. : h --- .. :-*.. I | OF I ORNL P 2435 r A i . .. . . Imi co .. . . 'i .. MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS -1963 ORNL-P-2435 Conf.660703-2 SEP 2 2 1966 P!IYSICAL ASPECTS OF SEED IRRADIATIONS* DO TRADIATIONS, SITE Resni pauces LFSTI PRICES J. W. Poston Health Physics Division Oak Ridge National Laboratory Oak Ridge, Tennessee , MASTER N Hc. + 2 Cá MW 52 For the past two years the Radiation Dosimetry Research Section at Oak Ridge National Laboratory has participated in seed irradiation studies in conjunction with the University of Tennessee-Atomic Energy Commission Agricultural Research Laboratory, Morehead State College, and the Japanese National Institute of Genetics. The principal radiation facility has been the Health Physics Research Reactor (HPRR),"") which comprises a portion of the Dosimetry Applications Research Facility (DOSAR), at ORNL. This paper outlines the portion of the seed irradiation study undertaken by the DOSAR staff in conjunction with the University of Tennessee program. The primary objectives were the determination of the energy and spatial 22. --- distribution of the radiation fields, normalization between irradiations, and calculation of the absorbed dose delivered to the seeds. The HPRR is a small, bare, metal, fast reactor used primarily for health physics and radiobiological research (Figs. 1 and 2). The reactor was designed to produce copious quantities of fast neutrons with a minimum of gamma rays in a short, intense pulse and at steady state power levels up to 10 kw. The reactor core is a right cylinder, 20 cm in diameter and 23 cm in height. The fuel material is fully enriched 2550 alloyed with 10 wt % molybdenum giving a fuel mass of approximately 115 kg (Figs. 3, 4 and 5). ... Research sponsored by the U. S. Atomic Energy Comnission under contract LEGAL NOTICE with the Union Carbide Corporation. This repor: ms prepared us in account of Government sponsored work. Neither the Valted stalas, por the Commission, nor any person acung on behalf of the Commission: A. Makes way warranty or representation, expressed or implied, with respect to the accu- racy, completeness, or usefulness of the information contained in this report, or that the use of any information, appuratw, method, or procesu disclosed la this report may not infringe RELEASED FOR ANNOUNCEMENT prinatoly owned righto; or B. Anemos Lay labiules with respect to the we of, or for damages resulung from the un of any informatioa, appuntos, method, or proces disclosed la this report, As und in the above, "person acting on behalf of the Commission" includes way em. ployw or contractor of the Commission, or employee of much contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disuminatas, or provides acces lb, way Information purnuat to his employment or contract wild the Commission, or he employment wild such contractor. IN NUCLEAR SCIENCE ABSTRACTS . " .همسرام .... مه۱۰۰۰) .. مج24، ومن . ؟ ... عنهمنمسصعص ومم مه وب .ملغمتيقنمند تفهمنش - 10 .. و ا معبد ::: UNCLASSIFIED ORNL-LR-DWG 65074A PLUGGED HOLE FOR SAMPLE INSERTION- _MASS ADJUSTMENT ROD (U-Mo) Y BOLTS AND BOLT PLUGS (U-MO) BURST ROD (U-Mo) ht THERMOCOUPLES -REGULATING ROD (U-MO) CENTER PLUG (STAINLESS STEEL) - Ode LE BAYONET LATCH T. SAFETY CAGE (ALUMINUM)- -SAFETY BLOCK (U-Mo) P re pore autonoomsed IV Iquod 10000 - - - - - looooo Beeno - - ... rr SAFETY TUBE (STAINLESS STEEL)- . - - ma' - - N E S Health Physics Research Reactor 1 M . :... . . 