Shell Structure and Shape Symmetries in Heavy Neutron-Rich Nuclei
Studied by Deep-Inelastic Heavy-Ion Reactions
P.H. Regan, Zs. Podolyàk, P.M.Walker, W. Gelletly and W.N. Catford
Dept. of Physics, University of Surrey, Guildford, GU2 7XH
Part 1: Previous Research and Track Record
The evolution of shell structure with increasing neutron excess relative to the stable isotopes is one of the
main thrusts in current nuclear physics research, however, very neutron-rich nuclei are difficult to produce. While
a wealth of bound neutron-rich nuclei awaits access with radioactive beams, some of the key physics questions
can already be addressed. This research proposal seeks to investigate new physical phenomena in heavy, neutronrich nuclei following their population via deep-inelastic reactions with intense beams of stable ions. The proposal
is timely since it is only very recently that the combination of large multi-detector gamma-ray spectrometer
arrays and dedicated heavy-ion reaction detectors have been coupled together to give access to the areas of study
outlined here. The investigators have established their expertise in this area by leading a number of the initial
experiments using deep-inelastic experiments which attack a number of pertinent physics questions. These
include (i) the investigation of vibrational-to-rotational phase evolution and shape competition in the A~100
region [1,2] and (ii) the residual interactions between specific proton-neutron configurations and their effect on
the nuclear shapes [3-8]. We now seek the funds to apply novel experimental techniques to study these questions.
A key element of the proposal is the use of the CLARA detector array, coupled to the PRISMA spectrometer at
INFN-Legnaro, Italy. The CLARA array consists of clover germanium detectors from the partially EPSRC
funded EUROBALL spectrometer, redeployed to address new physics in neutron-rich systems.
The five investigators comprise one EPSRC Advanced Fellow and four permanent university-based
academics, all of whom have established international reputations in the field of nuclear spectroscopy. This
group’s recent output can be gauged by the extensive list of refereed publications, invited conference talks and
other output by the investigators since 1999. Publications in this period in core journals such as Physical Review
Letters (5), Physics Letters B (9), Physical Review C (45 including 12 Rapid Communications), Nuclear Physics
A (17), Journal of Physics G (6) Nuclear Instruments and Methods (5) European Physical Journal (9) have been
accompanied by dissemination in sources which accord a rather wider readership. These include articles in
Nature (2), the Daily Telegraph Science page (3), Laser Physics Letters (1) and feature articles in Physics World
(2) Nuclear Physics News International (2) , Europhysics News (1) and Education in Chemistry (1).
Dr P.H. Regan: Dr Regan is the principal investigator for this grant. Prior to his appointment at Surrey in 1994,
he held post-doctoral research positions at the University of Pennsylvania and The Australian National
University. In 2002 he was a Visiting Research Professor at the Wright Nuclear Structure Laboratory, Yale
University and he also currently holds an Adjunct Associate Professorship at the University of Notre Dame, USA.
He was promoted to a Senior Lectureship at the University of Surrey in 2003. He has co-authored more than 100
papers in refereed physics journals. He has been spokesperson for large-scale collaborative experiments studying
exotic nuclei using (i) radioactive beams, following isomeric decays from projectile fragmentation reaction
products [9] and (ii) stable beams via deep-inelastic collisions [2,7,8,10]. He has managed research programmes
which have won competitive, peer-reviewed beam time at facilities in the USA, Canada, France, Denmark,
Germany, Italy, Australia, South Africa and Finland. Of particular relevance to the current application, he was an
invited speaker at the Legnaro workshop for Physics Opportunities with PRISMA and CLARA held in 2003.
Dr Zs. Podolyàk: Dr Podolyàk was awarded an EPSRC Advanced Fellowship (AF) in October 2001. The
physics outlined in the current grant application, namely the study of heavy, exotic nuclei is compatible with the
main physics focus of his AF research. He has already established himself as a key international figure in this area
of nuclear structure research. Prior to his AF, he was an EPSRC funded PDRA at Surrey, following on from his
former research position at the INFN Laboratory in Legnaro. Over the last three years, Dr. Podolyàk has led
experiments using deep-inelastic and projectile-fragmentation reactions to identify isomeric states in previously
unobserved, neutron-rich nuclei between mass 180 and 230 [3]. Dr. Podolyàk was the spokesperson for a
successful ‘backed target’ experiment using deep-inelastic collisions between 82Se projectiles and a 192Os target at
INFN, Legnaro [11].
