Duncan, W. G.

Ohlrogge, A. J.

Wilkinson, S. R.

English

Open Access Journals at IU Indianapolis

The Influence of Radioactive Fallout on Agronomic FieldExperimentation with Radioisotopes 1S. R. Wilkinson, W. G. Duncan and A. J. Ohlrogge, Purdue UniversityRadioisotopes, such as phosphorus 32, are frequently used in agro-nomic field experiments. The success of the experiment depends in partupon the elimination of significant ionizing radiations from other sources.Any external source of ionizing radiation increases the likelihood forerror, and makes it much more difficult to detect and measure small dif-ferences due to treatment. Plant material normally contains smallamounts of radioactivity, but the amount is generally insignificant inrelation to the amounts normally used in biological experiments.In a band fertilization experiment on soybeans conducted at thePurdue Agronomy Farm in the summer of 1957, an external sourceof ionizing radiation was discovered. The soybean treatments in thisexperiment were sampled at approximate weekly intervals starting onJuly 11, 1957. In the second sampling on July 16, 1957, approximately15 untreated plots showed activity 15 to 18 times normal background.This high activity in the experimental plots was unexplainable onthe basis of experimental design or technique. The possibility ofcontamination due to experimental technique was thoroughly examined,and found to be practically non-existent. The possibility of untreatedsoybean plant roots feeding upon fertilizer placed in adjacent rowswas discounted since equally high activity was observed outside theexperimental area in corn, weeds, and soybeans. Since there was littleactivity present in the first sampling on July 11, and very high activitydiscovered in the second sample on July 16, it is assumed that the radio-activity was associated with the 1.86" rainfall which occurred on July13, 1957.The high levels of activity encouraged the collection of sampleswhen convenient during trips around the state. Sixty-four soybeansamples collected for a soybean nutrition survey were also used inmeasuring the distribution of fallout in the state. The soybean samplesin this survey were taken from an area approximately 50 miles wide,extending from Walkerton to Evansville, Indiana. These plus othermiscellaneous plant samples from Indiana, Kentucky, Michigan, andWisconsin were used to determine the magnitude and probable areasof fallout in the state, its half-life, type of ionizing radiation, and theapproximate energy of its radiation. Table I shows the plant sampleactivities corrected to July 31, 1957. The range of activity of these sam-ples ranged from practically none in Northern Indiana to very higharound Lafayette, Indiana; Louisville and Henderson, Kentucky; Patoka1 Journal No. 1184, Purdue University Agricultural Experiment Station, Lafa-yette, Indiana. Contribution from the Department of Agronomy. Acknowledge-ment is made to United States Industrial Chemicals Company for funds whichsupported in part this work.234Soil Science 235o>aW-Pa3(—1oQwhH* toPQ o>«! +3H '><n P S"O ,_|*°ft os0) aO M^ o <<«H T3o <D jjcu Jhcbxj 1.p| X crf^2- Cb-^ *TT3 OSlOrHa cnT rs <M »ou5 «<< CO5 ° SO 1 CO oCO 1 «3< o^ 1 rH C4CM rj<CMCO00 OSCM CMCDCOCOr~%b-t» lO t>m O) ioOS tH Oi4-3 +i -Pa Ph &0> 0) COco co co„00 Oi oH N (N W>> >5 tuo bJO3 3•-3 1-53 3< <>> o £1 j"rH K^. r>»bS)&. as^ o t«co +> J5h £h o3 o SCm £ Eh® a* a?3 oo uCO feW OT WS C C03 03 030) CD 0)X5 ,fi rQ5>> >» >»o o o72 CO mLO Tl< otH CO CO.'/&c .a.S gW Oa ycm «« .3to J >.o3 a «* -fl 4J ,£) +?W W S o03 o»n ? d O-£ bp E 03OCOHaO rt<(M O(M TfLO LO CO CO00 tH t- r-itH (Nb- i>b- LO tbLO 05 <5j05 rH -hCM 1-1 CMCO CD 5co co <!t- r^, t- t- r^LO {>, LO LO S-.o o rco co ^&jo &i >><j <j £"> oTCO ^a a03 03flf fir? a - ^<So!POaOoOOOO03*> ^Jc 2« « 8? 5?o2 -. ^w >H O<D —9 S« U ^.a h s> >53 -Q 53o cd orH ^ ^o "r-236 Indiana Academy of Scienceand Rockville, Indiana. It appears from an examination of the rainfallon July 13th and sample activity that the amount of fallout was roughlyproportional to rainfall.The half-life characteristics of the fallout were separated into twogroups, one of 18.3 days and the other 38.2 days. Since this undoubtedlywas a mixture of isotopes, these half-life groups were of no value inidentifying the radioactive isotopes in the mixture. The type of particleemitted was found to be predominantly beta, with probably very smallamounts of weak gamma radiation. The beta particle was assumed tobe negatively charged. The energy of the beta particle was determinedas approximately 1.5 Mev and 1.6 Mev in two different determinationsapproximately two months apart. Its energy was slightly less thanthat of phosphorus 32. Identification of the components of the mixturewas not considered within the scope of the project.The contamination of an isotope tracer experiment is serious, par-ticularly when the type and energy of ionizing radiation emitted is sosimilar to that emitted by phosphorus 32. Contamination must be con-sidered in the analysis of the treatment differences. This means thedetermination of a correction factor to account for the ionizing radia-tion due to external sources, or fallout.The experimental work on the fallout's effective half-life indicatesthat the material is sufficiently long-lived to influence activity measure-ments over a period of several months after its formation. This empha-sizes the necessity for continuous monitoring by measuring the level ofactivity in the check plots.With the increasing use of nuclear energy, nuclear weapons testing,and nuclear experimentation, it will be especially necessary to be on thealert for this new variable in all field experiments with radioisotopes.The properly designed experiment will provide a means for controllingor minimizing the effect of fallout on field experimental data.

The influence of radioactive fallout on agronomic field experimentation with radioisotopes

https://journals.indianapolis.iu.edu/index.php/ias/article/download/6570/6601

The influence of radioactive fallout on agronomic field experimentation with radioisotopes

Abstract

Similar works

Full text

Available Versions

Open Access Journals at IU Indianapolis