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10
Recommencled Priorities for
Nuclear Physics
Federal funding for basic nuclear-physics research in the United
States began in the late 1940s, first by the Office of Naval Research and
then under the auspices of the Atomic Energy Commission. It contin-
ues today under joint sponsorship of the Department of Energy (DOE)
and the National Science Foundation (NSF). Without the support of
these organizations, this vital discipline could not have made the many
significant contributions to basic and applied research that have helped
to place the United States in a position of world leadership in science
and technology. It is the perception of the Panel on Nuclear Physics,
however, that American leadership in our discipline is eroding, owing
in part to the aggressive pursuit of major research programs in Europe
and Japan. Decisive steps must be taken if the United States is to
maintain a position in the vanguard of international research in nuclear
physics.
In October 1977, the DOE/NSF Nuclear Science Advisory Commit-
tee (NSAC) was established in answer to the need for a committee of
experts to oversee the general activities and trends in the various
subfields of nuclear physics and to make appropriate recommendations
to the funding agencies. In 1979 NSAC produced its first Long Range
Plan for Nuclear Science; its second Long Range Plan was completed
in 1983. The purpose of these studies is to review previous and ongoing
programs, evaluate current requirements, and anticipate future needs;
they also seek to ensure that existing facilities are maintained and
169
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170 NUCLEAR PHYSICS
upgraded appropriately and that new ones are developed to provide the
capabilities required for continuing major scientific advances. The
Panel met independently and also joined with NSAC during its
week-long Workshop in July 1983, when the major draft of its 1983
Long Range Plan was formulated. The recommendations that follow
are a result of these extensive interactions and discussions.
ACCELERATORS IN NUCLEAR PHYSICS
Because accelerators are the basic tools of nuclear physics research,
we will briefly review their current status. The probes needed to
examine the atomic nucleus are projectile beams of nuclei and
subnuclear particles, which must be accelerated to sufficiently high
energies to be able to penetrate into or scatter from target nuclei. The
projectiles must arrive as a focused beam in the target area, which is
often located far from the point at which the beam emerges from the
accelerator. One or more detectors are used to record and measure the
particles produced by the nuclear interactions. The planning, design,
and construction of first-rate accelerators and their associated experi-
mental facilities have become increasingly important to the nuclear
physics community at large. Designs must be optimized to support
those programs most likely to produce new results in critical research
areas and to satisfy the needs of the largest number of users.
An accelerator's capability for providing beams of a given particle
with a specific energy can be described by three parameters: the beam
intensity, or the number of particles striking the target per second,
expressed as beam current; the energy resolution, or the narrowness of
the energy spread of the beam, usually expressed as percent of total
energy; and the duty factor, or the fraction of time that particles
actually strike the target. Some beams, for example, are pulsed: the
duty factor is then the ratio of the pulse duration to its repetition time.
Optimizing all three parameters is desirable but seldom possible, so
designing a particular experiment requires that decisions be made
regarding which of them can or must be optimized. A low beam
intensity or a low duty factor can greatly increase the time required to
accumulate the number of events (nuclear interactions) necessary to
make statistically meaningful measurements. Poor energy resolution
restricts the accuracy of measurement attainable. Often a trade-off is
made; for example, beam intensity might be optimized at the expense
of energy resolution, or vice versa.
Accelerators range in size from large, multiuser facilities designed to
serve the needs of both resident physicists and users from other
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RECOMMENDED PRIORITIES FOR NUCLEAR PHYSICS 171
institutions (both domestic and foreign) to smaller, dedicated univer-
sity accelerators. Although the latter are generally also available to
outside users, they are more closely tailored to the special require-
ments of their own faculties. All of these facilities make it possible to
conduct forefront research in nuclear physics while providing for the
education and training of undergraduate and graduate students and
postdoctoral fellows.
Existing Facilities
The accelerators in use today provide a wide range of projectiles,
energies, and beam intensities for a great variety of research programs.