Prof. P.M. Walker: Professor Walker was the Head of the Nuclear Physics Research group at the University of
Surrey from 1993 until 2002. He brings more than twenty-five years of relevant research experience in
experimental nuclear physics, specialising in gamma-ray spectroscopy. He is an acknowledged international
expert on the physics of isomeric decays in heavy nuclei and recently led an international collaboration
investigating the first use of deep-inelastic and binary reactions to populate multi-quasi-particle K-isomeric states
in heavy, neutron-rich nuclei [4-6]. In addition to his experimental work, he has initiated a number of significant
theoretical studies, which have demonstrated an impressive predictive power for low-lying, multi-quasi-particle
states in deformed nuclei. He has published over 170 refereed journal articles, including a review article in Nature
devoted to nuclear isomers in deformed systems [5]. Prof. Walker’s studies of isomeric states in heavy nuclei
have forged a number of links to other areas of physics, including the effect of isomeric states on the creation and
destruction of Nature’s rarest naturally occurring isotope (180Ta) in astrophysical neutron capture environments
[6]; and the potential for using isomeric states for energy storage and release via X-ray and -ray stimulation. He
has served as a member on the ISOLDE-CERN Programme Advisory Committee. He is a former Chair of the
Institute of Physics Nuclear Physics Group.
Prof. W. Gelletly: Prof. Gelletly is the Distinguished Professor of Nuclear Physics at the University of Surrey
where he has held the posts of Head of Physics and Head of the School of Physics and Chemistry. Prior to his
arrival at Surrey in 1993, he served as Director of the Nuclear Structure Facility at the Daresbury Laboratory for
five years. He has published over 180 papers in refereed journals on nuclear physics and has been a leading figure
in the field of nuclear structure physics for more than thirty years. His awards include the OBE for Services to
Science and the Holweck Medal, awarded jointly by the French and British Physical Societies. He has served on
numerous International Nuclear Physics Advisory Committees including chairing the GANIL programme
advisory committee (PAC). He is currently a member of the INFN-Legnaro PAC, chairman of the SPIRAL2
International Advisory Committee and Chairman of the GSI NUSTAR Board of Representatives. Prof. Gelletly
has also long been heavily involved in developing the interface between fundamental research into nuclear
physics and its application to industry. In this context, he served for 9 years as a member of the Measurement
Advisory Committee of the DTI and Chair of its Radiation Science Committee. He currently serves as a member
of the National Radiological Protection Board. Prof. Gelletly played a major consulting role in the construction
of the PRISMA spectrometer, particularly with regard to the coupling of this device to the EUROBALL clover
germanium detectors, which will be exploited in the current proposal.
Dr W.N. Catford: Dr Catford is a Reader in nuclear physics at Surrey and has 25 years experience of
experiments which exploit magnetic spectrometers, gamma-ray detection and charged particle techniques for
nuclear structure studies. He led the first ISOL in-beam fusion-evaporation experiment using a gamma-ray array
[12] and the first experiment to use particle-transfer reactions with fragmentation radioactive nuclear beams for
spectroscopic measurements of 11Be. He has extensive experience in the use of semiconductor and gas-filled
detectors to measure charged particles from nuclear reactions. He commissioned and led experiments on the
MDM2 spectrometer at Oxford, has used various other spectrometers and played an important role in the
formulation of the design for and commissioning of the VAMOS spectrometer. He is the leader of the TIARA
project which combines charged-particle and gamma-ray experimental techniques in the spectroscopy of neutronrich nuclei [13]. He is currently a member of the GANIL PAC.
REFERENCES:
[1] P.H. Regan et al., Physical Review Letters 90 (2003) 152502
[2] P.H. Regan et al., Physical Review C68 (2003) 044313
[3] Zs. Podolyàk et al., Physics Letters B491 (2000) 225
[4] C.Wheldon, P.M. Walker et al., Physics Letters B425 (1998) 239
[5] P.M Walker and G.D. Dracoulis, Nature 399 (1999) 35
[6] P.M. Walker et al., Physical Review C64 (2001) 061302(R)
[7] C. Wheldon, P.H. Regan, Z. Podolyàk et al., in press, European Physical Journal, A (2004)
[8] P.H. Regan et al., Laser Physics Letters 1 (2004), in press.
