3 t 0.4 min.

The next step was to find out if So49/Lal40 ratios were reproduc-able within the irradiation tube. The first irradiation was made on

six samples containing a known ratio of CaCO3 and La(OHi) 3'

Large

quantities of 15.0 hr Na2 4 were produced making it virtually impossible to accurately determine the 40.2 hr Lal40* An attempt was made and the results were as follows:

Sample Sc4 9 / La140 la 15.46

lb

16.28

le 15.62

id

16.83

2

16.33

3

16.41

4

15.97

5

15.71

6 16.13

The results vary much more than the expected .1% but analysis after subtraction of the 15.0 hr Na2 4 was not possibly accurate. The amount of radioactive sodium varied in each graph. That means either that

analysis

was not correct, or different amounts of radioactive sodium

were added to each sample by the polyethylene. The letter was responsible for the major variations.

The next irradiation was to find out the actual amount of contaminants in the reagent grade CaCO 0 The experiment gave results for Ca4 5, Na2 4 and Sc49 at the end of irradiation, the results were

M a 5 c C4

Using G.E. chart (11) values for isotopic abundances and cross sections the percentage of sodium in the CaCO3 is shown to be 0.16 %. To reduce this value ion exchange techniques would have to be used which might fractionate calcium isotopes.

The third experiment was designed to reduce the Na2 4 activity after irradiation by dilution using sodium hold-back carrier. The experiment failed, however, when too much sodium was added and sodium carbonate

precipitated.

The next series of experiments should be designed to produce a two component curve, 40.2 hr. La140 and 57 min. Sc4 9. The 160 day Ca4 5 activity can be eliminated by counting through an absorber. The 15.0 hr. Na2 4 must be eliminated either by purification before irradiation

Conclusion and Recomnendations

The method of activation analysis for determination of isotopic variations is a satisfactory one. Mass spectrometry cannot be used to determine Ca4 8 to closer than three percent accuracy. With pre-cautions, accuracy by this method will approach the theoretical accuracy of 0.1%.

The cyclotron bombardment results produced a very good value for the half life of So4 9, 57.3

t

0.4 min, necessary for accurate evaluations of Ca4 8,

The reactor irradiations indicate that the presence of Sodium must be eliminated. Without radioactive sodium the activity curves would be pure enough for accurate analysis.

Two recommendations are made:

(1) High speed computational techniques should be used in analyzing data from decay analyses. A general program should be written to handle this problem which could also analyze any radio

active decay data.

(2) A method should be tried which directly cmnpares the abundances of Ca4 4 and Ca4 8. If Calcium is activated the products are 160d Ca4 5 and 57 min. Sc49 in a ratio of about 1 : 3200. After 10 hours the ratio is about 1 : 3. After 20 hours only the Ca45 is important. Therefore from calcium itself we have a good built-in flux monitor. Analysis of the radioactivity will determine the rela-tive ratios of Ca44/Ca48. The variation of these ratios should be

about half as great as those of the Ca48/Ca ratio.

A problem here is that impurities must be virtually, non-existant because initial quantities of activities will be much greater and data will be counted over a long period of time.

APPENDIX A

Equipment

Three different radioactivity determining devices were used. The automatic sample changer is a Baird Atomic Co. proportional type sample changer model 750. A Baird Atomic Multiscalar II, model 132 operating a Clary time printer. This is a magasine loaded device which holds 50 samples. It can also be operated manually.

The manual Beta counter is an Atomic Instriunent Co. proportional type counter with a model 1020A Scalar with a Dimoo-Gray timing clock.

The gamma counting device is a scintillation type counter using two model 510 Atomic Instrument Co. pulse height analyzers which are

fed into a model 1020A Atomic Instrument

Co. Scalar. A Baird Atomic

Co. timer model 960R was used.

Chemical work was done in the Geochemistry Lab at MIT.

Irradia-tions were performed at the MIT Reactor and deuteron bombardments were

done at the MIT cyclotron.

AD

- W 0=26- __

IFP"'O-APPENDIX B

Appendix B

The objective of this application of activation analysis is to produce a method which will accurately determine the relative abundance of Ca4 8 among several samples.

'Te would like to determine these ratios to within about 0.1 % error. The following few pages will contain a brief discussion of the mathe-matics of the analysis, giving us same proof that the problem can be done.

After the data reduction we want an expression of this sorts

function of data t error

The methods generally used to obtain data are to count a radio-active sample for either a predetermined length of time and record the number of counts during that time, or to count a sample until a certain number of counts is reached and record the time interval re-quired to reach that number of counts. By dividing the number of counts by the time interval we obtain the desired units, counts/time unit.

There is also a relative time (clock time) at which the sample was counted. This must be recorded so we will know the rate at which the sample decays. Usually scme arbitrary time is chosen as the

origin (t=o), often it may be taken as the time at the end of irradia-tion, the time counting began, or any convenient time.

