@htont Editor &@isiont Editor

~.~~~@$@&$h~ Editor v&&@ Production Editor f i&%‘&oriol Assistant

How Foreign Countries Are Using U. S. Bilateral Agreements.. . 30

Russian Physics at Geneva.. ~ 40 H. PALEVSKY

U. S. Reactor Operating History: 1943-1954.. . 42 RICHARD H. GRAHAM

Simple Spot Tests for Aluminum Contaminants.. . 46 H. S. HILBORN and R. C. PUGH

’ Critical Assemblies at Los Alamos.. . 48 H. C. PAXTON

How Radiation Ch anges Polymer Mechanical Properties.. . 51 C. D. BOPP and 0. SISMAN

For LOW Specific Activity: Use Scintillation Counting.. . % C. D. WAGNER and V. P. GUINN

. Radioactive Species Induced in Reactor Cooling Water. . . 60 W. S. LYON and S. A REYNOLDS

Localking Scintillation Counlng-Rate Meter. . ; ._

_, :64’.~- ,(I .,

. . .I [’ y- HERFERT JONAS $5’ +y;; :.

Shielded Box for Chemical Work; 1’; -& .‘-- JAN RYDBERG--‘ ---- -.

‘1 I

Inhibitor Breakdown in Zinc Bromide Shielding Windows; ; . 06 ,; DANIEL 1. HAWORTH .

.*:.., i il

‘Q I ..it j

General Motors Builds Radioisotope Laboratory. . . 68 * A SOMERVILLE

h/i ., @ ‘I

Operating a Hurst-Type Fast-Neuhon Dosimeter in High Gamma Fields.. . 70

J. T. BRACKEN, E A ROLLOR. and J. A MOHRBACHER .

Design of an Inexpensive High-Intens& Gamma Source.. . :~~‘~‘:‘. . . ‘3 ~1: 1 i ; i, :!

MILTON BURTON, A GHORMLEY, .md C. J. HOCHANADEL

.___-_- __. Nuclear Engineering

Windows for Viewing Hanford Reactor Face. . - 78 L T. PEDERSEN

How Reactor Temperature and Power Vary with Reactivity. . . 78 H. GAUS and R SCHULTEN

Space-Saving Hot Cell. . . 79 M. C. ATKWS and W. N. LORENTZ

Graphical Method Speeds Production Scheduling of Radioisotopes. . . 80 A D. ROSSIN, C. J. BILLERBECK W. S. DELICATE, A W. WENDLING,

A S. HOFFMAN, and R. C. REID

Flux Perturbations by Material Under Irradiation. . . 84 WM. BRADLEY LEWlS ‘r

LATE NEWS . . . . . . , . . . . . 9 WASHINGTON REPORT 14 BOOKS.. . . . . . . . . . . . . . . . 90

NEWS.. . . . . . . . . . . . . . . . , , FOREIGN NEWS.. . . . . IS PRODUCTS AND MATERIALS 96

REACTOR NEWS.. . . . . . . 12 EDITORIAL . . . . . . . . . . . 29 LETTERS................. 101

P(WSTRIAt APPLICATIONS I 3 TKHNICAL ADVANCES 89 NEWSMAKERS.. . . . ,. . . . . 102 . ;

T’NO LABORATORIES that contain remotely controlled assemblies are colled Kivas after ceremonial chambers of Pueblos

CONTROL ROOM is in main laborat-. building located c@#$ one-quarter mile from each Kiva. Note use of television 5

i’ “.*I ; 7;‘. p. .ijr

“TOPSY,” IS OLDEST critical assembly, o “JEZEBEL,” IS NEWEST criticd assembly, small lF metal core surrounded by a bore Pu without a reflector. Under thick reflector of normal U metal. Safeties operating conditions sections are brought drop a section of core and reflector and together to form smallest, simplest critical shift another large block of reflector away system there is. A Pu control rod rides in from its normal operating position to moke channel through sphere. After its choroc- system safe to approach. Control rods of teristics are determined OS completely as is normal U move in channels through reflector. practicable, it is expected thot this assem- Topsy has been operated with Pu core bly will be dismontled