2 . . .'.* 2. . . 2 - . i. : _ . : ..... " :.:.:. . " . 4 " اما * . ه . . . . . ... . .. .. 1 . دهه ۱۲۰::':1 .. ترا .۰۰۰ ..... 14 : :... .۹ اد,...نن | - = = = = ذا . مضت. مسخ . :. ::التمسك ، ..! ۰۰ هشتم من... . ه ه \ ا وا ا ... ... ... ء می : يع = | | - . . .. . . . - .. .. .. . . . ۱۰، ۲۰، ۲۳۰ -- مد - . . . ا ما ۱۰ ۱۰ : . . ا. فسمعه .. .. ، . ' ' . | . . . . . . . . ....مما/ ۵. ... مد .. . . .. . ه . . . . م . . . . . . . بها وطنننننننننننلمننده One of the principal things of interest to users of the HPRR is the somewhat unique mode of operation. Operation of the reactor in the steady- state mode is much like any other critical assembly except that there are rio poison rods to control the excess reactivity. The power level is readily controllable, through assembling the proper fuel mass, from a fraction of a watt to a maximum of 10 kw. This range of power levels makes the reactor a versatile research tool, since it is possible to vary the neutron dose rate at one meter from the reactor from 3.5 mrad/min to 500 rad/min by simply adjusting the reactor power level. In the burst mode, the reactor undergoes a self-limiting nuclear excur- sion caused by the rapid insertion of a fuel piece called the burst rod. The additiona. fuel places the reactor in a super-prompt critical condition causing a power excursion. Thermal expansion of the fuel and the negative temperature coefficient of reactivity quenches the burst giving a total fission yield for a maximum burst of 10'' fissions with a duration of approxi- mately 60 usec (full width @ half maximum). (Fig. 6.) Comparison with the dose rates in the steady-state mode shows the dose rate at one meter to be 5 x 10' rad/min when averaged over the 60 usec. The DOSAR Facility is a useful tool for scientists performing research in health physics, radiobiology and radiobotany. The DOSAR staff has contin- uing research programs in neutron and gamma-ray spectroscopy and dosimetry. Radiobiological research is carried on in conjunction with the ORNL Biology Division (Figs. 7, 8 and 9) and the UT-AEC Agricultural Research Laboratory. The well-known genetic studies carried on by the Drs. Russell represent one of these collaborations. A continuing program is carried on with several universities. UNCLASSIFIED ORNL-LR-DWG 66466R (x 1021) 3.0 fissions/sec YIELD: 9.8 x 107 fissions PEAK RATE: 3.0 x 1021 fissions/sec _MAX. TEMPERATURE RISE: 400°C PERIOD: 16 usec HALF-WIDTH: 48 sec REACTIVITY ABOVE PROMPT CRITICAL: 19 cents 50 100 250 300 150 200 TIME (usec) 350 - - - - ... - - - در ۱۰ من مارے - - - - :-". --- - - :: - ه ا ا :: ور\ ختم.... و - م . مه 1سمم ن .. .دن د د .. .. ۱۱:۱۱۲۰۱۲۹۰ د منتهم .. ام ...... بتمن.... د سمنهن د من ره مه نه ،مد.. تتت . ت تتتتتتتتتتتتتتنفسنده :: ... * زدن بنت : ۰۹۱۰۰,۰۰۰۰۰ . . . . .:::ة : را . . . . ه .... .. . و ساممم . مانند:ن لیا۔ . . خانه منم . نا ا ; . . .ع در ۰۰۰۰۰۰ ۱۰ه . - م امده . م ---- م مسد. ا. اما " ܝ ܂ ܕ | | ܀ '"n | ܕ . ܝ ܚܢܛܽ| .| . ' Lowland i lirico . ;. .. . . .. ܚ----- 1 . : -. ! . ܐ: ܐ ܕܪ ܀ ܗܠܝܢ ܐ ܂ . ܝܚ. ; ܫ . ܀ . ܙ ' ܘ . ܕ ܘ ܂ ܐ !. ܀ ܕ 1111 ܚ-P ܙ 1 ܂ ܙ ܀ ܐ : ܝ. ܪܐܗ . . ...,. ܙ..ܚܕ . . ܀ .a 8 : -- ܢܚܝ: . i;:- 1 ܪ ܂ ܫ ܙܐ r.܊ ܃ ܃ : ; ܘܫܬܙܫ...ܫ.ܬ. .ܙܫܙ. . ܘ. ܙܙܚ. 1 ܢ ܝ ܝܺܝܫܚ̈ ܟ݂ܵ ܣ. ܚ̈ܚܚܽܘܪܗܲܝܚܵܐ ܕܝܪܝܪܬܕܪܝܪܙܝܕܪܚܶܝ ܀ ܝ. ܐܚܝܢܫܒܚܢܝܚܝܢܝܐ ܐܢ ܝܽܘܠܝܚܪܐ ܝܚܐ ܚܝܠܪܚܐ * ; " " ا و ن = " usva) . | | | .:: ... .:۰۰ . . . - .: امی . | . . | ا.