. h ! . : - I OF L ORNLP 2897 . ... . . : 2 EEEFEFFE . 071 17|lsz @ MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS - 1963 i ܙ ܕ im ORN pra897. 7 1967 1. Conf-660920-14 MAR DOSE DISTRIBUTION FUNCTIONS FOR NEUTRONS AND GAMMA RAYS IN ANTHROPOMORPHOUS AND RADIOBIOLOGICAL PHANTOMS* T. D. Jones, J. A. Auxier, J. W. Poston, and D. R. Johnson Health Physics Division Oak Ridge National Laboratory Oak Ridge, Tennessee OFSTI PRICES H.C. 902.00; MN 165 Abstract--A right circular cylinder, 30 cm in diameter and 60 cm in height, was assumed to be composed of standard soft tissue, and dose as a function of penetration depth was computed for plane beams of incident neutrons. Data are presented for monoenergetic neutrons of various energies up to 14.0 MeV as well as for the neutron spectrum from the Health Physics Research Reactor (HPRR). The calculations were of a Monte Carlo nature using a slightly revised version of Snyder's linear energy transfer (LET) code. (-) New LET curves were obtained for C, N, O, B, Be, protons, tritons, and alpha particles, and recently obtained values of cross sections for these same elements were used with the code. (2) Many previous theoretical treatments of similar problems tended to ignore inelastic scattering reactions due to (1) the complexity of coding, (2) the difficulty of obtaining appropriate inelastic cross sections, and (3) inadequate "fast memory" capacity of many computational machines. Results of these calculations were compared with (1) those for the infinite slab 30 cm thick in the National Bureau of Standards (NBS) Handbook 63, (2) those obtained for a burro cadaver exposed to the neutron spectrum from the HPRR, (*) and (3) those presented by Auxier et al., (5) in their description of a belt containing various radiation detection devices to be used in the determination of the orientation of persons exposed to unscheduled criticality excursions. *Research sponsored by the U. S. Atomic Bnergy Commission under contract with the Union Carbide Corporation. RRIRA SKD FOR ANNOUNCEMENT IN NUCDEAR SCINCZ ABSTRACTS TEXT The Monte Carlo Linear Energy Transfer (LET) code used by Snyder in previous work (1,5) has been modified and extende t so that a more realistic treatment of various exposure situations is now possible. New stopping- power data (6) have been obtained for ions of C, N, O, B, Be, protons, tritons, and alpha particles, and are shown in Fig. 1. These curves are similar to those previously used by Snyder() for ions of C, N, O, and LIKES protons, except the low energy tail is now assumed to fall as the inverse power of velocity rather than the inverse power of energy. The code has been extended to include neutron inelastic scattering reactions in which the emitted neutron is assumed to come off isotropically in the center of mass system. Por elastic scattering, preliminary calculations were made for incident neutron energies of 7 and 14 MeV. An energy cutoff of . 2.5 MeV was used to determine the maximum influence of the assumption that - - . -A . all reactions were of an isotropic nature. The phantom is shown at the bottom of Table 1, and the results of the calculations are as shown in the table. Although the errors due to the assumption of isotropy are well within the bounds of the values of the coefficients of variation given in TO columns 4 and 6, the calculations, for the elastic case, were made without this simplifying assumption. Cross sections used in the code were presented by Auxier (a complete discussion of the 33 nuclear cross sections would be