Ames Laboratory ISC Technical Reports
Ames Laboratory
7-1951
Short-lived synchrotron-induced radioactivities
Forrest I. Boley
Iowa State College
D. J. Zaffarano
Iowa State College
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Boley, Forrest I. and Zaffarano, D. J., "Short-lived synchrotron-induced radioactivities" (1951). Ames Laboratory ISC Technical Reports.
28.
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PhysicaL Sciences Reading Room
UNIHD
STATES
ATOMIC
ENERGY
COMMISSION
ISC-154
SHORT-LIVED SYNCHROTRON-INDUCED
RADIOACTIVITIES
By
Forrest I. Boley
D. J. Zaffarano
July 1951
Ames Laboratory
L
I
,I
'.
Technic a I Inform· at ion Service, 0 a k Ridge, Ten n •
55
e•
PHYSICS
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ISC-154
3
TABLE OF CONT2NTS
.
Pa ge
I.
II.
III.
ABSTRACT
4
I NTRODUC'l ION AND TIEV IE'•1i OF THE LITERATURE
6
DJVESTIGATION
9
1
A.
. B.
C.
D.
Objectives
Experimental Apparatus
Procedure
Results
1. Instrumenta l resolution
2. Results with known beta-spectra
3. R~sults with Prl40 and Fe53
4. Re sults with nuclei of the
Z - N
1 t y pe
=
9
10
20
26
26
26
27
35
IV.
DISCUSSION
65
V.
CONCLUSIONS
68
LITERATURE CITED
71
ACKNOWLEDGM.EN'l'S
73
VI.
VII.
.r
4
IS C-154
SHORT-LIVED SYNCHROTRON-I1~UCED RADIOACTIVITIES 1
Forest I. Boley and D. J. Zaffarano
From the Department of Physics
Iowa State College
I.
ABSTRACT
The use of a scintillation spectrometer for measurement
of the energy distri bution and half-life of sho~t-lived betaemitters is described. The instrumenta tion is espe c ially
suited for use with ra d ioactivities of low intensity resulting from photonuclear rea c tions produced by the Iowa State
Colle ge 70-Mev synchrotron. Such activities are unsuited for
study with a: convention a l ma gnetic spectrometer of s mall
solij an gle, particu~arly if the ac t ivities a re s h ort-lived,
.but may readily be analyzed with a scin tillation s pectrome ter,
'for which t he solid an g le of acc ep tance is close to 50 per
cent.
Ttie hi 6h energies of the beta-spectra associated with
short-lived radioactivities permit the attainment, fnr
energies above 3 Mev, of ~n instrumental resolution better
than 10 per cent. Suitable re c ording devices pr ovide i nformation concerning both tne ene rgy s ) ectrum and .the half-life.
To insure proper operation of t he e qui pment, preliminary
studies were made using radioactive materials for wh ich the
charac .t eristics of the beta-s pectr a we re well known. These
tests yielded endpoints in essential agreement with previ ous
ma gnetic spectrometer work .and a lso ind icated that the firstforbidden character of t h e yttrium9 0 decay could b e detected.
The short-lived radioactivities studies with the scintillation spectrom~ter ma y b e divided into two groups. In
the first are those with half-lives of the order of minutes
while in the second are t h ose of the order of seconds. The
first group consisted of praseod ymiuml40 and iron53. Endpoints of 2.35± 0.10 Mev and 2.60 .:t. 0.10 Mev respectively
were obtained for these a c tivities.
l
Taken from a Ph.D.
July 1951.
tl~sis
submitted b;y Forrest I. Boley
ISC-154
5
Those nuclei investigate~ in the secon~ group all have
one more p roton tha n neutron. On ~ecaying a positron is
emitte~ .
The ~ata concerning these nuclei may be used as a
check of the Wi gner theory2; which asserts that ~ue to the
existing symmetry the Coulomb repulsion energy accounts for
the entire ener gy ~ifference between the two ground states,
provided the positron emission is between such states. A
reasonable confirmation of the theory is shown for these data.
The data also appear to obe y the predi ct ed approximate
proportionality b etween the inver·se of the fifth root of the
half-life and the endpoint ene r gy of tho p ositron spectrum .
The endpoints and half-lives obt ained are shown in Table 1.
ft values obtained appear to support the Gam ow-Teller modificati s n of the Fermi theory of beta-decay.
Table 1.
Nuclei
Determimi. tions of endp oint, half-life , and f t- va l ue s
for Z - N
1 nuclei
=
Endpoint
( Mev)
Half-life
(s e conds)
ft
(seconds)
27
:J:.4
4460
±
1300
± 0.10
12.3
* 0.4
4670
:1:.
800
Si27
3.48 .:1::: 0.10
5 .4
0.4
3740
:!.
700
s31
4 .06
3.2 ± 0.3
4320
± 1200
Cl33
4. 43 .::1: 0.20
1. 8
~
0 .1
3440
±
900
K37
4 . 57 ~ 0 .20
1.2
± 0.2,
2700
±
1000
ca39
5 .13
~
1.1
!
3990
±.
1300
Na21
2.53 ± 0.10
Mg23
2. 99
± 0.20
0.20
~
2
E. Wigner, Phys . Rev. 51 , 947 (1 937 )
0.2
6
I.
INTHODUCTION AND
ISC-154
EVI:::!:W OF THE LITl-:::RATURE
The Iowa State Colle ge 70-Uev synchrotron is ca pab le of
producing many radioactive isotopes. The x-ray beam intensity
is not , however, in general great enough to pr oduce be taactivities of suffici ent strength to pe rmit their convenient
study by magnetic spectrome ters of s ~a ll solid anGl e . Also
many of the produceab le activities are of such short halflife that obs e rvation by thes e me thods would be difficult
me chanically. Previously , the solution to these t wo p rob le ~ s
has been the use of absorption an.:l cloud char:1ber t e chniques .
The first :nethod suffers frorn the uncel'tainties of the
absorption and scattering probl ems while t h e second is
statistically poor unl e ss lar ::;e numbe rs of cloud chamber
pictures are taken and observed.
The purpose of the present investigation is to us e a
scintillation spectrome ter to study several of the short-lived
isotopes which may be pro duce d by 70· Mev s ynchrotron x-ray
irradiation. The scintillation co~~t e r circumvents bo t h the
source strength and the short half-l ~ fe difficu lt ies , since
one c an approa ch 50 per cent solid angle s and the me chanical
problems of source p l a c ement are minimized . Si nce the scintillation spectro ~e ter is a l mo st continu ously s ens itive and
sinc e l arge qt~ntit i es of data may be analyzed in a reas onable
time , statistical variations may be mini mized. Provided with
appropriate reco r ding method s, data concerning the energy
spectrum and half-life of a ra di oactive species may be ob taine d
si mu ltaneously.
The various nuclei which wo re invest i gated may conveniently be placed in two groups. In the f irst ar c thos e with
half-liv~ s of the order of minute s, name l y praseodymiuml40
and ironb3. Although c ertain feat ure~ of both the se isotope s
have been studied previously , neith er has been observe d with
the techniques used here . Inf or mati on concernirtg endpoints
and half-lives of those nu clid e s in this first group is
interesting as a check on pre vious a ~ s or p tion measurements o
'Ii-1e second group of nuc lei consists of those with hal f l i ves of the order of seconds and \Ji th one ~r1o r e pr oton than
neutron. That is , Z - N = 1, whore Z is the atomic number
and N is the number of neu trons . 1l'hese nuclei, when decay i nc; ,
convert one proton to a neutron anj emit a positron. The
u pper limit of the continu ou s ener~y distribution found for
the p osi trons emitted by such nu clei is of s pe cial theor e tica l
interest, as will be indi cated in the fo llowing paragraph .
.,
7
ISC-lE 4
Theoretical calculations concerning beta-spectra have
been made by Fermi (1), with modificati ons by Gamow and
Teller (2). The particula r set of nuclei with one more pr oton
than neutron derives int eres t in that, according to the
Wigner {3) theor y , when decay occurs be t we en the ground state
of one of thes e and the ground sta te of the product nu cleus
the total energy difference should just be that attributab l e
to the Coulomb ene r gy of ex chancing the extr a proton for a
neut ron. That is, the on ly excess energy involved in p-p
( proton- proton) inte rac t ions ove r n -n (neutron-neutron ) ones
is that due t o the Coulomb forces act ing in the p-p case. If
this is t rue , ~1ue to the h i gh degr ee of s ymme try be t wee n these
Z - N = 1 nuclei a nd the f i nal n ucle i, this Cou lomb ener gy
may be ca lculated quite generally by use of r athe r simp l e
a ssumptions, such as the uniformi ty of the charge di s t r ibut ion
within the nuclei and the proportionality of t h e nuclear
volume to atomic mas s numbe r. The r esult (4) of such a
calculation l e ads to a value f or the Cou lomb ener gy of
'
where C = ~ ~
e is t he electronic char ge and r 0 is the
, v ro
1/3
consta nt in tne expression R = r 0A
for the nuclear radi us.
