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 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 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 the nucleus of boron 11. Chromium 56 can be investigated by the same method as the boron. Neutron bombardments of chromium enriched in mass number 5^4- and lithium chromate can determine whether there exists a chromium 56 which has a measurably long half-life. The neighborhood of C r ^ is shown in Figure 2. In view of the possibility that a long-lived isomeric state of titanium 51 might exist, it is desirable to make a neutron bombardment of titanium enriched in mass number 50 and chromium enriched in mass number 54- respectively. As shown in Figure 2, the neutron capture by Ti^® and (n,o( ) reaction of C r ^ may produce Ti"^. The existence of manganese 53 has been under discussion for the past several years, and in order to investigate this problem a sample of enriched chromium isotope of mass number 50 was bombarded with alpha particles. The resulting acti- 5 3 vity was expected to show that Fe is formed by an (c£ ,n) 53 53 reaction, and then F e ^ decays into M n ^ by K-capture and positron emission. As shown in Figure 2, (<^,2n), (o(,3n), and ( W 50 5 / 5-2 53 SF 5 5 56 o/o Percent abundance of nuclide in nature 6 Neutron capture cross section in barns 5.4 % 5 . 5 % Half-lives of radioactive nuclei are in sec, 6 ./if min, hrs, or yrs. TL 7£77? V 3.6m Cl too °/o 5 13.4 2.58 h n Tt 6" SY7?oO 5 34 % 3.0 y <7/. 6 3 % Fe Fig.2. - Titanium, Chromium, and Manganese Region of the Chart of Atomic Nuclei(2) desirable to establish a relationship of cross sections of (t,p) and (t,o( ) reactions. Neon and argon gases were chosen as targets of triton bombardment. Using these gases, trouble some processes such as chemical separation to remove im purities can be avoided. As a preliminary test, neutron bombardments of compressed neon and argon were made respectively. In order to achieve the (t,p) reaction, lithium and gas molecules must be closely combined so that triton from lithium may irradiate the gases more effectively. When the argon gas is bombarded by triton, both (t,c<), and (t,p) reactions are detectable. The reaction Ne^(t,p) N e ^ clarifies the existence of Ne^. The neighbor hood of argon and neon is shown in Figure 3» 20 21 22 23 24- 25 6- .036 /o/Ve /oo % 27 S £.60 y /5.06A I /.Cm ii Na. IZ^f 35" 36 37 38 37 70 7 / 72 n Cl J3.ft 60X10 6 17 K Fig.3. - Neon and Argon region of the Chart of Atomic Nuclei(2) HISTORICAL REVIEW Boron 13 It has been suggested(3) that B-*-3 should be a delayed neutron emitter, which decays by negatron emission followed 12 promptly by a neutron, going finally to C . Several such isotopes have been observed as fission products, and two more have been produced in cyclotron reactions. The best identified of the fission activities Br®? and , 9 17 and the cyclotron activities(6,7) LI and N , all have in common the property that the end product of the decay con tains a closed neutron shell. Sheline(8), using a 50 Mev 18 betatron, did not observe B ^ in a search for new low Z beta activities of half-life greater than 0.1 second. Barkas(9) predicted B*^ to be particle stable with a mass of 13*0207. This gives a beta plus neutron excitation of 7 .14.5 Mev. Assuming an allowed transition with ft ■ 5 x 10-3, as is the case of one gets a minimum expected half-life of 0.2 second. With outside limits on the mass and the ft value, one finds a minimum possible half-life of 0.002 second. Hubbard, Ruby, and Stubbins(lO) made a search for B1! Three holes were bored in a large block of paraffin, one for the targets and one on either side for a BF^ counter. Vari ous low and middle Z targets were exposed to the deflected 3I4.O Mev proton and 190 Mev deuteron beams of the l8 Lj.-inch cyclotron. No neutron activity was found which could 7 8 correspond to the decay of B^® as a delayed neutron emitter with a half-life in the range from 0.5 millisecond to 0.5 hour. According to Heiberg(11), neutrons from a pulsed deuterium beam impinging on a tritium target were used to bombard a boron trifluoride proportional counter containing the normal ration of to B ^ . The half-life of the acti vity and the energy of the particles indicated that they O were due to the immediate breakup of Be into two alphas after the 0.88 second beta decay of the Li® formed by B-^ (n, o( )Li^ reaction. The reactions B ^ ( n , o ( )Li^, B^(n,t)Be®, and B^(n,p )B e ^ were also detected. Energy levels of have been studied by Bigham, Allen, and Almqvist(12). In levels were observed at 3*08, 3*77, 6.89, 7.63, 8.96, 10.00, 10.99, and 11.67 Mev. It was found by Allison, Murphy, and Norbeck(13) that B^® could be prepared by means of the reaction Li^(Li^,p)B^®, A 2 Mev Van de Graaff accelerator was used to accelerate Li ions, obtained by evaporation from a hot filament coated with lithium salts. The Q-value of the new Li^(Li^,p)B^® reaction is 5*97 + 0.03 Mev, giving B^, presumably in its ground state, a value of ( M-A ) equal to 2 0 . 3 9 + 0 . 0 3 Mev, or a physical atomic weight of 1 3 .02190 + 0.00003. It was stated that a search for the beta activity and possible delayed neutrons would be made. Several experimental evidences of the (t,p) reaction 9 were established by Kundu and Pool(li|). Prom these experi mental evidences, it would seem possible that two neutrons could be introduced into a boron nucleus by the bombardment with H3 . Titanium 5l Activities produced by bombardment of TiOg with pile neutrons have been investigated by Hein and Voigt(15). A chemical separation on the irradiated TiC^ was effected for the purpose of identifying radioactive products from (n,y ), (n,2n), (n,p), and (n,ot ) processes. The following acti vities were identified : Ti^'1*(5.8rain), Sc^(19.5 sec and 8 ij.d), Sc^-?(3*^i-d.) > a n d Ca^(l61j.d). These identifications were based on observed beta-ray energies and half-life measurements as well as chemical evidence. The presence of a contaminant, Sb^^, was also detected. The two cases of isomerism, C a ^ and T i^, for 29 odd neutrons in even-odd nuclei were discussed by Mateosian and Goldhaber(16). The first case could not be confirmed. In the second case, some doubt was thrown on the existence of the 72-day activity of Ti^(17)» isomeric with 6 min. Ti"’1 . A source of Ti^(72d) obtained from Oak Ridge was further in- vesitgated by Miskel, Matiosian, and Goldhaber(18). The presence of Hf1 ^1 (i4.6 d) and Sb1^^'(60d) was established. The spectroscopic analysis accompanying the Ti02 sample had re vealed neither Hf nor Sb. After purification a sample of 10 T10 2 showed a reduction in intensity from the original acti vity by a factor of approximately 10£. It is therefore pro- bable that no 72 d Ti^51 exists, and that previous observers were measuring an apparent activity caused by a number of impurities of comparable half-life. In agreement with expectations from the spin orbit coupling model(19) of nuclear shell structure, no cases of isomerism for less than 39 odd nucleous are now established for even-odd nuclei. Forsling and Ghosh(20) tried to formulate the decay scheme of 72 d Ti>x5l by studying the beta-and gamma-spectra. As the preliminary investigations were proceeding, the remark of Miskel, Mateosian, and Goldhaber(18) concerning the non existence of a long-lived isomer of T i * ^ came to their notice. Then the stress of the whole problem shifted from decay scheme investigation to impurities. Titanium from a pile-irradiated sample was separated in the isotope separator. No activity was found corresponding to Ti 51 . Chemical separation also proved that the activity of the sample did not belong to titanium