د. س ... نت !.. ا ::ز. -. : . : = ان ز | و | مسة . را ه ! - 5 منظم - - هتد .محمد معتمده TA 12 In the field of dosimetry, the HPRR serves as a standard for the Nuclear Accident Dosimetry Systems used by the major laboratories in the United States (Figs. 10 and 11). The various systems are intercompared annually during a comprehensive study in which many laboratories participate. - - --- The major task undertaken by the DOSAR staff in any irradiation study is the complete. characterization of the coexistent neutron and gamma-ray fields. The necessary measurements can be divided into several categories: (1) Measurement of the neutron energy spectrum; (2) Neutron and gamma-ray dose measurements as a function of distance from the reactor; and (3) Measurement of various parameters such as the number of leakage neutrons/fission, the isotropy of the radiation emanating from the source, and effects of neutron scattering from the floor as a function of the height of the reactor and experimental equipment. All the above measurements ure required in order to provide the experi- menter with a value of dose for a single irradiation. Once these measurements are made, however, the task becomes somewhat simpler and reverts to providing normalization between irradiations. A short discussion of each of these .. measurements, the techniques and results comprise the following portion of -- - - this paper. vi The primary neutron dosimeter system used at the HPRR utilizes a Hurst proportional counter(2) in conjunction with a "radsan" dose integrator(s). Briefly, the detector is a polyethylene-lined, cyclopropane-filled propor- tional counter that fulfills Bragg-Gray requirements for measuring neutron dose rates in polyethylene which can be directly converted to tissue dose ܕܝܐ ܀ ܕ . ܝ - ܂ ܀ ܟ . ܐ ' - . .. .-. . ܂ ܂ '. .. ܂ . . - ܘܫ - ܝ - - -- - - - ... .-; --- . ܝܢ - ܂ ܝܘܐ ܂ .ܬ . -. - .. t ܕܢ ܘ ܙ ܙ ܂ ܠܐ ܬܐ ܙܣܬ݁ܰܟ݁ܚܺܚܚܐܕ ܬܐܙ ܐܪܚܬܚ . 1. ܠܪܺܝܺܪܺܙ ; : : ܐܝܝܬܝܝܝ ܪܚܚ. ܚܬܩܚܚܐ;;f | ال * ه ها • : : مر همه دسته ( ول. 1 م = " ... همه همs-مم == م . .. د :. . ...... !لات / ". .. ..-.-.-.- . . : ... . .... ... .. 3 ا تسم راام ....ماع . هلمند سمند - . :: . . .اریا ارد . . لا ا مه IC عنده .... .:: !!! : " I !! من او لا ... کسم. ۲۴ 18 ... . میشه . . سمفنسة تضمنه .ضمه - :: . - - - - ته - ر . - - - - - - - - - - - - - - 15 rates using the conversion factor D.D. - 1.45 + 0.10. The dosimeter is insensitive to gamma rays since it is used as a proportional counter with a low energy bias sufficient to exclude gamma-produced pulses. The radsan dose integrator has a fixed low energy bias of approximately 160 kev. For the neutron energy spectrum of the HPRR, this low energy bias results in very slight underestimation of the neutron dose rate while effectively eliminating all response to prompt fission and fission product gamma rays. Gamma-ray measurements made in conjunction with the neutron-dose measurements use the Phil gamma-ray dosimeter.'