A is the mass number of the ge cay1ng nucleus.
Since the total ener gy d ifference be tween nuclear ground
state s is just the maximum ener gy of the positron plus its
rest mass plus the neutron- protron mass di f ference , one may
also write
..
=
Ec
Emax ~ mo + ( n-p ),
where Emax is the kinetic energy endpoint of the positron
spectrum ~ and whe re m0 y n and p are the mas s es of the electr on,
neutron and proton in energy ~~ it s. This, of course~ is
true only if the p ositron dec ay occur s be tween ground states.
That is, no gamma r ay acc ompanies the disintegration. No
gamma ray has eve r been detected for the spe cial class of
nuclei considered h er e.
Using the n-H value of 782 kev g iven by R. F. Taschek
et al (5), Emax b ecomes
Emax
=C
[(A - 1)
/ Al/3
J - 1. 0 0 Mev.
The constant C may be f ound by attempting a be st fit using
experimen tally determined value s of Emax for various values of
A. This has been done from time t o time by othe r i n ves tigators (6, 7 .• 8;> 9 ) using severa l value s of Emax' but not
8
IS C-lf 4
with all those currently available. The se worke rs have in
general found exper i menta l values of Emax ' in r easonab le
a gree ment with this t ype of pre dicti cn. This work was ,
however, done with cloud chamber and a bsorption techniques
with endpoints being de t ermine d without the assistance of a
Fermi plot.
Another inte r esting r e lationshi p sh ould be noted , Bethe
and Bacher (10) an d Wi gner ( 4 ) have p oin t ed out that the halflife could be pr edic ted from the Fermi the ory of b eta - decay .
If the nucleus of one of these p ositron e mi tter s g oes to
the 3round state of the final nuc l eus , the relationship between the half-life and the maximum total ene r gy i s r epresented
fairl y accurately by T.;t_ o( (W0 )- 5 f or light nucle i. Thus one
should obtain a strai gtit line .on plotting the inverse of the
fifth root of the ex pe ri ~e nta ll y de t ermined ha l f -l ifo a~ ainst
the value of W0 • W0 is t he maximum tota l positron ene r gy in
units of mc2 . This will be g iven more a t tention later.
Be ta- de cay theor y i nv olve s a f unction F(Z, p ) where p is
the total momentum in me units of the e mitted particle and Z
is the at omic numb e r of the resultant nuc leus. F(Z ,p) involves not only a statis tical factor of the s quare of _the
momentum, but a ls o a Coulomb cor r ection fa~tor to acc ount
for the effect of the nuc l ear attraction upon the e mi tted
beta-distribution. F(Z,p) ma y be calculated b y various a pproximation method s. The inte J r a l of this f unction times
(W 0 - W)2dp taken from zero momen tum to the max imum momentum
and multiplied by the ha l f -life of the activity gives what
is ca ll ed the ft val ue of transition .
Accor ding to the Fer mi theor y thi s ft value should be
constant for the Z - N = l n uc l ei. Comparison ft value s vvill
be calculated for the nuc lei investi gated here. The ratio of
electron K-c a pture t o p ositron e mi ss ion probab ility is .less
than l0-3 for thes e nuclei fro m the work of Feenber g and
Trigg (35).
It may be seen from this discussi on then that any nev.r
information obtainable concerning this particula r t ype of
nuc leus and conf irmation of pr ev ious absorpt ion and cloud
chamb er work b v the scint illation s pe ctrometer techni que
wou ld be worthwhile.
9
ISC-lf4
The scintillation spectrometer ap pears to be a r e ajy
me ans of exa minin;_; these s h ort-livej , hi gh ener gy b etaactivities in orjer to ob tain their half-l ives anj ene r gy
en::lpoints. That this t y pe of s p ectro meter l &njs its e lf well
to this work is seen by the facts that the reso l ution ~ o e s
inversely as the square root of the ener g y (11) becominr;
better tha n 10 per cent at 3 1 ev, that at these hi ~her
ener g ies anthracene provi ~ es a cry stal of g ooj pro p ortionality (11), anj that the ef f ective jea::l time ( 12) of the
counter is negligible c ompa re j to the r e lative ly hi gh in i tial
counting rates en count e r e j i n such activities .
In summary this inves t igation was carriej out in an
at t empt to obt a in half-lives an::l e n jpoints of seve ral of the
short -l l ve::l b eta-emitters p ro juce::l by high ene rgy x-rays.
Rather i n t e resting th eo~e t i c a l p r e ::lic t ions have been maje
c.oncerning the gro up to whi c h belong many of these activ i ti e s
stujiej .
Some of t he se ::leca y s h ave been observej p reviou s l y
by other techni qu e s . Re s ult s o b tainej wi ll be compar e j with
the theory anj with othe r exp eri ~ e n tal values.
II o
A.
I NVESTI GATION
Obj e ctives
In achievin 0 the primary objective of the investi gation,
that is the us e of a scintillation s pe ctrometer f or jetermining the ha l f-life anj e ne r gy e nj p oint of various shor t -livej
synchrotron injucej activities, the f ollowing gene ral course
of a ction was fol lowe j.
It was jesirable to look first at something with a long
half-life whose e n jpoint an j s pe ctral shape were we ll known.
For this purp ose phosphorus32 anj ytt rium9 0 were observej. A
check on the operation of the electr ical circuitry is thus
p rovi::lej, free of the co:nplica ti ons which woul::l res u lt fr om
the use of a rapijly je c ayin g sour c e .
In this way one may
f inj the accur · cy with which known enj p oints c a n 'o e jeter mi n ej
anj how close l y the known s pe c t ral sha p e can be re p ro::lucej .
\ h e n tho e xpe r imen t al te c hnique p r ovej satisfactor y for
these act i vities , the e xten sion wa s ma::le to others with halflives of the order of minute s .
F or these studies .LJraseod y miuml 40 and iron53 we r e chos e n .
Since these observations
involvej all the feat ur e s of the e qui p ment e x cept the rapid
10
ISC - 154
transfer of the cource from the x-ray beam to the s pec trometer box, reasonable checks could b e made of n e arly all the
operational feat ures of the equipment.
Next, of course, activit ie s with half-lives of the order
of seconds could be obs e rveda Here it was e ssential to
transfer the sample from the i rra diation position to the
counting p osition in the shortes t p ossib le time. If the
data thus accumulated in a period of se ve ral seconds are recorded photographically, to pe rmit l a ter examination at a
slowe r speed, one can obta in not only the s pectral d i stribution but also the half-life . It i s with j ust such a recording "time-stretcher" device t ha t t h e : : e stu.:He s we r e made. A
detailed description of the equ i pment used f or this work is
g iven in the next section .
B.
Experimental Apparatus
For the reasons discussed earlier, a scintillation
was chosen to s t udy s h ort-lived a cti vi ti e s.
The scin tillation spectrome ter ma y be de scribed as f ollovs.
~pectrometer
On intercepting particle s vJhich ar e given off by a
radioactive source, a scintillation crystal conve rts the
energy of the particle into a f lash of li8ht. This flash of
light is converted into an e lectr ~ c a l s i ~nal by means of a
photomultiplier tube and the electrica l s ignal a f ter b eing
suitable shaped is record e d •
. One of the properties of c r ys t a ls such as anthracene~
stilbene or napthalene is that when traversed by a particle
such as an electron a flash of li ~ht is produced. I n some,
notably anthracene and stilbe ne , the int ensity bf light is
very nearly proportional to the ener gy lost b y the particle.
If an anthracene crystal of thickness suf fici ent to stop the
particle, that is, to caus e it to los e all of its k ine tic
energy inside, is placed before a beta e mitter, t he c rystal
should ideally produce flashes of light the intensity distribution of which would r epr esent t h e beta s pe ctrum.
A photomultiplier tub e is a devi c e which will produce
an e lectrical signal when exc ited by li 6ht. It c on s is ts of a
photocathode which emits ele ctrons by the photoele ctric
effect. Followin6 this is a s e t of dynod e s between each of
which is a potential diff erence. The ele c trons fro m the
11
ISC-154
photocatho.:le are focuse.:l on the first .:lyno.:le surface, whe re
they pro.:luce many secon.:lary e lectrons. These are in turn
focuse.:l on the second .:lyno.:le where more secon.:lary electrons
are projuc e.:l . This mu lti p l y ing process is r epeatej at ea ch
j ynoje anj the final e lectron bur s t is collec tej by the ano.:le.
