Nuclear Chemistry in the Chemistry Department.
The National Laboratories were spawned from the Manhattan Project. Not
coincidentally, nuclear chemistry and nuclear physics burgeoned after World
War II, and they played a major role in the Physics and Chemistry
Departments of the Laboratories (including Brookhaven).
What differentiates nuclear chemistry from nuclear physics? A very
subjective definition. One difference is that (at least in the early years),
physicists used physical methods; they measured physical properties.
Chemists, on the other hand, used chemical methods. They used chemical
reactions to separate elements and isotopes. They used chemistry to
determine properties of new isotopes and to identify new elements
Recognizing the special place nuclear chemistry occupies in the Department's
history, the following is the first installment of the story of nuclear
chemistry in the Chemistry Department at Brookhaven.
High-Energy Proton Interactions with
BNL Chemistry Department 1947-1966: Rapid Growth
protons were first accelerated to hundreds of MeV after the end of World War
II, it became apparent that an incident particle could no longer be captured
by a target to form a Compound Nucleus. Instead of the expected peak
in yields well below the target mass, a broad distribution extending down
from the target was observed, a process termed Spallation*.
Nucleons, alpha particles, and other light Evaporated Particles were
also present. A peak due to Binary Fission, well separated
from spallation residues and evaporated particles, was observed from
heavy-element targets. A two-step picture was developed to account for these
observations. In an initial prompt IntraNuclear Cascade (INC), the
projectile interacts with individual target nucleons in a series of
quasi-free collisions, ejecting some. The excited residual nuclei
subsequently decay by particle evaporation, with fission competing in the
case of heavy elements. Detailed calculations using this Cascade plus
Evaporation/Fission model were not practical prior to the advent of
high-speed digital computers.
Introduction: A new
energy region opened in 1952 when protons were accelerated to 2.2 GeV at the
BNL Cosmotron. The energy range was extended to 28 GeV at the AGS
in 1960. Studies of the interactions of high-energy protons with complex
nuclei expanded during this period to become a major component of research
in the BNL Chemistry Department. Radiochemical techniques were
particularly well suited to study the broad distributions in charge and mass
encountered in high-energy interactions. While emphasis was on the unique
BNL facilities, university and other national laboratory facilities were
employed where appropriate. Collaborators such as J. M. Miller from
Columbia, N. Sugarman and A. Turkevich from Chicago, and L. Yaffe from
McGill brought their experience from lower-energy synchrocyclotrons to the
fledgling BNL group. Initial experiments [2,3] at 2.2 GeV led to
research in several areas:
Production: Production of nuclides such as 18F and 24Na
from targets from copper to uranium is a characteristic high-energy process.
Cross sections increase by about two orders of magnitude between 0.4 and 6
GeV , then become energy independent above 10 GeV . In the case of
copper, the rise can be accounted for as a broadening of the spallation
distribution. However, the observed copious yields of such light fragments
from lead targets at GeV energies were not anticipated from known mechanisms
and a new process, Multifragmentation, was proposed . Energy and
angular distributions of 24Na fragments  appeared to be
inconsistent with the slower time scale expected for evaporation or fission.
Follow-up studies sought to clarify the contribution of evaporation and this
new mechanism to forming specific light fragments. Some of these employed
non-radiochemical techniques. For example, 8Li fragments were
studied using nuclear emulsions , and cross sections for 9Li,
16C, and 17N were measured by counting their
beta-delayed neutrons . This early BNL work triggered world wide
experimental and theoretical studies of multifragmentation. The commonly
accepted picture is that the process involves statistical fluctuations
during the expansion of the initial hot nuclear system. Various mass
clusters form, interact, and dissolve during the expansion. At some low
density, interactions cease (freeze out) to give excited prefragments. These
are further accelerated by Coulomb forces and may evaporate additional
particles to give the observed light fragments.
Competition: The spallation and binary fission mass distributions
from heavy element targets are separated by a deep gap at energies up to 0.5
GeV. This gap has disappeared and the distributions overlap at 2.2 GeV .
The energy dependence of cross sections in this region of fission-spallation
competition (cesium through the rare earth elements), was examined using
radiochemical techniques combined with mass spectrometry . This showed
that the charge dispersion curve is double peaked at high energies.
Spallation adds a neutron-deficient component to the neutron-rich fission
products. Spectra and angular distributions  support this two component
picture. Energy spectra of 140Ba are narrow with high means
typical of fission, while those of 131Ba are broader and shifted
to lower energy. The angular distribution of 140Ba peaks at a
sideward angle as expected for a low-deposition-energy fission product at
high bombarding energies, but that for 131Ba is forward peaked.
Sections: Cross sections for high-energy reactions are normally
measured relative to some “monitor” reaction. Foil monitor techniques were
also important for diagnostic measurements of external beams at the
Cosmotron and AGS. BNL research played a major role in establishing a
consistent set of monitor cross sections. Absolute cross sections were
determined for the primary standard 12C(p,pn)11C
[12-14], and values for secondary standards such as 27Al(p,3pn)24Na
 and 197Au(p,X)149Tb  were established by
relative measurements. The high threshold for the latter makes it of
particular use where a background of low-energy particles is present.
Calculations: The Los Alamos MANIAC high-speed digital computer and
Monte Carlo techniques were used to model proton-nucleus interactions as
a series of quasi-free scatterings [17, 18]. Many simplifying assumptions
required by earlier hand calculations were avoided in these calculations.
