311635 June 16 1945 TO K T Ba1nbriafe FRo J SUBJ' CT DL NGT R o Hirschfeld r and J6fin Karee FRm ACTIVE T 'P IAL Ft LLI ' G FROi CLOUD DESIREi BILIT f OF B lNDDJG SOIL Nt f ZI ' ' iITH - COl CRr Tr ND OIL There 1s a definite danrer of dust containinf active 1i iu l ' ' r i • material ancl fission products fall fle on towrs near Trini'tif ii a• ·i· 1 t · 1 1 j necessi ta tint their evacuation This is shown by the folloPing o ·· icu calculations basea on the aesUI lptlons that t 1 r __ 1 The active material condenses on the surface of the noroal Trinity dust to give a distribution of activity with particle size si ilar to that observed by H L hndereon in the 100 ton shot 2 The dust on which the active material is de iosited is quickly 3 minutes raised to a heip ht of approximately 12 000 feet This is approximately the heieht to t1hich the smolte puff rose in the 100 ton shot and this sarr e height may be ex- ected in the next shot Between 1000 and 12000 feet the chanc e in terr ' erature with altitude should very nearly follow a dry aaiabat and therefore there should be no tendency for materiel which has risen above 1000 feet to stop berore it pets to 12 000 After 12 000 feet Hubbard expects a temperature inversion so thAt it will be Cifflcult for any material to rise much above the 12 000 foot level la 3 The duet settles in accordance with a modified Sto tes like normal industrial aust settling in st111 air 4 'l'he material as a whole ls carried aJ ong at a Pind velocity of 30 miles per hour This danrerous situRtion could be eli inated by reducln the number of dust particles of around 100 microns which get into the cloud This can be done by bonding the round in the vicinity of zero - preferably using-a lifht elurry of concrete in th vicinity of the future crater and a coatin of oil thinly distributed to a distance or 2000 feet from zero _ I Distribution of Active Material -· LAcking· any indications to the contrary it is nRtural to aseurne thct the distribution ·ar active material with particle size will be the 'sarne as Anaerson found in the last Trinity ehot This d1stribut1on ir dicatec1 that the active material ·i rae unif'ormly dletributed on the Furface of the and particles - the activity or the oartlcles being roufhly prono rtional to their surface area The follm •lnr table sur i - nrizes Anderson's observations to ether Pith some recent meaeurements of the particle size d1 tr1but1on of Trinity dtrt rne de by Kamm and Magee · rhich will be discussed in detail in another memorandum - ' rl'ltl El i ' L r ' •- _ UNCLWJtu • '·' 'l'r·u•p T Q1' I f' vl ll b' v PEftiloC R w jAfl w1 I - 2 Particle Diaraeter microns S4o Q1 ' • DIRT FROI CRATER Percentage Percentage Percentage Activity Surface Weic ht by Area Screeninp I Qfil t VI TR IN rrY DlRT Percenta e Wei ht Sar mle ill • Sa nle ti 2 3 s 1206 4 2 52 84o-250 32 21 4 s 250-149 15 14 5 10 149-74 16 HLl 9 2 g 5 35 7 6 2 1 9 74 16 51 0 2 4 6 73 3 30 45 It will be noticed from the last tHo columns that the weie-ht d1etr1bution of various sar ' les of Trinity dirt vary consiaerably Si ilarly Anderson found considerable variatione between different samcles of d1rt in the crater Therefore we cannot argue about the-amount of activity to be expected for a given rane-e of particle size to within a factor of two II f The Rate of Settling of Dust According to Stokeus Law particles of specific gravity and dla meter D microns should fall at the rate 0 00592 D2f reet minute According to John L Alaen Desifm of Industrial Exhaust Systems 11 Industrial Preee New YorkJ 1939 dust part1c1 es found in industry follow this law quite well for particles between 5 and 300 microns For larger particles the veloc1 ty of falling 1s sornewha t slot·Jer microns Velocity ft minute 5000 1000 1750 p 790 f D 500 555f - Using the above data it ie easy to calculate the length of time required for particles of var1 ous sizes to fall 12 JOOO feet • Here we assume that the specific ravity of the dust 1s 2 6 The