I:J.eally the magnituje of chart,e i n the fi nal burst shoul.:l be
proportional to the intensity of the incijent li 0ht pulse.
If such a photomu lti plier tube receives the li ght f las hes.
from the crystal, the output signals fro m the t 'ub e woulj be
pr oportiona l to the energy of the ori ~ ina l beta part icles ,
assu ~ing the photomu lti pli e r t ube to be a proportiona l dev ice.
These output pu ls es coul:J. then be re cor.:le:J. in any :J.esirable
manner .
Severa l effect s prevent th e foregoing fro ~ being more
than just an i.:lealizej :J.escription. First of all, some of
the electrons on entering the crystal follow a tortuous enough
path that they finj themselves onc e a gain outsije wi th some
unexpen.:le.:l ener gy remainin g . This occurs pr eferentially to
electrons which have lost the least ene r gy in the crystal,
since they are perfor ce neare r the surface. This l eajs to
an apparent preponjerance of lowe r ener gy electrons, thus
making i t jifficult to attach much signif icance to t he lower
half of th e ene r gy s p ectrt~n .
Seconj , the crystal joes not pro.:luce f lashes of light
of exactly equal intensity for monoener getic electrons.
Thirj, the photomu lti pli er joes not projuce output pulses
of exactly equal ampli tu:J.e f or equal intensity li ght .i.J ulses.
These last two effects are not only jue to the statistical
nature of the problem but also to t he va riation of li ght
pro.:lucing ability thr oughout the crystal anj to the variation
of phot oelectric res p onse of the photomul t ip lier ph otos urface. The net result of these effects is to projuce a
broa.:lening by the instrumen t of a ny monoenergetic line. It
is ajvantageous to make thi s eff ect as s mall as possible.
·.
Thus in setting up equipment of this type it is we ll
to have a large selection of ph otomu lti plier tub es an.:l
scintillating crystals from which to choos e , since the in.:livijual va riation of the resol u tion (partic u. larly in tube s) may
be ver y great . Although the tube . an.:l crystal use.:l in this
work we r e satisfac ~ or y , · several investi gators have reporte.:l
be tter resolutions. The jistortion of the jata wh ich r esults
from the imperfect resolution will b e jiscussej in the next
section.
12
ISC-154
Figure 1 shows a photogr aph of the system arran3e d for
observing the very short-l i ve d activit i es. Samp l e s are irradia te<:l by the s ynchrotron x -ray beam at the ri ght end of
the long aluminum tube (A) shown in t he upper ri Ght of the
pictur e . After irradiation they are shot through the tube
by compressed air into the b lack s pectrometer box (B) sh o\~
to the upper ri ght of the r e lay rack. The transit t i me f or a
sample in this tube is approxi!nat e l y 0.1 second but can be
made faster or slower by varying the air pressure. To aid
in accurately pla cing Lhe source at the counting p osition,
the tube was made with an oval cross se c tion. Th is also
pr·evented the sample fro m rotating during transit.
The irradiation is t i me d by a preset clocks At the end
of the irradiation the x-ray b eam is turned off, as are all
the pulsing circuits concerned with the synchrotron.- This
greatly reduces the care which must be taken with ele ctrical
shielding of the electronic equipment. At the time the
synchrotron beam is turne d off , a solenoid valve is actuated
allowing a blast of compr es s e d air to blow the sourc e down
the tnbe, and the motor drive of tho oscilloscope recording
earners is startede After s ufficient data are collecte d the
camera is turned off manually. The sample may be returned to
the beam by operation of a s olen oid valve i n the vacuum line.
After a time lapse suffici ent to allow longe r lived activit i e s
to die out, the cycle ma y be re peated.
Inside the s pe ctrometer b ox, the source is located a b ove
the crystal as sho1:m in Figure 2. The tube is surrounded by
a Mumetal magnetic shields The source holder consists of a
wooden plug backe d with l ea the r which s e rves as the carr ie r
for the source, and a 0. 005 inch n icke l foil into which a 7/8
inch cir cular hole is punched. The foil is secured to the
wooden plug with nicke l wire . The t h in source is p lace d in
the 7/8 inch hole.
·
Figure 3 shows a detail of the pho t omultip li e r tube
a rrange ment and also a block d iagram of the comp l e t e system .
An anthracene crystal (either one -half inch or one i nch
thick, de pending upon the maxi:num energy antic i 1Ja ted) is
mounte d with Canada balsam on a Lucite light pipe as shovm.
The li ght pipe in turn is cemente d to the face of the RCA
5819 photomultiplie r, a ga in u sing c anada balsam. Th e cry sta l,
li ght pipe and top of the photomultiplie r tub e ar e the n
wra pped with an aluminum foil, 0.00025 inch thic k , which
serves as a light reflector.
I-'
w
H
U)
0
I
I-'
\Jl
~
Fig. 1--Experimental arrangement for studying short-lived activities.
1--'
+-
H
(/)
0
I
1--'
VI
Fig. 2--Scintillation spectrometer box showing source, crystal, photomultiplier
tube and magnetic shield.
+-
ISC-154
15
SOURCE
~
ANTHRACENE
REFLECTOR
LIGHT
PIPE
~
~t; OR t"
i-11/2~
I 'Lz
-
•
-RCA
5819
CAMERA
J
~
l
POWER
CATHODE
SUPPLY
FOLLOWER
0
0
I
AMPLIFIER t--
PULSE
MODEL
I--
SHAPER
BLOCK
SCINTILLATION
~""""""'"
CRO
1000
DIAGRAM
SPECTROMETER
Fig. 3--Block diagram of scinti l l ation spectrometer .
16
ISC-154
..
·•
In studying the spectral distribution of ne gatrons or
positrons resultin g from short-lived beta-decay it is
necessary. to have some t y pe of many-channel pulse hei ght
sorter to eliminate the difficult task of making decay
correctionso Also, if possible, it would be well to incorporate into the equipment some means of measurin6 the halflife with reasonable accuracio
The method chosen to achieve this end was the photog raphic reco r din g of pulse hei;;hts which were displayed on an
oscilloscope screeno The ph oto graphic record, which was in
the form of a continuous strip~ could then be r ead b oth in
an amplitude and a time sense t o determine the s pe ctrum and
deca y time of the activityo
In order to record the data in this way the output pulses
from the photomultiplier were treated in the following
mannero Cathode follower cou p lin ~ was made to an amplifier
whose gain is variable fro m zero to flfbr. The circuit
dia gram of the photomultjplier tub~, preamplifier and amp lifier is shown in Fi gure 4 and that of the re gulated power
supply for the photomultiplier tube is shown in Fi gure 5.
This power supply is of t he same type as used by palmer
(13). The output of the amplifier is then sent to two pulse
shaping circuits for which Fi gure ~ represents a campo site
dia g ram. These circuits compri se a modification of the
Watkins circuit ( 14), VJ.hich was ori g inally used for a .somewhat different applic at iono The first circuit consists of a
peak readin g voltmeter whose output is~delay line shorted
three microseconds after · the incoming pulse has risen to its
m~ximum valueo
This· produces a flat-topped. pulse whose amplitude
is proportional to that of the incoming pulseo By use of a
conventional Los Alamos Model 1000 a mp lifier this . flat-topped
pulse i~ applied to the vertical deflection plates of a
5CPllA cathode ra y oscilloscope tubeo The second shaping
circuit pro.:J.uces a one-microsecond gating pulse· one microsecond after the flat-topped pulse h~s risene This gating
pulse is applied to the c ath ode of the cathode ray tubeo
If
the ca t hode ray tube is biased. nearly to cutoff and if no
sweep is applied, the r e sult will be a dot whose height a b ove
the baseline will be proportional to the a mp litude of an incoming signalo
17
RCA
Anode
ISC-154
Photomultiplier
5819
}
I
lOOK
56K
-1500 Volt
56K
Rtoulottd
Supply
05,U
"
"
"
"
+300 Volt
r---r---r--r--r-r-r---,--r---,--~-----,...----j Ro gulo to d
+210 Volt
Rt QUiattd
S u pp I y
supply
seon
39K
39•'
3~: ~ IBK:
18ti;
18t<:
·~
680 ~
.Oifl.
001/i
6J4
6AC7
--
-'-
~r
~,OifL
-:::_
r-------r-~ lr-T-r---~
..
.01 flo
lOOK
56fl
lOOK
seon
-~
220K
51fl
330~
27 K
220K
~i
Output
3 .3 K
I
IlK
/''
Cathode
Follower
Amplifier
Fig. 4--Circuit diagram of photomultiplier tube, preamplifier and amplifier
-l i;'
,a;
,a:
,o
I
-- .....