[9] P.H. Regan and B.Blank, Physics World 13(1) (2000) 29
[10] P.H. Regan et al., Phys. Rev. C55 (1997) 2305
[11] Zs. Podolyàk et al., Int. Jour. Mod. Phys. E, in press (2004)
[12] W.N. Catford et al., Nucl. Inst. Meth. Phys. Res. A371 (1996) 449
[13] W.N. Catford, Nuclear Physics A701 (2002) 1c
Part 2: Description of Research
Abstract
A linked series of experiments is proposed to investigate the effect of shell structure on heavy (A>100) nuclei with
significant neutron-excess relative to -stable isotopes. The nuclei of interest will be produced following heavyion induced deep-inelastic reactions. The research aims to identify the influence of shell closures, magic numbers
and exotic shape symmetries on the structure of heavy nuclei and study the effect of increasing angular
momentum on the shell structure. The physics areas of focus are: (i) competition between tetrahedral, vibrational
and superdeformed symmetries in neutron-rich zirconium and molybdenum nuclei; (ii) the nature of nuclear
quadrupole deformation and SU(3) dynamical symmetries approaching the valence maximum at 170Dy; and (iii)
the first excited states in a new range of Hafnium/Tungsten/Osmium isotopes as a probe of a new proton sub-shell
closure for heavy neutron-rich systems.
Background
The cornerstone of current understanding of nuclear physics is the concept of shell structure, which
arises naturally from the related concept of the nuclear mean-field generated by the mutual interactions of all the
interacting protons and neutrons in the nucleus. Within this framework, closed shells of nucleons are well
established at ‘magic numbers’ of protons and neutrons with N, Z = 2, 8, 20, 28, (40), 50, (64), 82 and (114) 126.
(The numbers in brackets refer to sub-shell closures which manifest themselves over limited ranges of nuclei.)
These magic numbers, which are usually explained in terms of a spherically symmetric nuclear shape, are
strongly influenced by the nuclear spin-orbit (l.s) interaction which perturbs the single-particle level spacing.
While this simple picture adequately describes many of the experimentally observed properties of near-stable
nuclei in the vicinity of these magic numbers, a broader understanding of nuclear structure is complicated by
collective modes which can compete energetically with nucleonic single-particle excitations. These collective
effects may manifest themselves as rotational excitations which are most naturally explained by a permanent
intrinsic deformation. It is found that such deformed ground-state structures are favoured in nuclei with
significant numbers of valence protons and neutrons outside closed-shell magic numbers [1], an effect which is
intimately linked to the character of residual neutron-proton interactions in valence orbitals.
A principal thrust of nuclear structure physics in the coming decade will be focussed on new properties
of shell structure away from stability, particularly on how it may be modified for nuclei with a large neutron
excess [2,3]. There is now a significant body of evidence that the ‘standard’ shell closures are altered in very
neutron-rich systems. Furthermore it is generally understood that the development of deformed nuclear shapes is
strongly related to valence neutron-proton interactions, and thus a knowledge of where closed shells occur is of
paramount importance to the understanding of the development of collective effects in nuclei.
Evidence concerning the modification of shell closures is now well established for the N=20 and 28
shell gaps [4,5], but the situation for heavy nuclei is wide open. The experimental evidence for such shell
quenching has in general come from experiments using radioactive ion beams, usually produced using the
projectile fragmentation method. The Surrey group has been a major proponent of this method, with particular
interest in the study of heavy, neutron-rich nuclei [6]. These pioneering studies utilised the existence of nano- to
milli-second metastable excited states (‘isomers’) to enable the first spectroscopic information to be obtained in a
range of heavy, exotic nuclei. The low intensities of the radioactive beams preclude the coincidence
measurements that are needed to confirm the nuclear decay schemes, however, the isomeric decays provide vital
gamma-ray ‘fingerprints’ for many nuclei. A systematic study of experimental signatures, such as the energy of
the first excited state and/or the ratio of the excitation energies of the lowest-lying 2+ and 4+ levels in even-even
nuclei, can vividly demonstrate the erosion of the standard magic numbers and appearance of new sub-shell
closures [1,6,7]. It is the aim of the current proposal to exploit the fingerprints from the radioactive beam studies
by performing state-of-the-art experiments that have just become possible using deep-inelastic reactions involving
intense beams (~1010 particles per second) of stable heavy ions.
