Production and properties of 50-year element 94

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Material Information

Title:
Production and properties of 50-year element 94
Series Title:
United States. Atomic Energy Commission. MDDC ;
Alternate Title:
Production and properties of 50-year plutonium 94
Physical Description:
5 p. : ill. ; 27 cm.
Language:
English
Creator:
Seaborg, G. T
Wahl, A. C
Kennedy, J. W
University of California
U.S. Atomic Energy Commission
Publisher:
Atomic Energy Commission
Place of Publication:
Oak Ridge, Tenn
Publication Date:

Subjects

Subjects / Keywords:
Plutonium   ( lcsh )
Plutonium -- Isotopes   ( lcsh )
Cyclotrons   ( lcsh )
Nuclear physics   ( lcsh )
Transmutation (Chemistry)   ( lcsh )
Radioactive decay   ( lcsh )
Uranium   ( lcsh )
Genre:
federal government publication   ( marcgt )
bibliography   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )

Notes

Bibliography:
Bibliography: p. 5.
Restriction:
"Date Declassified: March 5, 1947"
Statement of Responsibility:
by G.T. Seaborg, A.C. Wahl, and J.W. Kennedy.
General Note:
Manhattan District Declassified Code
General Note:
"Date of Manuscript: March 20, 1942"

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 005024491
oclc - 288609441
System ID:
AA00009323:00001


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ATOMIC ENERGY COMMISSION


PRODUCTION AND PROPERTIES OF 50-YEAR ELEMENT 94


by
G. T. Seaborg
A. C. Wahl
J. W. Kernedy


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This document consists of 5 pages.
Date of Manuscript: March 20, 1942
Date Declassified: March 5, 1947


This document is issued for official use.
Its issuance does not constitute authority
to declassify copies or versions of the
same or similar content and title
and by the same authors)





Technical Information Division, Oak Ridge Directed Operations

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li PRODUCTION AND PROPERTIES OF 50-YEAR ELEMENT 94


Si By G. T. Seaborg, A. C. Wahl, and J. W. Kennedy


The bombardment of uranium with deuterong in the 60-inch Berkeley cytlotron produces, in addi-
tion to the 2.3-day' S.M, a new isotope of element 93, which has a half-life of 2.0 days,. and beta and
gamma-radiation distinctly different from those of 93"23. Observation of the growth of alpha-particles
from this 2.0-day 93fled us to the discovery of element 94, and this report describes the preparation
of and the measurement of the physical properties of this isotope of 94. It is this isotope, which has
a half-life of about 58 years and 4.1.cm alpha-particles, whiqh -we have used for a tracer to study the
chemical properties:' element 94 4 described in another report.' It is not possible at present to
make a definite isotopic assignment for this activity, but the best assignment from the evidence at
hand seems to be 94"5 or 94"a, and,'in order to facilitate the discussion, we will refer to it as 94"2.*
In these experidtents the uranidm has been bombarded, sometimes in the form of black oxide (UO, ,
and sometimes in the;form of an alloy of uranium. In a typical experiment which demonstrates the pres-
ence of element 94 ib this bombarded uranium, the uranium is dissolved in nitric acid, and element 93
.iip)tein a: thj sample (approximately 0.3 mg,.cm2) with the help of lanthanum or cerium carrier
by the meUtod of precipitating the fluoride in oxidizing and reducing media. There is found to be pres-
e~li B S3' fraction, besides the 2.3-day 93~, formed by UI"(d,p)Ua" followedd by U2" 23 min. 9325"
and perhaps also by Une(d,p)93"', a'tbw radioactive isotope of element 93 with a half-life of 2.0 days
(93",). .
Absorption measurlmftls i:1tkniuininum show that the bet -particles of this 2.0-day 93"' have a
range of 0.38 gm/cm2, corresponding to an energy of 1.0 Mev, and lead absorption measurements show
the presence of 1.1 Mev gamma-rajs. The absoption measurements were taken with an air-filled
ionization chamber connected to an FP-~ 4 electrometer tube. The arrangement for the aluminum ab-
sorption meaurmpgWjLs is shown in Figure 1, and the absorption curve for the beta-particles of the
Mixture of 2.0-day 93"e and 2,. -dy 93m is shown in Figure 3. The absorption curve for the beta-
particles of the 2.3-day 93"', formed in the bombardment of uranium with neutrons, is shown, for the
purpose of comparison, in Figure 2. Both samples were very thin (< 0.3 mg/cm') and mounted on
cellophane. I '
By following the decay of the higher energy beta-particles and of the 1.1 Mev gamma-rays, neither
of which are present with the 2.3-day 93"1, it is possible to establish the half-life (2.0 days) of radio-
aetiusef:aal3 mrsspite'aerftw large amount o~f .3-day 93"S present with it. The growth of alpha-particles,
whilteare due tdi94"1-the eaghter of (ht 2O-diy 93" is observed in such a sample, using an ioniza-
tlum hamnb'r'ialinearjidlgle amplifier together with a magnetic field to bend out the very strong beta-
rpallittletebai reflNfadifddn. The '6oth cutvi'indicates a' alf-life of 2.0 days for the parent activ-
itpdadtelledipete '" '