6SC7
3omp
~-
00
:rl
a
~
0 ~
~
1'-~
<;tO.
fuse
(\J
-=::;;E
~
0
(\J
(\J
~
~
0
~
4r<
IIOV
2(Y:)QV
60
f-'
(X)
PHOTOTUBE
SUPPLY
AM PHENOL
91-PC3F
~ Female plug
Fig. 5--Circuit diagram of regulated power sup~y for photomultiplier tube.
H
(f)
0
I
f-'
IJl
+
i"
...
..
MODIFIED WATKINS
PULSE ANALYZER
6AG7
~
irri~G;-4
li ~
3~SEC .
DELAY LINE
+ 350
VOLT
REGULATED
POWER
SUPPLY
1--'
-yo
\0
- 150 VOLT
V.R.- REGULATED
POWER
SUPPLY
I~
I~
~
SEC. DELAY
LINE
t
I K
I~
I~
33K
H
(/)
(")
I
Fig. 6--Schematic diagram of modified Watkins circuit.
1--'
\J1
~
20
ISC-154
The dots obt a ined fro m the data in the manner indicated
in the prece:Hng para graph ar e then recorded photogra phic a lly
to gether with a neon bulb timing marker. A Dumont oscilloscope camera, Type 314A, is used. A sample of the film record
thus obtained is shown i n Fi e;ur e .? • The b ase line is the
solid line and the timin g marke r is the dashe d line~ while
the data are in the form of d ots. On projection in a Flofilm
microfi lm r e ading projec t or, the data may b e r e ad b oth as a
function of amp litude and a s a f unction of time. One may
take as many e n e r gy i n tervals as the dot size permits. For
the dots shown in the s amp l e stri p , approxi mately 25 i n tervals
ma y b e taken.
It is p ossible to vary the do~ siz e if
necessary by adjus tme nt of the c a thode ray tub e volta ges.
Since 75 dots per running inch of film may easi:y be accommodated, a spectrum of 20,000 counts ma y be obta ine d on 25 feet
of 35-mm film. The film cost is then not prohibitive. The
total error in r e produc t ion fro m oscillosco pe s creen to
viewer screen is less tha n 2 pe r cent of full sc a l e and is
g overned primarily by impe rfec t fil m tracking in the microfilm viewer .
C.
Procedure
After .preparation and irra .:1 iation of the samples, the
procedur e is essentially the same for all of the studies mad e .
Hence these procedures wi~l be discussed first. The lonc li ved emitters, csl37, p 3,- , sr 90_y9 0, used in the pr e li minary
tests of the equipment wore prepared as deposit s on thin
Zapon film in the manner cus t omar y in conve ntional betaspec tr o sc opy.
These sources wo re ob served by p lacin g them
1/8 inch above the aluminum foil r e fl e ctor cove ring the
anthracene crystal.
Praseodymium in the for : n of p owdered praseo dym ium oxide
( Pr6011) Was irradiat e d for e ight minutes in a te st tubeo
It was left as a powder, s pri nk l ed onto Scotch tape and
inverted on the aluminum f oil r e fl e ctor for ob s e rvation.
Iron was prepare j as f ollows. Strips of s pe ctroscopi cally pur e iron, 0.001 inch thick, we r e irradiated ei ghteen
minutes . The sodium act i vit y was ob tained b y irradiating
sodium iodide. The sodiu m i odide wa~ ground to a f i ne p owde r
and mixed with a small a mount of Za p on which ac ted a s a ·
binder. The bottom of the 7/ 8 inch hole in the sourc e holde r
21
ISC-154
· ··-------------------------------------------------------------------------~---·
••
<-,A, f [
T Y
f ll M
Fig. 7--Sample of data on 35-mm film record.
Cesium 137
Conversion line
500
400
0.624 Mev.
-
300
U)
c;::,
0
0
0
0
t-
200
100
0
Pulse Height in Arbitrary Units
Fig. 8--Spectrum of csl37 used in obtaining resolution of instrument.
22
ISC-154
was covered with strong paper, 0.00025 inch thick; an.:l the
mixture pressed into it. The source thickness in this and
in all other 11 powder -Zapon 11 pr eparations was approximate ly
0.1 mm. This _in general amounts to a we i ght of 20 to 30 mg
per square em. The sourc a is then covered with Scotch tape
to add strength. It should be note d that for transit ti mes
of one-tenth second for four fe e t of tubing rather large
~cceleration and deceleration forces on the sample are
involved. For this reason the criteria for a 11 thin 11 source
had to be relaxed somewhat in orde r to make the source strong
enough for the transit.
In all short irradiations the background activity due
to the source holder was at least a factor of 50 b elow the
mea sured activity. This activation was almost entire ly
attributable to the two-minute oxy;;_en which has an endpoint
of 1.7 l;Iev . Thus , besides being of ne gli gible quantity, the
ener gy is considerable below the lowest endpoint investigated
by the present technique . Apparently the carbon activations
are not strong for these irra.:liation times. Nickel was
par ticularly chosen as the source holder material because
it did not activate noticeably. The pr eparations of the
nther activities which .require .:l use of the fast pneumatic
tube are listed in Table 1.
Table 1.
Sample Preparations for Short-Lived Activiti es
Compound
Prepa ration
Irra.:liation Time
( seconds )
Nai
Powder-Zap on
20
Na21
Mg-metal
foil
15
HIT23
' 0
Al-me ta l
foil
20
Al25-26
Expected Activity
Si0 2
Powder-Zap on
5
Si2 7
s
Powder~Zapon
5
s31
NH4Cl
Powder-Zapon
3
Cl33
KI
Powder-Zap on
2
K37
CaF
Powder-Zap on
lo5
ca39
23
ISC-154
After irra.:iiation the various samples are shot through
the pneumatic tube to the spectrometer ano oata collecteo,
photographed., and. subsequently -r -e ad with a microfilm viewer
~s described. in the precetling section.
Two sets o~ data
resu.l t. 'One gives the number of decays detec ·Led in each
chosen interval of t1me and the other gives the amplitude
spectrum of the photomultiplier pulses. Approximately 15,000
to 20,090 · counts are obtained in·each spectrum. The decay
data may in general be plotted directly, no dead time
corrections being necessary. The half-life is determined by
making a weighted. least square oetermination~ using the total
number of counts in each time interva l as a weight factor.
Probable errors are calculated. using the methods oiscussed. by
A. G. Worthing ano J. Geffner (15).
The spectral distributions are first treated. to take
into account the finite resolution ~ f the spectrometer.
Calculations of this type 01 corrections have been made by
Palmer ano Laslett (16). End. corrections are a pplicable to
the high energy end of· the spectrum and. take into account the
resolution effect, namely that more counts are r e corded. at
and. near the a pparent endpoint than exist in the true spectrum.
These-corrections are shown in graphical form in Figure 9
which was taken from reference (1 6 ). The abscissa expresses
the ratio of the dist ance below the a pparent endpoint divid e d.
by the full width at half maximmn of the ! resolution curve at
the apparent endpoint. Thus E= 0 at the a pparent endpoint
and. € = 1 at a distance R below the apparent endpoint. The ordinate is the ratto of true corrected. counts divided by the
number of counts obtained. ex-perimentally.
The body correction~ w~ich involves the re st of the spec=
is given as a formula at .the b ottom of Fig~re 9. This
correction is seen to take accotmt of the slope and curvature
of the spectrum. It is obtained. by use of the f irst three
terms of a Taylor's expansion in the solution of the integral
equation relating the experi mental spectrum to the resolution
or transmission of the instrument and the true spectrum. Use
is made of the fact that the resolution goes inversely as the
square root of the kinetic energy {11). In- ~the . formula -given!>
K and. k are proportionality constants where 'E KV and kE 0 represents the second. momerlt of the normalized pulse hei ght distri~
bution taken with respect to the mean. E is the energy in Mev
and V is the pulse hei ght in arbitrary unit s . E 0 is the endpoint
energy. Nrr(E) is t.he nnmber of true corrected counts at energy
.E and. NE(V) is -.the number· of counts obtainej experimentally of
·pnlse height V. Primes denote differentiation with respect to
the argumento The ~od.y co~rections in general c6ntribute little
toward chan ging the spectrum or the subsequent Fermi plots 6
trum~
24
ISC-154
0.9,.--------------------------
0.8
END
CORRECTION
GRAPH
0.7
0.6
0.3
0.2
0.1
0
_
~-._-~
0
0.1
0.2
_._~--~-~-~-~---~~
0.3
0.4
8 =
0.5
0.6
0.7
0.8
0.9
U/K - V
R
BODY
CORRECTION
FORMULA
Fig. 9--Results of resolution corrections of Palmer and
L~s lett.