This proposal is focussed on the study of shell closures and collective effects in heavy, neutron-rich
nuclei through a series of experiments in three well-defined regions of the nuclear domain: (a) exotic, neutronrich species in the A~100-110 region searching for evidence of new forms of nuclear symmetry predicted by
Surrey (and other) theorists; (b) the growth of quadrupole collectivity and searching for hard evidence for the
SU(3) dynamical symmetry at the valence maximum nucleus 170Dy; and (c) revealing the potential new proton
sub-shell closure for heavy neutron-rich nuclei around A~190.
Figure 1 : Segre chart showing the -stable (black), neutron-rich (blue) and neutron-deficient (red and yellow) isotopes
which have been synthesised to date. Note that while the neutron-deficient isotopes are often known all the way out to
the proton drip-line and beyond, there are many nuclei predicted to exist inside the neutron drip line which are yet to
be observed experimentally. The paucity of data on the neutron-rich side is particularly evident for heavy nuclei. The
predicted rapid-neutron capture process which is thought to be responsible for the creation of about half the stable
elements heavier than tin is also shown for comparison. The three main physics objectives of this proposal, and the
regions where they can be explored are highlighted.
Figure 1 shows the chart of the nuclides with numbers indicating the standard, spherical shell model
magic numbers. While a large body of knowledge has been built up over the last two decades on the structure of
exotic nuclei with a proton excess, the contrasting effect of a large neutron excess in heavy nuclei remains largely
unexplored. Structural information on heavy, neutron-rich systems is highly elusive, partially due to difficulties in
identifying weakly produced channels in deep-inelastic reactions. For elements heavier than gadolinium (Z=64),
often only very limited nuclear structure information is available for the neutron-rich isotopes. In many cases,
even a knowledge of the ground-state lifetime extends just three or four neutrons beyond the last -stable isotope.
This is in stark contrast to their neutron-deficient counterparts, whose structure has often been studied out to and
beyond the proton drip-line, with upwards of thirty neutrons fewer than the lightest stable isotope.
The neutron-rich nuclei of interest for the current proposal are very difficult to study experimentally. It is
only with the development of ancillary devices for deep-inelastic reactions such as CHICO and PRISMA that an
unprecedented leap forward in the understanding of the structure of nuclei with a significant neutron excess is
now made possible. These devices will be further aided in their channel selection by the use of states identified
via feeding from isomeric states identified in our parallel programme with fragmentation-produced beams. In our
earlier work using deep-inelastic reactions, we have demonstrated that it is possible to separate the unique
fingerprint gamma-rays depopulating isomeric decays from the predominant flux of prompt beam-like and targetlike reaction products in deep-inelastic reactions (e.g., [8]) allowing clean selection for a specific reaction channel
to be obtained.
PRISMA is a large acceptance (~80msr) magnetic spectrometer [9], adapted from a UK design, which
was commissioned and became operational at INFN-Legnaro in 2003 for use with heavy-ion beams from the
XTV tandem-Alpi-PIAVE coupled accelerators. It is operated in conjunction with the CLARA Compton
suppressed gamma-ray spectrometer array, which includes UK-funded detectors. This system will ultimately
allow the study of deep-inelastic heavy-ion collisions with a wide range of beam/target combinations. In its final
configuration, PRISMA will enable the identification of individual reaction products from binary collisions eventby-event with mass and elemental resolutions ofandrespectivelyAdditional
elemental identification will also be available from the measurement of coincident K-shell X-rays in the CLARA
array following electron-conversion decays of the reaction products). The PRISMA experiments proposed here
will be aimed at the experimental limits of the nuclear landscape where little or no spectroscopic information
currently exists. These experiments will then be extended to explore states of higher angular momentum using
complementary techniques. They include the use of the GAMMASPHERE gamma-ray array at Argonne National
Laboratory in the USA, together with the position sensitive, gas-filled detector CHICO [10]. While CHICO does
not provide exact isotopic identification in the same way as PRISMA, it has the advantage of covering a much
larger solid angle. Coupled with the higher input angular momenta which arises from using high-energy, heavy-A
beams such as 208Pb and 238U (which are uniquely available with the ATLAS accelerator at Argonne), this will
allow a significant extension of the decay schemes initially identified using PRISMA. At these higher spins
changes in nuclear shape associated with competing spherical and deformed shell closures are predicted [11].