The customary procedure is to record the time from the origin (t-O) to the time at which the sample had been counted for half of the total count interval.

an interval of time during which counting was done, J, and a relative time, t, at which the information was recorded. The activity, A is obtained by dividing N and

J.

A a

N/

We will now define various errors:

statistical errors from random disentigrations error in recording the interval time

error in recording relative time

dead time error

long count error

fitting errors

All errors mentioned will be given as

%

deviation of activity A from each type of error. Thus a 4. l 2.59 means that the error of each data point combined produces an overall error in A of 2.5%.

The statistical errors, , are those that arise from the fact

that nuclear disentigrations are random processes which may deviate from the A law. Generally we speak of standard deviations which mean the first standard deviation, 9, within whose range 68j of the data lie. A complete analysis is available in Friedlander and Kennedy (3), only the results will be used here.

where

Mo x initial number of atoms at beginning interval P z probability of recording a disentigration

q

I - P

efficiency is 100% then

pa-and

=

Number of disentigrations if 0. & /

so that _{5 = -VNLP18II.}

_o-

_{biSsmnOQi77oNS}

If the counting efficiency, C, is less than 100 , then

q

C -- 'u)

G

-MO

7&C e4

)

(--c -g'

)

t observed number of counts, N,

then

W(

/- C

-CC-U)

For C z 0.2 6

= .99M

0.1 0.2 0.3 0.5 1.0 In general and 9 deviation of A so that Since .98 -0'

.97-1

.96

fR

.93

Ym*

r

Adding statistically,

-j.

:±1r~I

The errors in recording the interval time result from the stop watch or similar timing device. I feel that a safe estimate for timing errors is t _{0.005 min. for either a stop watch or an autaatic timing} device. _{With practice and a good stop watch the error might be cut} to -'0.002 min. but the larger figure is a safer estimate.

The error in A from an error in comes from A

=

N/5

AND AA - g Agr

so .$"6mw V

-A

_X

, is the sum of these, so

The error resulting from recording the relative rectly usually occurs from reading a watch or clock. attempt is made to obtain a figure better than t 0.1 6 sec. Since A A & time, t, incor-Usually little min. or about

AA=-Axe

tAt

AA

21

For Z data points

E

and

Therefore

The long count error results from the fact that we are unable to take an instantaneous counting rate at a given time. Instead we talae a finite interval, , and assume the counting rate is the same

every-where in that interval. _{If the interval is not much, much less than} the half life, then error results

for

.1

/0

error

07 .2

%

error .2 %- .3 .4 % .5 1.0 4%

This error is not statistical in nature and can be corre cted be-fore analysing the data.

The dead time error results from the fact that after registering a count, the counter is insensitive to another count for a finite time (see Appendix D).

AA ,

N--A

T

A s 1,000,000 c/ min 500,000 c/ min

100,000 c/ min

50,000 0/ min 20,000 c/ min 5,000 c/ min

This error is not statistical and can be analysis of data,

The fitting error results from assigning the half life to a component.

Since

20

%

10

%

2 % 1 %

.4

%

.1

%

corrected before an incorrect value of

AAe-

At

where T is the half life,

4A-

-:O:-f-

Ae e'

A

T

sot

A

La A'

This error can be quite large. For this reason an accurate determination of the half life of Sc49 was determined. The most

ac-curate estimate is 57.3 t 0.4 min. The error is

This error is not entirely statistical in nature because if we are comparing the So4 9/La140 ratio in several analyses we will make the same mistake in half life for all analyses. The problem comes from

long backward extrapolations using an incorrect half life. In all oases we must extrapolste to a reference time.

If all analyses make the extrapolation for the same time length we are still all right. Call tel the length of time over which the component in curve 1 was extrapolated to the reference time and the

same for te2 in curve 2 to the same reference time. Let te2 .tel z te and compute the maximum Ate that can be permitted for a 0.1% error.

Then

_T

_A

and

4

.

If there is an error we want

k,

o.14

Left a A-r t-,.a

L44.2

AT

or 0.1%

-o-which is

t

.001 -

2 AT

For the case of So4 9 (57.3 - 0.4 min)

max.

te.

"

If the Sc49 half life were known to the nearest 0.1 min the extra-polation could cover a difference of 72 min.

If we make short backward extrapolations and correct for dead time errors and long count errors, the only errors remaining are statistical. Working out a special case will give an idea of these errors.

Take Z = 25 points of data, assume a one component curve with 60 min. half life. Count each point for 90,000 oounts over 5 half lives and let there be no interval between counts. Ao will be 26,700 counts/min. Make all non-statistical corrections. The statistical error

4. I- A

~

'f

The interval error is

A

+J':± e. csince all counts are for 90,000 counts,

the time interval S must increase as titne increases.

or Jf r

Snbstituting:

a

**

&0

-

"'1

V

(.o)

The summation l . may be approximated by

the integral

(AVE. "n T)4

which equals .',

6,4-The OI error is

or

-..