The type of projectile and its energy determine the nature of the
information that the experiment will yield. Some experiments require
electrons, with their particularly well-understood interactions; others
require intense beams of protons or secondarily produced mesons; still
others require high-energy heavy ions. The ability to bring such
complementary experimental techniques to bear on a variety of re-
search problems in nuclear structure and nuclear reactions has been a
crucial element in many of the major advances in nuclear physics
during the past decade. There are currently nine large, multiuser,
national accelerator facilities spanning this experimental range; the two
largest are the Los Alamos Meson Physics Facility (LAMPF), a proton
linear accelerator at the Los Alamos National Laboratory, and the
Bevalac Complex, a relativistic heavy-ion accelerator at the Lawrence
Berkeley Laboratory. In addition, 13 dedicated university accelerators
are supported primarily for nuclear-physics research and provide
specialized probes for their quite diversified research programs. These
22 accelerators (many of which have been substantially upgraded in
recent years), their capabilities, and examples of the kinds of research
problems for which they are used are summarized in Appendix A.
With continuing advances in both physics and technology, it is
inevitable that accelerators eventually become obsolete as primary
research facilities. Since 1976, federal funding by DOE or NSF for
basic nuclear-physics research has been withdrawn from 17 accelera-
tors. Although invariably painful and often accompanied by a substan-
tial disruption of graduate-student and postdoctoral training, judicious
attrition has been necessary for the evolution of the field, in order that
pioneering new machines can be built and operated at maximal
efficiency. The 22 accelerators described in Appendix A constitute, for
the near future, a vital, highly productive, and balanced force for our
development of modern nuclear physics. The imperative to push the
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172 NUCLEAR PHYSICS
frontiers ever further also demands, however, that major new initia-
tives be undertaken. Several of these are described in the following
sections.
The Planned Continuous Electron Beam Accelerator Facility
The electron accelerators designed and built in the 1960s for nuclear-
physics research contributed much to our understanding of the distri-
bution of electric charge in nuclei, the coherent collective excitations
of the nucleus, and the incoherent electrodisintegration of the nucleus.
These accelerators, however, had relatively low energy, poor energy
resolution, and poor duty factor. In the last decade, a new generation
of electron accelerators has produced electrons with energies of up to
750 MeV with excellent energy resolution and with duty factors of 1 to
2 percent an order-of-magnitude increase over those of the earlier
machines. Experiments at these facilities have had an enormous impact
on our knowledge and understanding of nuclear spectroscopy, meson
production, and meson-exchange currents. Over the same period of
time, experiments on the lightest nuclei done at the very-high-energy
but low-duty-factor machine at the Stanford Linear Accelerator Center
suggested the need for a broader view of nuclei, encompassing the
quark structure of the nucleons.
Significant connections between nuclear physics and elementary-
particle physics have emerged from these electron experiments, and it
appears that a smooth transition in the behavior of the nucleus occurs
with increasing energy. This behavior is well described at low energies
by independent-particle models of nuclear structure, which take into
account only the nucleons as constituents; at higher energies, account
must also be taken of the effects of baryons and mesons and, eventu-
ally, of quarks and gluons. Coincidence measurements, in which
significant results come from only a small fraction of the total number
of events, are of extreme importance in these studies and require
accelerators with much higher duty factors than now exist. Higher
energies and higher beam intensities are needed to extend investiga-
tions to the scale of very short distances, where the nucleus can best be
described in terms of its fundamental quark and gluon constituents.
This research frontier can be reached by an accelerator producing
4-GeV electrons, an energy that is also sufficient for studying the
production of baryon resonances (excited states of nucleons), heavy
mesons, and "strange" particles in the nuclear medium.
On the basis of both the DOE/NSF Joint Study of the Role of
Electron Accelerators in U.S. Medium Energy Nuclear Science (the
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RECOMMENDED PRIORITIES FOR NUCLEAR PHYSICS 173
Livingston report, 1977) and its own deliberations, NSAC, in its 1979
Long Range Plan, found a critical need for a high-duty-factor electron
accelerator with variable beam energies of up to several GeV. Subse-
quently, in the 1983 report of the NSAC Panel on Electron Accelerator
Facilities, a specific recommendation for such a machine, to be
operated as a national facility, was made: a 100 percent-duty-factor,
4-GeV linear-accelerator/stretcher-ring complex now called the Con-
tinuous Electron Beam Accelerator Facility (CEBAF), which was
proposed by the Southeastern Universities Research Association. The
research and development funding for this machine began in FY 1984,
and construction funding is proposed for FY 1987. A total accelerator
cost of $225 million (in actual-year dollars) is projected; this includes
$40 million for the initial experimental equipment.