! This dosimeter employs a Geiger-Mueller counter suitably shielded with lead, tin and fluorothene to make the response per roentgen more uniform at low photon energies.lo This dosimeter has inherent low sensitivity for fast neutrons with some response to thermal neutrons that can be reduced by an additional "Li shield (Figs. 12 and 13). A second system used for neutron and gamma-ray dosimetry at the HPRR is of the Nuclear Accident Dosimetry type. This system is comprised of a set of threshold detector foils() and silver metaphosphate glass rods(7,8). Six foils are used in the threshold detector system. Two 0.013-cm-thick by 1.11-cm-diameter gold foils are used with one of the foils enclosed in cadinium; the difference in activation of the two foils is related to the thermal neutron fluence. Three fissile foils (~58 Pu, -"'Np and 45° u) each encapsulated in copper and further enclosed in a 30-mil-thick admium cup are placed in a 10B sphere. The "OB sphere provides an artifical threshold of 1 kev for the 239 pu foil and shields all the fissile foils from thermal neutrons. Effective threshold energies for 29 Np and 2580 are 0.75 Mev and 1.5 Mev . --- -* . -it t s E ORNL-DWG 64-6443 A 104 . a - Ñ ') w a on NEUTRON DOSE RATE (mrad hr N o N ő 0 2 4 10 12 94.. 6 8 DISTANCE (rn) ORNL-DWG 64-6441A 103 HEIGHT OF REACTOR = 2 m HEIGHT OF DETECTOR = 2 m GAMMA-RAY EXPOSURE RATE (mr hrs w16 o 2 4 10 12 14 6 8 DISTANCE (m) 18 respectively. The remaining foil in the system is a 22 gram sulfur pellet for the 325(n,p) 32p reaction with a threshold at 2.5 Mev. Silver metaphosphate glass rods used to measure the gamma dose are 1 mm in diameter by 6 mm long. Gamma-ray irradiation of the silver-activated glass produces luminescence centers which yield orange light when the glass is exposed to ultraviolet light. The number of luminescence centers produced is linearly related to absorbed dose up to 104 rads. The presence of Li, B and Ag in the glass make it sensitive to thermal neutrons so a 'Li shield is used when the rods are exposed in mixed neutron-gamma fields. The fast-neutron energy spectrum of the HPRR was determined by using a spectrometer consisting of two closely spaced surface-barrier detectors, (*) one of which was coated with a thin layer of 'lif. Fast neutrons incident on the spectrometer give rise to 'Li(n, a) 'H events. The undesired (n,p) and (n,a) reactions in the silicon detectors were measured and subtracted by use of a background unit identical to the neutron spectrometer except for having no 'Lif coating. The spectrum peaks at approximately 0.6 Mev with an average energy (from the dose standpoint) of about 1 Mev (Fig. 14). The mean dose per neutron was calculated by utilizing a computer code and the measured neutron energy spectrum and "first collision tissue dose" curve shown in NBS Handbook 63. The calculated value was 2.52 x 10” rads/neutrons/cm which agrees well with the measured values determined by techniques previously described. The neutron leakage per fission is of interest for checking the accuracy of dosimetry measurements. Care must be exercised to measure only the "direct" neutron leakage from the reactor core since the ratio of scattered to total dose is increased as the reactor and experiment approach the floor. ORNL-DWG. 65.6268 MTTTTT HPRR FISSION SPECTRUM -- - > --zo. - ----- - - . = 0.01€ (E) N thithert100000 E (MeV) 20 : A threshold detector unit was employed for the leakage measurement. The detector was exposed at a separation of 2 meters with the reactor and detector at a distance of 6 meters above the floor. The value of 1.31 neutrons/fission agrees well with the calculated leakage value of 1.33 neutrons/fission. Normalization between reactor irradiations was performed by exposing a sulfur pellet in a