Disintegration of barium-140, lanthanum-140, tantalum-182, rhenium-186, rhenium-188, and gold-199

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DISIHTEGRAT 1ON OF Ba 140, La 140, Ta 182, H© 186, Re 188 and Au 199,

BY LOUIS A, BEACH

SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL IK PARTIAL FULFILLIIEYT OF THE RSQUrEFETTS FOK THE DEGREE, DOCTOR OP PHILOSOPHY, IF THE DEPARTMENT OP PHYSICS, INDIANA UNIVERSITY. AUGUST 1949

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ProQuest Number: 10295192

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uest, ProQuest 10295192 Published by ProQuest LLC (2016). Copyright o f th e Dissertation is held by th e Author. All rights reserved. This work is p ro te c te d against unauthorized copying under Title 17, United States C o d e Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106 - 1346

Acknowledgements The author wishes to express M s

appreciation

to Dr. Roger G. Wilkinson for his aid and guidance of the research reported herein*

He gratefully acknowledges the

assistance of his co-worker, Dr* Charles L* Peacock*

He

is indebted also to Dr* .Hilo B* Sampson for the cyclotron bombardments of rhenium.

ii

Table of Contents Introduction Barium 140 Previous Work Chernis try Preparation of Beta-Source Hesults of Beta Hay Studies Gamma Ray Studies Auxiliary Experiment Conclusions Lanthanum 140 Previous Work Chemistry Results of Beta Studies Discussion of Gamma Radiation Conclusions Tantalum 182 Previous Work Beta Sources and Results Gamma Ray Studies Conclusions Rhenium 186 Previous ’ Work Beta Sources and Results Gamma Ray Studies Conclusions

Rhenium 188

Page 47 »

47

h

47

n

50

Previous Work

it

50

Chemical Process

n

51

Beta Results

»

51

Previous Work Results Gold 199

G-amma Radiation Studies

w

54

Discussion

IT

56

Summary

n

60

References

tt

62

List of Tables

Table I,

The conversion lines of tantalum 182,

Table II,

The photoelectron lines of tantalum 182,

ff

36

Table III,

Analysis and summary of the conversion line and nhotoelectron line data,

"

37

Table IV,

The Gamma-Rays of Gold 199

fT

57

Table V,

Pinal Summary of All Data

”

61

v

Page 30

/ Figures Fig. 1 .

Beta-ray Spectrum of Eiarlitm 140.

Fig. 9.

Fermi Plot of Beta Bays from Barium 140.

Fig. 3.

Compton- and Photoelectrons Ejected from a Lead Radiator by the Gamma Rays of Barium 140 and Lanthanum 140,

Page

5

n

7

it

10

Fig. 4.

Proposed Decay Scheme of Barium 140.

n

13

Fig.

Beta Rays from Lanthanum 140,

it

18

•

t 20

Fig. 6 .

Fermi Plot of Beta Rays of Lanthanum 140,

Fig. 7.

Tentative Decay Scheme for Lanthanum 140.

Fig. e .

Beta Spectrum of Tantalum 182 in the Low Energy Region.

tt

27

Remainder of Beta S p e c tr u m of Tantalum 182.

It

28

ft

51

tt

34

Fig. 12. Compton- and Photoelectrons Ejected from a Lead Radiator by the Gamma Rays of Tantalum 182.

II

35

Fig. 13. Beta Spectrum from Rhenium 186,

Jt

40

Fig. 14. Fermi Plot of Beta Rams of Rhenium 186,

tt

41

Fig. 15, Photoelectron Suectrum from Gamma Rays of Rhenium 186.

n

43

Fig* 10. Disintegration Scheme of Rhenium 186,

rt

45

Fig. 17. Electron Spectrum from Gold 199*

ii

58

Fig. 18. Fermi Plot of Beta Rays of Gold 199,

tt

53

Fig. 19. Photoelectrons Ejected from a Lead Radiator by the Gamma Rays of Gold 199.

tf

55

Fig. 20. Possible Decay Scheme of Gold 199.

if

58

Fig. 9.

Fig. 1 0 . Fermi plot of Beta Rays of Tantalum 182. Fig. 11 . Photoelectrons Ejected from a Lead Radiator in the Low Energy Region by the Gamma Hays of Tantalum 182.

vi

f!

24

Introduction

In recent years, many investigators have studied the artificial radioactivities that may be produced by various nuclear reactions in order to determine their modes of decay, A variety of techniques have been used to obtain information about the nature and energies of the radiations from these isotopes*

Some of the early worb was done with cloud cham­

bers in a magnetic field] but since the number of observations was usually small, the statistics of the results were poor. Better values for the energies of the radiations were obtained with absorption methods, but there is still considerable varia­ tions between the results of different investigators using this method,

Probably the most dependable values for the

energies of beta- and gamma-rays from these unstable isotopes have been found with the various types of magnetic spectro­ meters , Also much valuable data has been found lately by means of coincidence absorption experiments,

This type of experi­

ment is a great aid in determining the decay scheme*

The befca-

gamma coincidence rate may indicate whether the beta soectrum is simple or complex,

The question of cascade or

parallel

emission of gamma-rpys may be answered In many cases by deter­ mining the gamma-gamma coincidence rate* Many of the heavier unstable elements have quite com­ plex disintegration schemes.