We conclude this section by quoting from the NSAC 1983 Long
Range Plan (A Long Range Plan for Nuclear Science: A Report by the
DOE/NSF Nuclear Science Advisory Committee, December 1983,
page 751:
It is clear that electromagnetic probes will play an increasingly important
role in many areas of nuclear physics. Questions about the nucleon-nucleon
interaction, about connections to QCD and the quark structure, about the
hadronic structure of nuclei, elementary excitations, and nuclear-structure
symmetries, all require electromagnetic probes. The new 4-GeV electron
facility at NEAL National Electron Accelerator Laboratory, the original name
for CEBAF] is clearly the major near-term new initiative in nuclear physics.
The Panel on Nuclear Physics endorses the construction of CEBAF
THE NEXT MAJOR INITIATIVE: THE RELATIVISTIC
NUCLEAR COLLIDER
.
As discussed in Chapter 7, our increased understanding of the strong
interaction between hadrons has led us to believe that, under condi-
tions of greatly increased temperature and density in nuclear matter,
there will be a transition from excited hadronic matter to a quark-gluon
plasma, in which quarks, antiquarks, and gluons will no longer be
confined inside individual hadrons but will be free to move about (for
about 10-22 second) within a much larger volume. This extreme state of
matter is believed to have occurred in nature at the very beginning of
the universe, in the first few microseconds after the big bang, and it
may exist today in the cores of neutron stars, but it has never been
observed on Earth. Its production and analysis in controlled laboratory
experiments would provide us with scientific information cutting
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174 NUCLEAR PHYSICS
across the traditional boundaries of nuclear physics, elementary-
particle physics, and astrophysics and would create a common ground
on questions relevant to cosmology the universe and our place in it.
Present theoretical estimates suggest that collisions of heavy nuclear
projectiles with energies of the order of 30 GeV per nucleon can
generate temperatures and densities high enough to liberate the quark
and gluon constituents of the nucleons and more importantly- to
create large numbers of quarks, antiquarks, and gluons from the energy
of the collision. At such relativistic energies, the head-on collision of
two heavy nuclei will create an extremely hot, dense region of nuclear
matter encompassing hundreds of cubic fermis in volume. The enor-
mous energy density achieved throughout this large volume will
constitute a unique combination of conditions not available in the
collisions of electrons, protons, or light nuclei-for creating the
quark-gluon plasma. The accelerator needed to produce these condi-
tions, a relativistic nuclear collider (RNC), would be the world's
highest-energy accelerator capable of providing nuclear beams over the
full range of the periodic table, from hydrogen to uranium.
Although the production of the quark-gluon plasma- in the regions
of both high energy density (the central region) and high baryon density
(the fragmentation regions)- would represent a major focus of re-
search at the RNC, this accelerator would provide many additional
new research opportunities in nuclear physics, including the following:
· Extension of the study of quantum chromodynamics (QCD) to
large distances (roughly the diameter of a nucleus), complementing its
study at very short distances (less than the diameter of a nucleon), in
which electrons or hadrons are used as probes.
· The possibility of studying conditions under which the masses of
the light quarks go to zero (as predicted by QCD) and the states of the
system of quarks obey a right-hand/left-hand symmetry (chiral sym-
met~y).
· The first opportunity for investigating the dynamics of extended
objects with very-high-energy density conditions that can be
achieved only in relativistic nuclear collisions.
· The possible production of exotic objects, such as free quarks
(with fractional electric charge), quark "globs" with unique topological
(structural) properties or exceptionally high strangeness, and
Centauros mysterious events, observed in very-high-energy cosmic-
ray studies, that produce few or no neutral pions, which suggests a
hitherto unknown kind of nuclear interaction.
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RECOMMENDED PRIORITIES FOR NUCLEAR PHYSICS 175
In addition to producing colliding nuclear beams for a dedicated
program of study of the quark-gluon plasma, the RNC should also have
the capability for a variety of fixed-target experiments at energies of the
order of 30 GeV per nucleon. Some examples demonstrating the
breadth of this fixed-target research program are the following:
· Production and study of radioactive nuclei far from the valley of
stability and their use as exotic secondary beams.
· Development of a rich program of nuclear physics with very heavy
systems at relativistic energies, using intense beams to investigate rare
processes, such as coherent pion production (from a pion condensate,
for example).
· Investigations of highly excited hadronic matter (in which the
quarks and gluons are confined), providing new opportunities for
deducing the equation of state of nuclear matter under conditions far
from normal.