much too extensive for this paper) in his paper entitled "Neutron Cross Sections and Reaction Products for H, C, N, and 0 for the Energy Range from Thermal to 15 MeV," and calculations were made for various monoenergetic neut ron beams as well as the Health Physics Research Reactor (HPRR) neutron spectrum. The HPRR is an unshielded critical assembly of enriched 2351 LEGAL NOTICE This report was prepared as an account of Government sponsored work. Neither the United Stales, nor the Commission, nor any person acting on behalf of the Commision: A. Makes any 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 uso of any information, apparatus, method, or process disclosed in this roport may not Infringe privately owned rights; or B, Assumes any liabilities with respect to the use of, or for damages resulting from the use of any information, apparatus, method, or proceso disclosed in this report. As used in the above, "person acting on behalf of the Commission" includes any em- ployee or contractor of the Commission, or omployee of such contractor, to the oxtent that such employee or contractor of the Commission, or employee of such contractor prepares, nate., or provides access to any information pursuant to his employment or contract with the Commission, or his employment with such contractor. .. 1+1 .. . , producing neutrons having the spectral distribution shown in Fig. 2. The exposure situation was assumed to be a plane parallel beam of neutrons incident wilaterally on the cylindrical phantom shown in Fig. 3. The cylinder was assumed to be 30 cm in radius and 60 cm high, composed of H, C, N, and 0 in the proportions found in standard, soft tissue. (10) The cylinder was subdivided into 150 volume elements, but due to geometrical symmetry, only 60 different elemental exposures were possible. Table 2 shows the list of reactions that may occur in the phantom and the contribution averaged over the entire phantom from each of the various reactions. From this it is evident that many of the 33 pussible reactions could have been ignored since they contribute an almost insignificant amount to the total dose. The reactions are listed in three groups. The reactions in the first group, riumbers 1 through 4, are those of elastic scattering of neutrons by the nuclei in the medium. The second group, numbers 5 through 16, is that of the inelastic type in which a nucleus absorbs a neutron and is raised to an excited state and emits a neutron or two, in the case of the C(n,2n') reaction, and one or more gamma rays. The third group is that of the absorption type, in which a neutron is captured by a nucleus and one or more charged particles are emitted with or without accompanying gamma rays. . . The absorbed dose as a function of penetration depth, due to neutron reactions exclusive of the neutron-produced gamma dose, and the dose as a function of penetration depth, due to neutron-produced gamma rays, for representative energies are shown in Fig. 4. :. For instance, the n and y curves for a specific energy could be summed to obtain the total dose for a particular exposure situation. A 3 . Dose equivalent as a function of penetration depth is shown in Fig. 5 and was obtained through the use of ICRP-recommonded quality factors shown in the inset of this figure. The absorbed dose was soparated into 12 LET intorvals, and quality factors denoted by the arrows, representing the nean quality factor for that particular interval, were used to compute the dose-equivalent curvos shown in this figure. The coefficient of variation