Expert theoretical interpretation of the new experimental results is vital. This will be aided significantly
following the recent appointments of two lecturers in nuclear structure theory at Surrey (Dr. M. Oi who is an
EPSRC Advanced Fellow, and Dr. P. Stevenson). Both have already made pertinent contributions to the physics
interest of this project in collaboration with Dr. Regan and Prof. Walker [12-14]. The local theory support will be
underpinned by collaboration with Prof. Furong Xu, the Head of the Applied Physics Department at Bejing
University, China who has made significant contributions to structure predictions in the neutron-rich A~100 and
190 regions of importance for this grant [12,15,16]. Prof. Xu has obtained a Royal Society Fellowship to visit
Surrey for the next three years and as such gives significant, ‘added value’ and timeliness to this application.
Programme and Methodology
The three areas identified above are now detailed. (Note estimates of production rates have been made for each
case using the GRAZING code. Typical production cross-sections for the exotic nuclei of interest range from
the10b to 1mb level out of a typical total reaction cross-section of the order of barns).
(1) Shape Evolution and Searches for Exotic Symmetries in the A~100-110 Region
Tetrahedral shape symmetry, which corresponds classically to a ‘triangular-based pyramid’, has been
discussed in a number of physical systems including molecules [17] and metal clusters. Recent calculations by
Dudek et al., [18] predicted that such tetrahedral deformation (32) may also manifest itself in nuclear systems
and be responsible for very large ‘tetrahedral’ shell-gaps. The size of these gaps match, or in some cases even
exceed the magic spherical gaps at N, Z=20,28,(40) and 50. An understanding of any departures from sphericity
beyond the well-known quadrupole effects is fundamental to the physics of nuclei. However, the detailed
spectroscopy is lacking in the neutron-rich nuclei which are expected to be the best cases in which to observe
such a system. The proposed experimental signature for this new symmetry would be the observation of parity
doublet bands but with a lack of inter-band electric dipole (E1) transitions due to the zero intrinsic dipole moment
associated with the pure tetrahedral shape. In the special case of tetrahedral systems with low quadrupole
deformation, this would be accompanied by weak electric quadrupole (E2) transitions, leaving enhanced and
observable electric octupole (E3) decays between the members of the tetrahedral configuration as the clear
indication for such a symmetry [18].
The best cases identified for study are nuclei at the 32 shell closures predicted for the zirconium (Z=40)
isotopes with N=58 (98Zr) and N=70 (110Zr). (Note that 110Zr is also a doubly magic closed shell in the pure
harmonic oscillator basis). To date, 104Zr is the heaviest isotope of this element where any reasonable
spectroscopic information is known [19,20], although 110Zr has been observed following projectile fission at GSI.
As part of the proposed research, we plan to perform a detailed spectroscopy survey of this region using the
unique channel selection capabilities provided by PRISMA, following multi-nucleon transfer reactions between
82
Se and 116Cd beams and a range of targets, including 96Zr, 104Ru and 110Pd. We note that the initial level schemes
for the N=58 isotones 96Sr and 98Zr have been reported following their population via spontaneous fission using a
248
Cm source [19]. While this work has provided some evidence for states which could be interpreted as hints of
tetrahedral structures, more detailed spectroscopy is required to provide the definitive evidence. This can only be
achieved using the channel selection provided using the PRISMA device.
The evolution of prolate deformed shell gaps with angular momentum for nuclei with A~100-110 is
also of interest and can be explored at the same time. Our recent work using CHICO and GAMMASPHERE
extended our knowledge of 100Mo up to spin 20ħ using a reaction between a 100Mo target and a 136Xe beam [8].
This reaction had an intrinsic input spin limit of 20-25ħ according to ‘rolling mode’ estimates. A high-spin study
of this nucleus is of particular importance in the light of long-standing calculations of superdeformed (SD) states
(2~0.5) which are predicted to become favoured at spins of between 25 and 30ħ [11]. Microscopically this is due
to superdeformed shell gaps expected for prolate shapes with major-to-minor axis ratios of 2:1 at proton number
Z=42 (Molybdenum) and neutron number N=58. The homologues of these nucleon numbers are known to exhibit
superdeformed sequences at high spins in the neutron-deficient A~80 (N=42) and A~130 regions (Z=58). By
utilising heavy beams such as 208Pb and 238U at Argonne, discrete states with spins of 30 ħ and above should be
observable in 100Mo. The discovery of such SD structures would represent the first observation of
superdeformation (and by extension SD magic numbers) towards the neutron-rich nuclei side of the Segre chart.