· Creation of the maximum possible baryon density achievable in a
laboratory experiment, thereby opening a new avenue of experimental
research in nuclear astrophysics.
· Studies of few-electron, very heavy ions, enabling new domains of
quantum electrodynamics to be tested.
Recommendations from the NSAC 1983 Long Range Plan
Because the long-range plans for nuclear physics were reviewed by
the Nuclear Science Advisory Committee in 1983, it is important to
state the Committee's major recommendation for new facility con-
struction, taken from the summary (page vi) of its 1983 Long Range
Plan:
Our increasing understanding of the underlying structure of nuclei and of the
strong interaction between hadrons has developed into a new scientific
opportunity of fundamental importance-the chance to find and to explore an
entirely new phase of nuclear matter. In the interaction of very energetic
colliding beams of heavy atomic nuclei, extreme conditions of energy density
will occur, conditions which hitherto have prevailed only in the very early
instants of the creation of the universe. We expect many qualitatively new
phenomena under these conditions; for example, a spectacular transition to a
new phase of matter, a quark-gluon plasma, may occur. Observation and study
of this new form of strongly interacting matter would clearly have a major
impact, not only on nuclear physics, but also on astrophysics, high-energy
physics, and on the broader community of science. The facility necessary to
achieve this scientific breakthrough is now technically feasible and within our
grasp; it is an accelerator that can provide colliding beams of very heavy nuclei
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176 NUCLEAR PHYSICS
with energies of about 30 GeV per nucleon.... It is the opinion of this
Committee that the United States should proceed with the planning for the
construction of this relativistic heavy-ion colliderfacility expeditiously, and we
.~ I' n.c the hi~hest-Drioritv new scientific opportunity within the purview of
our science.
The Panel endorses the NSAC 1983 Long Range Plan in recommend-
ing the planning for the construction of an accelerator that can provide
colliding beams of very heavy nuclei at energies of the order of 30 GeV
per nucleon with which to create the extreme conditions of nuclear
matter described above. The cost of this facility, including initial major
detectors, is estimated to be $250 million (in FY 1983 dollars), with a
construction period of 4 to 5 years. Operating and research costs are
estimated at $35 million per year. Research and development will be
needed to refine the design of this accelerator and specify its costs.
Once designed, construction should begin as soon as possible, consis-
tent with that of the 4-GeV electron accelerator discussed above. Since
current funding levels are barely adequate to respond, with the present
facilities, to the exciting scientific opportunities confronting the field,
we recommend an increase in nuclear-physics operating funds suffi-
cient to support the necessary accelerator research and development as
well as the operations and research programs at these two new facilities
as they come into being.
Complementary Aspects of CEBAF and the RNC
Both of the new accelerators being planned by the United States
nuclear-physics community the Continuous Electron Beam Acceler-
ator Facility (CEBAF) and the relativistic nuclear collider (RNC - will
address extremely important questions concerning the quark aspects of
nuclear matter. The theoretical and experimental research programs at
these two accelerators will be dramatically different, however (see
Figure 10.14.
Using intense beams of high-energy electrons, CEBAF will probe
the short-range behavior of quarks in nuclei with surgical precision. It
will do this by implanting a localized, well-understood electromagnetic
disturbance in the nucleus and measuring the response of the nuclear
environment to this stimulus. Electrons, being pointlike particles, are
well suited to such studies. They will act as a powerful microscope,
able to focus on the ways in which the quark substructure affects the
properties and interactions of nucleons residing inside the target
nucleus.
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RECOMMENDED PRIORITIES FOR NUCLEAR PHYSICS 177
(a) Continuous Electron Beam Accelerator Facility (CEBAF)
Nucleus
-
(b) Relativistic nuclear collider (RNC)
.. q ~
mu.
Nucleon
"- ~
,~,
\~e'
r e
FIGURE 10.1 The complementary aspects of CEBAF and the RNC. (a) CEBAF will
test the response of nuclei to high-energy, pointlike disturbances caused by the
interaction of electrons with quarks, over distances much less than 1 fermi. (b) The RNC
will test the response of heavy nuclei to the high energy densities created throughout
large volumes (hundreds of cubic fermis) when they collide head-on at relativistic
velocities.