More than one beta-ray group

along with a large number of ga^ma-rays may be present in

1

their radiations.

Since many of the components have very

low energy values and therefore are absorbed in the windows of Geiger-Mueller tubes, the most frequently used detector, much of the data in the past has been rather Incomplete* Previously, the only reliable data in this low energy region was obtained with photographic plate detection.

However,

with the development of thin windows for G-M. counters, it Is now possible to measure energy values down to 5 kev with this tyo© of detector* In this study, a survey of the energies of the radia­ tions of barium 140, lanthanum 140, tantalum IBS, rhenium 186, rhenium IBS, and gold 199 has been made with a small 180 degree type magnetic spectrometer*

This instrument has

a radius of 7,5 cm, and a transmission of from 0*3$ to 0.4$, Its resolution permits internally converted gamma-rays to be measured with a half-width of 1,5$ and photoelectric lines with a half-width of 4 *

The general operation of this

instrument was exolained in a recent thesis by Charles L, Peacock.

Barium 140 Previous Work,

Barium 140 is a member of the

following fission product series found in most types of fission: Xe140 — -» 16s

Gs —

> Ba 40s

> La «— > G©'1*40 (stable) SOOli 40h

By absorption methods Born (B2) obtained a value of 1,2 mev for the maximum energy of the beta-r&ys emitted by barium 140,

Levy (LI) reported the end-point of the beta-

rays as 1,1 mev from his absorption measurements. From their study of this iso tone i^ith a thin lens spectrometer, Hall and Wilkinson (R.1) reported the maximum energy of the beta-rays as 1,05 rnev,

They also found a

gamma-ray of 0,54 mev which was partially converted,

hedsel

and Sampson (Ml) gave the energy of this gamma-ray as 0,529 mev. Kngelkemier (FI) found a complex beta spectrum for barium 140 consisting of two groups with maximum energies of 0*4 and 1,0 mev*

75 percent of the beta transitions go directly

to the ground state of lanthanum by the emission of the 1,0 mev beta-ray.

The remainder of the beta transitions lead

to an excited state and are followed by the emission of a 0,5 mev gamma-ray, Mandeville (M5) reported the maximum beta-ray energy to be 0*91 mev.

Lead absorption curves indicated two gamma

quanta of 0*14 and 0,6 mev.

Beta-gamma coincidences showed

that the beta spectrim is complex,

3

Chemistry#

All sources were prepared from a sample

of barium 140 in the form of BaClg obtained from Oak Ki&ge, Because of its long half-life compared with that of its daughter, lanthanum 140, the barium activity is in equili­ brium with the lanthanum activity#

To obtain pure barium

for a beta source, the following chemical procedure was used# After adding a large amount of lanthanum carrier to the chloride solution, an excess of IBN-hH^QB was added to precipitated the insoluble La(OK)^ * O remains in the filtrate.

The barium chloride

After the addition of barium

carrier, (Nli^JgGO™ was added to precipitate the insoluble BaCO3 •

This process was repeated to make certain the separa­

tion was clean.

The barium carbonate was dissolved in one

drop of 12I1-HC1 to give a barium chloride solution to be used in the preparation of the beta source. Preparation of the Beta-3ource,

A support for the

zanon source backing was mad© by cutting a slit 2 mm. wide end 20 mm, long in a oiec© of thin mica 10 mm* wide and 23 mm. long. After this support was laid across the rectangular source holder, a zapon film of about 0,08 mg per sq. cm. was placed over the support.

A thin line of Si water solution of insu­

lin was drawn, across the zanon over the slit in the support. As much as possible of the insulin was removed with a dropper immediately.

A couple of very small drops of the purified

barium chloride solution were placed on the film.

Since the

insulin destroys the surface tension, the drops spread over

4

CO to CD

d CO •H CD Hi •H to d

u •Ho CD

c

Q_

m CD d CD CD > -d d EH o a O

• CD d -p

4■p

0 o 3 d *H *«. d cd (0 d t>* cd d o 8 cd d ■p

i

to o a> CD Q,d w -P >» C*H CO O d 8 CD cd CO -p o CD d CQ •p

to

-o-

Q.

the entire area to produce a very thin line source when evaporated. Results off Seta Ray Studies,

The beta-ray

distribution from barium 140, obtained by using the source described above, is shown in fig. 1 where the number off electrons per momentum interval is plotted against the momentum in Hp units.

Three lines are seen to be superim­

posed on the continuous beta spectrum corresponding to the K conversion lines off three gamma rays off energies 0.160, 0.306, 0.540 mev, respectively.