results are summarised below - ·- Q am ••• UHClASSJRCD re·1· - tn ' a ASSIRCATION CANCEl L£D PER DOC REVIEW JAl 1973 Diameter microns 84o 500 250 200 149 110 74 60 33 22 6 16 0 ll 3 s o 5 65 3 Time to Fall l2z000 ft hours 0 110 0 139 0 205 0 325 0 585 1 08 2 37 3 61 1 2 0 25 5 50 s 102 204 4o8 I _ From the above table and Anderson's data 1t folloPs that 3 $ b of the activity drops ln the first 6 6 minut e 12 6% of the activity drops between 6¢6 and 12 5 minutes 14 5 -ii of the activity drops between 12 5 minutes and 35 minutes lS 1% of the activity drops between 35 minutes and 2 hours and 22 minutes and the remaining 51% drops at a much later time The dust particles which have diameters ranging- beti- reen 149 and 74 microns are therefore the most daneerous from the standpoint of nearby towns since they fall in the time intP rval between 35 minutes and 2 hours and 22 minutes Since they contain lS 1% qf the activity it follows that during this time interval the active material will be dropped at the averaee-rate of 10% per h iur If this dust is swept along at an averare velocity of 30 miles per hour each mile along the path will contain l J% of the active material It ls reasonable to suppose that at thie time the oath of the active material on the ground will be 3 miles Pide This fleure is completely soeculative but seems neither pesr if istic nor ooti istic Then each square mile along the oath at a dietai1ce between 17 5 and 71 miles contains 1 9% oi the activity III The Radiation Intensity Suffered by Person ln Nearby Town - - The - followlng calculaticrn was made the help of w1 th A Tur i tev1tch and agrees with a sinilar calculation made by L Hempelman Assume· that the gadeet is 5% effic1 ent so thci t 2 moles of fission products are formed Then according to a formula of Fermi's 15 f t eamma rays are emlttea per second after t seconds after the explosion Here f is the total nucber of f1s 1one If the total active material is spread uniformly over one square mile there will be emitted one hour after the exoloslon r' ' 1 lflCATlut CtJ• CE E · pnr Jl sl -P '' FJ · - PP - J 109 gammas sec cm 2 of surface area ----- '' - 1 UNCLA liJW lllllit ' I ' - - ····---· - --------·------ - - ' ' _ - 4 _·- o · ssmcAnoN CANcmm t R DOC REVIEW JAN 1973 Or spreading the 1 9 of 1% of the activi y over one square mile there · ill be erni tted one hour after the explosion 106 gammas sec cm 2 In unit solid ane le this will amount to ro 106 4 t gamrnas sec cm 2 unit solic angle But since the mean free path of the gammas in air ls of the order of A 1110 meters at a height h eql lfl l to one r eter above the ground the flux of gammas is approxlnately r rrI loge A2 h 2 1 2s1 2x10 6 gamrnas sec cm 2 0 0 Ana since one R unit corresponds to 109 ga mmas cm 2 we could there- fore ex· Ject a nerson 1 n the peth of the cloud at a distance of between-17 5 and 71 miles to receive radiation at the rate of 7 T R hour Here T ls the time after the exolosion in hours In the first day he receives approximately 22 R · Here we have only considered the danger of gamr a radiation ifoisslrnpf has made a similar co 1siderat1on for 49 and finds that over a long period of tine it too mifht be dangerous IV '· Suegested Remedy Since the danger fron the rad1 a tion ls aue to the Jresence in the cloud of a large percentage ot' dust rang1 ne in size between 149 and 74 microns the obvious solution ls to take stens to orevent such dust from getting the 'e This should be feasible by fili1ng the rerion which will become the crater with crushed rock from a nearby quarry and adalng a small amount of concrete slurry At larf er distances· up to 2000 feet 1 t -roula suffice to cover the ground with a thin film of oil Carlson estln ates that this would require approximately 750 000 gallons - a large amount but not prohibitive cc Col Warren Cant Jones Capt Nolan Bethe Carlson Eberstat Hernuelman Parsons Penney Oppenheimer Segre Weisskopr - · ··- ·J - - llNCLAss1n£D ·-ClM IMttl - - J