but to tantalum occuring as an impurity. The beta- spectra of the original sample and that of the separated tantalum showed the major features of the beta-spectrum of Tal82 repoi*ted by Beach, Peacock, and Wilkinson(2l). The half- life of the Irradiated titanium oxide sample was studied six months after the bombardment. The decay was followed for 7 months and the half-life was roughly established at about 115 days, which is in agreement with the value for Ta1®^. From 1 1 the thermal neutron cross section data for Ti^® and Ta^-®^ given by Seren, Friedlander, and Turkel(22), it is to be expected that an impurity of 0 .0%% of tantalum oxide in a titanium oxide sample would be enough to explain all the activity found in that sample. A series of cross bombardment with appropriate particles and enriched isotopes was done by Hammond, Kundu, and Pool(23) to remove any doubt as to the existence of a 6 -minute activity attributable to Ti-^. Prom the four types of reactions, such as C a ^ t oC ^njTi^1 , Ti5°(th n, jTi^1 , Cr^(fast n, o< jTi^1 , and V^Cfast n , p ) T i ' ^ , a consistant 6 -minute activity was observed. The radiations of Ti-^(5.8min) and Cr-^(27d) have been investigated with beta- and gamma-scintillation spectrometers by Bunker and Starner(2 I4.). Gamma-rays having energies of 0.323, 0.60£, and 0.928 Mev and relative intensities of 95*8 : 1}..2 , respectively, were observed to accompany the decay of T i ^ . The T i ^ sources were prepared by neutron irradiation of titanium enriched in T i ^ ( 8 l.L|ij$). The gamma-ray spectrum of Ti^, shown in Figure Lp, was obtained with a 2 x 2 inch Nal crystal. The entire spectrum of Figure I4. was found to decay with the half-life of Ti , which was measured to be £.80 + 0.03 minutes. The decay schemes suggested are shown below. IH- zak iZ O UJ t* I tO 16: I 10 1- o-J 8 ? >m<- M O 20 30 40 SO 60 70 80 ?0 FUISE HEIGHT (VOLTS) F IG ,4 . - GAMMA.-RAY SPECTRUM OF T i51, OBTAIN® WITH A 2-INCH N&I CRYSTAL. THE HI (21-ENERGY REGION IS SHOWN ON AN ENLARGED SCALE(24) 13 "1.0 Mev (3/2" 28d 605 0.928 -.0.5 M e v (5/2" (7/2") Stable V^1 The dotted lines at O.J4.8 Mev and 1 . 1 6 Mev are additional levels in indicated by inelastic proton scattering experiment s(2 5 )• The radiations for T i ^ was also studied with a scintillation coincidence spectrometer by Burson, Jordan, and LeBlane(26). Gamma-rays 0.32, 0.61, and 0 . 9 2 Mev were resolved. Their intensities were estimated to be in the ration 100 : 1 : 5 respectively. The 0. 3 2 and 0.6l Mev gamma-rays were in coincidence. No indication of a beta transition to the ground state of was observed. Manganese 53 In reporting the nuclide M n ^ , Livingood and Seaborg(27) found no trace of the nuclide M n - ^ . Batzel, Miller and Seaborg(28) observed the nuclide M n - ^ in the spallation of 14 copper, but did not observe M n ^ 3 . a careful search had been made for a short-lived activity by Sheline(29). No M n ^ 3 activity in the half-life region from 0.02 second to several minutes was found. In view of these experiments and because shell closure occurs at 28 neutrons, it seemed probable that M n ^ 3 would have a very long half-life. Wilkinson and Sheline (3 0 ) observed the nuclide M n ^ 3 by the nuclear reaction C r ^ 3 (p>n) M n ^ 3 in the bombardment of enriched C r ^ for a period of 8 hours with 9.5 Mev protons. By decay and absorption characteristics, a long-lived component M n - ^ was detected. The difference between the absorption curve of M n ^ 4 and that of the bombarded sample is the absorption curve of M n ^ 3 as shown in Figures 5 6 . Measurements of the decay and absorption data indicate that this muclide is an orbital electron capturing activity without gamma rays or positrons. With the assumption that the cross section for the reactions Cr^3(p,n)Mn^ and Cr^4(p,n)Mn^ are the same, it is possible to calculate an approximate half-life of II4.O years for this nuclide. The decay scheme suggested is shown on page 16. Triton Bombardment of Gases The excitation function of the reaction t,n)F^® was measured for triton bombarding energies of 0.680 to 2. 1 3 0 Mev(32). The half-life of the F^-® beta decay was measured to be 111 rain. Thin mica targets were irradiated by various energy triton beams from one of the 2.5 Mev Los Alamos electrostatic generators. iiiiliijt ACTIVITY COUNTS /MINUTE ACTIVITY COUNTS /MINUTE *0 o o o o o r o B o § oo s O TO FIG. 5. - ABSORPTION CURVE OF Mn' 16 (7/2“ )______8.9ra 26Pe53 Tl.O M e v 0.88 li|X) -Mh- Jo .(3/ 2. “J Ofc Stable oi.Cr^ The technique of observing trition-induced reactions by mixing lithium with a target element and irradiating in a pile is now well known. The slow-neutron reaction Li^(n,ai )H^ yields 2.8 Mev tritons. Sher and Floyd(33) observed the reactions 0 ^®(t,c^ )N^7 * 0 ^ { t,n)F^®, and N ^ U j p j N 17. The samples were 112003 and Li^N, and they were irradiated in the BNL reactor. INSTRUMENTATION The activities of the samples were measured in the following manners. (1) Half-life and Absorption Experiments The decay of the sample was followed by a Tracerlab TG-C-3 Geiger tube. The absorptions of the radiations in aluminum and in polystyrene were also investigated using the same tube. (2) Beta-ray Measurements The beta-rays were examined by 180° magnetic deflection in air, using a Tracerlab TGC-2 Geiger tube as a detector. By means of a reversible-variable-field electromagnet, the deflected particles can be identified as either negatrons or positrons. (3) Scintillation Method The gamraa-rays were studied by means of Detectolab apparatus consisting of a l" x 1 3/V1 Nal crystal, photo multiplier tube, linear amplifier, differential pulse-height analyzer, and scalar. Throughout these measurements, the scintillating crystal was protected from beta radiations of the source by an aluminum absorber sufficient to remove beta activities. (4) Coincidence Method Coincidence-counting experiments were performed in order to investigate the possible occurrence of coincidence among 17 .18 the observed gamma radiations and establish the decay scheme. The work was done using commercial equipment manufactured by Detectolab Inc. The single channels consist of Hal crystal lir" in diameter and 1" thick, Dumont photo-multiplier, cathode follower, amplifier, and single channel analyzer. Outputs from each of two single channel analyzers were applied to a coincidence circuit having a resolving time of 0.89 x 10”^ seconds, as calibrated in the laboratory using standard gamma- rays. A block diagram of the instruments used is shown in Figure 7* (£) Total Absorption Gamma Spectrometer Large sodium iodide crystals have a high gamma-ray efficiency, and gamma-rays from a source inside the crystal may be almost completely absorbed. This arrangement has many advantages; the Compton distribution accompanying the peak is greatly reduced, the efficiency can be more accurately deter mined, and self-coincidence or sum lines are strong(34)• A source having coincident gamma rays produces intense sum lines and the peaks representing the individual gamma-rays are reduced. A single sodium iodide crystal, having a height of.three inches and a diameter of three inches, is shown in Figure 8. The well-crystal is mounted on a photomultiplier. A three-eighth inch hole is drilled to the center of the crystal and radioactive sources, with or without absorber, are inserted in the hole. A lead absorber is also shown in Figure 8• 19 Photomultiplier Photomultiplier Crystal Crystal Tube Tube Pre - Amp. Pre - Amp. or or Cathode Follower Scalar Cathode Follower Linear Linear Amplifier Amplifier Conoidence Circuit Analyzer FIG.7. - BLOCK DIAGRAM OF COINCIDENCE COUNTER 20 Lead Absorber Spun 2S