The RNC, on the other hand, will cause beams of heavy nuclei to
collide violently with each other. These nuclei are relatively large
objects, with volumes of up to several hundred cubic fermis. When
they collide head-on, all the nuclear matter can interact and be heated
to such enormous temperatures and energy densities that the quarks
and gluons become Reconfined from the nucleons, and large numbers
of quarks, antiquarks, and gluons are created. These particles can then
move about inside a relatively large volume the quark-gluon plasma.
It is expected that the macroscopic behavior of quarks will be revealed
under these conditions.
Thus, to see how quarks will modify and extend our understanding
of nuclear physics, both of the accelerators are needed-to elucidate
both the microscopic and the macroscopic aspects of quarks in nuclear
matter.
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178 NUCLEAR PHYSICS
FURTHER RECOMMENDATIONS
In evaluating the prospects and promise for nuclear-physics research
in the next decade, it is also vital to consider facilities and opportunities
beyond the construction of the two major new accelerators discussed
above. Our analysis of the current state of nuclear physics leads us to
make the following recommendations for other important aspects of
the field.
-
Additional Facility Opportunities
A number of additional opportunities are under discussion in the
nuclear-physics community. The most important ones are listed in
Table 10.1. Here it is again appropriate to quote from the summary
(page v) of the NSAC 1983 Long Range Plan:
The major questions facing nuclear physics point to a number of important
scientific opportunities beyond the reach of the facilities in existence or under
construction. Many of these opportunities may be attained by a variety of
possible upgrades and additions to the capabilities of present facilities. Among
these are the capability for high-resolution continuous (COO) electron operation
below 1 GeV, substantially enhanced kaon beams, improved medium-energy
neutnno capability, antiproton beams, improved proton beams of variable
energy between 200 and 800 MeV, and also above 800 MeV, intense neutron
sources with energies up to a few hundred MeV, capabilities for accelerating
very heavy ions with easily varied energy between 3 and 20 MeV per nucleon,
a high-intensity pulsed muon facility, and a number of other options. We
estimate that a reasonable fraction of these opportunities can be realized within
the currently envisioned base program. Decisions on relative priorities should
be made at a later time and with more specific proposals in hand.
It should be noted that a number of the capabilities listed in Table
10.1 (specifically, the second, fifth, sixth, and eighth items), addressing
many of the physics topics mentioned above, could be encompassed by
another major new multiuser accelerator. As currently envisioned,
such an accelerator might comprise a synchrotron producing very
intense proton beams at energies of up to tens of GeV, followed by a
stretcher ring to produce a nearly continuous spill of protons that
would yield secondary beams of pions, kaons, muons, neutrinos, and
antinucleons. The intensities of these beams could be typically 50 to
100 times greater than those available anywhere else, allowing a
substantial improvement in the precision and sensitivity of a large class
of important experiments at the interface between nuclear physics and
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RECOMMENDED PRIORITIES FOR NUCLEAR PHYSICS 179
TABLE 10.1 Additional Facility Opportunities for Nuclear
Physicsa
Research Program (Examples)
Structure of elementary nuclear
Capability Required
excitations; form of nuclear momentum
distributions; nature of long-range and
medium-range nuclear interactions
Spin dependence of the nuclear
interaction; fundamental symmetry
tests; nuclear structure at high-
momentum transfer
Microscopic optical model; nuclear
structure and nuclear shape transitions;
studies of Gamow-Teller resonances
Nuclear spectroscopy of isotopes far
from stability; nuclear astrophysical
reaction rates; search for exotic nuclei
and superheavy elements
Hypernuclear physics; rare kaon decays
and other weak interaction studies;
exotic atoms
Tests of electroweak interactions; weak
interactions of leptons with nuclei;
muon spin resonance studies of solids
Energy dependence of nuclear-reaction
mechanisms; multiparticle decay of
highly excited compound nuclei; giant
resonances
Nuclear physics with antinucleons;
antinucleon-nucleon interactions to
study few-quark dynamics; anti-
nucleon atomic systems
Nuclear astrophysics solar neutrons
measurements; neutr~no oscillations
High-duty-factor electron beams with
good energy resolution at energies
below 1 GeV
High-quality, high-intensity polarized
proton beams spanning in stages the
energy range from 50 MeV to several
GeV
Secondary neutron beams (polarized and
unpolarized) with good intensity and
energy resolution at energies of up to
several hundred MeV
Intense secondary beams of radioactive
nuclei
Intense kaon beams of high purity
Intense muon and neutrino beams of high
quality
Heavy ions through uranium, at energies
between 10 and 100 MeV per nucleon
Low-energy and medium-energy
antinucleon beams
Solar neutr~no detector sensitive to low-
energy (less than 300-keV) neutrinos
a The sequence of items is not intended to suggest relative priorities.
