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Rcport written : July 20, 1965 Report dlatrlbuted: Auguet 23, 1965 of Radioactive Microspheres Biological and Medical Rescarch Group
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sph eric reentry and destruction of space nuclear power systems uill bc influenced by the size of particles returning will be mort, ~ idel yd is per sed but will be in there s pir able size range,with the possibility of entering the exchange space of the lung where biological elimination is relatively quite slow. Larger particles will be less widely dispersed but will constitute more intense discrete radiation ~ ource s. The size of particles reaching the earth ' s surface vi11 depen don the net hod of system destruction. As regard spot en - ti al hazard control,the method of choice will depend on a number of factors, among which are the biological effect u which maybe produced by radio act lv ? particles too large to be inhaled. This report covers some preliminary o beer v atl on ~ believed pertinent to assessing the biological ef lect r of microspheres in the size range of about 100 to8 fer buD-
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seem to be afn ctor 111 rate of passage. When placed in situ, un coated particles underwent disintegration and so lub i liza tio ii t o 12 wccks.The disintegration process involved en cap sula - tion,fib rob last ic infiltration ot the particle mass and,in case of the coated particles, vigorous macrophage ingestion Emergent beta - ray spectra of fission ed spheres were measu red and dose as a function of depth in the skin calculated and compared with measured dose using photographic ? mule ion dos ime try. Colculrted values(based on exponential abs or p - tion) were approximately 20 percent higher than measured Le rion ~p rod u ced on the rk in of the brcks of ron key8 by Dosea above about 10,ooO rads produced mull areas of e-- them which pe mia ted for 3 reeks. Yi cro a cop i call ~ ,theme
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Integrity of 2351;C2 Microspheres In Gross Gastrointestinal Transit Time of Lou- and High - Density Microspheres Reaction and Fate of Interstitial ly Emergent Beta-Ray Spectrum of Fission ed Beta Radiation Depth - Dose In T lee ue Average Depth of the Basal Layer of the Skin from Fission ed 235UC2 Yicroerheres in Contact rl tb the Skin Surface Contact with the Skin bur f8ce
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235L:C2 Microspheres before and aftcr 24-hour Immersion in Primate Gastric Yicrosphcrcs before and after 24-hour Immersion in Primate Gastric Juice Grosfi Gaetrointestinol Transit Times f o r Snall Particles of Different Gross Gastrointestilol Transit Times f o r SG;a11 Particles of Different Calculated Beta Rndiation Doses from P is alone d 235UC2 Microspheres Uaed i n Calculated a n d Measured Bet. Radiation
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S CCi one d UHTREX particle shoving 235LK2k ern eland du3lc x coating of 1an ; in ar and column ar pyro carbon Car-Ta-ray spectrum o f ht-nan fecal sample Gross transit time in relation to time of day particles were ingested E airless mouse with two carbon - coated 235K2 beads as placed subcutaneous ly 26 days prior to photograph Sub cut icu lar implant of ric ro sphere Encapsulated microspheres removed from the peritoneum 02 arat8 reeks after In trap or trl lp implanted micro up be re6 Pox - pi beta - ray spectra e ter
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dc cap spectra at four times aftcr fisCalc ul at rd beta radiation depth-dose profile in percent of thc dose at a depth of 100p, assuming exponential Skin mock up for film do imetry oi Measured and calculated lateral betaray dose distribution at loC, p below. micro sphere(1601 in diameter) 55 and exposure grid system (B) 62 Fig urc VII-2 Pictorial record of the 52,100-rad
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Asscssrne1:t of the potential hazards of inspired radio - active aerosols poscs pci - hap s the most complex and difficult health protection problc-n: facing the nuclear energy industry. Atmospheric reentry and burn up of nuclear rocket propulsion reactors and auxiliary po u er supplies will create potential radioactive particle inhalation hazards specifically affect - ing the use of nc clear energy in space missions.One POSsibi lit y of alleviating the potential Inhalation hazard l e to control the size of the radioactive particles returning to the earth ' s surface such that they will not be inthe respirable size range or a t least above the size range that may enter the exchange space of the lungs(larger than - 10 p), where the removal rate is relatively quite slow. Into to the problem is, o f course, not that simple. The larger the particle size,the fewer will be their number and the lower will be the probability that a specific individual or group