Aluminum 0.040" Wall Reflector Aluminum Oxide l/8" Glass 3 FIG.8. - SOURCE AND CRYSTAL ARRANGEMENT FOR TOTAL ABSORPTION SPECTROMETER STUDY OF A LONG-LIVED ISOMER OF Ti^ 1 A. Cr#J- n (1) Source preparation. - A sample of enriched chromium isotope of mass number 5 ^1- was bombarded with high flux neutrons. The resulting activity was expected to be T i ^ by a (n,ot ) reaction. The enriched chromium, obtained from Oak Ridge National Laboratory, was in the chemical form CrgO^ and its composition is as follows:: Isotoplc Analysis Mass number % 50 52 The spectrographic analysis indicated that the impurities were Mg, Ag, Al, Ca, Mn, and V. A one-week irradiation of the enriched material, 27mg of C*r2®3 in a quartz tube, 8 mm in diameter and IfO mm in length, was performed in the Oak Ridge reactor, the neutron flux being greater than ten to the thirteenth power. (2) Chemical separations - Chromium trioxide was dis solved in nitric acid, and potassium chlorate (KCIO^) was added to the solution. The manganese fraction, with the addition of a carrier, was precipitated in the orange solu tion. The chromium fraction, with the addition of a carrier, was filtered with iron and cobalt fractions precipitated in 2 1 22 the blue solution. The method of separation used is shown below. If any titanium had been in the sample, it would have been included in the manganese fraction as titanium cannot be dissolved in nitric acid. Sample, C r ^ + n dissolved in HNO^ heat on hot plate add KCIO^ \ s Orange Solution add carriers, Mn, Fe, and Co MnO Filtrate treat with HoO add NaOH Filtrate Filtrate & Co(OH) add BaCl BaCrO Residue (3) Measurement of half-life - At the beginning of the measurements, the activities of the sample were very high due to the presence of some impurities. The half-lives of gamma - energies, 1.33* 1-71» 2.13, and 2.7 Mev were studied with the gamma-scintillation spectrometer 2 1\. hours after the bom 23 bardment. As shown in Figure 9, the half-life was estab lished at 1 5 «0 hours, which is in agreement with the value for N a ^ . One week after the bombardment, the decay of the beta- ray, 1.7 Mev, was followed with the beta-ray spectrometer. Figure 10 show that the activity is due to p32{iij_.5d). The decays, with several aluminum absorbers interposed between sample and detector, were also followed with a Tracer Lab TGC-3 Geiger tube, as shown in Figures 11 and 12. From these data it is concluded that there must exist at least three different radioactive sources, which are P3 2 ^ an unknown with a half-life longer than 2 l\. days, and a second unknown with a half-life longer than 5^4- days. After the chemical separation and gamma-ray experiments, the first tin- known was identified as Cr^^(28d). The stress of the whole problem then shifted to an investigation on the activities of the second unknown source. Two months after the bombardment of the decay of the beta-ray, 0.65 Mev, was followed with the beta-ray spectro meter, which confirmed that the half-life of the remaining unknown is longer than 50 days. At the same time, the decay of the total activity was followed for 1^50 days with a Geiger counter, as shown in Figure 13• The figure in dicates that the half-life of the unknown source is 76 days. However, 28d C r ^ appears at the beginning of the measure ments. The decays of the gamma-energies, 75 , 3 1 5 * V 70, 6 2 5 , and 785 Kev, were followed by the scintillation counter, as shown in Figures lij. and 15. From these observations the ACTIVITT SET REOISIffiS / MUTOTB COURTS PER UNIT TIME I.9 - AM-EA O Cr64-^ OFFIG. GAMMA-DECAY - 9. n, 4 OR ATR BOMBARDMENT AFTER 24 HOURS ACTIVITY NET COUNTS / SECOND NET COUNTS / SECOND J3 NET COUNTS / SECOND LZ O 5 •-9 FIG. 13. - DECAY CF Cr + n, TWO MONTHS AFTER BOMBARDMENT :C , J , 82 ACTIVITYMET REOISTSIS /MIHUTB O H s § FIG. 14. - DBCAY OF 75 AM) 515 SEV GAMMA RAYS FROM Cr5*4- n, mo WEEKS AFTER BOMBARDMENT 3Agj» l-5ft,~cr IK) CaUflUSTkt "08*8BL I iib i m t i M ~BTK B*y». t i,aoo TOLts- iLCMkwiU sosg \\'3m 200 76 dayi 470 lev Qau 100 M a CO o s a Mo 30 IS'io -- "To laSTS TIME, DATS FIG. 15. - DBCAT OF 470, 625, JLND 785 KB7 GAJ4U-RAY FROM Cr6*+a, 5 W28K8 AFTHt BOMBARDIBKT 3° half-life of 7 0 , 6 2 5 , and 7^5 Kev gamma was established at 76 days, which is in exact agreement with that of Figure 13* The 75 and 315 gamma-energies show both 76-day and 28-day half-lives. The 28-day half-life is due to Cr^. Four months after the bombardment, the main sample was separated into three fractions, Mn02 , C'o(OH)^, and BaCrO^. In order to confirm the existence of Cr-51, the decay of the BaCrOj^ fraction was followed, as shown in Figure 16. The decay of the long-lived activity due to the MnC>2 fraction, which might include TiC>2 , was carefully studied, and, as shown in Figure 1 7 , the 7& + 2 -day half-life was confirmed. Beta-ray experiments by aluminum absorption, and beta-ray spectrometer, 180° deflection type. - Absorption in aluminum of the radiations from the source, employing Geiger tube(Tracerlab type TGC-3), yielded two beta end points indicating beta radiations with maximum energies 1.7 Mev and 0.65 0.05 Mev. Figure 18 shows the absorption curve by aluminum two weeks after the bombardment, and Figure 19 two months after the bombardment. Absorption data of Mn02 , including the Ti02 fraction, taken five and eight months after the Irradiation exhibits a beta end point corresponding to the energy of 0.65 + 0.05 Mev due to the long-lived source. They are shown In Figures 20 and 21. The beta activities were further investigated by the beta-ray spectrometer, 180° deflection type, and all of the particles were found to be negatrons. In Figure 22 the count rate is plotted as a function of the magnetic field M w 7T O NET COUNTS / SECOND / COUNTS NET Ui 0 A O o o * * o FIG. 16. - DECAY OF Cr FRACTION FROM Cr04+ n, FOUR MONTHS AFTER BOMBARDMENT HIT COT ITS / SBOQHt) ^ ze 33 SO 63f, CrSf+~ 60 20 AREAL DENSITY OF ALUMINUM AND POLYSTYRENE ADSORBER, UC/CU2 FIG.18. - ABSORPTION OF BETA-RAYS FROM Cr64-*. D, TWO WEEKS AFTER BOMBARDMENT -TO-ianra nr 00 300 500 AREAL DENSITY OF ALUMINUM ABSORBER. MO/CM2 FIG.19. - ABSORPTION OF BETA-RAYS FROM Cr54+ n, TWO MONTHS AFTER BOMBARDMENT / SECOND FRACTION CP Cr54 + n, FIVE MONTHS AFTHl BOM AFTHl Cr54 n, MONTHS CP FIVE FRACTION + ABSORBER MG/CM2 POLYSTYRENE OFAND ALOUDTDU DENSITY AREAL FIG.20. - ABSORPTION OF BETA-RAYS FROM FROM Un07 BETA-RAYS OF - FIG.20. ABSORPTION atTart iwh. kJRMxm m JUSZ2 C - N CCTBia 54B CCTBia - C N Un.ttl Ao»qr Q6- 60 20 ' D300 3D FRACTION CP Cr54-*- FRACTION BOMBARDMENT AFTER EIGHT MONTHS n, FIG.21. - ABSORPTION OF BETA-RAYS FROM MnO» FROM BETA-RAYS OF - ABSORPTION FIG.21. AREAL DENSITY OF ALUMINUM MG/CM2 ABSORBER, OF DENSITY ALUMINUM AREAL too m c a f » T f f i ' ; i « B ; ; 3 7 d >50 F-fr E K BEGISTERS / i 160 /oo 200 20 80 20 I.2 - BETA FI0.22. PHOSPHORUS n,AMD -RAY Cr6* OP + SPECTRA (NBQATROH) 3.0 AMFBRAOB 35 3 6 strength. The beta spectrum of p32 j_n Figure 23 was taken to make a comparison with that of Cr-^-f- n. (£) Gamma-ray experiments. - The gamma rays were studied by the scintillation method using the Detectolab apparatus consisting of 1" x 1 3/4" Nal crystal. (a) 24 hours after bombardment As shown in Figure 24, gamma activities of 2.7 2.13, 1*71, and 1.33 Mev were detected. The spectrum is in agreement with that of N a ^ obtained by Bell^. (b) 20 days after bombardment Figure 2£ shows the high gamma-energy spectrum. Because of the weak gamma-ray activities, decay measurements of gamma-rays were not carefully followed. However, the half-life could be roughly established at about 30 days. As previously stated, it was ex pected the double neutron capture of C r ^ might pro duce Gr-^6. The spectrum obtained is comparable with the gamma activities of M n ^ shown below. 