(2) The Structure of Nuclei Approaching the 170Dy Doubly Mid-Shell Valence Maximum
Nuclear ground-state collectivity requires many interacting particles and/or holes and is thus usually
found in regions away from the standard spherical magic numbers. By this simple argument, the most collective
nuclei should be found in the doubly mid-shell regions between proton and neutron major shells. Calculations by
Dr Regan, Prof. Walker and Prof. Xu et al., [12] predict that the doubly mid-shell system 170Dy exhibits an
unusually rigid quadrupole deformation, implying an exceptional stability of the K quantum number (K is the
projection of the total nuclear angular momentum on to the nuclear axis of symmetry). The purity of the K value
associated with these deformed systems is a measure of the axial symmetry of the nucleus. Assuming the
standard spherical magic numbers, 170Dy (Z=66, N=104) is the only even-even doubly mid-shell system with
A>100 which can realistically be reached experimentally. No excited states are currently known in 170Dy. Indeed,
its ground state has only recently been observed for the first time in a fragmentation reaction experiment led by
Drs. Regan and Podolyàk at GSI. Furthermore, only the first two excited states of the adjacent even-even nucleus
168
Dy have been identified following a -decay study using the ISOL radioactive beam technique [21].
Intriguingly, the double mid-shell at 170Dy may also represent the single best case in the entire Segre
chart of the SU(3) dynamical symmetry [22]. This would be of fundamental interest to group theoretical
descriptions of nuclear structure. Whereas good examples of the U(5) and 0(6) dynamical symmetry have been
identified in a variety of nuclei, the specific signatures which are evidence of the SU(3) limit have been more
challenging to demonstrate empirically. It was pointed out by Casten et al., [22] almost 20 years ago, that while
many axially deformed prolate nuclei display some of the very particular features of the SU(3) symmetry, no
nucleus convincingly displays all of them. These specific signatures include equal excitation energies for the 2+
states in the  and  vibrational bands and suppressed transitions between the  and  bands (due to the fact that
these structures are from different representations of the SU(3) symmetry). Only with the advent of the channel
selection allowed using PRISMA can nuclei near 170Dy be studied in detail. Therefore, we propose to study the
structure of these nuclei via a series of experiments using PRISMA, using heavy beams such as 82Se and 116Cd on
thin, self-supporting 170Er, 176Yb and 180Hf targets to measure channel-tagged -coincidence data.
(3) Sub-shell closures and Single-Particle Properties for Neutron-Rich W,Os and Pt Nuclei
A Surrey-led experiment exploited the fragmentation of a relativistic 208Pb beam at GSI to enable a
major breakthrough in the spectroscopic knowledge of the neutron-rich W/Os/Pt region [6] by observing isomeric
decays. We intend to use this new insight into the spectroscopy of this region from the recently identified
isomeric states to enable access to new, even more exotic nuclei. One of the intriguing results from the
fragmentation work was the energy ratio deduced for the first 4+ and 2+ states in 190W. A perfect, axiallysymmetric deformed nucleus would have a value for this ratio of 3.33, while a perfectly vibrational (spherical)
system has a value of 2.0. As figure 3 shows, the value observed in 190W is at variance with the trend expected
from the lower-Z members of the isotonic chains in this region. Surprisingly, the energy ratio for 190W is lower
than for the N=116 isotone 192Os, although 190W has more valence nucleons (eight proton holes compared to six
in 192Os, assuming Z=82 is the nearest proton shell closure). This appears to contradict the overall trend that the
greater the valence product, the more collective the ground state (as described by the so-called NpNn scheme [1]).
Figure 2: E(4+)/E(2+) ratio for even-even nuclei between barium and mercury. The left-hand plot shows the even N=86-92
isotonic chains highlighting the existence of the Z=64 shell closure for N<90 isotones. The right-hand plot shows the current
extent of the data on the neutron-rich gadolinium to platinum region for the even N=108-120 isotonic chains, including the
recent results for 190W and 194Os. A dramatic change in behaviour is shown by 190W.
We have suggested that the discrepancy observed for 190W may be evidence for a new proton subshell closure in this region [6] which arises due to the increased spatial overlap between the i13/2 neutron and h11/2
proton orbitals. This would be consistent with an independent prediction more than 15 years ago by Mach [23].