By H. C. PAXTON Los A.l5nwa Scientifi Labor University aj Calijomiu Los Alamos, New Mezico

GODIVA OUTDOORS and

AIamos critical assemblies, much iike bare Po system, I.. r^rTl.‘: II mc. .‘r(,r.

rT’.i’ 1.1 Relative I

Ed.9 %;S

0.036 f 0 .006

:$6.07 %.17

0.210 f 0 .019

0.192 0.409 0.027 0.022 :.;gq -e + $&&o.on 0.135 * 0.008

;& 0.018 0.018 f 0 .004

I < . Relative Relative

Period, ;>‘r abundance, Period, 7% abundance, .’ (zec) ai/a bet) ada

53.0 * 1.7 0.011 zk 0.003 53.7. f3.6 0.037 & 0.016 22.0 f 0.6 0.128 -f 0 .013 22.9 3~ 1.1 0.265 + 0.037

4.94 f 0.10 0.182 rt 0 .018 6.11 + 0.24 0.193 + 0.019 1.77 iO.04 0.405 + 0.017 2.14 + 0.06 0.378 + 0.013 0.39 3~ 0.03 0.240 i- 0 .015 0.40 + 0.03 0.120 + 0.007 0.117 * 0.015 0.034 +0.008 0.15 + 0.05 0.007 + 0.004

? Absolute yield (neutrons/&on)

Pen’od, ~$4 (zec)

Relative abundance,

aila

54.0 rL 1.0 0.033 * 0.003 22.0 It 0.5 0.133 * 0.015

6.2 F 1.0 0.172 f. 0 .050 2.1 Ik 0.4 0.458 z!z 0.055 0.52 zk 0.1 0.169 i: 0 .025 0.18 i: 0.02 0.035 If: 0 .010

0.044 * 0.003 0.006; + 0 .0003 0.063 IO.006

FQ '/ ". /:':..z ,.,, '. $y:“ '

i_ '"1,‘ ; .'I .^., - .' ." '"1 i

'i!v: b':, ‘ $i’:s Systems of bare fission,able metal n;lade critical by remote assembly -i,d’

?” . . . ..provide valuable information basic to fast-reactor design. ‘!-Y,

il' : G &&;. Results of studies of delayed neutrons from fission are also g

g&&& :,;.,i., ~. ..J.Tl&.i:‘jr :: ; f *: ..“, C,.:’ : ,‘Z ven here

: I -*

t&=” m.&ms used at in the characteristics of elementary, ties have provided valuable fastneutron critical assemblies is to on about fast-neutron sys- check results of detailed calculations by hey’ve also served as a source modern high-speed computers. If dis-

i&i bursts of -lo’* neutrons for $&&ous irradiations in studies of

crepancies between predictions and ob- servations can be eliminated, there will

ons from lifzzion. be increased confidence in calculated characteristics that are not readily ob- servable in the laboratory (1).

s critical-assemblies The exnerimental auantities that are I A

ated a few miles from the useful for checking calculations include Alamos in Pajarito Canyon. critical masseq‘and results of traverses

control room, and by threshold neutron detectors. For ical assemblies are uranium assemblies, experiment and

theory agree except in a few extreme

are of two types: simple but cases (e.g., at low UfS6 concentration). For plutonium systems, however, small

s for nuclear safety but significant discrepancies call for a revision of the plutonium parameters which are used in calculation.