2.6 Mn t 2.0 Mev -■1.0 Mev 0.845 ------s— I— I i w i / -L 0 StableFe^o REGISTERS / MINUTE / REGISTERS o w FIG .23. - BETA-RAY(NEGATRON) SPECTRUM OF MnOg FRACTION FROM Cr THRESHOLD VOLTAGE FIG.24. - GAMMA-EWERGY SPECTRUM OF Cr54+- n, 24 HOURS AFTER BOMBARDMENT (BOSS EEGISTEBS / lOHUTE too cU to iMtXQl .01 A3801B11 FIG. 26. - GUUIUrENERGY SPECTRUM, HIGH ENERGY REGION, OF Cr®*+- n, 30 DAYS AFTHl BOMBARDMENT AFTHl DAYS 30 n, Cr®*+- OF REGION, ENERGY HIGH SPECTRUM, FIG. -GUUIUrENERGY 26. Or L,3 roici THRESHOLD VOLTAGE THRESHOLD 39 ■M v; fo "7o5“ The lower gamma-energy spectrum is shown in Figure 26. Gamma-energies of 75* 1&5* 315* V70» 625* and 785 Kev were found. The 315 Kev gamma^ray has the highest intensity. (c) Two months after bombardment Figure 26 shows the faster decay of 325 Kev gamma-ray. The rest of the gamma-rays seem to decay at the same rate. (d) Four months after bombardment The gamma-energy spectrum of the chromium frac tion is shown in Figure 27* and 315 Kev gamma rays were found to be due to C r ^ . The high gamma- energies of the manganese and cobalt fractions were investigated, and as shown in Figure 28, the 1.17 and 1.33 Mev gamma-rays are due to Co^O. The entire spectrum of the manganese fraction is shown in Figure 29* and 315 Kev is also found in the spectrum. (6) Gamma-gamma coincidence experiments four months after bombardment. - The main sample, without chemical separation was used in this investigation, since most of the impurities had died off. The gamma-rays of 315* h-70* 625* and 785 Kev in Figure 26 decay at the same rate, as shown in Figures lij. and 15* and it is concluded that they are all from the same source. The decay scheme of the un known source can be obtained from the coincidence experi ments. The coincidence spectrum was taken with a scin- CROSS REGISTERS / ICHDTE I -G B § tl* + S »-» B 3 >■5 ACTIVITY REGISTERS / MINUTE xooo (too IOO FRACTION FROM Cr5* BOMBARDMENT Cr5* AFTER FROM MONTHS + FRACTION n FCUR FIG. FIG. 27 . - . GAMMA ENERGY 8PECTRUM OF CHROMIUM OF 8PECTRUM ENERGY GAMMA THRESHOLD VOLTAGE THRESHOLD 0 O S 30 42 3 K-H-S7: O S O S \ 43 100 banns, irt-yg qah 9 _ liUMIN JM_ABS 3RBER L.17 y »v L«33 M it 20 IO a a ©5 8 8 O.b 02 SO 6 0 THRESHOLD VOLTAGE FIG. 2 8 . - GAMMA-ENERGY SPECTRA OF MANGANESE AND COBALT FRACTIONS FROM Cr54 + n, FOOR MONTHS AFTER BOMBARDMENT 44 100 30 20 t-t CO H m Om 10 20 30 60 SO 6 0 7 0 VOLTAGE FIG.29. - GAMMA-ENERGY SPECTRUM OF MANGANESE FRACTION FROM Cr54 + a, FOUR MONTHS AFTER BOMBARDMENT 45 tillation coincidence spectrometer having a resolving time of 0.89 x 10-7 second, as calibrated in the laboratory using two gamma-rays from different sources. The coincidence- counting rates between each of six gamma-energies and the whole spectrum scanned in a sodium iodide scintillating crystal, are plotted versus the threshold voltage of the pulse- height analyzer which was employed to select only those pulses corresponding to photon energies lying within a selected narrow band. Net coincidence-counting rates are computed from the difference of the total coincidence rates and the computed random coincidence rates, which are given by the formula, N' s 2 N-j_ Ng x 6I4/ 6O. Figure 30 shows coincidence lines in Cr^4 + n sample; one channel of the spectrometer is focusing on the 75 Kev peak and the other is scanning the whole spectrum. The peaks of net coincidence counting rates are found to be at 75, 315, aad 470 Kev. Figure 31 shows coincidence lines when one channel of the spectrometer is focusing on the 315 Kev peak. According to the figure, 315 Kev gamma-rays are in coincidence with all of the gamma-rays including 315 Kev, but there is no coincidence between 315 and 7^5 gamma-energies. Focusing on the 470 Kev peak, Figure 32 shows that 470 Kev is in coincidence with 315 Kev, but not with 625 and 785 Kev. Finally, 625 Kev is set in one channel, as shown in Figure 33, and is found not to be in coincidence with 47° Kev. 46 [Q-CHEM.IflTRY. GHASHEL I A]ID I I OH GADI €4 & E i 2.0 75 0.1 —Single Chn:m e! Cftunt- RiAa- ^-Chan; »3— 1---- — I— —;---- 470J lay : ' i T : 70 30 SO THRESHOLD VOLTAGE FIG.30. - COINCIDENCES BETWEEN CHANNEL I AND 75 KEV SET IN CHANNEL II 4 7 ,3,1 ji KEV, 20 30 60 SX) 60 so THRESHOLD VOLTAGE SETTING OF FUU3E-HEIGHT ANALYZER, CHANNEL I FIG.31 . - COINCIDENCE BETEBEN CHANNEL I AND SIS KEV SET IN CHANNEL II registers / vnms to F I G . 3 2 . - C O I NCIDENCE BETWEHJ C H A N N E L I AND 4 7 0 KEV SET IN C H A NNEL II NNEL A H C IN SET KEV 0 7 4 AND I L E N N A H C BETWEHJ NCIDENCE I O C - . 2 3 . G I F 20 THRESHOLD VOLTAGE SETTING OF PULSE-HEIGHT ANALYZER, CHANNEL I CHANNEL ANALYZER, PULSE-HEIGHT OF SETTING VOLTAGE THRESHOLD JO 315 KEV 315 48 cco so f?4f 0 7 00 49 BBIGIjE OH/L1BBL 6 R JB, :— — -KgE-jpmcinarcBB- L70 ft n o - z w u s n a - AlUMT m t AB SOHBER to 20 JO #0 J-O 60 SO THRESHOLD VOLTAGE SETTING OF PULSE-HEIGHT ANALYZER, CHANNEL I FIG. 33. - COINCIDENCE BETWEEN CHANNEL I AND 625 KEV SET IN CHANNEL II 50 The summary of the gamma-gamma coincidence experiments is shown in Table I . TABLE I Gamma peaks set 75 165 315 ij.70 625 785 in one channel 75 Kev *>h;* X 4\ XX w •J1 v' 165 'Kev ’/rtf 4* X «« \r 315 Kev •JHC* 4\ 4* X lj.70 Kev 4H* 4% 4% 4 \ 4K X X X 625 Kev X -:c- ~4\ Implies net coincidences are almost equal to chance coincidences at the peak of coincidence line. ■sw Implies net coincidences are much larger than chance coincidences at the peak of coincidence line. X Implies no peak of coincidence line. Similar results were obtained from the coincidence experiments on the manganese fraction from C r ^ + n, but not from the chromium and cobalt fractions. (7) Gamma-beta coincidence experiments. - Six months after the bombardment, experiments were performed in order to investigate the possible occurrence of coincidence between the observed beta-rays and gamma-rays. It was necessary to employ a Geiger tube in channel I for the detection of beta-rays, and ganma-rays were scanned in channel II. As shown In Table II, the higher rates of net coincidences were found at the 75 and 315 gamma-energy peaks, 51 TABLE II Gamma- Bias Voltage Gross Coin, Random Coin, Net Coin, Energy (volts) (reg/min) (reg/min) (reg/min) (Kev) 75 12 0.022600 0.000053 0.022547 scan. 17 0.005750 0.000055 0.005695 scan. 40 0.003950 0.000020 0.003950 315 4-9 0.020700 O.OOOOip. 0.020659 Channel I ...... Gain 16, Scintillation counter, High Voltage: 1550 volts Channel II ..... Geiger-Mueller counter, High Voltage: 1050 volts (8) Measurement s by the total absorption gamma spectro meter* - Fifteen months after the bombardment, an investi gation on gamma-ray and gamma-gamma coincidence was made to confirm the previous results. The sample of C r ^ + n, (no chemical separation was performed) was used for the measure ments by the total absorption gamma spectrometer. The gamma- energy spectrum obtained (shown in Figure 34) indicates a newly discovered peak at 940 Kev. The gamma-energy peaks due to C o ^ are also shown in the figure. An attempt was made to separate sum lines from the peaks representing the individual gamma-rays. The lead absorber shown in Figure 8 was inserted in the well-crystal. As shown in Figure 35, the gamma- TO '0 1ST IO 20 3 0 60 7 0 *0 FIG. 3 # . - GAMMA.-ENERGY SPECTRUM OF Cr54 + a w i t h o u t LEAD ABSORBER BY THE TOTAL ABSORPTION GAMMA SPECTROMETER 53 .ui 300 hj: 200 7 ir m j« tQ_ 10 ao 3 0 *0 SO so too THRESHOLD Fi&. 