64

\

0

2)6

a'

t .1

1.0W I

JS5X

T

Sto

V.

a."fi

at

-. -.At

The sum of these three statistloal errors is

'SE .

OooO4S)7 4

C.O00003.Sa +

(- ooaor')2L

This shows that with this simple case the error is small that an accuracy of .1

%

is readily obtainable statistically. or not chemical procedures can match this accuracy is another

enough Whether quost ion.

-APPENDIX C

CYCLOTRON BOMBARDMENTS

(Determination

68

So49 half life)

CYCLOTRON BOMBARDMENTS Determination of So49 half life

Four bombardments were made on calcium in the Y.I.T. cyclotron, producing the decay chain Ca4 8(dp) CagS 49- 149. The purpose of the cyclotron bombardments was to find out if a very accurate value

for the half life of Sc49. The "G.E. chart of the Nuclides" lists the value of the half life as 57 min. Koester (5) lists the value as

57

±

1 min. and O'Kelley (7) lists the value as 57.2

t'

0.7 min. The first experiment was a bombardment of 108.5 mg. of reagent grade CaCO3 in an aluminum packet. The bombardment was five minutes

of 15 MEV deuterons with an ionic intensity of 20 micro amps. The sample was allowed to cool for 10 minutes after the irradiation. The sample was unwrapped and the CaCO3 was dissolved in HCl. Ten milligrams each of Sc3 4 and K± carrier were added and the solution was heated. NH40H was added to precipitate Sc(OH)3. This scavenge removed con-taminants insoluble as a hydroxide, especially the 3.9 hr Sc4 3 and 400 hr Sc44.

The Ca49 in the remaining solution is allowed to decay for 15 min. by which time about 3/4 will have decayed to Sc 49 Ten milligrams of Sc3 carrier were added, then all the So was precipitated as Sc(OH)3. The precipitate was centrifuged and washed, then transferred in a slurry to a Hirsch funnel and filter. The precipitate was dried with methanol and then ether, then counted on the manual Beta counter.

the results can be resolved into two components, 57 min. SoO and 112 min. F18. The Fluorine was introduced from the oxygen in the car-bonate by the reactions 01 7(d,n) F18 and 01 8(d,2n) F 18* The half lives of these two components are too close for an accurete analysis by the graphical method.

Several absorber curves were run using absorbers of different

thicknesses. The results are the graphs on pages 34 , 36 , and 36.

From Feather analysis the range of the Sc49 Betas is 2.2 MEV. Koester (5) lists this value as 2.05 t 0.05 MEV. From a subtraction the range of the second component is about 0.8 t 0.4 MEV which does not disagree with the listed value for F16, .65 MEV. The most conclusive evidence that the contamination is F1 8 comes from diermination of the gamma energy. The indication is a positron gamma annihilation, .51 YEV,

which agrees with F1 6.

In the second cyclotron run an attempt was nde to eliminate the 112 min. F18. Pure calcium metal was used instead of CaC03. Calcium metal oxidizes very ran'idly so fresh surfaces were cut and the metal was immersed in kerosene. The weight of the calcium slab was 140.4 mg. The bombardment and the separations were the same as in the first bom-bardment except the first Sc scavenge was done twice. The sample was counted on the manual Bete counter and another absorber curve was run.

The results are shown on pages Vg, 4 and 4" . The F18 contamination

49 was still to high to determine a good value for the half life of Sc

A festher analysis was run on the Sc4 9 absorber curve, suggesting a range of teo* mg/cm2 or a Beta energy of 2.1 -a" MEV.

The third attempt was run in an attempt to further eliminate the F18 activity. A 97.5 mg. target was bombarded as before. Two Sc

scavenges were made. A fifteen minute delay was allowed to let the Ca4 9 decay to S04 9. Sc30 was added and So(OH)₃ was precipitated with NH₄0H. The precipitate was centrifuged, the supernatent liquid

de-canted and the precipitate disolved in HCl. HF wqa added then NaOH was used to precipitate the Sc(OH)₃. The experiment failed, however, because the NaF was slightly insoluble when added in concentrated quantities and the activated Sc(OH)3. precipitate was confused with the NaF precipitate containing 112o9f F18 activity. This run was

con-sidered a failure.

The fourth bambardment was by far the most successful. The pro-cedure was similar to the preceding propro-cedure except KOH was used to precipitate Sc(0B)3. KF did not precipitate. The precipitate was washed and dissolved with HF, then precipitated again with KOH. The precipitate was washed, slurried, and filtered through a Hirsch funnel.