1.0
25
ISC - 154
I n usins these corrections , one must, of co urse, know
the fu l l 1.vid. t h at half maximum of the resolution curve of the
ins t rumen t . This was obtained i n the pr es ent investi 6a tion
b y observing the Csl3 7 conversion line which corresp ond. s to
an e l e ctron energy of 0 . 624 Mev . Since the reso l ution is
known to g o i nve rs e l y with the square ro ot of energy~ it may
be calculat ed. at a ny gi ven energy .
Resolution corre ctions have b e en applied. to all d.ata
reported. her e .
It should. be noted. t hat examp l e s of the effect of
app l y ing the s e corrections to the s_tJe c tra are shown as solid.
d.ots on a numbe r of the gra 1)hs appearinG lat er . Af t er these
corr e c tions have b een ap.tJlied a Fermi p lo t may be mad e to
d.et e r mi ne the max imum ener 8Y . rrhis is d. one in the c onvent ional manner using the Be the approximation ( 36 ) ,
F (Z, p)
=
(1
4-
p2 )
(1 + 4 , 2) - 1
4
.
Js
'
for ob ta ining the Fermi fun ction,
where Z is the atomic number of the resu l tant nuclei
p i s t h e momentum of the emitted. e l e ctrons in units of me
1
r( 1 • p2 ) z-
y
=
s -
p
l
( 1 - ( 2)2- 1
=f
'r =f- z o< )=
+
Z .<.
-
Z/137 for negatron em iss i on
;~/13?
for po si tron emis s ion
In contrast to d.ata obtQinod. with magne tic s pectrome t e r s 9
the c ounting rat e in the present work is obtained. d.irectly
as a funct i on ,of tb.e total e l ectron energy , Vi . The number~
N(W) , of elec tr on s obta ined per unit e n e r gy interva l is
related. to the numb e r N(p ) psr unit momen tum interval by the
r e l ation N(W ) = N ( p ) ~;. = W N( p ), where the der i va tive d.p/d.W
is eva l uated by d.iff~~entration of the id.entity w2
p2 + 1 .
It is accord. i n gly appropri ate to construct a Fermi plot with
·
( 1WN(~ ) ) )~ as or d inate and. W as abscissa .
=
1
I
F ( ,p
26
ISC-154
Energy calib ration of the equipmen t was achieved by
observing the endpoints of y90 and Cl34o Yt trium90 in
equilibrium with strontium90 was used for the 2.25±0.03 Mev
(17) endpoint. The Cl34 was prepared by irradiating a test
tube full of finely ground sodium chloride for twenty minutes
and placing a thin layer of the powder on 0.00025 inch paper .
The twenty-three-second sodium21 activity was allowed to die
out d1~ing a ten-minute period fol lowin ~ the irradiation.
The 4.45 ~0 .11 Mev endpoint (18 ) of Cl3~ was then observed.
Do
1.
Results
Instrumenta l resolution
An essential piece of information to be obtained concerning the spectrometer was a meas ure of its resolution. R
is the full width at half maximum of the resolution cur ve.
As was indicated i n Section C, this was obtained by use of
the conversion line Csl37o The spectrum obtained for a
- ~ irich anthracene crystal is shown in Fi gure 8. This yields
a value of 24 per cent for R at the energy of this conversion
line . A value of 44 per cent was similarly obtained for the
1 inch crystal used with the hi gher energy studieso All data
through out this investi6ation have b een corrected f or
resolution.
2o
Results with known be ta-s pectra
Check runs were made using the effectively long-lived
ties of p32 And Sr90_v90
The sn"3(')t,...,,.., and Fermi plot
of the p32 aP e shown in Figure 10 and Fi gure 11, respectively .
In general, probable errors are shown for all data g iven
where the error e xceeds the dot size. Errors are not g iven
in Fermi plots for points which are breaking away from the
straight line at lower energieso by use of the csl37 conversion line as a calibration a value for the endpoint of 1.78 $
0.07 Me v was obtained. Thi s is in satisfactory a greement
with ma gnetic spectrometer results which g ive lo72 Mev (19,
20 ). A cons picuous feature of the Fermi plot shown in Figure
11 is the manner in which it breaks away from the strai ght
line at 50 to 60 per cent of the endpoint energy. This is
act~ v~
27
ISC-154
believed to be attributable to the over-abundance of low
energy counts resulting from the scattering out proces s discussed in Section B.
The spectrum of Sr90_y90 is given in Figure 12. The
conventional Fermi plot which is given by the solid circles
in Figure 13 is obviously somewhat S-shaped about the straight
line and does not break away from the straight line in the
neighborhood of 50 to 60 per cent of the en~point. This is
presumably due to t~e first-forbidden character of the y90
decay, it being kn0wn from magne~ic sp~ctrometer work (17 )
that these nuclei do give an S-shaped character to the Fermi
plot. The S-shape ls apparently strong enough to overshadow
even the over-suppl~ of ~owe r ener gy events. · Application
of the a
(W 0 - W) ~ p correction factor due to ~onopinski
(21) is known to produce a. strai ght-line modified Ferm:. plot
from the S-shaped first-forbidden plot of y90. When this
correction is applied, the open cLrcles result. Near the
endpoint these lie quite well on a stra i ght line and break
away at the usual 50 to 60 per cent. Thus, it is possible
to detect first forbiddenness with this scintillation
spectrometer. On the basis of the Csl37 calibration, the
endpoint was found at 2.27* 0.06 Mev, which is a gain in satisfactory agreement with magnetic spectrometer work (17).
=
3.,
Results with Prl40 and Fe53
Having obtained reasonable results for the "well-known"
spectra, it was felt that a somewhat less compl_e tely known
activity could be investigated. Praseodymiuml40 9 which was
k~own to activate strongly 9 was chosen.
The decay curve and
posi tr;on spectrum are shown in Figure 14 and Figure 15. The
praseodymium was irradiated as pra seodymium oxide (PreQll)
for eight minutes. The half~lives observed were 3.4::,0.1
minutes and 15:1::.1 minute. The 3 .4-minute activity (22, 23ll
24) is undoubtedly due to Prl40. The 15-minute activity is
unexplained. No energy spec tr·um was obtained for this
15-minute activity. No evidence for the presence of the
expected two-minute oxygen activity was observed. It is
apparently masked by the strong praseodymium activation.
The Fermi plot for Prl40 is shown in Figure 16. An endpoint
of 2.35± 0.10 Mev is obtained on the basis of the Csl37
conversion line and y90 endpoint. Three other groups of
28
ISC-154
0
en
c
::s
0
(.)
600
-
0
0
~
400
Pulse Heivht in Arbitrary Units
Fig. 10--Negatron spectrum of phosphorus32.
29
ISC-154
10
\
8
\
\
\
\
7
6
\
\
~
~4
3
2
0
Kinetic
Eneroy in Mev.
Fig. 11--Fermi plot of phosphorus32.
ISC-154
30
....enc
::::J
0
u
....00
1-
0
2
4
6
8
10
12
14
Pulse Height in Arbitrary Un1ts
16
Fig. 12--Negatron spectrum of strontium9°-yttrium9°.
18
ISC-154
31
6
\
5
\
\
\
\
\
\
\
\
\
\
\
\
\
\
\
\
\
\
\
4
\
\
\
' '\
\
'
\
\
\
\
~3
....0
....
<(
A- Type
Correction
2
2.24Mev.
0
0
o.s
I. 0
I.S
2 .0
2.5
Kinetic Energy in Mev.
Fig. 13--Conventional and a-corrected Fermi plots of strontium90-yttrium9°.
ISC-154
32
IOOPOOr---------------,----------------r--------------~----------------~~
Pra~eodymium ~ide
Decay
10,000
...
•
.,
Q.
c
:I
0
u
100~------------~~------------~~------------~~------------~~
0
20
5
25
10
50
15
35
Time In Minutes
Fig. 14--Decay curve of Pr6011 after 8 minutes irradiation.
20
40
33
.,
c
::J
0
0
-
0
0
1-
Pulse
Height in Artiltrary Units
Fig. 15--Positron spectrum of praseodymium140.
ISC-154
34
ISC-154
15~------------~--------------~--------------1
10
5
Mev.
0
2.0
1.0
Kinetic
Energy in
Mev.
Fig. 16--Fermi plot of praseodymiuml40.
3.0
35
ISC ·· 154
investigators ( 22~ 23$ 24), by use of absorption and cl oud
chamber measur ements~ ::;i ve 2 o 4 lv1ev as the endpoint o The
a gr eement with these previous results is satisfactory.
"
The je cay curve, spectrum anj Fermi plot of Fe53 are
shown in Figure 17 , Fi gure 18 and Figure 1 9 ~ respectively.