particle physics. In particular, many experiments that are currently
impractical because of low count rates or cosmic-ray backgrounds
would become possible. In this context, we quote once more from the
NSAC 1983 Long Range Plan (pages 74-751:
A major new "Kaon Factory," a 10-30-GeV proton accelerator with
10~4-lO`5 protons per second, would provide substantial opportunities for
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18O NUCLEAR PHYSICS
physics in all of these areas. This physics is clearly very fundamental,
important, and exciting. Given our commitment to the construction of the
National Electron Accelerator Laboratory [now called the Continuous Elec-
tron Beam Accelerator Facility] and the heavy-ion collider discussed above,
the financial assumptions of this report preclude a major additional facility. But
as circumstances change, we want to keep this important option readily
available: it clearly presents many unique opportunities.
Nuclear Instrumentation
A serious national problem exists in the area of appropriate contin-
ued support for nuclear-physics instrumentation. The NSAC 1983
Long Range Plan notes that the amount spent by the United States for
basic nuclear-physics research relative to its Gross National Product is
less than half of that spent in Western Europe or Canada. The effects
of this disparity can readily be seen in the quality and sophistication of
European instrumentation, which in many instances far surpasses that
found in American universities and national laboratories. An increase
in dedicated funding for instrumentation at both large and small
facilities is therefore deemed essential.
Examples of the need for new equipment abound. Obtaining infor-
mation about the de-excitation of high spin states formed in heavy-ion-
induced reactions requires the use of large, spherical arrays of scintil-
lation detectors called crystal balls. The study of relativistic heavy-ion
collisions requires large-mass, fine-grained detectors that allow the
simultaneous localization, tracking, identification, and energy detec-
tion of large numbers of emitted particles. Magnetic spectrometer
systems have been steadily improving in performance, and even
greater improvements (as well as significant cost reductions) can be
made by using superconducting magnets. Studies of effects arising
from the aligned spins of particles require both polarized targets and
ion sources that will efficiently produce high-intensity polarized beams.
Equally pressing is the need for advances in data reduction techniques,
as the number of measured parameters grows with the increasingly
complex experiments.
Research and development programs are also necessary to deter-
mine the most effective solutions for the rapidly increasing require-
ments for sophisticated instrumentation. Higher-energy beams, for
example, will require the development of detector systems whose
capabilities far exceed those that have been used in nuclear physics to
date. An extensive research and development program for the imple-
mentation of detectors at the CEBAF will be needed, as well as a
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RECOMMENDED PRIORITIES FOR NUCLEAR PHYSICS 181
program to develop detectors with large solid angle, high segmentation,
and good particle identification for the RNC.
Nuclear Theory
In nuclear physics, as in all other branches of physics, theoretical
work provides both interpretation and guidance. Although in every
field of science there are always some experiments that produce
significant and sometimes dramatic progress in and of themselves,
steady progress is made for the most part through the informed choice
of experiments. Theorists working closely with experimentalists can
provide direction in the best choice of experiment by suggesting what
the most critical test of a concept would be and the measurements or
conditions that would make a complete theoretical analysis feasible.
The closer the link between theory and experiment, the more effective
they both become in synthesizing a coherent and elegant body of
knowledge.
Although the NSAC 1979 Long Range Plan stressed the need for
increased support of nuclear theory, a comparison of the current FY
1984 budget for nuclear physics with the FY 1979 budget shows that
during the intervening 5 years, funding for nuclear theory has remained
essentially constant as a percentage of the whole (5.8 percent in FY
1984 versus 6.0 percent in FY 19794. We believe that there is still a
clear need for a substantial relative increase in the support of nuclear
theory, especially in light of the new and challenging frontiers that are
opening up in nuclear physics. Among these are the study of the
behavior of nuclear states ever farther from stability, the study of the
nonnucleonic substructure of nuclei, the search for the quark-gluon
plasma, and the increasing interaction between nuclear physics and
particle physics.