Three samples were prepared, one was counted on the automatic

counter through a 162.4 mg/om2 aluminum absorber, the other two samples were counted normally. One contained much more activity than the other in an attempt to calculate a dead time correction for the counter. The results of the dead time calculations are shown in Appendix D. There is a slight contamination in the samples at the tail end of the graphs of 8o49 activity, pages 33,

5q

and vS . The method of analysis was to take the first section of the curve, consider it pure S049 and determine a value for the half life. This is legitimate be-cause of the small amount of impurity present.

From the tail end of the curve we obtain an idea of the amount of impurity. If we can guess what the impurity is we can extrapolate backward and obtain a correction for the previously obtained half life.

Some good guesses for the impurity are 15.0 hr Na2 4, 112 m F18_, 3.9 hr. So, 4 3, 400 hr. Sc44, and 2.68 hr Mn. The range of the F1 8 Betas is 350 mg/cm2. The 168.4 mg/cm2 absorber should cut down approximately 90% of the F18 Beta activity. This means that the graph without the absorber should contain 10 times the impurity, but as

can be seen from the two graphs this is not the case. This rules out F1 8,

For purposes of calculation 4.0 hr Sc4 4 and 3.9 hr Sc4 3 will be added together and called 4 hr. Sc. Assume that a (dpn) reaction is as probable as a (dp) reaction and that a (d,2n) reaction is 1/5 as likely as a (d.p).

Possible reactions and abundances:

Reaction Abundance of Reaction

Ca4 8(d, p)8.7mCa49-- 67mSc49 .18%

Ca4 2(d,n)3.9hr Sc43 .64%

Ca4 3(d,2n)3.9hr So43 .14%

Ca4 3(d,n)4.Ohr Sc44 .14%

Ca4 4(d,2n)4.Ohr S44 2.1%

Considering the 3.9 hr Sc4 3 and 4.Ohr Sc44 as a 4.Ohr isotope ard using the reactio probabilities mentioned above, the ratio of production of Ca4 9 to 4.Ohr Sc is 0.18 : 1.23 or about 1 : 7. The Second Scandium scavenge in the fourth irradiation was over 14 minutes efter the

irrad iati on.

This means that about 2/3 of the Ca4 9 had decayed to Sc4 9 and was precipitated as the hydroxide. The remaining 1/3 Ca4 9 was allowed to

_4 2

decay to Sc49 and then precipitated as Sc(OH)3'

The two scandium scavenges should have removed almost all of the initially created 4.Ohr Sc. If we assume that the contamination of the graph on page 544 results from 4.0 hr So then some must have escaped the two scavenges. The graph on page 6a suggests that at the time of the precipitation of Sc(OH)3 during the second scavenge, 08:37, the ratio of So49/4.0 hr So was 190,000/150 or about 1300/1.

The ratio of production of Sc4 9 : 4 hr So was I : 7, the ratio of activity of Sc4 9 : 4 hr So was 4 : 7 at the end of irradiation. At the end of the second scavenge, if no 4.0 hr So were lost during the

scavenges the ratio of activities would be about (3:7)(1/3:1) or 1 : 7. Therefore the two scavenges result in lowering the So4 9/4.Ohr Sc from 1/7 to 1300/1. This shows the two scavenges result in a lowering of the 4.0 hr Sc by a factor of 1300/1 . 7/1 or about 9000/I. Since there were two scavenges, each scavenge reduced the 4.0 hr So by [ or 95/1. This suggests that 1% of the 4.0 hr So evades the scavenge.

These results show that the Scandium scavenges were 99% quantitatives, a very reasonable result, also providing more evidence that the contami-nation in the graph on page Sq is 4.0 hr So.

If the amount of 4 hr. So shown on page Ig is subtracted the re-vised half life is 57.3 min. with a possible error of 0.4 min.

10.

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37

DA-TA FROM CYCLOTRON BOMBARDMENT

4

1 Feb. 23, 1960

Manual Beta Counter, 2nd Shelf,

Sample Stand ard So 9 " S49 ", Clock Time 09:36:00 39:00 40:15 41:4C 43:05 -44:32 49:05 54:40 55:50 57:20 10:02:40 04:00 05:30 11:05 12:20 14:05 19:35 21:50 24:00 26:25 27:35 29:05 31:35 32:50 34:35 36:05 37420 38:50 42:25 41:40 43:20 44:50 46:05 47:35 48:50 50:35 51:45 53:50 56:50 59L10 11:02:15 03:25 04:45 15:10 16:45 18:10 25:50 27:00

counting -Rate (o/min)