The anticipated reactions of gamma -n on Fev4 to g ive Fe53
and gamma -p on Fe 57 to give the 2.59 hour Mn56 we re observe d
in decay st~dies. The Mn56 appear ed to be about 4 per cent
of the total a ctivity at the time the spectrum was taken~
No other activity wa s found. The half-life of Fe53 is g iven
a s by''other i nves ti ga tors (2 5, 26) with 8 .9 minutes r ep orted.
In noting the Fermi plot of Fe53, it is seen to be strai 3ht
line and curves upwar d a t a bou t 60 per cent of the endp oint.
An endpoint of 2.6*0.1 Me v is obtained . In this cas e , the
ener gy calib ration was maje by uti lizing the known endp oint
of ytt rium9 0. Ne l s on and Pool (27) gave the endpoint as
2. 8
4.
±: 0 .1
~le v~
Results with nuclei of the Z - N
=1
~
In stating ·the r esult s obta ined from the remaining activities whicl:l a re all of the Z - N :: 1 group, only t"vvo need be ·
given special consid eration a part from the other s . After
sodium iodide was irradiated it gave the s pectrum shown in
Figure 20. The shape is obviously qu ite different from those
obtained earlier from other decays. Sodium was also irradiated as a nitrate but with the same spectrum resulting .
It was suspec te d that be sides the l ower ener gy Na21 ac ti vity
anticipated, t he re might have b een produced a small amount
of some other is otope yieljing higher ener gy b eta~particles.
That this was the ca se be come s clear by a study of the jecay
curves shown in -Fi gure 21. He re the upper data were obta ined
by taking on ly those pulses below an energy of 2.7 IVIev 9 while
the lower one resulted from taking only counts lying above
2.7 Mev. The Na21 endpoint is expected to lie between 2.6
and 2.7 Mev. There were undoubtedly two activities involved- one with a half-life of 2 7 ± 4 se c onds and the other of 9 t 3
s e conds. Fermi plots of th ese activ ities are shovm i n Figure
22 • . The endpoint of the shorter ~ lived , hi gh-ener gy activity
is fo\).nd t o be 4 .9± 0.3 Me v~ while by sub traction tha t of the
longer-lived is 2.5* 0.3 Mev. It is only possible to obta in
a reliabie subtr a ction of these acti vities because the higher
energy group is activated so much l e ss strongly than the
IOOPOO·r---------------------~r----------------------.-----------------------.----------,
Iron Decay
o Total oetivity
• Indicate• re111lt of 1UIItroeH011 of
IOftl-llved activity fr- total octlwtty
•
-;
c
j
...
l.AJ
•a.
~
0'\
1000!
~
Ti- • 10
8
* 1 minute
0-170 Minute Time Seale
000
CD
0000
0
0
1- • 156 z
0
0
0
0
0
5 mlnutea
0
!2
!2
~
~
J!
J!
~
2
100
0
50
100
170
220
270
Time
in
0
.....
Minutes
H
(J)
Fig. 17--Decay curve
o~
iron
a~ter
18 minutes irradiation.
0
I
1--'
\J1
+=-
37
I SC-154
en
c::
~
0
0
0
0
1-
0
2
4
6
8
10
12
Pulse Heio ht In Arbitrary
14
Units
Fig. 18--Positron spectrum of iron53.
16
18
20
38
ISC-154
25~------------------------------------------~
20
0
0
15
0
10
5
0~------~----~~------~------~----~~----~
0
0.5
1.0
K I N E TIC
2.0
1.5
ENERGY
IN
M E V.
Fig. 19--Fermi plot of iron53,
2.5
3.0
39
ISC-154
Beta
800
of
Spectrum
Sodium21
plus
Fluorine 20
en
600
c
~
0
0
-
0
..,_0
400
0
2
4
6
8
10
12
14
16
18
20
22
Pulse Height in Arbitrary Units
Fig. 20--Energy spectrum observed from sodium iodide after 23-second irradiation.
40
ISC-154
IOOOr----------------r----------------~--------------~--------------~
Sodium Iodide Decay
(Irradiated 23 Seconds)
Low eneroy component
r~~,
I
•
27 """ 4
seconds
100
"C
c
0
u
CD
Hioh eneroy component
(/)
r.,. = 9
~
-
3
se conda
CD
Q.
..
II)
c:
::J
0
u
10
0
10
5
Time
in
1!5
Seconds
Fig. 21--Decay curves of sodium iodide after 23 seconds irradiation.
20
41
ISC-154
2.~---------.----------~---------r--------~--------~
Fermi Plots of Fluorine 20
and Sodium21
2.
1.5
1.0
. 20
Fl UOrlnf
o.s
21
Sodium
2.5.:1:: 0.3 Mev
2
3
5
Kinetic Eneroy In Mev.
Fig. 22--Fermi plots of activities resulting from irradiation of sodium iodide.
42
ISC-154
lower energy groupo If the two br oups had been activated
nearly equally, the subtraction woulj not have been valid
since the breaking away from the straight line Fermi plot
jue to the scatterin3 out process could enrily have obscured
the true endpoint of the lower encr0y group . Fluorine20
has a r e ported half-life of 12 seconds and a end-point of
5.0 Mev (37, 38). On the basis of energy and half-~ife it
seems reasonable to assign the short period to p20 and the
longer one to Na21.
,
Aluminum should also be considered separately. When
alunhrum under g oes irradiation b oth gamma -n and gamma -2n
reactions probably occur. S5nce the resultant nuclei Al25
and Al26 have comparable h~lf-lives (7o3 and 6.3 seconds
respectively) and endpoints (approximately 3 Mev), it is
nearly impossible to separate accurate information concerning either from e;a:nma irradiation of aluminum . The decay
curve and spectrum of the aluminum activities a re shovm in
Figure 23 and Fi aure 24, res pe ctively. A half-life of
7 .O! 1.0 seconds and an en::lp oint of 3 .03 .::1:0.10 I:Iev -..vere obtained. It is sa f e to say that these are probably ::lue to
a composite of Al25 and Al26 9 but beyond this nothinJ further
may be concluded from this investigation.
The results ob tained from all the other of these
Z - N = 1 nuclides are quite straight forward and these
results are 0iven in Table 2o Cali~ration was achieved by
use of the endpoints of y90 and 0134. The probable error
quoted for the endpoint dete rmination could be~reased con~
siderably if the endpoint of Cl34 were knovm to greater
accuracy. Spectra and Fe~ mi plots of these calibration
activities are 0i ven in Fi~ure 25 and F10ure 26 .
Table 2.
Emit ter
Endp oints anj Half-Lives of Positr on Emitters in
the Z - N = 1 Class
Half-life
(sec o)
27 ~ 4
12.3 ~ 0.4
Endpoint
( !.lev )
.2 •5
'*
0 0 3 ·:~
2 99 :t 0.10
0
Al25-26
3 e 03 ~ 0 o lO-lHl7.0*1.0
Si27
5.4]::0.4 .
3 48 t 0 • lQ.~ .
s31
3 .,'2 ;t 0.3
4.06;t: 0.20
Cl33
4 43 ~ 0. 20.,
1 .. 8 *'0.1
K37
1.2 ± 0.2
4.57* 0.,20
ca39
5.13 ~ Oo20
lol±0.2
·''~~Obtained by subtraction.
""Inconclusive ( mixed activities ) .
0
0
~igure
20' 21.9 22
27, 28, 29
23p 24
30,
33,
36'
39 ~
42 2
31.?
34 ~
37'
40'
43 ~
32
35
38
41
44
ISC-154
43
400~----~--------------------~------------~
Aluminum
Decay
300
-o
Tt=
c
0
.,
.,...
•c:
7 ±I second
(,)
(/)
Q.
200
~
:I
0
(.)
150
100~----~------~----~------~----~~----~
0
2
4
6
8
10
Time In Seconds
Fig. 23--Decay curve of aluminum foil after 20 seconds irradiation.
12
ISC-154
44
en
~
;:,
0
400
(.)
0
0
t-
200
2
4
6
8
10
12
14
Pulse Height in Arbitrary Units
Fig. 24--Positron spectrum of aluminum2 5- 2 6.
16
18
500~--~----~----~----~--~----~----~----~--~----~
Beta Specta of
Yttrium90and
Chlorine34
....-
Solid dots indicate result of
resolution correction.
f/)
c::J 30
0
0
+
c
\.)1
0
00
2
4
6
Pulse
8
Height
10
12
14
16
18
20
in Arbitrary Units
Fig. 25--Spectra of Cl34 and y90 for energy calibration of instrument.
