Ames Laboratory ISC Technical Reports Ames Laboratory 7-1954 Photodisintegration of light elements in nuclear emulsions Raymond D. Cooper Iowa State College D. J. Zaffarano Iowa State College Follow this and additional works at: http://lib.dr.iastate.edu/ameslab_iscreports Part of the Atomic, Molecular and Optical Physics Commons, and the Nuclear Commons Recommended Citation Cooper, Raymond D. and Zaffarano, D. J., "Photodisintegration of light elements in nuclear emulsions" (1954). Ames Laboratory ISC Technical Reports. 88. http://lib.dr.iastate.edu/ameslab_iscreports/88 This Report is brought to you for free and open access by the Ames Laboratory at Iowa State University Digital Repository. It has been accepted for inclusion in Ames Laboratory ISC Technical Reports by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Photodisintegration of light elements in nuclear emulsions Abstract The cross-sections for the reactions C-12 (gamma, 3 alpha) and O-16 (gamma, 4 alpha) have been measured as a function of photon energy from threshold to 50 Mev, and agreement with known levels is good in the former case. New levels are observed in the region 23 to 30 Mev for the latter reaction. The cross section for the reaction N-14 (gamma, 2 alpha) is observed to peak at 25 Mev, with a long tail to 45 Mev. The er action N-14 (gamma, np)3 alpha occurs at least four times as often as the reaction N-14 (gamma, d)3 alpha. Keywords Ames Laboratory Disciplines Atomic, Molecular and Optical Physics | Nuclear | Physics This report is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/ameslab_iscreports/88 ..,., . "" ,. -·· f .• UNITED S7S ATOMIC ENERGY COMMISSION ISC-535 PHOTODISINTEGRATION OF LIGHT ELEMENTS IN NUCLEAR EMULSIONS By Raymond D. Cooper D. J. Zaffarano July 1954 Subject Category, PHYSICS. Work perf'ormed under Contract No. W-7405-eng-82. F. H. Spedding, Director 1 Ames Laboratory. The Atomic Energy Commission makes no representation or warranty as to the accuracy or usefulness of the Information or statements contained in this report, or that the use of any Information, apparatus, method or process disclosed In this report may not Infringe prtvately~wned rights. The Commission assumes no ltabtltty with respect to the use of, or for damages resulting from the use of, any Information, apporatus, method or process disclosed In this report. This report bas been reproduced directly from the best available copy. Reproduction of this information is encouraged by the United States Atcmic Energy Commission. Arrangements for your republication of this document in whole or in part should be made with the author and the organization he represents. Issuance of this document does not constitute authority for declassification of classified material of the same or similar content and title by the same authors. ISC-.535 3 TABLE OF CONTENTS Page ABSTRACT •• I. INTRDDUC TlON . .5 II.. LITERATURE SURVEY" • ... • .. .. .. .. .. • • .. & .. • • · .. • .. .. • • • • • 6 III. NUCLE/\R EMULSIONS 7 A. Irradiating •• . 7 B. Processing • • • • . 7 C. Scanning and Measuring . 9 IV. S ELE CTIO~ Oii' EVENTS I N EMUT"SIO NS FOR STUD~ . 10 A. Identification . 10 B. Possibility of Events Involving an Emitted Neutron or Ray . ll c. Corrections Applied • . • • ll v. REST TLTS . 13 A. Carbon Disintegrations •••••••• . 13 B. Oxygen Disintegrations •••••••• . 18 c. Nitrogen Disintegrations . 18 D. Othe r Identifie d Events • • • 2.5 VI. CO NCLUSIONS . 25 VII. LITER A. TURE CITED • . 26 VIII. APPENDIX . 27 A. Composition of Lithium Loaded Ilford Photographic 27 Emulsions • • . • • • . B. Composi tion of Modifi ed Van der Grin ten Developer • .. 28 4 PHOTODISINTEGRATION OF LIGHT ELEMENTS IN NUCLEAR EMULSIONS1 by Raymond D. Cooper and D. J. Zaffarano ABSTRACT The cross-sections for the reactions c12( 0',30c:.) and ol6(0',4~) have been measured as a function of photon energy from threshold to 50 Mev, and agreement with known levels is good in t he former case. New levels are observed in the rer, ion 23 t:o 30 Nev for the latter reaction. The cross section for the reaction Nl4((1',2<X) Li6 i~ observed to peak at 25 Mev, with a long tail to 45 Mev. The reaption Nl ( Q',np)3~ r:>ccurs at least four times as often as the reaction N14( (f, d )3 cx.. 1 Th.is report is based on a Master's t hesis by Raymond D. Cooper submitted July, 1954 to Io>-m State College , 1\mes, Imva. This work was done under con tract 1vi th t he Atomic Energy Commission. ISC-535 5 I. INTRODUCTION It is a Hell known fact