(534 0/) 76135 74698 73039 72107 71129 211 63980 63195 252 58855 57762 612 54084 53575 2254 50284 49584 6009 47601 46915 10302 45638 44739 15188 43401 42844 25005 41808 41109 36039 39856 39883 39546 38638 38459 37730 (538 o/s) (535 o/s) 35612 34588 34199 136 30769 30409 142 28370 27690 1700 840 I1Q 1700 840 625 433 273.1 165.9 Absorber (mg/m2 99.6 34.5 6.32

Sample Absorber (mg/cm2₎ 625 433 If If If If If If If It If If It If it If If It If If If Standar S inder "

~

" "f " "f " Stndrd Stndrd So49 "f " ,#A0 Clock Time 11:29:05 34:35 35:45 37:30 39:50 40L55 43:00 44:25 47:35 49:05 50:50 51:55 53:40 55:00 56:05 57:25 58:45 59:50 12:01:35 03:20 04:25 05:55 07:35 09:55 17:40 18:45 29:30 30:40 31:50 33:00 52:45 54:00 13:05:15 06:20 15:20 16:25 26:35 27:40 37:00 38:20 49:00 50:05 51:35 52:40 56:2V) 57:38 14:05:00 06:05 18:20 19:25 27:30

counting Rate (c/min) 265 26382 25983 881 25151 25002 2315 24156 23247 3889 22864 22633 6271 22298 21997 18751 21532 21182 11237 20662 20309 17421 (532 a/p) (533 a/s) 18067 17880 16394 16495 16195 16174 13239 13224 12390 12323 11652 11237 10494 10461 9898 9933 8762 8949 8683 8799 8333 8164 7966 7853 7168 7109 6775 273.1 165.9 89*6 6.32 34.5 6.32

Sample Standard ScYa " " "' " " " " " S'9 Clock Time 14:28:35 34:10 36:290 38:45 39:50 41:30 52:00 53:05 54:25 15:04:50 06:30 08:35 18:50 19:55 21:40 32:05 33:10 34:30 41:05 42:10 43:45 48:20 49:25 51:00 54:00 55:05 56:30 58:55 16:00:00 01:45 03:05 04:15 05:55 08:10 09:20 18:20 19:30 31:00 32:05 40:05 41:10 45:15 17:26:05 27:10 30:35 38:50 52:30

Counting Rate (o/min) 6650 (531 0/;) (531 0/B) 6111 6209 46.3 5666 5529 48.8 5083 4980 55.9 4637 4678 83.4 4307 4240 177 3970 3994 271 3808 3937 587 3656 3658 1595 3502 3550 2917 3416 3408 (532 o/) 3348 3307 3072 3110 2871 2751 2596 2658 15.6 1951 1865 1878 (528 c/o) 1623 Ail 1700 840 625 433 273.1 165.9 8906 34.5 6.32

Selective Gamma Counter, Gain - 16, 1/2, High Voltage -J,

Analyzer 617-19, Scaler 617-18, Pulse Height Selector, -9

0e01 standard Base Line (volts)

1 volt channel width 46.0 45.0

46.0

44.0

43.0

47.0

46.0

45.0

44,0

counts

/

sec.

355.9 344.4 342*1 340.0 300.8 317.7 359.1 348.2 333.1

Base Line (volts) 40 39 38 37 36 35 34 33 32

31

30

Cyclotron sample

counts

/

min. Background (c/r)

113

169

225 251 309

242

206

147

119

41

( Peak)

' ₄ I".WtV 4 in

c.qc lossD

cb- x

4

105

Nt:lc

A

A

A

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ci.,

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16:60

.j .1 1400

13:b

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e

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,

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/

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14

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DATA FROM CYCLOTRON BOMBARDMENT

#

2

Feb. 25, 1960

Manual Beta Counter, 2nd. shelf,

High Voltage 2.15 KY, Pulse Height Seleotor

+25.

Sample Background Standard " 9 " " S " " " "t "

Counting Rate (o/min)

ClookTime 08:00:00 09:42:45 09:44:15 45:30 46:35 47:55 50:15 52:00 57:40 58:45 10:00:15 10:03:35 04:45 06:15 07:36 08:45 10:00 11:20 12:30-13:45 15:05 16:15 17:30 18:50 20:00 21:25 22:45 23:55 25:20 26:40 27:45 29:10 30:30 31140 33:15 35:35 36:45 38:05 43.25 44:35 46:15 51; 30 52:40 54:00 55:25 56:35 57:50 59:05 11:00:15 Absorber (mg./om2₎ 14*6 (532o/s) 314176 311534 306948 303109 299096 292500 81.0 270750 268616 3320.3 254111 250340 3979 242849 240052 22242 232726 229538 61516 224120 221832 106388 215473 213343 142034 207481 203190 167619 197822 195914 183638 189460 187681 53360 179387 177098 58.2 163785 162114 200.4 150274 148846 2269 144448 142255 12341 138419 136964 840 625 433 273.1 165.9 89.6 3405 6.32 1.700 840 625 433