3 S G a n n a - e n e r g y s p e c t r u m of c ? * + n w i t h LERD ABSORBER BY THE TOTAL RBSORPTIOH SPECTROMETER 54 energies of 625, 785, and 940 Kev indicate a remarkable drop in intensity compared with. Figure 34* Therefore, it will be concluded that these three energies represent sum lines or a combination of a sum line and pure gamma-energy. The region of 75 Kev to 315 Kev was also investigated, and no peaks were found between 75 and 315 Kev in both cases, with and without absorber. However, it was questioned that in Figure 35, the intensities of 315 and 470 Kev were not reduced by inserting the lead absorber. In order to clarify this point, the spectrum of a Co^® source was taken as shown in Figure 36. It indicates that the intensities of 1.17 and 1.33 Mev gamma- rays were reduced by the lead absorber; however, the intensi ties of the lower energy region were increased due to the interaction of lead absorber and high gamma-energies. In Figures 34 35, the high energy region above 940 Kev was /I A not clearly shown because of the existence of Go • However, some high gamma-energies above 1.33 Mev were detected, as shown in Figure 37* B. Ti^0-fr n (1) Source preparation. - The T i ^ sources were prepared by neutron irradiation of titanium enriched in Ti^°. The enriched titanium, obtained from Oak Ridge National Laboratory, was in the chemical form TiOg, and its composition is as follows: 55 COURTS GHITCOURTS PER TIME BUS VOLTAGE FIG. 3 6 . - GAMMA-ENH!GY SPECTEDM OF Co60 IJITHOOT AMD WITH T.Rtn APgoPFER NET REGISTER / MINUTE FIG. 3 7 . - GAMMA-ENERGY SPECTRUM, HIGH ENERGY REGION, OF OF REGION, ENERGY HIGH SPECTRUM, GAMMA-ENERGY - . 7 3 FIG. IO TOTAL ABSORPTION TOTAL 0 3HANNEL VI JGAIN O CHEMISTRYI JO -903i, N 3AMPLK 20 THRESHOLD VOLTAGE VOLTAGE THRESHOLD 3 0 56 SO CrbA+ n Si Isotopic Analysis Mass number % 46 1.25 47 1.23 48 10.99 49 1.84 50 8^.69 The spectrographic analysis Indicated that none of the im purities were detected. A one-week irradiation of the enriched material, 11.6 mg of TiC>2 , was performed in the Oak Ridge reactor, the neutron flux being greater than ten to the thirteenth power. (2) Measurements the total absorption gamma spectro meter . .- The gamma-energy spectrum of Ti^®+ n is shown in Figure 38, and a careful calibration with Ba"**33( 31.8 and 380 Kev), Co^7 (115 Kev), Sni:L3(393 Kev), Ca137(66l Kev), Mn^4 /L O (81|0 Kev), and Co (1.17 and 1.33 Mev), gave energy values iSi 31S» 470, 625, 78S* and 940 Kev. The spectrum is In exact agreement with the one of C r ^ + n, as shown in Figure 34* It was also found that there was no C o ^ Impurity, but instead several high gamma-energies were observed (Figure 38). The low energy region of gamma activities is shown in Figure 39, which indicates more gamma-rays than those from C rSk- + n sample as shown In Figure 40» (3) Absorption experiments. - The absorption curve of the Irradiated sample was taken, as shown In Figure 41* The half-thickness was found to be 175 mg/cm^. This value of half-thickness is close to the calculated value of the manganese K j x-ray of 180 mg/cm . cn oo K Q K u MIN -sr NET REGISTERS/ ACTIVITY, rno F i 6. 38 g F\nnf\-Rny s p ectruh of Tc°+n 59 4X; IO 20 30 «o so THRESHOLD VOLTAGE FIG. 38 ^ - GAMMA-ENERGY SPECTRUM, HIGH ENERGY REGION, OF Ti60+ n ACTIVITY, NET REGISTERS/ MIN >0i n £ 3 = ih - 3*1 = 3S Furthermore, the dec ay scheme of 3l£» 6 25, and 9lj-0 Kev agrees with that of 5*8 minute T i ^ as shown on page 13« Therefore, it is assumed that the activities obtained from C r ^ + n and Ti^+ n sources are due to a long-lived isomer of Ti-^. A proposed decay scheme is shown below. (y 2-)-z6j - n g . 5.8m Td3l 470 T 1,000 Kev 315 -- £00 Kev 625 315 0 Stable There are several possible ways to place the 75 Kev gamma-ray in the decay scheme diagram: (a) The 75 Kev may be placed on top of the lj_70 Kev gamma-energy, according to the results of gamma-gamma coincidence as shown in Table I; 64 (b) The 75 Kev may be the energy of the Isomeric transition, as no sum peaks of 75 Kev and the rest of gamma-energies were found in Figures 34 and 35; (c) The 75 Kev may be an escape peak due to the high gamma-energies. It was assumed in the decay scheme diagram shown on page 63 that the energy of the isomeric transition is very small, and the beta- transition takes place with release of 650 + 50 Kev beta- rays. The 1.72 and 1.49 Mev sum lines in Figure 37 will also indicate the consistency of the proposed decay scheme diagram. D. Discussion As stated in the section of Historical Review, there were several impurities in the Ti5l. An attempt was made to make a comparison of those impurities and the 76-day activity obtained from Cr54+ n and Ti^®+ n reactions. The presence of Hf-^^(46d) was established as an impurity In the T i ^ by Miskel, Mateosian, and Goldhaber(18). By beta emission, H f ^ l decays into Ta^®^. The decay of Ta^®-*- is shown below. 22.JJL, sec t 500 Kev 132 10“8 sec 612 --250 Kev 3 4 5 480 1 2 1 -*-0 Talol &5> lSZL As Hf was found as an impurity in the Ti^1, it is nec- I'jd essary to show that JG day source does not contain Hf ^ (70d)* The decay scheme of is shown below. _ 200 Kev 228 318 — 100 Kev 113 By comparison of the two decay schemes, it was concluded that no hafnium impurities were present in the sample. Miskel, Mateosian, and Goldhaber also detected the presence of Sb^2^(60d). As Sb**"^ has no gamma-energies lower than 600 Kev, the 78 day source does not contain Sb12i+. The activities of T a ^ ^ l H d ) are reported as an impurity(20) in the Ti*^. The gamma-and beta-energies of Ta-*-®^, according to Boehm, Marmier, and DuMond(39)> are as follows: 6 6 gammas : 1*3, 66, 68, 85, 1 0 0 , ill*., 1 1 6 , 1 52, 156, 179, 198, 222, 229, 261*,, 127, and 960 Kev; 1.00, 1 .12, 1 .16 , 1.19, 1 .2 2 , 1.23, 1.30, 1.38, 1.1*1*, and 1 .1*5 Mev beta : 510 Kev The Intensities of the gamma-energies are shown in Table III. TABLE III Energy Intens w 1*3 Kev 4%. 66 Kev 9 68 Kev 100 85 Kev 6 100 Kev 1*6 111* Kev 9 116 Kev 2 152 Kev lf-3 156 Kev 11* 179 Kev 19 198 Kev 9 222 Kev 1*5 229 Kev 21* 261* Kev 27 927 Kev 960 Kev •if 67 TABLE III, Cont1d. Energy Intensity 1.00 Mev 1.12 Mev 120 1.16 Mev 8 1.19 Mev £6 1.22 115 1.23 58 1.30 1.38 i.i*4 1.14-5 * Indicates value unknown As shown in Figures 38 and 39» several garama-energies, similar to those of Ta^®^, were detected in the sample of T i ^ + n. However, the s an pie of Cr-^+ n does not show any of these gamma-energies. The sample of Ti^^V n, therefore, may contain Ta^-®^ and 76 day activity. In contrast to the 76 day half-life of the Cr^lj-*. n sample, the half-life of Ti^®+ n shows more than 90 days, which is considered to be the resultant life of 76 day activity and Ta^®^. It is obvious that the activities of Ca^(l6Ij.d) and Sc ^6 (19-5 sec and 8i|.d) reported as impurities by Hein said Voigt(l5) were not present in the sample. In order t o distinguish pure photo peaks and sun peaks 6 8 caused by the several gamma-rays In the sample, the lead absorption method was used. In Figure 1+2, the absorption curves of 75* 315» k-10 s and 625 Kev are shown. The energies of these gamma-rays were obtained from the absorption co efficients. The obtained values of 315 and I4.7O Kev gamma- rays are in excellent agreement with those found by the scintillation counter. However, It Is still questionable whether 75 Kev is a pure gamma-ray or an escape peak. As shown in Figure I4.3, the gamma-energies, 315 Kev, obtained from both C r ^ + n and Ti^®+ n are exactly identical. In order to identify the 76 day activity as a long- lived isomer of Ti^1 a titanium fraction from the sample should be extracted. However, due to the weak activity of the sample and some technical difficulties In the chemical separation, it was impossible to obtain the titanium fraction. The Q, value of Cr^Hn,d ) T i ^ reaction was computed Q = MC r ^ * “n " “t i ^1 " M* " ” 0.0020.1a.m.u. ■ - I .96 Mev It is a fact that slow neutron reactions accompanied by the emission of a charged particle, e.g, an alpha particle (n,6k ) or a proton (n,p), are rare. These reactions are only true for a few elements of low atomic number, for which the nuclear electrostatic repulsion is small. (n,^ ) and (n,p) reactions of nuclei with fast neutrons, having energies of 1 Mev or more, frequently occur more readily than the (n, ) reaction. o> v> \ REGISTERS /1QNDTE M a ca ! 