L lines off these gamma

rays were not obtained because the measurements had to be completed before an appreciable amount off lanthanum activity could grow from the decay off the barium after the separation was made. The Fermi analysis off this beta distribution is shown i in fig. 2. This is a plot off (h/ff} as a function off o -~ (1 + n°)y ♦ n is the momentum in me units, M is the number off counts per Hp interval, and ff is the Bethe (Bl) approxi­ mation for a Z of 57 off the Fermi function.

\/-e

/

/j7

S= (

i

-

J

4

=

n.

i~37

The citrve is seen to have a definite break with two distinctly different slopes indicating a complex sooctnusi with two groups off beta-rays«

The analysis off the two

groups is accomplished in the following manner.

Starting

>

LjJ CJ

3

U rcdO CH O 05

5* *4 l i cd +CD> .O © -p

U

o

'ft

©

ft I— -j

Cd

6 O •rJ £ © o CM

*hHO ft

from tli© end-point, the first straight portion of the curve is extrapolated back to zero energy#

This straight line

represents the Fermi plot of the entire high energy group and can now b© converted back to the beta-ray distribution* This distribution of the high energy group is subtracted from the total distribution, and th© difference is sub­ jected to a Fermi analysis to give a Fermi plot of th© low energy group*

The ratio of the areas under the beta-ray

distributions of the two groups when plotted as > ’il/Hp} against Ho is th© ratio of the relative intensities*

The

distribution of the low energy group used to obtain this ratio must b© obtained by extrapolating the Fermi Plot back to zero energy and converting back to the beta distribution# This is necessary because absorption in the counter window voids data in the low energy region* The end-points of the two Fermi riots occur at values of 3*00 and 1*94 for (l*n^)-, and these values correspond to energies of 1#022 and 0*480 mev for th© maximum energies of the beta-rays of the two groups *

The ratio of the relative

intensities was found to be 80/40 with the higher energy group having the greater intensity. Gamma Hay Studies *

The Sources for the study of

the gamma radiation were prepared by depositing the equili­ brium mixture of chlorides obtained from Oak Hidge on the back of a copper boat mad© of 10 mil sheet copper*

Since

some of the beta radiation from lanthanum 140 has a high

8

energy, 0*02 inches of copper was added to make a total of about 750 mg* per sq* cun of copper cover in:;’ the material to absorb the beta radiation.

A 30 mg. per sq. cm. thick

lead sheet was placed over the copper to serve as a photo­ electric radiator.

The source was 2 mm. wide and the copper

absorber was 3 mm* in width.

The lead sheet was cut one ram.

wider than the copper to increase the photoelectric yield. The results of th© gamma-ray studios are shorn in fig. 3 where counts oer minute are plotted against the momentum in Hp units.

The nhotoelectr-on spectrum is. seen

to be quite complex with seven well resolved lines and throe small oeaks rising above the Compton distribution. ? These lines may be resolved into' K and L components of five gamma-rays of energies 0*335, 0*49, 0*54, 0*82 and 1*60 raev. The lines have a half-width of 4% except the first which probably has its front edge perturbed by the 0.306 mev gammaray found converted in the barium beta spectrum. Of th© resolved gamma rays, only the 0.54 mev gamma ray is assigned to the barium 140.

The assignment of this

gamma ray to barium is verified by the presence and non­ presence of its conversion lines in various beta suectra* Its conversion lines appeared in the purified barium beta spectrum and did not grow with the lanthanum activity.

They

are not present in a separated lanthanum beta spectrum (see fig* 5), although they are clearly visible in an equili­ brium beta distribution that was studied.

9

The assignment of

CM

O GQ

o

isotope of lanthanum 139 and by th© (n,p) reaction on cerium 140, the most abundant isotope of cerium.

It also grows from

the decay of barium 140, a fission product. Born (B2) used absorption methods to obtain a maximum energy for the beta-rays of lanthanum 140 of 1,4 mev and strong gamma radiation of various energies, Welmer (W2) found In a study of lanthanum with absorp­ tion measurements a group of beta-rays of 1,41 mev and a 2,00 mev gamma-ray. From the Compton-electrons of an aluminum radiator, Mitchell (B8 ) determined th© most energetic gamma ray of lanthanum 140 to be 2,0 mev, another gamma ray of 300 kev.

Th© absorption curve Indicated He estimated from the gamma-

gamma coincidence rate that there was two gamma quanta per disintegration,

lie gave the beta ray end-point as 1,96 mev,

The number of beta-gamma coincidences ner recorded beta-ray was independent of the beta-ray enei»gy indicating a simple spectrum. Rail and Wilkinson (Rl) reported the beta rays of this isotoo© to have a maximum energy of 1,45 mev,

From ohoto-

electrons, they determined five gamma rays of energies 0,335,

15

0.49, 0.87, 1.65 and 2,3 mev. These latex" results were checked by Miller and Curtis (M7) in the same thin lens spectrometer, using greater reso­ lution*

They gave the energies of the garama-rays as 0.335,

0.49, 0*83, 1.63 and about 2.3 raev. Osborne and Peacock (02) obtained similar values for the gamma ray energies b\it found a

c o m d Io x

lanthanum 140 with a magnetic spectrograph,

beta spectrum for A Fermi analysis

of their data indicated three beta groups of energies 0.90 (20$), 1.40 (70$) and 2,12 mev (10$) with some evidence of a weak beta group at 0.40 mev.