ab*

1700

Counting Rate (o/min) Sample Sofa " " " " " " Stndrd 8if9 " "f " " Standard So9 11:01:40 11:03:00 11:04:10 11:05:25 11:06:45 11:07:50 11:09:10 10:30 11:35 12:50 14:00 15:05 16: 30 17:50 19:00 20:30 22:50 23:55 25:25 30:45 31:50 33:10 38:25 39:35 40:45 42:05 43:10 44:30 45:50 46:55 48:20 49:35 50:40 52:00 53:15 54:20 55:35 57:00 58:05 59:20 12:00:30 12:01:35 12:02:55 12:04:10 12:05:15 06:45 09:00 10:05 11:40 16:55 18:00 Absorber (mg./m 2) 273.1 165.9 89.6 34.5 6.32 35418 131310 130658 61468 127236 125777 82184 121082 120166 98034 116670 116109 107916 112355 110618 53401 105954 104510 222 96437 94693 676 88477 87111 1289 84596 82925 7084 81212 79882 20346 78037 76803 35004 74708 73667 47640 71505 70406 56933 68720 67921 63164 66141 64912 53036 61969 61626 159 56918 55988 1790 840 625 433 273.1 165.9 (534 els) 105954 104510 44.4 135.2 (530 o4s) 31.8 1700

44q

89.6 34.5 6.32 Clock Time

809 " " " So9 " p "1 " Stndrd So49

Counting Rate (0/min) Clock Time 19:25 24:40 25:45 27:05 29:30 30:35 31:45 12:33:20 12:34:25 35455 37:15 38:20 39:35 41:00 42:05 43120 44:50 45:55 47:15 48:35 49:40 51:15 52:40 53:45 55:30 58:20 59:25 13:07:00 13:08:05 13:17:20 13:18:25 24:15 25:25 32:30 33:35 40:00 41:05 47:25 48:30 56:25 57:40 14:01:00 14:07:00 12 :35 21:00 23:30 26:15 31:20 37:00 44:00 81.8 719 Absorber (m./m2) 840 625 433 273.1 165.9 409 52038 51251 1438 49012 48349 4055 47010 45870 11472 44771 43994 20251 43062 42404 27495 41076 40987 32583 39120 38894 36085 37082 36942 53782 35101 34502 31830 31201 27990 27780 25918 25649 23556 23122 21118 20983 19852 19348 17723 17500 16701 31161 29111 26418 52948 24776 23676 21866 20422 6.32 (538 c/o 15580 14556 13209 (530 o/s) 12388 11838 10933 10211 'C

wk

A

89.6 34.5

Sample Clock Time Counting Rate (o/min) Absorber (mg./cm2) S049 46:45 156 22.3 1700 54:10 18030 9015 56:45 166 33.2 840 15:02:15 16488 8244 4:55 645 129 625 13:10 14500 7250 15;40 1767 589 433 19:00 13390 6695 21:30 3258 1629 273.1 24:00 12858 6429 27:30 5436 2718 105.9 31:10 5789 34:00 3526 89*6 37:00 5598 41:00 4276 34.5 44:00 5166 47:00 4766 6.32 49:30 4820 Standard 52:00 (533 a/s) S04 9 55:05 4488 16:01:00 4167 06:30 4024 11:15 3702 16:00 3443 20:30 3288 26:20 3156 33:00 2914 38:30 2764 43:10 2559 48:20 2498 54:00 2272 58:50 2185 17:05:50 2018 Standard 17:11:30 (532 o/s) So49 13:45 1888 21:25 1728 26:50 17.2 1700 37:15 1477 42:30 24.1 840 53:00 1249 58:30 39.2 625 18:08:45 1079 18:14:10 94.6 433 24:30 924.6 29:50 206.4 273.1 37:00 831.6 42:20 291.6 165.9 47:35 735.6

91

Sample S049 "1 * Standard S04 9 Background Standard Standard Sc 4 9 Background Standard So49 Standard Background 8,049_{S o4} Background So49 Standard Standard Baekground Standard S049 Background So49 Background Standard So49 Background Standard

Counting Rate (c/min) 53:05 58:30 19:03:55 09:20 14:45 20:15 25:40 27:50 33:10 43:50 50:00 20:05:00 20:20:10 20:40:20 55:20 21:11:00 25:10 21:40:00 21:55:00 22:06:30 22:15:45 34:10:00 34:12:00 34.:-27 :55 34:48:10 35:03:30 35:28:45 36:39:50 36:55:10 36:57:00 36:56:50 41:07:00 41:18:00 41:30:00 41:40:00 58:15:00 58:18:00 60:28:00 60:31:00 61:08:00 63:46:00 64.:44 :00 65:15:00 65:18:00 67:23:00 70:45:00 71:25:00 89.6 34.5 6.32 374.4 664.6 450.6 601.8 522.6 556.0 (534 o/s) 215.2 14.0 464.0 431.3 379.3 342*9 302.3 268.0 245.2 224.7 205.3 196.0 179.6 (531 c/0) (536 o/s) 52.7 16.7 49.9 16.9 (538 o/s) 48.5 (539 o/s) 16.3 44.4 41.8 15.0 40.8 (537 c/1) (530 0/s) 15.8 (531 o/s) 29.4 15.6 29.1 14.1 (533 c/s) 29.4 29.4 13.3 529 1700