o tf&6e addd "at9 tze ao publication. This.alpha-radiLoativity, referred to in.the original report as
wl atr .to be dueto the, isotope 94"' with a slight admixture of alpha radioactivity due
#t .l.en jert a ad confusion ths paper Ihs been vfted. so that it always refers to
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er.en Thseexpr ents have shown that -the. 9 .activity isqparabefro lthra te j'
including element and a description these exer i in another epo .
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a hhap t hes particles are dIue to element 4.od, a complete counting rateon a el ieaaLes-
pertinient-. These experiments have shown that the 94.'. activity is, sepuarable frosa4UIL.thermlemBsfa,
Including element 93, and a description of these experiments igtves in another report, *Thusi .s1d3
dition to the method of allowing 94 to.grow in a chemically isolated 93 fraetiks, 94 .ana a t.!f IOstdbJa
direct chemical separation, after the decay of the 2.0-day 932', from the deutenon activated wurmalmi.
The range of the 9411 alpha-particles has been measured rather roughly by two methods. (I) The
alpha-particles were absorbed by air. In this method, a plot of the counting rate times the dtce
.rom the ionization chamber squared vs. the distance from the chamber was iopa*y ed whasl.t
plot for the alpha-particles from polonium. (2) The alpha-particles were dbsordeM i um .adF
comparison made with the absorption of polonium alpha-pairtiflest alum.ihiun.'Both favet.s
the (extrapolated) range in air (15"C and 760 mm) of the 942g*'al-ll isclstles'k ifeerfhd-f.
0.1 cm.
No decay has been observed in the alpha-activity of 94b over a period of many months. In prin-
ciple, one could evaluate the half-life of 94=' by using the measured value of the intensity of the beta-





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Figure 2. Ab"o.p no t( 93n5 radiatiqP in aluminum. Radiation consists of approximately equal
number conversion electrons and disintegration beta-particles.

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particles pie d2'y 93i together with the corresponding measured value of the intensity of alpha-
particles 'rom the daughter 94'. However, it is difficult to make a reliable estimate of the intensity
of the beta-particles from 928', because, as mentioned above, the deuteron bombardment of uranium
producers i :j-.0W i ind 2lsi oi3', an lhe similar hal-lives make it difficult tc
resolve accurately te decay curve.
There are three methods which can be used to estimate the fraction cf 932n which is present in the
mixture of 93" 93S, and, although they are all rather rough, they all give approximately the same
result. (1) The rough resolution of the decay curve (taken without absorber) into its 2.0-day and 2.3-
day components. (2) The extrapolation to zero absorber of the high energy portion (the portion due to
93"' of the complex (f" 4 93") beta-qbsorption purve. The complex bqt (9a" + 9. ) absorption
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curve (Figure 3) was resolved into its two components with the help of the j3" beta-absorption curve
(Figure 2), after the subtraction of the gamma-rays from each of the t The dotted ine in
Figure 3 represents the 932" beta components of the absorption curve. ( ise of the ntensity of
the ionization of the 1.1 Mev gamma-ray (due to S'me) to estimate the inteity to the corresponding
beta-particles due to 93:-, using the usual ratio of efficiency between beta and gamma-lonisation as
determined with other well-mknou*it1b -gatma eij 7i r JAH -- ;.


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ire'. Absorption o mixture 9" and 93"' radiatn in alumim.
Feigurel3. Absorption oi mixture of 935s and9gas" radiation in aluminum.


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eq. a .that fa Ui an assignment of the activity to the mass number 236 would mean that the yield
t tl eal.tto. n {d,n)93'" (plus that of U""(d,p)U"Se if Us" should be a short-lived beta-emitter) must
be of;the order of 15 timesas great as the sum of the yields of U s"(d,n)93" and U"(d,p)Ur", and this
does not seem to be very likely. If the activity is assigned the mass number 238, the yield of. the
reaction t$"(dAn)98" must be~oly 12 per cent as great as that of the sum of the reactions U'"(d,n)
93'" and TbI(d,p)I" while, if the activity is.given the mass number 235, the yield of the reaction
U3(d,2n)932s must be about 15 times greater than the sum of the yields of the reactions Uz"(d,n)93"
and Ue(d,p)U"'.: However, the competition of the fission reactions may considerably alter the ordi-
narily expected relative yields, and for this reason. a choice between the mass numbers 235 and 238
cannot be made on the basis of yield arguments.
Whether the activity is formed in a d,2n reactiba can probably eventually be settled by observing
i" how the yield varies with the energy of the denteroas. If the activity actually is due to an isotope of
.Ii^:r" mass number 235, then there probably should be formed about 140 times as much 932" as 93s25, since
.. IP is 140 times as abundant as U"'. This would mean that a thousand-micro-ampere-hour bombard-
ment of uranium would form of the order of micrograms of 93"e. Such an amount of 932s8 could prob-
ably be detected and the amount estimated by neutron fission tests, and since this might afford a
... better means of making a choice between 94"5 and 942" for the isotopic assignment of the 50-year 9S
activity, we propose to perform this experiment in the near future.
Following are the approximate yields per.thousand micro-ampere-hours of deuterons in the 60-
inch cyelotraon aa piwrethila uranium target: .about 1.0.mllicuries of 2.0-day 93 and, from the de-
Scay of U.hi, about ioe aieiocurie of 50-year 94"'; abaut 80 miilicuries of 2.3-day 932" and, from the
decay .f W, abOt 0.0? .ierqc ries of 30,000-year '4".: For purpose. comparison it may be
statd M0fle iarmib eat .of,2 kg of uranyl nitrate hexahydrate (UO,('SQ,),.6H,O) with the neutrons
Sf: .. in ptM icro.-appere-hours of deutertoah n beryllium in the 60-inch cyclotron produces
A: .'' .isy 83"id from -the decay of this, about 0.02 microcuries of 30,000-year






a t W. Keintty, Pysa. Ie. (Ipublicatlon submitted March 7, 1941).
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It:torts the fact that the 2.3-day 930" radiation contains, in addition to the disinte-
F : Naut a1 n equal number of conversion electrons.
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