The occurrence of a spherical sub-shell would have significant consequences for the existence (or lack) of Kisomerism in this region, since such states require an axially symmetric nuclear shape. The Surrey group led an
exploratory experiment to study these nuclei following deep-inelastic reactions between a 136Xe beam and a thin,
self-supporting 198Pt target [24] resulting in the first report of the yrast sequence in 194Os. We envisage
complementary studies using both the heavier beams (such as 208Pb and 238U) at GAMMASPHERE+CHICO, and
also PRISMA + CLARA using reactions on 186W, 192Os and 198Pt targets with 82Se and 116Cd beams. These will
take place during the later stages of the current programme to investigate the low-lying states of 178,180Yb, 186,188Hf
and 192-4W, all of which are so far unknown.
Justification of Resources
(i) Staff Costs:
PDRA: The PDRA will shoulder much of the day-to-day progression of this research. The PDRA’s prime area of
responsibility will be for the PRISMA-based work, requiring significant time to be spent in Legnaro in order to
become expert in the operation of PRISMA. He/she will also be in charge of the software development required
for the Surrey-based data analysis. The PDRA, aided by the project student will be responsible both for setting up
the experiments and the data analysis. In the initial period of the grant, the PDRA will be trained in the relevant
analysis techniques using existing data sets from deep-inelastic experiments performed by the Surrey group at
both Legnaro and Argonne.
Project Student: A three-year project studentship is required for the GAMMASPHERE+CHICO experiments. In
order to analyse the high-spin data sets obtained, the student will spend significant training time at both Argonne
National Lab and at the University of Rochester to master the complicated computational analysis techniques
required for this work. He/she will also help set-up the CHICO detector for these experiments. Good quality
supplementary supervision is in place (see letter of support from Dr. Janssens) and this is an excellent opportunity
for a student to gain overseas scientific and hands-on experimental training at a leading laboratory.
J. Fogg (Clerical 5, point 8): Mrs. Fogg is responsible for processing group purchase orders and expense claims at
Surrey. The group’s travel for experiments, meetings, conferences etc. means that our direct research activity
counts for approximately 10% of her time.We request 10% of her salary for the grant period.
J. Dahlke (Computer Administrator, C scale point 6): Mr. Dahlke is the department’s assistant computer systems
manager who plays a network and workstation support role for the nuclear physics research group. The research
proposed here is totally reliant on an efficient computer network for the analysis and we require 20% of his salary
to achieve this.
(ii) Equipment:
Computing Needs and Data Visualisation: PC/Workstations are required for the PDRA and project student, for
data analysis. Each will also require both EXABYTE and DLT tape drives. A colour printer will also be required
for particle identification contour plots. DLT and EXABYTE drives cost £3.5k and £2.5k respectively plus £1.5k
for each PC-Linux workstation and together with an A3 colour laser printer (£2k) giving a total computing cost of
£17k(+VAT).
Consumables: Consumables required for the project are (i) isotopically enriched materials for the targets used in
the experiments (£10k); (ii) printing materials for data analysis (£1k); (iii) DLT and EXABYTE tapes for data
acquisition and storage (£1.2k); (iv) maintenance costs for PCs and tape drives (£2k); (v) DLT and EXABYTE
drive repairs (£1.5k) The total request for consumables is thus £15.7k (plus VAT).
(iii) Travel:
This research demands a substantial amount of travel to overseas experimental facilities. Travel funds are
requested for the five investigators, the PDRA and the project student on a pro-rata basis. These will cover the
experimental field work, collaboration meetings, PAC presentations and conference travel. Travel,
accommodation and subsistence costs for a one week experiment are estimated to be approximately £1000 (£50
per night for a hotel and £25 per day subsistence) plus travel costs to Italy and the USA. We expect an average of
two Surrey-led experiments associated with this grant per year plus additional costs for PAC and conference
presentations. The requests for Drs. Podolyàk and Catford reflect the fact that the former’s EPSRC Advanced
Fellowship finishes in October 2006, while the latter is calculated pro-rata reflecting his reduced time on this
project compared to the other investigators. A request of £5k is included for the travel and living costs of the
student and PDRA during extended stays at Legnaro and Argonne while they are trained in the operation of
PRISMA and CHICO. This results in a total travel request for the four-year period of the grant of £90.4K, which
should be considered against the (free) cost of beam time from Argonne and Legnaro over the course of the grant
which amounts to almost £1M (see letters of support from Drs. Janssens and DeAngelis).
