Nuclear Chemistry in the Chemistry Department: 1968-1976
Experimental nuclear chemistry frequently requires access to accelerators and nuclear reactors. Brookhaven nuclear chemists and physicists enjoyed (and still do) the use of state-of-the art accelerator facilities: in the early days, the Cosmotron; later, the Alternating Gradient Synchrotron, (AGS), and its associated machines. (Today, the Relativistic Heavy Ion Collider (RHIC) has been added to the mix.) Reactors included the Brookhaven Graphite Research Reactor (BGRR), the High Flux Beam Reactor (HFBR), and the Brookhaven Medical Research Reactor (BMRR), all now closed. In addition, scientists at Brookhaven had very early access to large scale computing facilities, first at the NYU Courant Institute of Mathematical Sciences, later onsite at BNL. With this abundance of tools, nuclear chemistry has flourished at Brookhaven.
Nuclear chemistry research in the Chemistry Department during this period fell into two broad areas: nuclear reactions and nuclear spectroscopy. A new application of the techniques of nuclear chemistry appeared, the use of nuclear methods to study molecular dynamics.
Experiments primarily based at the AGS centered around investigations of reactions of high energy protons with complex nuclei. Measurements were made of reaction cross sections and energy spectra of products in order to provide understanding of the reaction mechanisms involved: binary fission, spallation, or other mechanisms. Theoretical efforts1 progressed simultaneously to aid interpretation of the experimental results. An example is the measurement of cross sections for the formation of rare-earth nuclides from the collisions of 28-30-Gev protons with uranium. Both chemical separations and electromagnetic isotope separations were utilized to analyze the products. Results2,3 confirmed an earlier conclusion that neutron-excessive products are produced by fission at moderately low excitation energies, and neutron-deficient products are formed by processes accompanying high excitation energies. As beams of heavy ions became available, studies of heavy-ion induced fission appeared, supplementing those using proton collisions. These experiments, using Cu and Au targets with 2.1, 3.9 and 29-Gev 14N ion projectiles, revealed details of nuclear reaction mechanisms using light vs. heavy projectiles. The ancestors of RHIC heavy-ion-heavy-ion collision experiments appeared.4,5
Measurements of nuclear decay lifetimes, reaction cross sections, and particle and photon emission energies yield detailed information about nuclear structure. In addition, during this period we also observe the emergence and maturation of electron spectroscopy as a chemical analysis tool, having been spawned from b-ray spectroscopy, originally a tool of nuclear chemistry. An example is the determination of decay characteristics of 57Co-57Fe,6 a pair of nuclides important in Mössbauer spectroscopy. A particularly intriguing example of nuclear spectroscopy research was an investigation of the mechanisms of how the chemical environment influences the half life of 125mTe.7 It had been shown elsewhere that the half life of this species as Te metal is different from its half life when Te is incorporated in Ag2Te. These measurements reveal changes in bonding electron densities at the nucleus in different chemical environments, and form an exquisitely sensitive probe of electronic structure.
Nuclear Methods in Molecular Dynamics
"Molecular Dynamics" refers to the detailed state-to-state, collision-by-collision elucidation of unimolecular or bimolecular reactions. By counting ionizing radiation from specific radioactive species, very small concentrations of those species can be determined against effectively zero backgrounds. Variations in spatial distribution of radiation from bimolecular reaction products can therefore be used to probe diffferential reaction cross sections in crossed-molecular beam reactions or rapid rotational effects in reactions in solution.
A program was established8-10 to demonstrate the feasibility of such experiments using the radioactive halogen, 217At, which has a half life of 0.032 s. The translational energy dependence of the reaction Br + HAt → BrH + At was determined, revealing a small (<3 kcal) energy barrier for the reaction. Experiments using radioactive isotopes of B, C, N, and O were planned.
During this period the nuclear chemists also exploited the high current capabilities of the new 200 MeV linac injector to the AGS. The CLIF (Chemistry Linac Irradiation Facility) was built. It allowed both proton and secondary neutron beams to be used to produce a wide range of new isotopes and novel isomeric nuclear states. Rapid, high purity radiochemical separation procedures were developed to isolate these nuclides.11-13
1. "Extension of the Isobar Model for Intranuclear Cascades to 1 GeV" G. D. Harp, Phys. Rev. C 10 2387 (1974.
2. "Interaction of 28-GeV Protons with Thorium: Study of Charge Dispersions and Mass Yields" Y. Y. Chu, E.-M. Franz, G. Friedlander and P. J. Karol, Phys. Rev. C 14 1068 (1976).
3. "Production of Nuclides with 43 £ A £ 51 in the Interaction of 1-28.5 GeV Protons with V, Ag, In, Pb, and U Targets" Y. Y. Chu, G. Friedlander and L. Husain, Phys. Rev. C 15, 352 (1977).
4. "Spallation of Cu by 3.9-GeV 14N Ions and 3.9-GeV Protons" J. B. Cumming, P. E. Haustein, R. W. Stoenner, L. Mausner and R. A. Naumann, Phys. Rev. C 10 739 (1974).
5. "Spallation of Copper by 25-GeV 12C Ions and 28-GeV Protons" J. B. Cumming, R. W. Stoenner and P. E. Haustein Phys. Rev. C 14 1554 (1976).
6. "The Conversion Coefficients of the Fe57 1414-keV Transition, the K Capture Fraction in Co57 e--Capture, and the K Fluorescence Yield of Fe" W. Rubinson and K. P. Gopinathan, Phys. Rev. 170 969 (1968)
7. "Long-Lived Metastable State of Te125" G. Friedlander, M. Goldhaber and G. Scharff-Goldhaber, Phys. Rev. 74 981 (1948); this is the fourth (!) publication from the Chemistry Department.
8. "Molecular Beams of Short-Lived Radioactive Nuclides" J. R. Grover, F. M. Kiely, E. Lebowitz and E. Baker, Rev. Sci. Instrum. 42, 293 (1971).
9. "Reaction of Hydrogen Astatide with Atomic Chlorine" J. R. Grover and C. R. Iden, J. Chem. Phys. 61 2157 (1974).
10. "Reactions of Chlorine and Bromine with Hydrogen Astatide" J. R. Grover, C. R. Iden and H. V. Lilenfeld, J. Chem. Phys. 64 4657 (1976).
11. "A Medium Energy Intense Neutron Facility at the Brookhaven 200-MeV Linac" S. Katcoff, J. C. Cumming, J. Godel, V. J. Buchanan, H. Susskind and C. J. Hsu, Nucl. Instr. and Meth. 129 473 (1975).
12. "Decay of the New Isotope 62Fe" E.-M. Franz, S. Katcoff, H.A. Smith Jr. and T.E. Ward, Phys. Rev. C 12 616 (1975).
13. "A New Neutron-Rich Isotope 190W" P.E. Haustein, E.-M. Franz, S. Katcoff, N.A. Marcus, W.A. Smith Jr. and T.E. Ward, Phys. Rev. C 14 645 (1976).
Last Modified: June 28, 2012