- .I. ,,., ,I,-.- .r +.-.” ‘. > .-j , ; .- f $a!; I .,

reactivity booster that takes it rapidly from slightly above de-layed critical to

“) ’

slightly above prompt critical. A UZa6 slug is shot into the assembly

and stopped near its most effective lo- cation. When system is a bit above prompt critical, the fission rate rises extremely rapidly, the uranium heats, expands, thus dropping the reactivity enough to terminate the fission burst. Thus, a potentially run-away burst is stopped by thermal expansion. W ith a typical Godiva burst the initial rise in fission rate is exponential with a period of about I5 psec and continues to a maximum power level of nearly 10’ watts, then falls off in a manner similar to the buildup. The burst is about 50- psec wide at half-height, and the energy developed is that of 10” fissions or about 100 watt&s. Typical ,burs& 1 are shown in Fig. 1. . .: ,: -, ..‘, ,r,:+.:: .,:

. ‘) j , .;, ,..;;.&i :

Godiva bursts show a mriok~effeet ,:::~~z+;~;~~,;~ due to room-scattered heutro&.’ ‘I ,The

i:

, . _^ -,,$ j ! I .’ .I’:: .li

-,. . ,ri ;@ .:,; .;-.:i;d’: . -41>., >

i_ J ? 1, :* ., ::

I----- - I=” Burst 23-c m”“‘Bpcr--& ;,zec. 0.75 millisec - -.A I :,

Burst 65 Period=I5.?j (Marker frequency * w

.r FIG. 1. Typical bursts from Godiva used with reactivity booster

Remotely operated control mekhonisms

Detec!ar- signal cable (to tmw-dslov anal~ztr in

(for bare U”’ and transf-- system)

Phototube sample positioner

\

level trlqqet unit

counting paition

FIG. 2. Fissionable specimens are transferred from point sf irradiation within Godiva to heavily shielded counter in 0.05 sec. Multichannel time-delay anolyrer (2) gives delayed-neutron activity versus time OS shown in Fig. 3

shape of the trailing edge of a burst should be sensitive to short-period delayed neutrons,-and, in fact, bursts obtained with Godiva indoors do ap- pear to be influenced by neutrons de- layed the order of a millisecond. 4s this effect disappears tith Godiva sus- pended outdoors, it can be attributed to neutrons scattered back from the laboratory walls.

Delayed-Neutron Studies An example of the use of Godiva

bursts is a study of the periods and relative abundances of delayed neu- trons from various fissionable materials conducted by G. R. Keepin and T. F. Wimett. See Figs. 2 and 3.

Figure 3, supplemented by data from a long steady irradiation, may be resolved into a set of delayed neutron periods and relative abundances.

Periods and abundances of delayed

10.5~~~~~~ 0 0 20 20 40 60 a0 40 60 a0 I00 I00

Reactivity tcents) Reactivity tcents)

Decoy Time (eec)

FIG. 3. Delayed neutron decay following ation of 99.9% lJza6. irradiations of 3-gm sample. Least-squares tit to data:1 gives U’s’ delayed-neutron groups listed in table an p;‘$

, *I &a .i

.,‘,ti

&y&s :of &&;a ,,Gj

measurement phow a spe&.&* crease in period near prompt”? as the influence of delayed &$j drops out. (See Fig. 4.) *” evidence against the existenci ,_ delayed neutron period in the$ millisecond range. ::$

Briefly, the data for V5 and,? are similar to the periods and r&i abundances reported for Vii.’ Hughes and his co-n-orkers (&:I@ for CY8 the shorter periods are ‘$ig predominant. Data of this type basic to the problem of reactof co&@

* * * Some of the people responsible for th$?

to ?ohich I have referred---people xho8e.k I hope you will see on an imreesiny f’ *” of declassified publications are: Leo* Glen Graves, Jim Grundl, Gord0n.g George Jan&, Grant Koonk, Gus Linei John Ornda~, Roll Peterson, and Ro$

FIG. 4. Godiva period OS a function of

neutrons from fast-neutron fission of reactkity in cents

the principle fissionable elements as determined by Keepin and Wimett are given in the table on p. .$9. half-lives of 3, ‘12, and 125 minutes These do not include ultra-low-yield and yields per fission of 5.8 X lo-+, groups that have been reported with 5.6 X IO-lo, and 2.9 X 1O-1o (3). 50

1. H. Hummel, D. Okrent. ‘: A$ . . ~.,....-:-..^i^l ..“....“‘“‘“rc.