They quoted the gamma ener­

gies as 0*335, 0.505, 0,832, 1*61 and 2,52 mev with the 1*61 gamma roughly five times as Intense as the others.

Their

coincidence studies indicated that the 0*333 and 1*61 gamma rays may be in cascade. Prom the energy of the photo-neutrons obtained from the interaction of the gamma radiation of lanthanum 140 with heavy water and beryllium, Wattenberg (wl) determined the energy of the highest gamma ray to be 2.49 mev.

He considered

it to be very we ale* Mandeville1s (M2) coincidence absorption experiment agreed in general with the results obtained by Mitchell, referred to above.

He resolved the absorption curve into two

components, giving quantum energies of 1*60 and 2,16 mev.

He

also found the number of beta-gamma coincidences nor recorded beta-ray to be independent of the beta-ray energy but noted

16

that this may not he a reliable indication of a simple spec­ trum if the second grotto has a low Intensity relative to the n rincip al group* Chemistry*

Th© lanthanum 140 used in this

study was obtained from the same equilibrium, mixture of barium, and lanthanum mentioned above.

The following chemical process

was used to obtain a beta source of uure lanthanum 140 separa­ ted from its parent, barium 140,

After adding lanthanum carri­

er and a large amount of barium holdback carrier, the lantha­ num was precipitated as the insoluble La{OF■^ by adding 16$NH4OH*

The lanthanum hydroxide was dissolved in HC1 and the

above process repeated several times to make certain that no barium activity remained in the precipitate.

The final pre­

cipitate was dissolved with one drop of 122MIC1 to give a concentrated solution of LaCl*O for us© in the source ureaaration.

The technique used in making the source was the same

as that discussed for the barium beta source.

The decay of

the source was followed for 5 half-lifes and found to have the characteristic Period of lanthanum 140, thus indicating that the separation of the lanthanum from the barium was complete and that no other long lived activities wore present* Results of Feta Studies .

The distribution of

the energies of electrons emitted by lanthanum 140 is shown in fig. 5 where 1T/Hp is plotted against Hp*

The K and L

conversion lines of two gamma ravs of energies 0*335 and 0,488 mev as well as three peaks in the low energy rev,ion are seen

17

Fig.

5

Beta-ray spectrum of lanthanum 140* The energies of the gamma =»rays, not the conversion lines.

0.33

OJ given

are

those

to be superimposed on the continuous beta distribution*

The

lowest line Is most probably due to Anger electrons resulting from, the rearrangement of the electrons In the atom after the Internal conversion of the gamma-rays *

The remaining two

lines are weak and their identification uncertain*

As K and

L components they would correspond to a gamma-ray of 0.093 mev in energy*

The beta spectrum seems complex with two or

more groups present. Pig* 6 shows the Fermi analysis of the beta spectrum of lanthanum 140* This Is a plot of {N/f) as a function of O i (1 + )3 where N and n have the usual mean!ngs and f Is the Bethe approximation for a Z of 58 of the Fermi function*

The

curve is seen to have two definite breaks dividing it into three straight portions. consisting of atleast

This Indicates a complex spectrum

three groups of beta rays*

The analy­

sis of the snectrum was carried out as previously explained with two complete subtraction processes being necessary* o A The three Fermi clots Intersect the (1 + n^)^ axis at values of 5.425, 4.280

and 3,580 which correspond to energies

of 2*26, 1.670 and 1.318 mev for the maximum energies of the three grouos of beta rays*

The ratio of the relative inten­

sities, found by comparing areas under the beta distributions, is 1:2:7 with the lowest energy group having the greatest intensify. The Form! plot of the low energy group rises above the straight line below 0*50 mev.

19

This may Indicate a fourth beta

e

o

-d-

a -p

s: ^ -p C' O CVI

*H I

o 4°; W> •H

group of low intensity but the presence of the conversion lines in this region makes this rather doubtful* Discussion of the Gamma-Hadiafcion

As previously

mentioned, four gamma-rays assigned to lanthanum 140 were obtained from the photoelectron spectrum of an equilibrium source of barium and lanthanum.

(See fig, 3)

The photo

lines corresponded to gamma-rays with energies of 0*335, 0,49, 0*82, and 1.60 mev.

The very strong Compton-electron

curve is primarily due to the 1*60 mev gamma-ray*

This

gamma-ray must be quite intense not only because of the large number of Comoton-e1©ctrone but also because of the high nhoto line even though the photoelectric efficiency is very low at this energy.

