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RADIOACTIVITY OP SOME OP the LIGHTER ELEMENTS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree D RADIOACTIVITY OP SOME OP THE LIGHTER ELEMENTS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By AKIHIKO YOKOSAWA, B.S.,M.S. The Ohio State University 1957 Approved by: Advisor Department of Physics & Astronomy ACKNOWLEDGEMENTS I take this opportunity to express sincere appreciation to my advisor, Dr. M. L. Pool, for his interest, suggestions, and encouragement. Thanks are also due to Dr. L. S. Cheng and Miss I. Riekstins for having done the chemistry associated with this work, and to Dr. R. Jung, W. L. Carey, and P. R. Sullivan for their helpful advice on experimental techniques. ii TABLE OP CONTENTS Pag© I. INTRODUCTION .............................. 1 II. HISTORICAL REVIEW ......... 7 Boron 13 Titanium $1 Manganese 53 Triton bombardment of gases III. INSTRUMENTATION ........................... 1? IV. STUDY OP A LONG-LIVED ISOMER OP Ti^1 ..... 21 A. Cr^ + n .............................. 21 (1) Source preparation (2) Chemical separation (3) Measurements of half-life (ij.) Beta-ray experiments by aluminum absorption, and beta-ray spectro­ meter, l80& deflection type (5) Gamma-ray experiments (6) Gamma-gamma coincidence experiments four months after bombardment (7) Gamma-beta coincidence experiments (8) Measuraments by the total absorption gamma spectrometer B. Ti^°+- n .............................. 51*. (1) Source preparation (2) Measurements by the total absorption gamma spectrometer C. Proposed Decay Scheme for the Long-Lived Isomer of TI^1 ......................... 63 D. Discussion ............................. 61± V. A SEARCH FOR Cr^6 ........................... 71 VI. MANGANESE 53 .................................. 72 A. Chemical Separation .................... 72 B. Results ............................... 7ij. (1) Gamma-ray experiments (2) Gamma-ganma coincidence experiments (3) Aluminum absorption experiments iii Page C. Discussion ............................ 85 VII. A SEARCH FOR B 13 .......................... 88 A. Lithium Borate •+• n ....... 88 B. Boric Acid -+> n ......................... 92 C. Carbon + n .................... 95 D. Li6 + n .............................. 95 E. Discussion............................. 97 VIII. NEUTRON BOMBARDMENT OF ARGON AND NEON GASES 98 IX. SUMMARY AND CONCLUSIONS ................... 99 BIBLIOGRAPHY.............................. 102 AUTOBIOGRAPHY............................. lOlj. iv LIST OF TABLES Table Page I. Gamma-gamma Coincidence Experiments ....... 50 II. Gamma-beta Coincidence E:xperinients ....... 5l III. Gamma-ene rgi es of ...... ............. 66 IV. Composition of Enriched Boron and Lithium . 89 v LIST OF FIGURES Figure Page 1. Boron Region of the Chart of Atomic Nuclei.... 2 2. Titanium, Chromium, and Manganese Region of the Chart of Atomic Nuclei ................... !}. 3. Neon and Argon Region of the Chart of Atomic Nuclei........................ 6 Ij.. Gamma-ray spectrum of Ti^, obtained with a 2- inch Nal Crystal............................... 12 5. Absorption Curve of Mn^3 and M n ^ ............. 15 6. Absorption Curve of Mn3*3........... 15 7. Block Diagram of Coincidence Counter ......... 19 8. Source and Crystal Arrangement For Total Absorption Spectrometer .................... 20 9. Gamma Decay of Cr^-t-n, 2\\. Hours after Bom­ bardment .................... 2ij. 10. Negatron Decay of Cr^*+ n, One Week after Bom­ bardment ....................................... 2 I4. 11. Decay of Cr^ n with Aluminum Absorber One Week after Bombardment ........................ 25 12. Decay of Cr^J- + n, Two Months after Bombard­ ment ................... 26 1 3 . Decay of Cr^b- +■ n, Two Months after Bombard­ ment ........................................... 27 II4.. Decay of 75 and 315 Kev Gamma-rays from Cr-3^- + n, Two Weeks after Bombardment ............ 28 vi Figure Page 15• Decay of 1|70, 625, and. 785 Kev Gamma-Rays from C r ^ + n, Three Weeks after Bombardment....... 29 16. Decay of Cr Fraction from Cr^- * n, Four Months after Bombardment ...................... 31 17. Decay of MnC>2 Fraction from Cr^ n, Four Months after Bombardment ................ 32 18. Absorption of Beta-rays from Cr^-*- n, Two Weeks after Bombardment ............ 33 19* Absorption of Beta-rays from Cr^- + n, Two Months after Bombardment ................ 33 20. Absorption of Beta-rays from MnOg Fraction of Cr^k +■ n, Five Months after Bombardment ...... 3^J- 21. Absorption of Beta-rays from MnOg Fraction of Cr^ +■ n, Eight Months after Bombardment 34- 22. Beta-ray, Negatron, Spectrum of Cr^U- ■+• n 35 2 3 . Beta-ray, Negatron, Spectrum of Mn02 Fraction from Cr^-*- ....... 37 2i|. Gamma-energy Spectrum of C r ^ + n, 2l\. Hours after Bombardment ....................... 