Absorber

(mg./m2

Olook Time

13@W0EfVA. 4I4

jL

kn

4-Wa

oA.

taeq

c.r

TIM c~4*meet.gt /OK~ A4 Q 10:06 fe 4. C/o% x o c Kx 54'

G./m,

IQ 1 3 o As

18

on%'

'1h+3

ye

t ...

.6+ %or

4/0%x 14 3

e.o

r (t.

4.

xt 4 oLva4M c..t X IQ

Ao-,

k

.-4-, 5'<.~ c.ar~ft. GhES4v~'ttJ V..@u~ f/.I A i10 ,'4. Go _oo.0G o

'4

10:.0

ALl 41 /49. 4 6/, A

t4

So

:.,..reni

c,/p'vt x

F

1~

+

d

-4

_{5 74.±}

CJ

i

Cs5-

1

--)( oIhcA~ a gJs~ g. 6 w 1ilo/

DATA FROM CYCLOTRON BOMBARDMENT

#

4

Automatio Beta Counter,

High Voltage 2.30 KY, Pulse Height Seleotor +0.2

4 samples:

1. hot sample of bombarded Ca, no absorber let. shelf

2. weaker sample of bombarded Ca, no absorber, 3rd. shelf

la. sample of bombarded Ca, 168.4 mg/om

2

_{absorber 3rd. shelf}

ii 1 2 Standard 1 2 Standard 1 2 Standard 1 la 2 Standard 1 la 2 Standard 1 la 2 Stand ard 1 la 2 Standard 1 la 2 Standard 1 la 2 Standard 1 la 2 Standard 1 la 2 Standard 1 2 Stand ard 1 2 10:00:10 10:03:20 05:00 06:10 07:35 09:10 11:40 13:05 14:45 18 t20 19:50 21:20 22:50 24:15 26:40 28:10 29:35 31:00 32:25 34:05 35:35 37:05 38:35 40:00 41: 30 43:00 44:25 45:55 47:30 48:55 50:20 52:00 53:25 54:45 56:25 57:55 59:20 11 :00:45 02:30 04:15 05:45 07:20 08:55 10:30 1155 13:25 14:55 16:30 18:05 289600 54266 30382 270626 51412 29718 56754 251064 47132 30226 2228160 49494 42182 30274 214864 46432 40280 30324 200506 42636 36530 29902 186044 39840 34800 30209 174518 37196 32144 30128 163650 34872 29834 30000 151518 32566 27802 30208 140916 30076 25546 30230 130494 27780 23560 30036 122014 25818 22056

61

55048 52112 57592 47717 50124 46999 42649 43113 36878 40253 35114 37554 32380 35173 30059 32839 27997 30303 25709 27975 23690 25985 22175

Standard 1 la, 2 Standard 1 la, 2 Standard 1 la. 2 Standard 1 la. 2 Standard 1 la 2 Stand ard 1 2 Standard 1 la, 2 Standard 1 la 2 Standard 1 la 2 Standard 1 la. 2 Standard 1 la. 2 Standard 1 la, 2 11:19:35 21:10 22:55 24:30 26:10 27:50 29:40 32:00 35:00 36t40 39:00 41:00 43:00 44:50 46:45 48:45 50:45 53:00 55:00 57:00 59:00 12:02:30 05:45 07:00 08:45 09:30 11:15 12:30 14:00 16:45 18:00 20:00 21:45 24:30 26:00 27:30 29:00 32:45 36:30 40:15 43:00 46:30 49:00 51:45 54;45 56:45 59:00 1 to 30 30160 113196 23702 20282 30198 104842 22104 18578 30024 94340 19796 16678 30172 85796 18028 15094 30054 77942 16458 13704 30284 69824 14798 12456 30272 64406 13500 11334 30228 59488 12166 10558 30398 53572 11443 9542 30220 48464 9974 8215 30218 41102 8438 7053 30538 36740 7539 6202 23840 20380 22223 18658 19896 16740 18103 15141 16517 13741 14844 12485 13535 11356 12193 10575 11465 9553 9988 8220 8444 7053 7541 6199