The Comoton-electron soectrum

continues beyond 1*60 mev and finally goes to zero at about 2.5 mev.

No appreciable evidence of a photoelectron line

due to a gamma-ray of this energy was found, indicating that it -must be very weak.

Stronger sources and a thorium

radiator, which has a higher photoelectric yield than lead, were used in an attempt to emphasize the photoelectric line of this gamma-ray.

However, sine© only about 9 cm. of lead

separates the source from the detector in this instrument, the background due to th© numerous strong gamma-rays is unusually high

in this case,

Th© presence of this back­

ground makes it impossible to reliably locate the ohoto line of a gamma-ray of this intensity even with these addi­ tional aids *

Conclusion*

Tir. 7 shows a. decay scheme pro­

posed to summarise the results of the study of the radia­ tions of lanthanum 140,

Three beta-rey groups are present

with maximum energies of 1,38 (70y), 1.67 (29yS), and 2.26 (103) raev.

The various excited states of cerium 140 return

to th© ground state by the complex emission of six gammarays with energies of 0.093, 0.335, 0.49, 0.82, 1.60 and 8,5 mev.

The 0.093 mev gamma-ray is not shown in the figure

hut is postulated to follow the 0.49 and 0.82 mev gamma-rays leafing to the 1.60 state.

The energies and relative intensi­

ties make the scheme remarkably consistent arid no alternate scheme seems possible.

The 0.49 and 0.82 mev gamma-rays

have about the same intensity while the 0.335 mev gananaray is somewhat weaker.

The 1.60 mev gamma-ray is the most

intense, while the 2.5 mev gamma-ray is probable thl weakest. Tf the 0*093 mev gamma-ray is to follow two of the stronger gamma-rays as proposed, it must be ores art In almost DOvI of the disintegrations and must consequently be considered strong.

It is difficult to determine Intensities of gamma-

rays of this energy since they are too low in energy to show an appreciable ¥. component in a oho toe le c tron soectrum. Since th© assignment Is based on two weal" conversion linos, the conversion must be assumed to be weak. tion Is subject to question.

Such an assump­

The energy of the 2.5 mev gaimna-

ray was estimated from the visial end-point of the Cometonelect ron distribution and can not be considered as accurate 22

as the others *

However, the value obtained is consistent

with th© oreposed decay scheme and the value obtained by \7attenberg (Wl) who measured the energy of photo-neutrons from deuterium and beryllium produced by this gamma-ray*

25

La 140

Ce 140 3.75 Mev 70%

2.43

2.10

1.61

0.00 Fig, 7

Tentative decay scheme of lanthanum XL0«

Tantalum 185« Previous Work*

The 117 day isotooe assigned

to tantalum 182 can be made- by the (d,p) or (n, K ) reactions on the 100

isotope of tantalum 181*

Oldenburg (01) reported that tantalum 182 decayed by beta emission to tungsten with a rather long half life* By absorption methods, Houtermans (H2) determined the maximum energy of the beta rays of tantalum 3.82 to be 1*0 mev*

He resorted that there was some gamma radiation

■^resent indicating excited levels in tun sten 182* Zumstein (21) used absorption techniques to find an intense gamma radiation of 1*6 mev and a complex beta spec­ trum in the activity of tantalum 102*

The beta spectrum

was interpreted as composed of three groups of beta rays w.ith energie s 0,98, 0*52 and 0 *050 mev * Using a magnetic lens spectrometer, Jnanananda (cl) obtained 0*499 mev for the maximum enorgv of the beta rays of tantalum 188, Ball and W 1Iblnson (HI) reported a single beta-ray frrour of energy 0*55 mev from their study of this isotone with a thin lens soectrometer* snectrum, they obtained

Prom the oiiotoeloctron

vnrmu—rays with, energies of

0*3.5, 0*22, 1.13, and 1*22 mev.

They also noted that the

first of these gamma-rays was converted* decently, Cork (Cl) made a study of the internal

25

conversion electrons in the low energy region by means of a 180 degree magnetic spectrometer with photographic elates as a detector.

He reported 54 conversion lines which were

resolved into about 16 gamma-rays of energies less than 0.3 mev. Mandeville and Scherb (M) reported beta-gamma coin­ cidences as well as gamma-gamma coincidences.

However, they

concluded from their low gamma-gamma coincidence rate that it was innrobable that the two gamma-rays of high

energy

reported by Hall and Wilkinson were in cascade. Beta Sources and Results.

Sources for the

present studies were prepared from a sample of TaOo irradia­ ted by slow neutrons in the Oak Ridge pile.