This work provided the first extensive theoretical predictions for
comparison with experimental data at energies up to 1.8 GeV. Features such
as the empirical correlation between excitation energy and momentum transfer
appeared as a natural consequence. Of particular interest, the rapid rise of
many cross sections above 0.5 GeV was shown to correlate with the onset of
meson production and reabsorption.
Evaporative decay of
excited nuclei, such as those resulting from high-energy proton-nucleus
interactions, was also examined by Monte Carlo techniques . Predictions
of these calculations are sensitive to nuclear properties, and comparisons
with experimental excitation functions  obtained at the BNL 60-inch
Cyclotron were valuable in defining parameters such as level densities
and paring energies.
* The first publication  from the BNL
Nuclear Chemistry Group on this topic, a collaboration between G.
Friedlander and J. M. Miller of Columbia, described a spallation study at
the 0.4-GeV Nevis synchrocyclotron. This collaboration would continue in
subsequent research at BNL and elsewhere. Their text, “Nuclear and
Radiochemistry”, 2nd Edition, by Friedlander, Kennedy, and
Miller, is known worldwide as the source book for the field.
High-Energy Proton Reaction Studies 1947-1966
1. Yields of Iron Isotopes in High Energy Nuclear
J. M. Miller and G. Friedlander, Phys. Rev. 84, 589 (1951).
2. Nuclear Reactions of Copper with 2.2 GeV Protons.
G. Friedlander, J. M. Miller, R. Wolfgang, J. Hudis, and E. Baker, Phys.
Rev. 94, 727 (1954).
3. Disintegration of Bismuth by 2.2 GeV Protons.
N. Sugarman, R. B. Duffield, G. Friedlander, and J. M. Miller, Phys. Rev.
95, 1704 (1954).
4. Production of 18F and 24Na
in Irradiations of Various Targets with Protons between 1 and 6 GeV.
A. A. Caretto, J. Hudis, and G. Friedlander, Phys. Rev. 110, 1130
5. Production of 7Be, 22Na, and
24Na Fragments from Heavy Elements at 3, 10, and 30 GeV.
J. Hudis and S. Tanaka, Phys. Rev. 171, 1297 (1968).
6. Radiochemical Studies of the Interaction of Lead
with Protons in the Energy Range 0.6 to 3.0 GeV.
R. Wolfgang, E. W. Baker, A. A. Caretto, j. B. Cumming, G. Friedlander,
and J. Hudis, Phys. Rev. 103, 394 (1956).
7. Study of a Fragmentation Reaction by Thin-Target
Recoil Techniques; Production of 24Na from Bismuth by 2.9-GeV
J. B. Cumming, R. J. Cross, Jr., J. Hudis, and A. M. Poskanzer, Phys. Rev.
134, B167 (1964).
8. Emission of 8Li Fragments from Cu, Ag,
and Au by High-Energy Protons.
S. Katcoff, E. W. Baker, and N.T. Porile, Phys. Rev. 140, B1549
9. Cross Sections for the Production of 9Li,
16C, and 17N in Irradiations with GeV-Energy Protons.
I. Dostrovsky, R. Davis Jr., A. M. Poskanzer, and P. l. Reeder, Phys. Rev.
139, B1513, ( 1965).
10. Excitation Functions and Charge Dispersion in the
Fission of Uranium by 0.1- to 6.2-GeV Protons.
G. Friedlander, L. Friedman, B. Gordon, and L. Yaffe, Phys. Rev. 129,
11. Fission of 238U by 2.2-GeV Protons.
V. P. Crespo, J. B. Cumming, and A. M. Poskanzer, Phys. Rev. 174,
12. The 12C(p,pn)11C Cross
Section at 2 and 3 GeV.
J. B. Cumming, G. Friedlander, and C. Swartz. Phys. Rev. 111, 1386
13. 12C(p,pn)11C Cross
Section at 28 GeV.
J. B. Cumming, G. Friedlander, and S. Katcoff, Phys. Rev. 125, 2078
14. The 12C(p,pn)11C Cross
Section at 1.0 GeV.
A. M. Poskanzer, L. P. Remsberg, S. Katcoff, and J. B. Cumming, Phys. Rev.
133, B1507 (1964).
15. The 27Al(p,3pn)24Na/C(p,pn)11C
Cross Section Ratio in the GeV Region.
J. B. Cumming, J. Hudis, A. M. Poskanzer, and S. Kaufman, Phys. Rev. 128,
16. Cross Section for Production of 149Tb
from Au by High-Energy Protons.
E. M. Franz and G. Friedlander, Nucl. Phys. 76, 123 (1966).
17. Monte Carlo Calculations on Intranuclear Cascades
I. Low Energy Studies.
N. Metropolis, R. Bivins, M. Storm, A. Turkevich, J. M. Miller, and G.
Friedlander, Phys. Rev. 110, 185 (1958).
18. Monte Carlo Calculations on Intranuclear Cascades
II. High-energy Studies and Pion Processes.
N. Metropolis, R. Bivins, M. Storm, A. Turkevich, J. M. Miller, and G.
Friedlander, Phys. Rev. 110, 204 (1958).
19. Monte Carlo Calculations of Nuclear Evaporation
Processes. III. Application to Low-Energy Processes.
I. Dostrovsky, Z. Fraenkel, and G. Friedlander, Phys. Rev. 116, 683
20. Excitation Functions for Alpha-induced Reactions
N. T. Porile, Phys. Rev. 115, 939 (1959).
Last Modified: June 28, 2012