1 i 1 ? i ? LEAD ABSORPTION OF QAIMA-RAYS o -a I MET REGISTERS / MINUTE / REGISTERS MET m FI0.V3 . - 815 KEV GAMMA.-PEAKS OF Cr64 + n AMD Ti60 + A SEARCH FOR Cr^6 The irradiation of the enriched chromium isotope of mass number Sk-* as previously discussed, with high flux neutrons was also done to investigate a possible existence of Cr^k. Th© resulting activity is expected to be C r ^ by the double neutron capture. The thermal neutron capture cross section of C r ^ is 0.23 barn. Cr-^ can be easily identified by observing M n ^ , whose decay scheme is shown on page It was proved by the chemical separation that the 76 day activity is not due to chromium. This fact is further supported by the difference in decay schemes of M n ^ and 76 day source. It is also concluded by the com parison of decay schemes that the 76 day activity cannot be an isomer of M n ^ . The activities obtained, 10 days after bombardment, show gamma-energies similar to those of manganese $6 . However, those gamma-rays shownin Figure 25 were weak in intensities, and the half-life was not exactly determined. It is estimated to be less than 30 days. A reaction Cr^( t,p)Cr£6 was attempted by neutron bombardment of a lithium chromate target, and some gamma activities of 580 and 750 Kev with long half-life were detected. Because of the presence of several impurities, the investigation was not completed. 71 MANGANESE $3 A sample of containing LpL.2% Gr^®, 52.1$ Cr^2 , 3.8% Cr^3, and 2. 6% Cr^k was obtained from the Stable Isotopes Research and Production Division of the Oak Ridge National Laboratory. The spectrographic analysis indicated that the impurities were AgcO.Oi$, Al< 0.08^, Gu < 0 . 0 2 $ , M g < 0.02%, M o < 0.1$%, and Si< 0.0$%. Fifty mg of this sample was bombarded with alpha particles in the cyclotron at the University of California for a period of hours. The resulting activity was expected to be Pe^-^(8.9m) by an ( ct> ,n) reaction. The Fe^3 nuclei decay into Mn^3. A. Chemical Separations At the beginning of the measurements activities of Mn^2 by an (o( ,2n) reaction and C r ^ by an (c£,3n) reaction were detected. Since the activity of C r ^ remained con siderably high after the Mn^2 had died off, it was necessary to separate the manganese fraction from the sample of Ov^^+tL, as shown on page 73* The sample of Cr^®+ el was further chemically separated to determine whether the sample contained some vanadium impurity or not. The vanadium fraction was obtained as shown below. 7 2 73 Cr^°+ dissolved in HNo. add KClOo Orange Yellow Solution add Mn carrier MnO, CrOL and Fe add Mh( 1103)3 repeat pre cipitation with KClOo MnO, Cr Fraction Cr^°+ dissolved in HNO3 * KCIO^ add carriers, V and Mn Mn02 Filtrate neutralize with NHi.OH dissolved in HoO add PbAc MnO PbVOo and PbCrO Filtrate 74 B. Results Several days after the bombardment, most of the acti vities are due to the presence of 5*8d Mn^2 and 28d Cr^. In the manganese fraction, there were at least two activities with longer half-lives observed after M n - ^ had died off. Figure 44 shows the half-life plot of gamma-rays, 510, 730, and 9^.0 Kev, and gives a £.6 day half-life which is in agree ment with the value of Mn^. After the chemical separation, the decay of the chromium and manganese fractions was followed. A 28 day half-life was obtained from the chromium fraction. The positron decay of the manganese fraction was followed by the beta-ray spectrometer, as shown in Figure l\S$ and a 16 day half-life was obtained. After the 16 day activity had died off, the decay of the long-lived activity was followed for a period of 15 months. The decays of the radiations transmitted through 0 and 35k mg/cm2 Gf aluminum with a Geiger tube as detector a 470 and a 350 day half-life res pectively, as shown in Figure 46* (1) Gamma-ray experiments. - Figure 4-7 shows the gamma - energy spectrum obtained four days after bombardment, and the activities were mainly due to Mn5^-. After the chemical sep aration, it was found that the 320 Kev photo peak had com pletely disappeared in the gamma-energy spectrum of the man ganese fraction, and in contrast to this, the chromium fraction showed an intense photo peak of 320 Kev, as shown in Figures 48 and- 49* As shown in Figure 48* two months after -o CJl .i LL .i x'J l i i i JjT. r r r COUNTS PER UNIT TIME H 1.! i vrrn vrrn IT TTt 10 10 ft «D o 10 0 a CO 5 FIG. 44 . - GAMMA-DECAY OF Cr°°+ oC » 24 HOURS AFTER BOMBARDMENT REGISTERS / MINUTE giBffii i l f f B m a g g e a FIG. ( 4.5 . - POSITRON ,DECAY24 OFo TIME, DAYS FIG, SIMPLE-f-S2S CiANNEL IiflN JAIN 13 polystyrene ajsorbe? 350 m / m * too r£ 10-KBV-j& a ih UatfrLo a-Peak 30 to1 to IO 20 PIG. ^7 . - GAMMA ENERGY SPECTRUM OF Cr60^- oC , 4 DAYS AFTER BOMBARDMENT 79 Uoo 510'12 V — ~ - Aanl] AlB-tlon Pb o I: 200 too 60 w \ 30 :iin p m m ; prom; g?30- 20 ABSOR iER 560 MG/i01l2 IO u. 20 30 60 7 0 THRESHOLD VOLTAGE FIG. V-8 . - GAMMA-ENERCT SPECTRUM OF MANGANESE FRACTION FROM Or 5° + ^ , TWO MONTHS AFTER BOMBARDMENT 8 0 320 KEV 1000 loo Ci- mcTiowiroii cr1” -ft ILY3TYBBHH A1 BOBBER 360 I U } /C U £ C1IAHNEL I ON HAIN 300 100 eo 60 6° 30 Ei m 20 10 t o 20 30 «o THRESHOLD VOLTAGE FIG. 4? . - GAMMA-ENERGY SPECTRUM OF CHROMIUM FRACTION FROM C r5 0 + ^ , TTC MONTHS AFTER BOMBARDMENT 81 bombardment, a I.J4.O Mev gamma-energy was found in the man ganese fraction. The half-life of 1.1^0 Mev was definitely longer than 5.8 day M n ^ but much less than 320 day M n ^ . The problem was whether the l.ij.0 Mev gamma-energy was due to Mn-^ or some other isotope. The existence of V^-® was considered as an impurity in the manganese fraction of Cr^Q+dU Therefore, the manganese and vanadium fractions were carefully made from the Cr-^+el source. Before the chemical separation, the intensity ratio of the 8 )4.0 Kev of Mn-^ and the l.lj.0 Mev gamma-energy was determined to be 300, as shown in Figure 50. In the manganese fraction, Figure 5l shows that the ratio went up to 94-0 proving I.I4O Mev is not due to manganese. In contrast to this, in the vanadium fraction, the ratio of two gamma-energies shows a remarkable drop, and a careful calibration gave energy values of 1.33 Mev and 990 Kev (Figure 52). Hence, it is concluded that the 1.33 Mev, 990, and 510 Kev gamma-rays are due to V^-®, and that the 8)4.0 Kev gamma-ray is due to Mn^K Fifteen months after bombardment, the gamma-energy spectrum of the manganese fraction from Cr^+o( was obtained by the total absorption gamma-ray spectrometer as shown in Figure 53> and no new gamma-energies were detected. (2) Gamma-gamma coincidence experiments. - The presence of V^-® as an impurity was also confirmed by the method of gamma-gamraa coincidence. Coincidence lines were obtained from the vanadium fraction from Cr-^+-«! ; one channel of the REGISTERS (00 20 30 60 /o 4 E N 14 E AMSFO r0+ cA + Cr50 FROM GAMMAS MEV 1.40 AND KEV 840 - . 0 5 . G I F 040 30 82 O S 0 6 83 r r<>- rtrr: 20 SO FIC5. SJ . - 840 KEF AND 140 MEV GAMMAS FIG. £-2. - 840 KEV AND 1.33 MEV GAMMAS OF Mn FRACTION SEPARATED FROM VANADIUM OF V FRACTION SEPARATED FROM MANGANESE NET REGISTERS / MINUTE FIG.S 3 . - GAMMA-ENERGY SPECTRUM OF Mn. FRACTION FROM Cr50+ c< , 12 MONTHS AFTER BOMBARDMENT AFTER c< MONTHS 12 ,Cr50+ FROM Mn.OF FRACTION SPECTRUM GAMMA-ENERGY - . 