68

Counting Rate (c/mm) Corre~~ted Lor Dead Time

Standard 1 la 2 Standard 1 la, 2 Standard 1 la, 2 Standard la 2 Standard 1 la 2 Standard 1 la 2 Standard 1 la 2 Standard 1 la 2 Standard 1 la 2 Stand ard 1 la 2 Stand ard 1 la 2 Stand ard 1 2

Counting Rate (c/min) 1:05:30 09:45 11:30 14:30 17:30 21:00 22:45 24:45 28:30 30:45 32:35 36:25 40:05 42:00 43:45 48:30 52:30 54:15 56:00 14:0035 05:10 07:00 08:55 13:35 18:15 19:50 22:15 26:55 31:30 35:00 37:30 43:15 53:30 55:15 57:15 3:05 :00 14:00 16:30 18:30 28:55 39:10 41:00 43:40 54:25 16:07: 35 09:15 13:00 28:45 Stmple 29953 31460 6412 5364 30?16 27460 "5694 4763 30664 24232 4954 4107 30556 21060 4376 3548 29774 18320 3785 3096 30084 15653 3175 2660 30162 13424 2739 2249 30334 11484 2282 1783 30204 9002 1787 1418 30318 7036 1390 1083.2 30098 5225 1027.4 794 29864 3669 709.9 527.3

Clock Time Corrected for Dead Time

6410 5358 5689 4756 4947 4098 4368 3538 3775 3085 3164 2648 2728 2237 2270 1770 1774 1405 1376 1069.9 1013.4 780.7 695.9 514

- I

sample Clock Time Counting Rate (o/min) Correct

Standard 16:44:20 30090 1 46t05 2374 la 51:40 466.3 452.3 2 17:07:20 351.3 338 Standard 23:00 30126 1 24:35 1600 ila 30:15 296.3 282.3 2 -Standard 46:00 29940 1 47:35 124.4 la 53:15 241.2 227.2 2 18:08:45 184.9 171.6 Standard 24 t20 30230 1 25:50 808.4 la 36:40 176.4 162.4 2 52:15 127.2 113.9 Standard 19:08:15 30296 1 10:20 528.2 la. 21:20 105.7 91.7 2 37:00 88.0 74.7 Standard 47t35 30214 1 49:10 365.6 Background 59:40 14.4

t*1

APPENDIX D

For 'ILM II&

Taidng the logarithm of both sides

Lt,

AA

L

C4

IL,

,

In the fourth cyclotron bombardment, two samples of identical radioactive composition were counted, one being of considerably more activity. If there were no dead time loss the shapes of the two curves would be identical. Since there is a deed time, the more active curve will suffer a greater loss than the weaker. This amount of loss may

be used to calculate . The two graphs that were compared are on pages g S . The Af vs R were plotted on the graph on page 64 and a line of slope 2 was drawn through the points. The line drawn indicated a dead time of 12 microseconds. If can be seen that the points bend away from the line in the lower region. The explanation

Dead Time Caloulations

The dead time of a counter is the length of time that the counter is insensitive after receiving a count. If the counting rate is high, a good portion of the counts may not be counted. Friedlander and Kennedy (3) show that the loss from this dead time is A49T 4r where AR represents the forgotten counts,

T

is the dead time, R is the observed counting rate and R* is the number of counts that would be

counted were there no dead time. Thus R*

=

R 4 A R.

i.5:-for this is that the weaker curve also suffered a slight dead time loss. An iterative procedure was used to recalculate the dead time using each previously calculated dead time to calculate the loss of the weaker curve. The recalculated dead time is 14 microseconds for the automatic Beta counter.

s

lop. =4

,AR

C /fnl x -10

DeA.J

-ftato

af.A,JloAavn

102,-Z

IPsc.

R-

V"

14

U4

APPENDIX E

Appendix E

Three neutron irradiations were made at the MIT Reactor. The purpose of the first run was to see if results are reproducable with-in the desired accuracy.

The same mixture of calcium carbonate and lanthanum hydroxide was irradiated in six separate polyethylene containers.

From the reactor production formula:

A'

N EB (i/

*e

where A a activity

4

a neutron flux

C a cross section of reactant a a isotopic abundance of reactant N Number of atoms of element

X Decay constant

tirr Length of irradiation

td a Time of decay after irradiation

we can figure out the amount of CaCO3 and IL203 needed to produce a certain activity. To produce 10,000 disentigration per second of Sc 9

and 250 disentigrations per second of Lal4 0 we need 0.32 mg CaCO₃ and

0.090 N gm La203*

The mixture of these solutions was then precipitated by bubbling through C02 gas and NH₄ gas simultaneously. The precipitate, CaC0₃

-La203 was then placed into the six polyethylene vials number 1-- 6. After irradiation, the mixture was dissolved with acid within each vial. An eyedropper was used to place each radioactive solution on planchets suitable for counting. A drop of concentrated hydrofluoric acid was