Chemical sepa­

rations were performed to insure ourlty, with special atten­ tion given to th© separation of cale5.um, iron and tungsten. Beta sources were made from TaqOp precipitated from h8f ^a3^19, A few droos of a water suspension of this oxide was evapora­ ted on a backing of zapon 0.003 mg, per sq. cm, thick,

for

th© low energy work the source was less than 0.2 rag, per sq. cm thick and had a very high specific activity. fig, 8 shows the low energy region of the beta spec­ trum of tantalum 182 obtained with a thin window G--M detector with a zapon window of 0.04 mg, per sq. cm, thickness.

The

remainder of the spectrum, shown in fig. 9, was taken with a conventional mica window tube with a window thickness of

1800

182

Ta

electron spectrum

1600

1400

1200

1000

800

600

400

200

500

tooo

Hp Fig, 8

The beta-ray spectrum of tari •! 182 in the low energy region obtained with a G-M tube detec':.or laving a window 0.03 n-.g thick, See 'Tables X and 111 j.i, tic 'iergies and idehtif ■:c •

o o o

ro

O O m on

o o o

CM

e units, gives the number of conversion electrons,

'hr the

0,138 mov gamrsa-ray, it is found that o(^s2 •8;j and dCcs 7/i>. Th© ratio of the 1C conversion to the L conversion is 0.40 and suggests a soin change of 2 or 3 for this gamma-ray transition, according to the curves of Kebb and Nelson (HI)* The validity of these curves at this high Z is subject to If

some question since they were calculated for a Z of 35,

the 0,212 mev gamma-ray is converted at all, the conversion must be weak.

TJnfortunately, the K conversion line of this

gamma-ray would be superimposed on bhe M lino from the mev gamma-ray.

0.138

The conversion coefficient of the third line

shown in fig, 13 is 1*2% and represents the sum of the K conversion of th© 0.218 mev gamma-ray and the F conversion of the 0.138 mev gamma-ray,

Comparison of these values of

the conversion coefficients with the tables of dose and his associates,(R2 ) indicates that both gamma-rays are probably electric dioole radiation,

Th© 0.158 mev gamma-ray is

placed following the 0,212 mev garama-ray since it is natural to assume it to be nearer the ground state because of i ’ .:s hi rrho r convers ion,

46

Rhenium 188# Previous Work,

The IS hour activity assigned

to rhenium 188 may be produced by the (ct.p) or (n,

) reac­

tions on the 63b abundant rhenium. 187* The maximum beta-ray energy was reported to be 2*5 mev by Sirana (SI) and 2.05 mev by Ooodman and Pool (G-l) . The latter reported that there was less than one gamma quan­ tum per four beta-rays in rhenium 188. '■"iller and Curtis (M7) measured the gamma-rays of rhenium 188 in a thin lens spectrometer, obtaining the foll­ owing values: 0.16, 0.48, 0.64, 0.94, and 1.13 mev.

The first

of these was more intense than the others and was also con­ verted, bandeville (K4) in his absorption experiment on rhen­ ium 188 obtained a maximum quantum energy of 1,39 mev.

His

absorption curve indicated a second group of beta-rays at 0.225 mev.

He interprets his low beta-gamma coincidence rate

as an indication that the majority of the gamma-rays reported for this isotooe must be coupled with this weak beta group. Cork (C2) reported a single converted gamma-ray of 153.6 mev for rhenium 188, Results.

The samples used in this study initi­

ally contained the activities of the 90 hour rhenium 186 as well as the 18 hour rhenium 188.

After making an initial

survey of the combined radiations, the decay of all components was followed.

Those components following the 18 hour oeriod

47

are attributed to rh©nittra 188,

In order to obtain th© beta-

ray snectniM of the short period activity froia a source of this tyoe, the distribution in energy of th© beta-r&ys iVoxa both Isotooos was determined,

Then after the IB hour activ­

ity had died away to a low level, the beta spectrum of the source was a' ain neasured«

This spoctivm. was hue to the

beta-rays of th© long period rhenium ICS« Hi© original amount of xiicmiivy IBS -.••resant was obtained by correcting for decay-, and this teen subtracted off to give the distribu­ tion duo to rhenium IBS# It was nroven quite conclusively, Particularly with later sonnies oreoared by deuteron bovhardment, with the Indiana Cyclotron, that only one grown of beta-raya is present 1n the rhenium 188 activity.

The maximum energy

of those beta-rays was found to be B*10 moy*

ho evidence

was found tor --he second grouo of bota-rays of 0*815 mov

reported by rundoville*

However * the

and L eon version

lines due to a gprrma-ray of ororgy 0,15 mev are "■••rosont in t M s royion* :?he gemra source desorb -od above in connection with rhonlum 106 was also used to study th© gama-ravo of vhoirivm 100 by taking measurements before the short had died away#

however, the

'©rhxi active ty

•resence of bota-rays In excess

nf two mev in th© rhenium 188 necessitated the addition of

more c o y m r to absorb all th© beta radiation in tlba ease# S fnee tli© thick absorber made the g©owetry for

48

hotoolec trie

production very poor, the observed photo lines were rather weak.