for both the rad and ren dose curves range from about 7% at the front where the volume elements are large to 22% at the center where they were much smaller to about 17% at the rear where the volume elements are largo, but attenuation of neutrons. Por the spectrum from the HPRR, the coefficients of variation range from 5% at the front to 40% at the center and rear. The incident neutrons. figure 6 shows dose as a function of LET for incident neutrons of energies 2.5, 5, and 14 MeV at penetration depths of 1.5, 13.5, and 28.5 cm. This illustrates the changing LET spectrum with both penetration depth and energy. . Por example, the LET spectral distribution of dose for 5 MeV neutrons at a penetration depth of 1.5 cm is not very unlike that for 14 MeV neutrons at a penetration depth of 13.5 cm. Calculations of the above type have been completed for incident neutrons of representative energies between thermal and 14 MOV. *. . :: . i .. : .-. 12 .. I .. 3.) . REPERENCES 1. W. S. Snydor, "The Let Distribution of Dose in Some Tissue Cylinders," Biological Effects of Neutron and Proton Irradiations, vol. I, IAEA, Vienna (1964), p. 3. J. A. Auxier and M. D. Brown, "Neutron Cross Sections and Roaction Products for H, C, N, and 0 for the Energy Range from Thermal to 15 MeV," submitted for presentation at the first International Congress of the International Radiation Protection Association, Rome, Italy, September 5-10, 1966. 3. J. W. Poston and D. R. Johnson, Oak Ridge National Laboratory, Personal communication (1966). 4. J. A. Auxier, F. W. Sanders, and P. N. Hensley, Health Phys. 5, 226 (1961). 5. W. S. Snyder, "Distribution of Dose and Dose Equivalent Resuiting from Broad-Beam Irradiation of a Man-Sized Cylindrical Phantom by Mono- energetic Neutrons," Health Physics Society Meeting, Los Angeles (1964). 6. D. R. Davy, Oak Ridge National Laboratory, Personal communication (196). 7. Health Physics Division Annual Progress Report for Period Ending July 31, 1965, Oak Ridge National Laboratory Report ORNL-3849. 8. Health Physics Division Annual Progress Report for Period Ending July 31, 1964, Oak Ridge National Laboratory Report ORNL-3697. 9. J. A. Auxier, Health Phys. 11, 89-93 (1965). 10. "'Measurement of Absorbed Dose of Neutrons, and of Mixtures of Neutrons and Gamma Rays," Nat. Bur. Stand. Handbook 75 (1961). 11. ICRP Publication 4, Report of Committee IV (1953-1959), Recommendation of the International Commission on Radiological Protection, Pergamon Press (1964). . L cristianesite na teritories - - - - -- - . ..*xa ., M A . A . IV -*-- -** - : ...-.. . - -- , - "... CRNL DWG. 66-8833 Energy .456 - 1.8 . 1.7 Table 1. Results of an isotropic treatment of anisotropic reactions in a slab phantom Isotropic Anisotropic {*° 10°8 rad) of V. 1x 10^8 rad) (Mev) Error Slab No. of v. neutron cm? (i-iso./aniso.) ~100 (neutron cn2 (%) 7 (2.5 cutoff) 6.8 . 448 6.2 .253 7.1 .249 . 120 10.4 10.8 .126 15.9 .054 12.0 + 4.8 .059 17.0 + 9.5 14 (2.5 cutoff) .526 7.2 .457 .336 • 11.5 3.3 .323 9.9 . 192 11.5 - 4.1 10.2 .099 17.4 + 2.3 11.3 + 14.2 14 (no energy cutoff) .562 6.2 .484 6.2 .329 11.5 16.1 7.2 .203 9.8 + 0.8 .214 8.9 . 106 + 5.2 11.3 .137 19.7 + 22.6 6.4 .196 .i15 .332 - 60cm ' INCIDENT NEUTR SNS No. 2 Na 3 Na 4 SLAS No. 1 .: SLAB PHANTOM ORNL DNG. 66-8834 Table 2. Contributions to dose averaged over a cylindrical phantom from reactions in tissus HPRRT 5 MeVt Reaction 10 MeVt 14 MeVt 28.26 .59 6.9232 .1780 .0146 .4228 22.44 .57 .06 1.36 33.58 .63 .06 1.50 .06 1.97 34.10 .60 .06 1.44 + gh .03 .03 .26 .05 .59 + + + .0099 .0001 .0004 .0002 .0001 .69 .14 .01 .03 .02 . + + .03 + + .0083 .0036 1.36 . 