Project Milestones
The expected project milestones are outlined on the GANNT chart attached to the application.
Relevance to Beneficiaries
The main beneficiaries of this work will be the international nuclear physics community and in particular theorists
attempting to understand changes in nuclear shapes and shells. The results on shell structure will also be of
interest to the nuclear astrophysics community. The grant will also provide manpower trained to a high level of
technical expertise in radiation physics, who may subsequently be employed in areas of national interest such as
the nuclear power industry, environmental and waste management and nuclear medicine.
Dissemination and Exploitation
The results will be disseminated by presentation at national and international nuclear physics conferences and by
publication of peer-reviewed journal articles. In addition to the standard nuclear physics journals, the group have
also published in Laser Physics, Hyperfine Interactions and Nature in recent years. The Surrey group also has a
long tradition of publications in media which are aimed at a wider readership including New Scientist, Physics
World, Chemistry in Britain, Europhysics News and The Daily Telegraph science page.
Timeliness
The experimental tools for the spectroscopy of heavy neutron-rich nuclei are only now available.The physics
openings arise from the Surrey-led work on isomeric studies following fragmentation of heavy beams. The
proposal builds on these successes. The PRISMA spectrometer has only recently come on-line and the Surrey
group’s experience in deep-inelastic reactions using CHICO+GAMMASPHERE provides new insights into the
potential for populating the high-spin regime of neutron-rich nuclei. The fact that the pan-European EUROBALL
community has agreed to move the full complement of clover germanium detectors to Legnaro for use with the
PRISMA spectrometer highlights the importance of this project at a European nuclear physics level. Prof. Xu’s
Royal Society Fellowship during the grant period will be very timely for theoretical interpretation of the results.
Landscape Factors
In line with the EPSRC notes for guidance for responsive mode grant applications, we have identified the
following Landscape Factors in our current proposal. (1) Dr Podolyàk is midway through a five year ESPRC
Advanced Fellowship, the physics aims of which are consistent with those proposed in the current application. (2)
The Surrey group has a long tradition of showing industrial connectivity. Prof. Gelletly’s position on the NRPB
Board also helps greatly in this area as does his advisory role for the National Measurement System and Dr.
Regan’s role as Director of the Surrey MSc in Radiation and Environmental Protection. (3) The project has direct
connectivity with other areas of physics, specifically nuclear astrophysics and molecular physics.
REFERENCES:
[1] R.F. Casten, Nuclear Physics A443 (1985) 1
[2] J. Dobacewski et al., Physical Review Letters 72 (1994) 981
[3] T. Otsuka et al., Physical Review Letters 87 (2003) 082502
[4] T. Motobayashi et al., Physics Letters 346B (1995) 9
[5] T.R. Werner et al., Physics Letters 335B (1994) 259
[6] Zs. Podolyàk et al., Physics Letters 491B (2000) 225
[7] J.A. Cizewski and E.Gulmez, Physics Letters 175B (1986)
[8] P.H. Regan et al., Physical Review C68 (2003) 044313
[9] A. Stefanini et al., Nuclear Physics A701 (2002) 217c
[10] M. Simon et al., Nuclear Instruments and Methods in Physics Research A452 (2000) 205
[11] J. Skalski et al., Nuclear Physics A617 (1997) 282
[12] P.H. Regan, et al., Physical Review C65 (2002) 037302
[13] M.Oi et al., Progress of Theoretical Physics 146 (2002) 609
[14] A. Rath, P.Stevenson et al., Physical Review C68 (2003) 044315
[15] F.R. Xu, P.M. Walker and R. Wyss, Physical Review C62 (2000) 014301
[16] F.R.Xu, P.M.Walker and R.Wyss, Physical Review C65 (2002) 021303
[17] W.G. Harter, Principles of Symmetry, Dynamics and Spectroscopy, (Wiley, New York, 1993)
[18] J.Dudek et al., Physical Review Letters 88 (2002) 252502
[19] H. Hua et al., Physical Review C69 (2004) 014317
[20] W. Urban et al., Nuclear Physics A689 (2001) 605
[21] M. Asai et al., Physical Review C59 (1999) 3060
[22] R.F. Casten et al., Physical Review C31 (1985) 1991
[23] H. Mach et al. Physics Letters 185B (1987) 20
[24] C. Wheldon et al. Physical Review C63 (2001) 011304
Figure 3: Diagrammatic work plan for proposed research from Oct 2004 to September 2008 .