standard, reproducible position on the reactor super- structure. The measured activity of the foil, corrected for radioactive decay, can be related to the neutron tissue dose in air at any distance from the reactor by referring to the air dose curve previously shown. The sulfur pellet activity also indicates the total number of fissions taking place in the core during the exposure. This was accomplished by exposing a sulfur pellet monitor while exposing a fuel sample in the small "glory hole." Chemical analysis of the fuel sample yielded the number of fissions taking place in the sample; these results were related to the number of fissions in the entire core by integrating under the fission distribution curve. Seeds were exposed to, the fast neutron spectrum of the HPRR during several different irradiations. Care was taken to assure that sample size was small and that the scattering from the floor was minimized. A total of 14 species was irradiated during these experiments. Results were reported for each . irradiation in units of neutron tissue dose in air. : . - -- - - In addition, a computer calculation of "seed dose" was performed utilizing the measured spectrum, the chemical compositions of the seeds as supplied by the University of Tennessee, the integrated fluence incident on each sample, the elastic cross sections for neutrons from BNL-325 (10) and the first collision dose equation from NBS Handbook 75 (Fig. 15). E RVA N -" e - r - - . . . . • ORNL-LR-DWG. 43850 TISSUE DOSE EQUATION FOR NEUTRONS OF ENERGY E DOME Eo.f 10*35031 = (3/4) . where 0; = cross section of atoms of type i f; = 2mM/(m + M)2 Q; = number of atoms of type i 2S ANAVY mii-4-- - - = . - . . -.-.- . . - - - - - - . . . - - - - - - . . S m r -. S. rs :7 *- - - --* *- *------ = - RYT A S ---- -- - -- - - - - . t e 22 : - -- - -- Comparison of the calculated first collision "seed dose" and the measured - dose expressed as "tissue dose in air" indicated agreement within ~10% for the large majority of the species irradiated (Table 1). - - . -. - - .: In summary, the Health Physics Research Reactor has served, and is . .-. - - continuing to serve, as a facility for seed irradiations. * The facility is Y . 4 highly suited for studies of this type since the irradiation space is large 2 and uncluttered and the character of the radiation fields is well defined. The wide range of dose and dose rates available and the large neutron-to-gamna ratio further enhance the utility of the facility. . . - - - - - - - . - - - - - - - - - - - 22a NA ORNL OWG. 66-6949 Table 1 Calculations of Dose for Some Common Varieties of Seeds Fluence & Oxygen % Carbon % Nitrogen. (neutron/cm2) Tissue dose Seed dose Seed dose - tissue dose - Secd dose Species % Ash & Hydrogen 5700 9000 6200 Onion Rape Cucumber Carrot Fescue Barley Lettuce Flax Tomato Alfalfa Clover Cotton 3.99 3.80 4.24 6.98 4.47 2.38 4.51 3.84 4.23 3.30 4.08 3.65 3.77 3.70 3.65 3.55 6.13 5.89 5.79 5.63 5.42 7.13 9.16 7.73 7.63 6.09 6.41 9.68 8.29 8.11 7.53 6.79 7.26 7.14 7.21 7.26 7.36 6.55 6.72 6.79 6.91 7.06 26.13 23.60 27.28 28.71 42.10 43.30 27.33 28.08 30.04 36.94 39.97 36.29 34.57 35.56 36.26 37.67 42.72 44.47 · 45.227 46.44 47.92 46.95 60.13 52.49 51.71 41.02 42.80 54.82 55.94 52.42 47.06 43.77 48.07 49.68 48.75 48.10 46.77 41.88 40.25 39.54 38.41 37.03 3.32 2.46 4.96 3.89 2.20 1.81 4.42 4.07 4.39 5.80 5.65 2.4 E12 3.0 E12 2.4 