Progress in current theoretical research depends on substantial
access to first-class computational facilities. Extensive calculations
based on the complex models describing today's experiments require
the large memories and rapid processing capabilities of Class VI
computers. Access by nuclear theorists to a major fraction of the time
available on a central, well-implemented Class VI computer could
initially meet this need.
Accelerator Research and Development
Accelerator research and development continues to be vital in
meeting the need for new advanced facilities and should be appropri
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182 NUCLEAR PHYSICS
ately supported. One of the most important recent breakthroughs has
been the successful use of superconducting materials in accelerators.
Radio-frequency (rf) superconductivity is now an established technol-
ogy, with numerous applications to electron acceleration and to
heavy-ion beam bunching and acceleration. Other superconducting
structures are also currently being investigated. For example, the
University of Illinois Nuclear Physics Laboratory is using a
superconducting linear accelerator (developed at Stanford) in a
microtron, and two superconducting rf linear accelerators are now in
operation as postaccelerators at Argonne and at SUNY-Stony Brook.
In a related area, the extremely strong magnetic fields obtained from
superconducting magnets reduce the size, the power requirement, and
hence the cost of cyclotrons that use them for the main field. Two
superconducting cyclotrons were begun in the mid-1970s. One is now
in operation at Michigan State University; the other, at the Chalk River
Nuclear Laboratory in Canada, will be operating in the near future.
A fundamentally new type of accelerator for low-velocity ions, the
radio-frequency quadrupole, has been pioneered at the Los Alamos
National Laboratory. Based on a theory originally developed in the
Soviet Union, it makes use of advanced techniques to capture more
than 90 percent of the beam from the ion source. It is an extremely
efficient preaccelerator for a larger accelerator and is currently being
developed at various laboratories in the United States and around the
world.
Borrowing a technique developed by elementary-particle physicists,
scientists at the Indiana University Cyclotron Facility are adding a
beam cooler a storage ring in which the accelerated beam will be
circulated and "cooled" via interaction over part of the ring with a
collinear electron beam of the same velocity to reduce greatly its
energy spread. This will provide a previously unmatched level of
precision for experiments with high-energy protons. The technique
represents a cost-eiTective way to achieve unusual capabilities at other
accelerators as well, and it is likely to be extensively developed in the
near future.
Studies are in progress to devise elective methods for producing
beams of short-lived radioactive nuclides with intensities that are
adequate for nuclear-physics and astrophysics experiments. For exam-
ple, radioactive beams can be obtained by methods in which the
desired nuclide is produced as a low-energy fragment from the target of
a primary beam in a bombardment reaction, captured in an ion source,
ionized, and finally accelerated toward a second target. In another,
more direct method, the radioactive nuclides emerge at relatively high
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RECOMMENDED PRIORITIES FOR NUCLEAR PHYSICS 183
energy from a suitable primary target in the form of a secondary beam
that can be used as is or accelerated or decelerated to different
energies.
The development of new ion sources has been rapid in the last
decade. The electron-cyclotron-resonance ion source and the electron-
beam ion source, both of which underwent their pioneering develop-
ment in Europe, are currently being put to use in the United States.
Along with various schemes for laser-driven ion sources and polarized
ion sources, they will be important elements of future nuclear-physics
research programs.
Training New Scientists
The Gardner report on excellence in education (A Nation at Risk:
The Imperative for Educational Reform, The National Commission on
Excellence in Education, U.S. Government Printing Office, Washing-
ton, D.C., 1983) points out that for the first time in U.S. history, the
educational skills of a generation not only do not surpass those of the
previous generation, they do not even approach them. These educa-
tional deficiencies, coming at a time when the demand for high
technical skills is accelerating, can result in the loss of America's place
of world leadership in intellectual achievement, technical innovation,
and material benefits. The report contends, furthermore, that the
security of the United States depends on the government's nurturing of
its intellectual capital. To maintain the highest level of achievement by
their students, colleges and universities must offer the best possible
learning tools.
The report states that: "The Federal Government has the primary
responsibility to identify the national interest in education. It should
also help fund and support efforts to protect and promote that
interest." It recommends that the government provide student finan-
cial assistance and research and graduate training with a minimum of
administrative burden and intrusiveness.