H
(I)
(')
I
f-'
\.)1
+
5----~----~----~----~--~----~----------~--~
Calibration Fermi Plots of
Yttrium90 and Chlorine34
4
n
D
lit:
n
Cl
34
D
~ 45~~e
I
.+
(;'
\j
00
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4 .5
Kinetic Energy in Mev.
Fig. 26--Fermi plots of Cl34 and y90 for energy calibration of instrument.
H
(/)
0
I
1--'
\Jl
.t:""
"
5000r----------------r----------------.----------------.--------------~
Magnesium Decoy
1:;,
c:
0
0
Q)
U)
~
Q)
2000
Q.
en
c:
:::J
0
u
+=-
-..:]
1000
500
L--------------~-----=~--~~~~~~----------~--------------~20
0
5
Time
in
10
seconds
15
Fig. 27--Decay curve of magnesium after 15 seconds irradiation.
H
(I)
0
I
1-'
V1
+=-
ISC-154
48
1000
Solid dots indicate result of
resolution correction
800
600
(/)
c::
:3
0
u
c
400
0
1-
200
0
2
4
6
8
Pulse Height in
10
12
Arbitrary
14
Units
Fig. 28--Positron spectrum of magnesium23.
16
18
49
ISC-154
10
8
6
4
2
\
0
0
I
2
Kine tic Energy in Mev.
Fig. 29--Fermi plot of magnesium23.
3
ISC-154
50
5000r----------------.----------------.---------------~
Silicon Dioxide Decoy
~
c:
0
o T
u
=
5 .4 ± 0.4 seconds
Q)
cn I 000
...
Q)
Q.
U)
c:
:J
0
u
500
200~---------------L----------------~--------------~
15
0
10
5
Time
in
Seconds
Fig. 30--Decay curve of silicon dioxide after 5 seconds irradiation.
51
ISC-154
Solid dots indicate result of
resolution correction
1500
(/)
+-
c:
~
0
u 1000
0
0
~
500
0
~----~----~----~----~----~----~----~----~~~
0
2
4
6
8
10
12
Pulse Height in Arbitrary Units
Fig. 31--Positron spectrum of silicon27.
14
16
18
52
ISC-154
18
12
l;e_•o
I
6
4
2
0~----~----~----~----~----~----~----~----~
0
O.S
1.0
L5
2 .0
2.5
Kinetic Energy in Mev.
Fig. 32--Fermi plot of silicon27,
3.0
3.S
4.0
"'
,! ;-·
oor--
--~----
I
I
i
I
Sulfur
0
Decay
0
2000
(l
(l
T_!,tt 3.2 :::b 0.3 seconds
0
0
"0
c:
n
0
0
<1)
(l
(/) 1000
n
n
b.
cu
[J
0..
n
en
c:
:::1
0
(.)
400
200~----~----~------~----~----~------~----~----~
0
2
4
3
Time
in
5
6
7
8
Seconds
H
(/)
0
I
Fig. 33--Decay curve of sulfur after 5 seconds irradiation.
1-'
\.)1
+:-
ISC -154
Solid dots indicate result of
resolution correction
1500
-
11)1000
1:
::J
0
<..:>
0
0
1-
500
0
4
6
10
12
Pulse Height in Arbitrary
20
Units
Fig. 34--Positron spectrum of sulfur3l.
ISC-154
55
15
1~10
5
4.06 Mev
j
4.5
Fig. 35--Fermi plot of sulrur31.
ISC-154
Ammonium Chi or ide
Decay
Counts
per
Second
1000
400
200~----~------~----~-------L------~----~----~
0
2
3
4
5
6
7
Time in Seconds
Fig. 36--Decay curve of ammonium chloride after 3 seconds irradiation .
57
ISC-154
800
Solid dots indicate result and
r•solution
correction.
..
•600
c
~
0
0
0
{ :.400
200
Fig. 37--Positron spectrum of chlorine33.
ISC-154
10
8
4
2
4.43 Mev.
j
0.5
1.0
1.5
Kinetic
2.0
Energy
2.5
3.0
in Mev.
Fig. 38--Fermi plot of chlorine33.
3.5
4.0
45
59
ISC-154
10000~----~------~------~------~------,
Potassium
Iodide Decay
4000
"C
c
0
(.)
G)
(/)
~
G)
1.2
* 0.2 second
2000
0.
Cl)
~
c
::J
0
0
10)0
400~----~------~------~------~----~
0
2
Time
3
4
5
in Seconds
Fig. 39--Decay curve of potassium iodide after 2 seconds irradiation.
60
ISC-154
1000
800
-
Solid dots indicate
result of resolution
correction.
~
c
::J
0
u
600
0
{:.
400
200
Fig. 40--Positron spectrum of potassium37.
61
ISC-154
6.---------.----------.----------.---------~--------~
5
4
3
2
2
0
Kinetic
3
Energy
in
4
Mev.
Fig. 41--Fermi plot of potassium37.
5
lopoo~------------,--------------.--------------r-------------,
Calcium Fluoride Decay
5000
1.1 z 0.2 seconds
'0
c
0
(.)
Q)
en
2000
~
Q)
0\
Q.
(\)
fl)
c
::s
0
0
1000
soo~----------~------------~------------~------------
0
2
3
4
Time in Seconds
H
(f)
(")
Fig. 42--Decay curve of calcium fluoride after 1.5 seconds irradiation.
I
I-'
Vl
~
ISC-154
63
800
Solid dots indicate result of
resolution correction
600
en
c:
::J
0
(.)
0
400
0
I-
200
0
2
4
6
Pulse
8
Height
10
12
14
in Arbitrary Units
16
Fig. 43--Positron spectrum of calcium39,
18
20
22
a~--~----~----~----~--~~--~----~----~----~----~--~
''
6
''
''
~4
0'.
+=-
2
0
I
I
0
5 · 13 M av.
I
0.5
1.0
1
1.5
I
I
2.0
2 .5
Kinetic
I
3.0
Energy
I
3.5
in
I
4.0
j
I
4.5
Ia
5.0
I
5.5
Mev
H
(})
(')
Fig. 44--Fermi plot of calcium39.
I
~
Vl
+=-
('J
65
III.
DISCUSSION
No further discus sion wi ll be __; iven the p32 ,. y 90, Fe53
and Prl 40 activities since the data conce rnin ~ thes e were of
a pre limina r y nature and were discussed at s ome l ength in the
prev i ous s e c t ion .
Tab l e 3 and Table 4 compare the va l ues obtaine d for
half-lives a nd endpoints in th is investigation with those
prev iously known .
=
Tab l e 3 .
Compa rison of Present Resu lts on Z - N
1
Ac tivitie s with Pre vously Known Va lues of Ha lf- Life
Nuclei
This Inve stiga tion
T~
(s e c.)
27 :1: 4
Pr evinu s Inves tigations
'I :1
(sec.)
2"
23
""20
12.3 .t 0 4
0
±
2
11.6±0.5
11. 9 :.t:. 0.3
5 .4.:!:0.4
4.9~
1
( 34)
( 7)
( 22)
( 34 )
4.5
s31
3.2:t.0.3
1. 8 :*:.0.1
1.1:1::.0.2
3.2:1::0.~
8)
9)
3.18 0.04
(
(
2.4ro.2
2.8
( 8)
(29)
1.3± 0.1
(30)
lo 06±0.03
(22)
Numbers in parentheses i ndica t e refe re n ces to literature o
The c a lculated values of Emax wer>e de ter> mined according to
the equation
·
Emax - C
[(A - 1)/A~] -
1. 80 Me v
66
Table 4 .
Nuclei
ISC-154
Comparis on of Present Results on Z - N = 1 Activities with Previously Known Va lues of Enjpo i nt
This I nvesti gation
'1:('
J.:Jmax
(;ilev )
±
Previous Investi::;at ions
Emax
( Idev)
Na21
2.53
Mg23
2.99 ± 0.10
2o 82
Si27
3.48 :l: 0 .10
3.74
3.54
0.15
None
Calc .
Em ax
(Iiiev)
2.63
( 7)
2. 93
( 31)
(2 8 )
3.49
3 . 85 ± 0.07
3.87 -:1: 0.15
( 8)
( 9)
4.03
4 .13 ± 0.07
( 8)
4 . 28
t 0.1
s31
4.06
± 0.20
Cl33
4.43
~
K37
4 . 57
* 0.20
None
4 . 78
ca39
5.13
±
None
5 o05
0.30
0.20
which was jiscussej earlier. The constant C was jetermine.:'i
as 0 . 61!- 0 . 03 !,Iev by plottins the va lue of E~ax obtained. experi~entally ( both in this anj in other work) vs. (A - 1)/A'b
an.:'i fin:)in g the shope of the best fitting strai ght line with
an intercept of 1. 80 Mev (S ee Fie;ure 45). The value of 0 . 61±:
0.03 is comparable to the 0.60 fou..'1 :1 by one other group of
investigators ( 8 ) anj tme l .592 usej by another group (9).