E12 3.0 E12 2.4 E12 3.0 E12 3.0 E12 2.4 E12 3.0 E12 1.6 E12 3.0 E12 9.0 E11 9.0 Ell 9.0 E11 9.0 E11 9.0 E11 1.3 E12 1.3 E12 1.3 E12 1.3 E12 1.3 E12 6000 7600 6000 7600 6000 7600 7600 6000 7600 3900 7600 2100 2100 2100 2100 2100 3100 3100 3100 3100 3100 0.052 0.!56 0.032 0.000 0.200 0.152 0.191 0.091 0.050 0.025 0.101 0.045 0.045 0.045 0.087 0.045 0.069 0.069 0.033 0.000 0.000 5000 6600 9400 6600 8000 4000 6900 2200 2200 2200 2300 2200 2900 2900 3000 3100 3100 3.16 3.10 3.06 2.97 1.34 1.28 1.26 1.23 1.18 Rice + 6 * - e .. n t re . -. -. - .- . - - * If 22 . - * - - - - * * :- -- =- .. ? - -- - -:: * V - * . r.o e ' . - , se - 24 REFERENCES 1. J. A. Auxier, "The Health Physics Research Reactor," Health Phys. 11, 89-93 (1965). 2. E. B. Wagner and G. S. Hurst, "Advances in the Standard Proportional - -- .- -c '.5 - , = .. Counter Method of Fast Neutron Dosimetry," Rev. Sci. Instr. 29, 153 (1958). 3. J. T. DeLorenzo and H. N. Wilson, "A Direct Reading Fast Neutron Dosimeter," (To be published), Private communication. 4. E. B. Wagner and G. S. Hurst, 'A G-M Tube Gamma Ray Dosimeter with Low Neutron Sensitivity," Health Phys. 5, 20 (1961). J. H. Thorngate and D. R. Johnson, "The Response of a Neutron-Insensitive Gamma-Ray Dosimeter as a function of Photon Energy," Health Phys. 11, 133-136 (1965) 6. G. S. Hurst and R. H. Ritchie, Radiation Accidents: Dosimetric Aspects of Neutron and Gamma Ray Exposures, USAEC Report ORNL-2748A (1959). C. H. Bernard, W. T. Thornton, and J. A. Auxier, "Silver Metaphosphate ---- -- - --- - -- -2 -- .* * * -.'.* . .- - - .. . * - Glass for X-Ray Measurements in Coexistent Neutron and Y-Radiation Fields," : * :- - - - . - * ***2.7* İR. - . 5 - 3, Health Phys. 4, 236-243 (1961). 8. J. S. Cheka, "Stability of Radiophotoluminescence in Metaphosphate Glass," Health Phys. 10, 303-314 (1964). 9. T. A. Love and R. B. Murray, ' "'The Use of Surface-Barrier Diodes for Fast Neutron Spectroscopy," I.R.E. Trans. Nucl. Sci.. 8(1), 91-97 (1961). 10. D. J. Hughes and R. B. Schwartz, Neutron Cross Sections, USAEC Report BNL-325 (1958). - -- n it - . . v . . . . A ... . .. : - .- - * : 5 1 ..B . ","MW LYON 14 T . • LIST OF FIGURES • • • • ,. . . : - * -- - - TO Figure 1 - Photograph of the HPRR Showing Core and Associated Equipment Figure 2 - Cutaway Drawing of the HPRR Core Showing Movable Fuel Pieces Figure 3 - Aerial View of HPRR Area Figure 4 - View of the Reactor Building Figure 5 - Interior View of Reactor Building Showing the Reactor Suspended from the Positioning Device Figure 6 - Burst Shape for Yield of 1.8 x 10" Fissions Figure 7 : A Typical Radiobiological Experiment in Position for Exposure . at the HPRR Figure 8 - Another View of a Typical Radiobiological Experiment Figure 9 - A Typical Radiobotany Experiment Positioned near the HPRR Figure 10 - Participants in a Nuclear Accident Dosimetry Study Arrange Their Dosimeters prior to Reactor Operation Figure 11 - Man Phantoms Used in Intercomparison Studies Figure 12 - Fast Neutron Doce Rate as a Function of Distance for Reactor and Detector 2 M above the floor Figure 13 - Gamma-Ray Exposure Rate as a function of Distance for Reactor and Detector 2 M above the floor Figure 14 - Neutron Energy Spectrum of HPRR Figure 15 - Tissue Dose Equation for Neutron Energy E P. :- ... : ) - 9 . - 7 . Lin... ... WW W WWWWWWWWWW -- --- - -- END . RE AN 10/21 / 66 . W X10 MW MY ! LP