30 .05 1.54 .38 1.58 t .77 1. H(n,n)H 2. C(n,n)C 3. N(n,n)N 4. on,n)0 5. Cin, n')*C; C Yi; Yi : 1.75 MeV 6. Cin,n')*c; + Y2; Y2 * 4.43 MeV 7. C(n,n')*C; *C + C + Y3; 73 : 6.8 MeV 8. N(n,n') *N; N + Yı; Yi : 1.63 MeV 9. N(n,n')*N; *N + N + Y2; Y2 : 2.31 MeV . 10. Nin,n') *N; *N + N + Y3; Y3 3 5.1 MeV all. Nin,n')*N; *N + N N + 74; 74 3 10.0 MeV 12. Nü,n')*N; N + Y5; YS - 11.0 MeV 13. on,n)*0; *O + 0 + Ti; Yi = 6.1 MeV 14. On,n")*0; *0 + 0 + Y2; 12 = 7.12 MeV 15. O(n,n') *0; *0 + 0 + Y3; Y3 3 3.8 MeV 16. 0(0,1') *0; *0 + 0 + Y4; Y4 3 4.8 MeV 17. C(a, az) *Be; *Be + Be + n; Be + 2a 18. C(n,n') *C; *C + Be + a 19. N(2,2N)N 20. H(n,r)H 21. C(n,ao)Be 22, N(0,00)B 23. O(n,ao)C 24. Can,a1) *Be; *Be + Be + Y; Y * 1.75 MeV 25. N(n,ai)*B; *B + B + yi; Yi : 2.1 MeV 26. Nin,ay) *B; *B + B + Y2; Y = 4.5 MeV 27. N(D, az) *B;' *B + B + Y3; Y3 : 5.0 MeV 28. O(n,ai) *C; *C + C + Yı; Y1 : 3.1 MeV 29. 0(0,02) *C; C + 72; Y2 : 3.8 MeV 30. O(n,a3) *C; Y3; Y3 3 7.0 MeV 31. N(n,p)*C 32. O(n,p)*N; *N + N + Y; Ya 6.1 MeV 33. N(n,t)c Total Doses .58 .51 .01 1.64 1.41 1.21 .11 . 10 .55 .06 .69 .10 73 1.7250 .0006 .0127 .0284 .0001 .0006 .0001 .0004 .0014 .0009 .89 .36 .11 1.11 .05 .04 .01 .01 .01 .05 .04 ¢ ¢ ¢ ¢ .11 .22 Uuu z .1495 .19 22 .22 .06. 1.03 2.46 1.00 .18 .51 .02 50.42 9.4809 26.95 33.69 .01 40.91 ** 10-10 rad/neutron/cm2 FIGURE CAPTIONS 1. Stopping power for recuží iont in soft tissue, 2. Neutron leakage spectrum from HPRR. 3. Numbering of volume eisments in the cylindrical phantom. 4. Absorbed dose as a fuction of ponetration üepth in a cylindrical phantom (30 cm x 60 cm) Dose equivalent. as a function of penetration depth in a cylindrical phantom (30 cm x 60 mm) 6. Dose as a function of LET. 1000 ORNL DWG 66-e656 O 200 -100 --87.5 -73 -62.5 -50. IKOVA -35 . 25 . . ALPHASA PROTONS TRITONS Lunden STOPPING POWER FOR RECOIL IONS IN SOFT TISSUE o karte - Okov u m or - her 1.OKOV IOKEY OOK V I MeV IOMOV DOMOV ENERGY Figure I PIS * * * ORNL DWG 66-8654 NEUTRON LEAKAGE SPECTRUM FROM HPRR N(E) 0.001 0.0001 - 0.00001Lu u .01 0.1 10 E(MV) 2 : . Figure a - - - - - UNCLASSIFIED ORNL-DWG. 63-4831 20 ---------------........... NUMBERING OF VOLUME ELEMENTS OF THE TOP AND BOTTOM TIERS - VOLUME ELEMENTS NUMBERED BY i VOLUME ELEMENTS NUMBERED BY ;+ 20 - VOLUME ELEMENTS -VOLUME ELEMENTS NUMBERED BY i + 20 VOLUME ELEMENTS . NUMBERED BY i birint: NUMBERING OF VOLUME ELEMENTS IN THE CYLINDRICAL PHANTOM .. Figure 3 . 75 . EUR 4. ORNL - DWG. 66-8657 ABSORBED DOSE AS A FUNCTION OF PENETRATION DEPTH IN A CYLINDRICAL PHANTOM (30 cm x 50 cm) 10 . n (14 MeV) n(5 MeV) DOSE ( REM/n/cms y (14 MeV) 7(5 MeV) n(PIRE IPARI n(10 kov) ono kev) ▸ PENETRATION (cm) Figure't. . . OANL-DMG_66-8655 DOSE EQUIVALENT AS A FUNCTION OF PENETRATION DEPTH IN A CYLINDRICAL PHANTOM (30cm x 60 cm) 14 MOV 5 MeV DOSE ( REM /n/ cm) LILIT ALITY FACTOR AS A FUNCTION OF LET Q.F. HPRR 200 200 1000 50175 ) 87.5 LET (keV/H) O kcV 6 8 10 12 14 16 18 20 22 24 26 28 30 PENETRATION (cm) 3.5 7 15 25 15 25 50/75 de L maintenant le milieu de trabalho arinellisemmin Figure is ORNL-DWG 66-11428 DOSE AS A FUNCTION OF LET 1.5 cm PENETRATION DEPTH 2.3 Mev 5 MeV 14 MeV ☆ OFF SCALE 13.5 cm PENETRATION DEPTH - 2.5 MeV -- 5 MeV ......14 MEV ☆ OFF SCALE 28.5 cm PENETRATION DEPTH - 2.5 MeV 5 MeV ....... 14 MeV OFF SCALE DOSE (rad /n/cm)/(keV/H) JU 10" 17125 50 75 100 713 | 35 50 75 100 625 87.5 3 25 50 75 100 625 87'5 35 S | 35 62.5 875 is a — LET ( keV/H) Figure 6 END . F & Y . . DATE FILMED 4 / 5 / 67 --- ! v. " Y TV