3 FIG.S 200 300 100 60 IfO 30 o to StO =pww i B=ffew R*y n* -oMnn: HEHL VOLTAGE THRESHOLD 0 3 84 O S HR: 6o 0 7 85 spectrometer focused on the 1.33 Mev peak and the other scanned the whole spectrum. The coincidence peaks were observed at $10, 990, and 220 Kev gamma-energies. Similar experiments were repeated on a V^-® sample to compare with the above result. It was found that the two results were in perfect agreement. (3) Aluminum absorption experiments. - Fifteen months after the bombardment, an aluminum absorption curve was obtained, as shown in Figure 54-* ^he curve Indicates that the X-rays are due to Mn-54- and possibly Mn-^8. C. Discussion Since there existed a considerable difficulty in finding Mn^8j was assumed that it might be very similar to a neighbor isotope, such as Mn52 and M n ^ , or short-lived, or long-lived. Therefore, the investigation was very carefully done with respect to the decay, measurements, beta and gamma activities, and the chemical separation. A great effort was made to identify the V^-® impurity. While this experi ment was in progress, the new isotope, M n - ^ was discovered by Wilkinson and Sheline(30), and was found to have a half- life of lij.0 years. Hoi^ever, a complete investigation on beta and gamma activities was not made by them. As shown in Figure 53* it is hard to look for some gamma activities from a weak sample because of the existence of the 84-0 Kev gamma-ray of M n ^ . The 54-0 Kev gamma-ray shown in the decay NET COUNTS / SECOND SO* Too FRACTION OF Cr&° + s( , FIFTEBf MONTHS AFTffi BOMBARDMENT FIS. • # 5 - ADSORPTION OF BETA-RAYS FROM MANGANESE IDEAL DENSITY OF ALUMINUM ABSORBER, MO/CM2 m O O T I too scheme on page 16 was sought but no peak of 5^-0 Kev was found (Figure 53)* Also no low gamma-energy values were found. Therefore, the only way to identify Mn^ by the decay measurement and comparison of aluminum absorption between Mn^3 and Mn^+, as was done by Wilkinson and Sheline A SEARCH FOR B13 A. Lithium Borate + n Tritons will be produced in a chemical compound or alloy of lithium that is subjected to a neutron flux. Con sequently, it is probable that a (t,p) reaction can be effected when a compound of lithium borate is bombarded with neutrons. £ (1) Source preparation. - As enriched isotopes of Li metal and B ^ in the chemical form H^BO^ were available, it was possible to' make a compound of lithium borate by the following procedures: 2 Li ■+• 2 H20 = LiOH + H2 and LiOH -*■ H3BO3 = LiB02 *»■ 2 H20 After evaporating the above solution, lithium borate was obtained. The composition of the enriched boron and lithium supplied by the Nuclear Carbide Corporation at Oak Ridge is shown in Table IV. A one-week irradiation of the enriched material, 220 mg of lithium borate is an aluminum cylinder, was performed in the Argon National Laboratory reactor, the neutron flux being 1.5 x 1013. (2) Chemical separations. - Carbon, BaSO^, and BaB frac tions were obtained from the sample of lithium borate -t- n. (3) Measurements of half-life. - For the first several days after the bombardment, the decays of beta-ray and gamma - energies 1.33> 1«71* 2.13> and 2.7 Mev were followed using 88 89 TABLE IV. Composition of Enriched Boron and Lithium Mass Number Isotopic Analysis Spectrograp hie Analysis Enriched Mass Number % Impurity /° B 11 10 3.7 11 96.3 Cu Li6 6 95*7 A1 0.03 7 14-3 Ba 0.05 Ca 0.2 Cr 0.1 Cu 0.05 Fe 0.5 K 0.03 Mg 0.02 Mn 0.02 Mo 0.1 Na 0.1 Ni 0.3 Fb 0.06 Sn 0.01 the beta-ray spectrometer and scintillation spectrometer respectively. The balf-life obtained was 15 hours, which is in agreement with the value for N a ^ . One week after the bombardment, the decays of two beta- rays of 150 Kev and 1.6 Mev were followed, as shown in Figure 55* The figure indicates the presence of radioactive sources having 14.5 and 8JL|. day half-lives. The decay measurements with an aluminum absorber were also done using a Geiger tube. The decay curves in Figure 56, with the 113 mg/cm^ aluminum absorber, indicate the presence of two periods, one being about 15 days and hie other being greater than 88 days. It is possible that the long activity was due to Be^® produced 9 0 B 1 M P ,B H-fl '6, LI 1 ■HIPM fliUTE 075 XL 70 2 0 JO -CO 5 0 fo FlO.fflf. - HBGATRON DECATS OP LITHIUM BORATE •+* n, OHE WEEK AFTER BOHBARDUENT JIST C0UMT3 / SBCOHD 0 4 •O 3 s g T n q o c O.56. «DCY F THTI BRT + a, OE * AFTER BOWAHDMHT H »*T ORE , DECAY a « LTTHITJII QF BORATE . + 6 5 . iO y MllRHTG MllRHTG 4 -n.t-tlQ aJUT g iagJtU.TJ DATS wti un fwttfim SM mrctf MO 92 by the B^(n,p )Be^ reaction. In contrast to the above results, the decay without the aluminum absorber gives 88 day half-life. Three months after the bombardment, the sample of lithium borate+n was separated into two fractions, BaSO^ and BaB. The 88 day half-life of 150 Kev beta-ray was obtained from the BaSO^ fraction. Therefore, p3^ and s3£ impurities were present in the sample of lithium borate n. (I4.) Beta-ray experiments. - As shown in Figure 57 > the absorption curves indicate two beta-rays, 150 Kev and 1.6 Mev, with different half-lives. The aluminum absorption curves of pure and s35 were obtained in order to make a comparison with that of the lithium borate n sample, as shown in Figure 58. The carbon fraction from the lithium borate +• n source showed no beta activity. (5) Gamma-ray experiments. - For the first several days after the bombardment, the gamma-energies 1.33* 1 *71* 2 .13* and 2.7 Mev were detected by the scintillation counter. No gamma-rays were detected from the sample of lithium borate + n after the N a ^ activity had died off. B . Boric Acid + n The component of the enriched boric acid is shown in Table III. A one-week irradiation of the enriched material of 1 lip mg of boric acid in an aluminum cylinder was performed in the Argon National Laboratory reactor, the neutron flux being 1.5 x 10^3, Boo- ■MTH»JC1 BOHiVTg rfr U 100- to- QHB W H ffT g sap -yncLrr to- BHD POtfMT ■TH&&E JmtGKS. ____ -XJfitQ— MtegHS aiTBfl aQfnaHPPWfiWTr f\FT MR B Q M A R D n t N T 0.3 SLND 5 HBLF A2 0.1 10020© 3oo 6 0 0 700 900 AREAL D e n s i t y o f a i / jv in u m a d s o r b s * , mg / c m 2 FIG . 5 7 . - ABSORPTION OF BETA-RAYS FROM LITHIUM 30RATE + a CARBON l¥ AREAL DENSITY OF ALUMINUM ABSOSEQi, MG/CM2 FIG. S i . - ABSORPTION OF BETA-RAYS FROM LITHIUM j ORATE + N, S35 AMD 95 The detected beta and gamma-energies were found to be the same as those of lithium borate+ n. The half-life obtained by the Geiger-counter without aluminum absorber was also 86 days. C. Carbon n Neutron irradiation of some Hilger carbon was performed in an attempt to produce B-^-3 by a (n,p) reaction. The alumi num absorption curve obtained was similar to that of lithium borate + n and boric acid + n samples. However, the low-energy beta seems to show activity due to C-^ and the half-life measured was more than 200 days. Because of the bulky sample, it was not possible to make a comparison of beta-rays from and C + n. A boron fraction from the sample of C + n showed no activity. No gamma-rays from the C + n sample were detected. D. Li6 n As the resulting activities of lithium borate+ n were expected to be not only B ^ + t and B ^ + n, but also Li^+ n, L it was necessary to investigate an activity of Li + n separately. Neutron irradiation of some lithium was performed under the same conditions as in the cases of lithium borate and of boric acid. According to the decay measurements, the intensity re mained constant for eight months. Two X-rays were observed by an aluminum absorption tests, as shown in Figure 59• on. qi HI HI 96 CEDklU - ABSORPTION OFX-RAYS FROM Li® + n AREAL DENSITY OF ABSORBER, MO/CM2 5 *1, FIG. Oil