38 25. Gamma-energy Spectrum, High Energy Region, of C r ^ + n, 30 Days after Bombardment .......... 39 26. Gamma-energy Spectrum of C r ^ + n, 30 Days and Two Months after Bombardment ............ I4.I 2 7 . Gamma-energy Spectrum of Chromium Fraction from Cr^J- + n, Four Months after Bombardment . \\2. vii Figure Page 28. Gamma-energy Spectrum of Manganese and Cobalt Fractions from C r ^ + n, Four Months after Bombardment ................................. 1+3 29« Gamma-energy Spectrum of Manganese Fraction from C r ^ + n, after Bombardment ..... 14!+ 30. Coincidences between Channel I and 75 Kev set in Channel II ................................ 1+6 31. Coincidence between Channel I and 315 Kev set in Channel II ....... 1+7 32 Coincidence between Channel I and 1+70 Kev set in Channel II .................... 1+8 33* Coincidence between Channel I and 625 Kev set in Channel II ...... 1+9 3l+. Gamma-energy Spectrum of Cr54 -+ n without Lead Absorber by the Total Absorption Gamma Spectrometer ................................. 52 35* Gamma-energy Spectrum with Lead Absorber by the Total Absorption Gamma Spectrometer .... 53 3 6 . Gamma-energy Spectrum Co^® with and without Lead Absorber ................................ 55 37* Gamma-energy Spectrum, high Energy Region of Cr5^--»* n ........... 56 3 8 . Gamma-ray Spectrum of Ti^-t n, no Lead Absorber ...................................... 58 39* Gamma-en ergie s, low Energy Region, of Ti-^-t- n 60 viii Figure Page i|0. Gamma-energiea, low Energy Region, of Cr^+ n 61 Ip.. Absorption of Beta-Rays from Ti^-+- n, 8 months after Bombardment .................... 62 ip. Lead Absorption of Gamma-rays ...... 69 i|3» 3 1 5 Kev Gamraa-peaks of C r ^ +■ n and Ti-^® ■+ n. 70 ip. Gamma-decay of Cr^Pcd , 2I4. Hours after Bom­ bardment .............................. 71? ip. Positron Decay of C r » 2ij. Hours after Bom­ bardment ...................................... 76 ij.6 . Decay of Mn Fraction from d 77 I4.7 . Gamma Energy Spectrum of Cr^-t <K , i|. Days after Bontoardment .................................. 78 4.8 . Gamma Energy Spectrum of Mn Fraction from Crat'd , Two Months after Bombardment ..... 79 ij.9. Gamma-energy Spectrum of Cr Fraction from Cr-^+ol , Two Months after Bombardment ..... 80 50. 8 ij.O Kev and I.I4O Mev of. C r ^ ^ .......... 82 31. Gamma-energy Spectrum of Manganese Fraction from Cr^°+ 4 83 32. Gamma-energy Spectrum of Vanadium Fraction from Cp30 + ^ ................... ........... 33* Gamma-energy Spectrum of Manganese Fraction from CP£° + °( , 12 Months after Bombardment . 81p 3p Absorption of Beta-rays from Manganese Frac­ tion of Cr5 0 + 4 f Fifteen Months after Bom­ bardment ............................ 86 ix Figure Page 55* Negatron Decay of Lithium Borate + n, One Week after Bombardment ....................... 90 56. Decay of Lithium Borate + n, One Month after Bombardment ............................... 91 57* Absorption of Beta-rays from Lithium Borate + n .......................................... 93 58. Absorption of Beta-rays from Lithium Borate + n, S3S, andC1^- ....................... 94 59 • Absorption of X-rays from Li +■ n ............ 96 x INTRODUCTION A search for some unknown isotopes of boron, titanium, manganese, and gases of the lighter elements is of consider­ able interest. These unknown isotopes may be produced by the bombardment of elements with neutrons, alpha particles, and tritons. Boron 13 may be expected to have a measurably long half- life, as the neutron number of boron 13 is 8• It is a fact that nuclides with 2, 8, 20, 5 0 , 82, and 126 nucleons are particularly stable. The neighborhood of boron isotopes is shown in Figure 1. A neutron bombardment of boron and lithium borate was done under the assumption that a (t,p) reaction of lithium borate and/or double neutron capture by & o boron 11 might produce boron 13. The reaction Li (n, dt )H 3 provides a convenient source of H , the energy of which is determined as (M , + M n - M , - M o ) = 5.08 Mmu Li n-1 He**- H = k*73 M e v k E^ ** "y Q = 2 . 7 0 Mev The experimentally determined value of E^. is 2 .7 I4.8 Mev(l). The approximate coulomb barrier energy of an isotope may be calculated from the relation Z. ‘B in M e v 1 1 (a h 3 )^ (Ag )3 1 HflSS NUHBER 8 7 to /I /2 /3 / S ’ !(o 1 1 o/o Percent abundance of nuclide in nature (5 Neutron capture cross section in barns Half-lives of radioactive nuclei are in sec, min, hrs, or yrs. too 2 .0 x io y & .007 /s.y-s-% 8 155% G3<190M .0225 <5 .2 (TJrt S .OSO A/OS% 98.872% <0 .000<f 9 m % 36£T% 7.38$ 2.0771 ? ? . 7 S 8 % 03 7 3 % Fig.l. - Boron Region of the Chart of Atomic Nuolei(2) where Z-q is the- atomic number of the target isotope. In the case of boron 11, the value of Is 1.37 Mev. Thus, the kinetic energy of H is high enough to penetrate into
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