that light nuclei consisting of multiples of the alpha o'l.rticle unit, vJhen bombarded by high energy photons, disinteSrate by the emission of one or more alpha particles . The first of these, Be , is unstable in the ground state rfV'ith respect to disi!1tec;r"ltion into two al;Jlla particlesi· it also breaks nn in V-is manner from several excited states. cl2 and 0 6 likewise break u~ into three and four R.lpha pa rticles r espectively upon bombardment vJi th energetic gamma rays. Various o thor light nuclei such as Li7, BlO, and Nl4 a r e known to disintegrate into alpha particles, p~o tons, and neutrons vJhen bombarded 'rJi th :1 i gh energy pho tons. Since ca.rbon , oxygen, and ni tro 1 ~en apDear naturally in t he gel:1ti ne making up a photogranhic emulsion, it would be reasonable t cJ bomb::J.r d photovraphic plates directly >·Ji th enerp;etic garna rays to produce photodisintegrations fo r s tudy. This, in fact, has been tl1e corn. :,on method fo r st11dying tJ-~ ese r eactions since 1946. Hi th t 11e exception of one paper (l), a ll of the wo rk done on the photo­ disin tep,ntion of the elements listed above was done be lorN" 30 He v. Be low this enerf:Y, the only generally observed reactions are the following two: 3 He 4 - 7.3 Mev (Rl) 4 He4 - 14.4 Hev (R2) /l.t higher enerp;ies it is expected tha t many other events will be seen in large enough quanti ties to enable study of their cross sections and :ne chanisms. Among them, the following reactions ·should be prominent: 012 + ?J ~ Li7 + He4 + H1 - 24 . 6 Me v (R3) cl3 + o ~ 3He4 + n -12. 2 Mev (R4) Nl4 + 0 --7 2He4 + Li6 - 16.1 !>1ev (R5) N14 + (J' ~ 3He4 + H2 - 17.6 Mev (R6) It Has the objective of this research problem to study t he cross sections and me chanisms of the reactions listed above up to 70 Hev . The Io;.Ja State Colle ~ e synchrotron provided a source of 70 .l'Iev bremsstrahlung intense enough t o allow the irradiation of nucl ear plates in a few minutes with good knorfV'ledge of the direction of the incoming .photon. It also provided a continuous range of energies over which the various reaction cross sections could be studied. In order to get good sensi ti vi ty for protons and deuterons, ' Ilford B2 a nd lithium loaded B2 emulsions '\•Jere used for this expe~iment. ~ grain gradation developing process was used so t hat singly charr,ed particl·es could be easily discriminated from multiply charged ones . Events were identified by a method developed by Goward and Wilkins. This consisted of adding vectorially all of the momenta involved in a certain star. If the momentum unbalance is found to lie within certain limits near zero, the assumption is made that the guess wa~ correct as to 6 ISC-535 the nature of the event. An energy histop:ram is t hen drawn by applying to each event t he eq~ation (R7) where ET is the total kinetic energy of the particles forming the star, EB is the binding energy of the reaction, and Er is the energy of the photon which disintegrated the nucleus. From this histogram, a cross section curve can be calculated if the bremsstrahlung spectrum is known. rgevious work has shown that in the case of the reactions c12 ( 0', 3-x.) and 0 ( o, 4 ::::(), the cross section curve has several strong peaks and decided valleys. The work undertaken for this thesis confirms these previous cross sections in most essential details. Tne data used in this present study have the a dvantage of being taken from only two plates which were irradiated sDnultaneously, thus minimizing error due to normalization. In addition, an enerr,y histogram was drawn for the stars which could be assigned unambiguously to t ~ e reaction Nl4 ( ?5', 2 q)Li 6, and a preliminary study was made of the mechanism. II. LITERATURE S1JRVE': Photodisintegration of the elements contained in a pho to graphic emulsion Has first discovered in Zurich by Hlinni, Telegdi, and Z1mti (2) in 1948. T'l.ey irradiated nucle"l. r emulsions 1-1i th ·p rays _:'roduced by the proton bom­ bardment of lithium. The reaction cl2 ( !), 3CX ) >vas discovered and, to some degree, studied by this p; roup. During t he follo1.ving year, ~v~ffler a nd ~ounis (3) studied t ~e above react5on, in addition t o several~ proton and If' neutron events a t 17.0 I1Sv, and fonnd the ·cross section to be a~proximately n.8 ~ O.J x lo-2 cm.2. The first use of pho tons from a synchrotron t o produce photodisintep;rations in emulsiong wa s marlP by Gowa rd, Ti tterton, and l-Jilkins (I.!) 1-Jho studied the reaction ol (if, J., -:.-<).