Five gamma-rays wore found with energies of 0.15,

0.43, 0.64, 0.95, and 1.40 mev.

The Compton distribution

due to the 1.40 mev gamma-ray from the thick copper absorber was quite strong, indicating that this gamma-ray is probably strong even though its ohoto line is rather small*

These

results essentially verify those reported by Miller and Curtis (•7) .

49

G-old 199. Previous Work.

The 3*3 day Isotooe assigned

to gold 199 oan be produced by the (d,n) reaction on plati­ num 198 and the (n, o ) reaction on mercury 199.

It also

grows from the decay of the 31 minute isotooe of platinum 199 , The studies of Krishnan and liahum (Kl) on gold 199 suggested that it decays with the emission of beta and gamma-rays.

Absorption methods gave a maximum energy for

th© beta-rays of 1,01 mev with indications of a lower energy grouo with an uncertain end-point due to conversion elec­ trons.

They concluded that a portion of the gold 199 decays

to the ground state of mercury 199 by the emission of the 1.01 mev beta-rays, whereas the rest decays to an excited state and are followed by the emission of a 0*45 mev gamma ray. I.Tandeville (M3) obtained a maximum energy for the beta-rays of gold 199 of 0.38 mev by absorption in aluminum. Lead absorption indicated a gamma-ray at 0*18 mev.

He found

beta-gamma coincidences as well as beta-beta coincidences but no gamma-gamma coincidences. Meem (M6 ) reported 0.32 mev to be the maximum energy of th© beta-rays of gold 199.

His lead absorption curves indica­

ted the presence of two gamma-rays of 0,24 and 0.14 mev.

He

obtained a beta-gamma coincidence rate that was independent of the beta-ray energy* Indicating a simple beta spectrum*

50

H© also reported, beta-beta coincidences and gamma-gamma coin­ cidences . Chemical Process.

The sources used in this

study were prepared by separating gold 199 from its 31 minute parent, Platinum 199, produced by neutron bombardment in the Oak Ridge pile.

The Platinum was dissolved In aqua regia to

give the chlorides of platinum and gold.

A little water was

added to this solution and then it was evaoorated almost to dryness,

10 c.c, ©ac: of water and ethyl acetate was added

to this residue.

0.1 mg. of AuCl^ carrier was added along

with 5 mg. of HgClQ to act as carrier for an • mercury Immuri•O ties.

3 droos of HC1 were added to oxidise all the mercury

into the mercuric state.

This solution was then placed in a

separatory funnel, shaken and allowed to separate into two levels.

The ethyl acetate extracts about 98;1 of the gold

wv'ile the mercury and platinum remain in the water layer. Afte

removing the 'water fraction, more water was added and

the ■'.''rocess repeated three times.

The ethyl acetate fraction

containing the gold was then evaporated to dryness on a steam bath to .leave gold chloride,

The water soluble gold chloride

was used to make a very thin beta source with hi h specific activity on a z&oon backing of approximately 0.003 mg. per sq, cm. thick.

The beta source was estimated to be less than

0.1 mg. oer sq. cm, thick.

Subsequent examination of the

decay showed that th© separation was good. Beta Results.

The beta spectrum emitted by gold

199 is shown in fig, 17 where (N/Bp) is plotted against Fp,

Fig®

IS

CM

CM CM

Fermi

plot of the beta-rays

(I + r f r of gold

m 199*

Since all the radiations are in the lo*w energy region, the entire soectrum was obtained with a very thin window G-F detector*

Sight conversion lines are se-n to be suoorim-

nosed on the continuous beta, distribution* A conventional Fermi plot of the continuous betarays is shown in fig. IB where (N/f)'* is clotted against o b (l-fn°)";, In this case, f(2,n) is the high Z Fermi aporoximation of (n +-0*355n^) •

ho correct:! on for Z was applied to

this function since the difference between the true Fermi function for a Z of BO and the approximation for a Z of SB .2 is small*

The end-noint of the Fermi clot occurs at O a value for (l-fn^)F of 1*62.6 corresponding to a maximum energy of the beta-rays of 0*52 mev.

ho attempt Is made to

account for the curvature of the Fermi "lot because it is perturbed by the presence of so raan:r conversion lines, Probably only one group of beta rays is oresent*

This con­

clusion was substantiated by fandevil1© (F3) and Feem (M6) since their

./^ coincidence curve was a straight line,

characteristic of a simple spectrum. Gamma Radiation Studios.

To study the photo-

electron spectrum, a source was or©oared by depositing the ourifiod gold chloride on a 10 mil copper strip*

Since the

beta rays have a low energy, this is sufficient copper to absorb the beta radiation,

A lead sheet of 32 rag, oer sq*

cm. was placed over the copper to serve as a photoelectric radiator.