to to to (HOOXB / S1MCO 131 97 E Discus sion The 86-day half-life observed and chemical separation proved that the activity of the sample did not belong to boron, but to sulfur occurring as an impurity* The beta- spectra of the original sample and that of the separated sulfur showed the major features of the beta-spectrum of S35. Boron fractions from lithium borate 1- n and C + n showed a very weak activity in comparison with the original sample. As the activity of Li + n was relatively weak, both the lithium borate + n and boric acid -t n samples showed similar activities. It is concluded that no activity corresponding to B^3 with a half-life of 1$ hours to approximately 200 days was observed from the products of lithium borate + n, boric acid •f n, and C + n* NEUTRON BOMBARDMENT OP ARGON AND NEON GASES When an investigation on (t,p) reactions of lithium silicate, lithium-magnesium alloy, and lithium-chromium alloy was made, there existed many impurities which caused serious difficulties in identifying the products. However, in the case of the reactions, A ^ (t,p )A^, and A ^ (t,c( } 01^9, the radioactive activities of A ^ and A^9 Can easily be separated from various possible impurities. A^(3»5>y) decays into K ^ , and Cl^^(56min) decays into A search for N e ^ by N e ^ ( t , p ) N e ^ was also planned. It was a difficult problem to determine a method of combining lithium and those gases closely, as no compounds of lithium with argon or neon have been reported. It was thought that some highly compressed mixture of lithium and gases could be made. As a preliminary test, small amounts of compressed argon and neon gases at three atmospheres pressure, were irradiated respectively. No activities were detected from either sample. Since the sealing was complete and no leakage occurred, it was concluded that a higher pressure was required. There exists many difficulties in making an irradiation of gases under high pressure. 98 SUMMARY AND CONCLUSIONS (l) Titanium £l Sources prepared from the products of a C r ^ t n bom bardment were found to exhibit an activity with a period of 76 £ 2 days half-life, involving the emission of gamma-rays of energies 75* 315* 470, 625 > 785* and 940 Kev, and ^ of 650 Kev. These six gamma-rays were also observed in samples pre pared from the products of a Ti£°+ n bombardment and were found to have the same relative intensities as those of Cr54 + n. ‘-The sum lines of gamma-rays by the total absorption gamma-ray spectrometer are also in agreement, as shown in Figures 34(0^4+n ) and 38(Ti^°+n). Therefore, the resulting activities were considered to be Ti^°(n,J )T1^1 and Cr£4(n,ot )TI^1 . Chemical separations showed the activities from C r ^ + n sources to be associated with manganese; however, as discussed in page 71, the decay scheme obtained is entirely different from Mn^. The 76-day activity is not considered to be an Isomer of Mn^. According to the chemical procedures employed in this separation, the MnOg fraction might include Ti02 which Is not expected to be in the cobalt, chromium, and iron fractions. In view of the foregoing considerations, it is highly possible that the 78-day activity is a long-lived isomer of 91 Ti-' , and the proposed decay scheme is shown in page 63- This 99 100 proposal is also supported by the fact that the main part of decay scheme is in excellent agreement with that of 5.8-minute Ti^. Antimony, calcium, hafnium, and tantalum were reported as impurities in titanium. The decay scheme and half-life of the proposed long lived-i3omer of Tl-^ are in disagree ment with those of these impurities. According to the beryllium absorption test on the products of T i -t- n, as shown in Figure 41, a value of K-Xray energy was 5*8 Kev, which falls near the manganese line. (2) Manganese 53 According to the historical review on Mn^3, it seemed probable that manganese 53 would have a very long half- life or an activity similar to that of some neighbor isotopes. A Cr£°+<* bombardment was performed to produce man ganese 53 , and the chemical separations and gamma-ray measurements showed both a 16-day manganese activity with 600 Kev beta-and 1.1^0 Mev gamma-energies, and 320-day M n ^ . After further chemical separations and coincidence measure ments, the activity was found to be due to V^-®. It is concluded that there is no Mn^-3 activity in the half-life regions from 2ij. hours to I4.OO days. The existence of M n ^ made It difficult to identify a reported li^O-year Mn^3. However, the decay of the manganese fraction was 101 followed, for 15 months, as shown in Figure I4.6 . The figure shows a LfiO day half-life with no aluminum absor ber, but 350 days with an aluminum absorber. The above result indicates that M n ^ has a long half-life and decays only by K-capture. One hundred and forty year Mn^3 was reported to decay into Cr-^3 by K-capture and no gamma emission(30). The gamma-rays of the manganese fraction from the (3 ) Boron 13 b!3 may be expected to have a measurably long half- life, as the neutron number of B-*-3 is 8 . A neutron bom bardment of boron and lithium borate was done under the assumption that a (t,p) reaction of lithium borate and/or double neutron capture by B-^ might produce B"^. Neutron irradiation of carbon was also performed in an attempt to produce B 13 *' by a (n,p) reaction. Boron fractions from lithium borate + n and C ■+ n showed a very weak activity in comparison with the original sample. It is concluded that no activity corresponding to B^3 with a half-life of 15 hours to approximately 200 days was observed from the products of lithium borate-h n, boric acid-h n, and C-i-n. BIBLIOGRAPHY 1. Facchini, Gatti, and Germagnoli, Phys. Rev. 81, 475 (1951) 2. M.L. Pool and L.N. Kundu, Chart of Atomic Nuclei, Long’s College Book Co. (1955) 3 . A.H. Snell, Science 108, 167 (191+8) 4. A.H. Snell, Phys. Rev. J2, 545 (191+7) 5. N. Sugarman, J. Chem. Phys. l£, 5 4 4 (191-1-7) 6 . L. Alvarez, Phys. Rev. 25* H 2 7 < 1914-9) 7 . W.L. Gardner, Phys. Rev. 8j}, 1054 (1951) 8 . R.K. . Sheline, Phys. Rev. 82, 557 (1952) 9. W.H. Barkas, Phys. Rev. 691 (1939) 10. Hubbard, Ruby, and Stubbins, Phys. Rev. _92» 1494 (1953) 11. S.A. Heiberg, Phys. Rev. 856 (1954) 12. C.B. Bigham, K.W. Allen, and E. Almqvist, 99* 631 (1955) 13. Allison, Murphy, and Norbeck, Phys. 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Rev. 8k, 671 (1951) 29. R.K. Sheline, Phys. Rev. 8j 557 (1952) 30. J.R. Wilkinson and R.K. Sheline, Phys. Rev. 99, 752 (1955) 31. Way, King, McGinnis, and Lieshout, Nuclear Level Schemes, kk> June(1955) 32. N. Jarmie, Phys. Rev. 98, kl (1955) 33* Sher and J.J. Floyd, Phys. Rev. 102, 2\\2. (1956) 3k* Beta-and gamma-ray spectroscopy, K. Siegbahn, p.155 35* Beta-and gamma-ray spectroscopy, K. Siegbahn, p.ll+2 3 6 . Way, King, McGinnis, and Lieshout, Nuclear Level Schemes, 52, June (1955) 37. F.K. McGowan, Phys. Rev. 22* l63 (195k) 3 8 . Burford, Perkins, aid Haynes, Phys. Rev. 92> 3 (1955) 39* F. Boehm, P. Marmier, and J. DuMond, Phys. Rev. 95» 86k (195k) AUTOBIOGRAPHY I, Akihiko Yokosawa, was born in Kofu, Japan, Nov ember 19, 1927. I received my secondary school educa tion in the public schools of Kofu, Japan, and my under graduate training at the University of Tohoku, Sendai, Japan, which granted me the Bachelor of Science degree in 1951* From the University of Cincinnati, I received the Master of Science degree in 1953. In April, 1954, I was appointed a Research Fellow at Ohio State University, where I specialized in the Department of Physics and Astronomy. I held this position for a year. Since then I have worked as a Teaching Assistant while completing the requirements for the degree of Doctor of Philosophy. 104 I