Tille latter jetermination was maje on the basis of only one
enjpoint , however, A value of 1.40 x l0-13 em. is in.:'iicate.:'i
for r 0 by the 0.61 value of C.
As a whole, the jata obtainej here a gree fairly well with
the work of others . Again it shoulj be polntej out that the
lar ge pr obab le errors are to a consijerable extent jue to the
uncertainty of t~e Cl34 enjpoint . Ove r-e mphasis must not be
placed. on the a greement between calculatej anj experimental
values in this case sinc e C is jeterminej by best fit.
Referen ce to Fi ~ure 45 will illustrate the jifficulty in
obta ining a precise value of C from the experiment ". l results
( in or de r to calculate a value for Emax for comparison with
the ori gina l experimenta l resul ts ).
.:
12
-~- •·---~-
----·
we~-
•-·-
--,-----
~
J
I
De terminat i on of C
;
/
•
Present work
o Previous work
10
8
C=0.610
A-I
~
6
c = 0.585
4
.
2
0 ' - - ' - - - - L - - - - - - - - L . - - _ _ I __ __
-2
4
2
0
Em ax.
j
1
6
in mev.
Fig. 45--Graph of maximum positron energy (Emax) vs. (A - . ) A-L/3,
is the atomic mass number.
w~:cre
4
68
ISC-154
Earlier it was ment ione.:l that the fifth root of the
half-life shoul.:l be inversely pr oportion to the maximum
energyo A plot of (T ! ) -~ vs W0 is shown in Figure 46e The
.:lata from this experiment i n.:licate tha t the rule may be
roughly obeye.:la A value for the constant of pr oporti onality
of 10.9 is obtaine.:l "
·
Any theory of beta-.:lecay pre.:licts that all of these
Z - N = 1 activities shoul.:l have fai rly '} Onstant ft values"
ft values have been calc u l ate.:l in.:lepen.:lently an.:l usin g
the Fe enber g an.:l Trigg curves (35) f or a ll activities
investigate.:l here an.:l the results ar e given in Table 5.
The ft value .:lepen.:ls ess entia lly on the fif~h power of Emax
an.:l linearly on the half-life. Thus small errors of eitne r
Emax or T~ coul.:l change ft consi.:lerab l y " The ft value of
K3'1 .:loes ~ppear to be somewhat lowo
Table 5o
ft Values Foun.:l in This Investigation of Z - N
Activities
Nuclei .
--
1
ft
Na21
4460 :t ·l300
Mg23
4670
. si27
:
800 .
3740 :t· 700
s31
) .';
4320 :J: 1200
Cl33
3440
K37
2700 & 1000
ca39
3900
IVo
t
. ~
900
1300
CONCLUSIONS
_,
lo Conclusions - re gar.:ling observe.:l en.:lpoints, half-lives
an.:l ft values are given in the la st cha pte r ( Tab l es 3,4 an.:l
5)a In a.:l.:lition, an en.:lpoint for Fe53 was obtaine.:l as
2a6 ±. Oal Mevo
.;..
ISC-154
69
I.Or---------,----------,---------,----------.----------r---r-----,
•
•
0 .8
Present work
o Previoua work
K = 10.9
0.6
.L
T._
/
0 .4
/
/
/
0.2
/
/
2
4
6
8
10
Fig. 46--Graph of inverse of fifth root of half-life vs. maximum positron
energy (Emax> •
12
ISC-154
70 '
2. The Wigner theor y of the Z - N = 1 nuclei is confirmej in these stujie8 with a proportionality c onstant in
the equation Emax = C [(A - 1)/A•o
1.80 of C
Oo61 ± 0.03
Mev resulting.
J-
=
3. ft values for the se nuclei a p pear to be reason ably
constant. Only K39 seems to jepart a ppreciably from the
others.
4. An attempt shoulj again be maje in the future to
observe gamma rays fro m the Z - N = 1 nuclei. This can conviently be jone by p r eparing thicker sources to g ive more
counts anj then int e r p osing abs orbers between the so urces
anj a Nai (Tli) scintillation crystal sufficie n t to stop the
emittej positrons. This t ype of crystal is quite efficient
for stopping gamma rayso One shoulj then observe the
annihilation rajiation of the positron p l us any other gamma
rays present.
ISC-15 4
~"" 1
V.
LITERATURE CITED
1.
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2.
G. Ga mow and E . Te ller , Phys . Re v. 49, 895 (1936 )
3.
E . rVigner, Phys .
4.
E . Wigner , Phy s. Rev . 56, 519 ( 1939 )
5.
R. F. Tasc he k: . H. v. Ar g o, A. Hemmend inger , and G.
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6.
w.
7.
M. G. White , L.• A. De lsasso, J. G. Fox, and E.
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M. G. White , E.
9.
D. R. Elliott and L. D. P . Ki ng , Phys. Rev. 60 , 489
( 1941)
ev .
5 1~
947 ( 1937)
A:
H. Barkas , Phys. Rev . 55, 694 ( 1939 )
...
Phys . Rev . 56, 512 (1939)
c.
Creutz,
c. Creutz, L. A. Delsasso, and R. R.
Wils on , ?hys . Rev . 59 , 63 ( 1941)
10.
H. A. Bethe and R. F. Bacher, Rev. Mod. Phys. 8,
( 1936 ) .
11.
J. L. Hopkins, Rev. Sci. Inst. 22, 29 (1951)'
12.
Arne Lundby , Phys. Rev. 80, 477 (1950 )
13.
J. P. Pa l mer , Applicat ion of Scintillation Counters to
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Iowa Sta te College Library, 1950
8~
Iowa~
14.
Dean Watkins , Rev. Sci. Inst. 20, 495 (1949 )
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A. G. Worthing and J. Geffner, Treatmen t of Experimental
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16 .
J. P. Palmer, and L. J. Las l et t, to be pub lished
17.
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18.
L. Ruby and R. Richardson, Phys . Rev.
~
659 (194 1)
72
ISC-154
19.
K. Sie gbahn , Phy s. Rev. 70, 127 ( 1946 )
20.
L. M. Langer anj H.
21.
E. J. Konopinski, Rev . Moj . Phy s. 15' 209 ( 19 43) .
22.
o.
Huber, o. Li enhar j , P. Scherrer, a n j H. Waffl e r,
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Helv. Phy s. Acta _,
23.
J.
w.
24.
G. Wilkinson anj H. G. Hi cks , Ph ys. Rev . 75 , 1687 ( 1949 )
25.
J. Livingooj anj G. Seab org , Phys . Rev . 54 , 51 (1938 )
26.
o.
27.
M. E. Nelson anj M. L. Pool, Ph y s. Rev . 77 , 682 (1950 )
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W. H. Barkas, E . C. Creutz, L. A. Delsass o, F . B. Sut ton ,
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A. Schelber g , M. Samps on ( anj A. C. G. Mi tche ll, Re v.
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30.
R. V. Langmuir, Ph ys. Rev . 74 , 1559 (1948 }
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R. McCrea r y , G. Kuerti, anj S. N. Van Voorh is, Phys.
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32.
H. Wa f f ler anj . 0. Hir ze l, He lv. Ph ys. Ac t a 21, 200 (1S48 )
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H. Brajner anj J. D. Gow, Phys. Rev. 74 , 1559 (1948 )
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E . C. Creut z , J. G. Fox , anj R. Su tton, Phy s. Rev . 57,
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E. Feenber g anj G. Tr i gg , Re v. Moj . Ph ys. 22 , 399 (1950 )
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L. Fe ister, Phys. Rev. 78 , 375 (1950)
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H. Crane, L. Delsas so , W. Fowl er , anj
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38.
E. Bleuler anj W.
c.
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-~
DeWire , M. L. Pool, anj J. D. Kuba tov, Ph ys. Rev o
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...
Zunti~
c.
Re v~
C. La uri t sen ,
He lv. Ph ys. Acta 19 , 37 5 (1946 )
73
VI.
ISC-154
ACKNOWLEDGMENTS
The authors wish to express their gratituje to
Prof. L. Jackson Laslett for many helpful discussions
and hel p with calculations; to Messrs. A. A. Reed,
Clarence Harper and W. Reinhardt of the electronics
shop for help in setting up the equipment; to Mr.
E. H. Dewell for preparation of samples; and to the
entire synchrotron group for their assistance.
It is also a pleasure to acknowled ge the support
3iven this work by the Socony-Vacuum Corporation in the
form of a research fellowship to one of us (F.I.B).
Equipment for this work was provided by the Ames laboratory of the AEC.
END OF OOCUMENT