54

Fig*

19

Photoelectron spectrum of gold 199® The energies gamma-rays, not the photoelectron lines®

K-.I56 Mev

ogiven

are

those

of the

The results of this study are shown in fig, 19 where the number of counts per minute is olotted against the mom­ entum in Ho units,

Since all the gamma rays have low energie

the number of Commton electrons is very small,

hive distinct

lines are seen in the photooloctron snectrum which can be analysed into K and. L components due to four gamma-rays of energies of 0,070, 0,156, 0,207 and 0*930 mev.

There is no

K component for the 0,70 mev gamma-ray since its energy is less than the K binding energy of lead.

The L component of

the 0.156 mev gamma-ray lies under the K line of the 0,230 mev gamma-ray while the L component of 0,230 mev is probably present but was overlooked v/hen the measurements were made. Discussion,

The analysis of the eonversIon-

and -vhotoelectron data is shown in table IV, aEstimation of the relative intensities is quite difficult since several of the components overlap.

The nhotoeloctrons shows that the

0*155, 3.207 and 0,230 mev gamma-ra^s are the most prominent, Using

rayfs (02) empirical curve for photoelectric effici­

ency, the 0,156 and 0,207 mev gamma-rays are found to have about the same intensity, while the 0.250 gamma-ray is about twice as intense as these.

Prom the beta spectrum, the

0.156 mev gamma-ray is seen to be the most strongly converted, with the L conversion being orob&bly stronger than the K conversion.

If any K conversion occurs for the 0,230 mev

gamma-ray, it falls under the L line of the 0.156 mev gammaray#

The fact that no L conversion component was detected

Table IV* The Gamma-Rays of Au^*V;^ ConversI on 1ine energy (mev)

Photo line energy (mev)

Oaiiima energy (mev)

0*0090 (L)

0,024

0*0360 (L) 0.0473 (F)

0 .051 0.054 (L)

0 ,070

0.0735 (K) 0.1470 L) 0*1590 (h)

0 .0SS (K)

0,156

0.1243 (K) 0.1970 (L)

0.119 (K) 0.189 (L)

0.207

0.1470 (K)

0,143 (K)

0.230

57

fQ

lO CM

O Possible decay scheme of gold 199

o >

for the 0.230 mev gamma-ray suggests that this gamma-ray is very weakly converted.

It may he assumed that these three

stronger gamma-rays are not in cascade and that they account .tor 30m, 25'3 and 45.1 of the transitions from the highest excited state of mercury 199*

This assumption is in accord

with the coincidence work of Mandeville (M3) In which he found no appreciable gamma-gamma coincidences*

he’would

not exoect to find the coincidences between these strong garnma-rays and the low energy gamma-rays since his counters do not detect gemma radiation below 100 kev* Fig* 20 shows a summary of the results and suggests a possible decav scheme*

The mode of decay is consistent

with the measured energy values, the estimated relative intensities and the coincidence data of other investiga­ tors.

One annarent inconsistency is the observed low inten­

sity of the low energy garnma-rays, since they must be assumed to he strong if they are to follow two of the more dominant gamma-rays •

Ikrwever, they rna'r be stronger t an Is apparent

from the data.

For instance, the 0.024 mev gamma-ray lies

too low In energy to he observed as a ^hoto line or to have a K conversion component.

Even its L conversion component

is in the region of strong counter cut-off and is -probably stronger than observed.

If this is true, the energy of the

gamma quantum, could be slightly less than the quoted value since the counter window tends to cut off the front edge of a 11p® *

59

Summary«

Table V gives a summary of the

energy values found in this study.

These results are

thought to be accurate to one oercent.

Relative intensi­

ties of the gamma-rays are not given since estimates for such complex disintegrations must necessarily be quite arbitrary.

Conversion coefficients have not been calcu­

lated for all the gamma-rays since this requires a rather exact knowledge of the branching ratios of the gamma-rays in the decay scheme.

60

Tablo V* 71 nal Snrmary of /111 lata.

Tl0':,-er,t

jeta-onox^yy (rev]

Oatr^a-ener o' 3

Bariur lio

0*480 (40 ') 1*022 (SO '■)

0.160 IV } 0.306 (10} 0 •510 ;ic)

L&nthaxiun 140

l*o 8 1*07 2*20

0.003? (ic) 0*335 (IC) 0.45 ;1C} 0*32 1 *60 2.50

Tantalum 132

0.85? 0 *58F

nr 1.15 1*22 1.04

"'heninn 136

1*07

l/.1•..• ’ {10} 0.812

,rn 138

8.10

0*15 .V03 0 .64 0 *06 1*40

O.OO

0*044 (10) 0.001 -00 0.070 .iuo —w / 0*207 (IC) 0 *230

h n r h

jold 100

(7 J) (20:;) (10 >

(IC)

(IC) si entries that internal arrivere,X on of the ga.rrmo.~vay was observed» v-? =\bout seventeen gama~rays in the enemy! region of SO to 530 kev were found in the radiations of t&rt&lwt 182 and all were observed to be interrally converted* (dee Table III Tor energy valres of* these raTmT>a-rays}

SI

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63