In addition to the general decline of trained personnel, a marked
decrease in the number of students pursuing graduate courses in
physics, and nuclear physics in particular, has become evident since
the early 1970s. If this trend continues, it promises to leave the field
seriously deficient in skilled scientists. The causes of the decline,
although varied, must certainly include as contributing factors the
severe financial problems faced by many colleges and universities. This
results in diminished financial aid for students, the loss of dedicated,
on-site accelerator facilities (indispensable tools for the teaching of
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184 NUCLEAR PHYSICS
nuclear physics), and the reduction of new academic positions (which
is intensified by the current low retirement rate in university faculties).
Futhermore, many who do obtain higher degrees in physics are
attracted by the much higher salaries in industry and are thus lost to
basic research.
Some recommendations to offset these tendencies are the following:
· Attract students to nuclear physics by funding undergraduate
nuclear-science research programs and by arranging for the participa-
tion of secondary school students in introductory studies.
· Increase National Science Foundation predoctoral fellowships in
general, and establish a specific program of Department of Energy
fellowships in nuclear physics.
· Increase the emphasis on support of new research initiatives by
awarding 3-year funded grants for proposals submitted by young
scientists past the postdoctoral stage.
· Increase the funding for university research groups to enable them
to hire their own nonacademic staff, such as scientists or engineers
specializing in technical problems.
· Instigate a program of temporary support of tenure-track faculty
positions to sustain nuclear physicists during the present period of low
university retirement rates.
· Consider the educational aspects of new facilities where practica-
ble; they should attract the highest-caliber graduate students and give
them the best possible training.
Enriched Stable Isotopes
The Calutron facility at Oak Ridge National Laboratory (ORNL) is
the major U.S. source of stable isotopes, which are used both in
scientific research and in the production of radioactive isotopes needed
for biomedical research and clinical medicine. Several stable isotopes
can occur in a chemical element; the isotope of interest, which may
constitute only a minute fraction of the total material, must be carefully
separated and purified from contamination by other isotopes. The
electromagnetic separation method used at ORNL is notable for its
ability to respond to changing demands; it represents an invaluable
national as well as international resource. The only comparable elec-
tromagnetic separation facility is in the Soviet Union.
Acute shortages of stable isotopes now exist (some 50 are currently
unavailable from ORNL), and severe funding insufficiencies forecast
rapid deterioration in the supply. The worsening shortages could have
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RECOMMENDED PRIORITIES FOR NUCLEAR PHYSICS 185
disastrous consequences in many areas of scientific research as well as
clinical medicine, where stable isotopes are indispensable tools. The
importance of enriched isotopes in nuclear-physics research derives
from the specific properties of the isotope in question. Virtually all
nuclear studies require separated isotopes, because the properties of a
nucleus can change drastically with the addition or removal of a single
nucleon. Consequently, an important priority is to replenish the supply
of separated isotopes before much nuclear-physics research is crip-
pled. To ensure that the problem is solved, corrective steps must
continue to be vigorously pursued, both by the scientific communities
affected and by the funding agencies.
Nuclear Data Compilation
For more than 40 years, compilers and evaluators have attempted to
keep scientists abreast of detailed nuclear data as they become
available. With the rapid experimental advances of the last two
decades, however, nuclear data compilations have begun to fall
behind. The continuing need for timely, cost-effective, and high-quality
evaluations led in 1976 to the formation of an international evaluation
network under the auspices of the International Atomic Energy
Agency. The network consists of 16 data centers in 11 countries; each
center is responsible for the evaluation of specified information in order
to avoid costly duplication of effort. All evaluated data are published in
Nuclear Data Sheets or Nuclear Physics and are entered into the
computerized Evaluated Nuclear Structure Data File maintained by
the National Nuclear Data Center at Brookhaven National Laboratory.
These data do not include a comprehensive compilation of charged-
particle cross sections, however; the need for such a compilation exists
in many areas of research, both basic and applied.
In addition to participating in the international network, the five
United States data centers coordinate their activities through the U.S.
Nuclear Data Network. These activities are funded primarily by the
Department of Energy (DOE) and are reviewed annually by the
National Academy of Sciences' Panel on Basic Nuclear Data Compi-
lations, which is advisory to DOE. Because the costs of this program
are relatively small, a modest increase in funding would greatly
enhance the ability to maintain a thorough compilation/evaluation
effort and to ensure the timely publication of these results in the
various formats required both by nuclear physicists and by applied
users of radioactive isotopes.
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Appendixes
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Representative terms from entire chapter:
range plan