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both size and s!Ivi-tc.r dc cay time as a consequence of their more rapid rate of fP.11.Whether control of reentry particle size lessens t!ic potc > nti al hazards of space applications of nuclear energy 2r)pc.nds on evaluation of all of these param - et ers in rel at - ion to t tle biological effects produced by radio - active particles too larg ? t o enter the respiratory tract. If insoluble, suck pr tr tic les may constitute discrete sources of alpha,beta, or gnm ~ ar adi ation or mixed sources of these radiation types.Discrete sources deposited on the skin surface may produce significant radiation lesions and If swallowed will ref - lt In irradiation of the gastrointestinal mucosa.If eo lub le,the radioisotopes present may b e 8b607b6d directly into the body or enter the ecological cycle and constitute 1potential internal radiation a ource.The latter problem may be circumvented by employing only highly insoluble materials for space application m.This report c0i.r ~aome preliminary ob ser v8t ions believed pertinent to aes es eing the biological ef iec tm of d lo crete r8di8tiOn
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Cori side ration of radiation dose from discrete radio - active particles to np or ari ly residing within the lumen of the gastrointestinal tract requires knowledge of particle integrity,so lub i liz ation,and as sir nil ation by the body. particle integrity is not maintained in body fluids,then so lub i liz ation and assimilation may assume primary The following tests were performed to assess the degree of 235UC2 particle integrity during controlled exposure to Integrity of Carbon - Coated 235UC, Particles Integrity of UHTRM particles,consisting of a kernel surrounded by a duplex layer of laminar 8nd columnar Acronym for Ultra High Temperature Reactor Experiment.
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was car c fully ucl ghc d and measured(diameter) bcforc and after being placed into monkey gastric juice for 24 hours. This time period was selected as it would almost certainly exceed the maxir.um time a particle would remain in the acid environment of the s to nach.It was assumed also that the acidic conditions of the stomach would be the most detrimental to the particles.The gastric fluid was obtained from anesthe ti zed monkeys (Ra caca spec los a) some 30 minutes after the first meal fol loving an overnight fast,Particulate rnaterials were removed frorr. the juice by filtration through a juice was adjusted to pK 3.5 with HC1. Each particle was placed in3to5ml of the filtered gastric fluid contained in P plastic receptacle.The contents of the receptacle were maintained at 37°C with continuous agitation throughout the Particle diameter rereurementm were made rith8 Vickerolight microscope. Calibration of the optic81 rystem w88 achieved by u eing stage - mounted lO ep graticule marker a t
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Fig. 11-1. Sectioned UHTRM particle showing 23521(32 kernel and duplex coating of laminar and column ar pyro-
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ably the differences are not real but merely a reflection of there let ive position of the particle during each set of measurements before and after immersion. Thus, asa first. approximation,clad UHTREX particles maintain their integrity when agitated in warmed primate gastric juice for 24 hours. No fracturing,pitting, or erosion was observed. The integrity of un coated235 ~ 2p articles in gastric fluid was investigated also,since rupture of the pyro cnr bon coating conceivBbly could result in exposure to the bare attendant problem in handling un coated 235UC2 particles, only diu e term ea eure rent e were rade ' rout l ne lp.Otherwise, the experimental protocol given in the previous section Was
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pr in atc gastric ju icc for24hours.Differences exceeding ticle was corr:~ic.tc.lyf rac tu red into two roughly equal halves which were still rna tu ally connected.In three other trials, the diameters after im ner sion were from 10 t o 20 percent smaller than the originally observed values.Because of (trial No. 14)In diameter measurement represents a decrease by a factor of 2in the volume and hence cannot be ignored. A5percent decrease in diameter represents a reduction in volume of -10 percent. tiC1eS not used In this study showed the presence of nUmerOUS surface imperfections.It is not unreasonable to lrssume that similar particles might have inadvertently been used in this study,as it is extremely difficult to observe the entire surface of a small particle of this nature. Regardless of
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