Development of experimental nuclear physics in Croatia
K. Ilakovac
Croatian Academy of Sciences and Arts, and University of Zagreb, Zagreb, Croatia
Organization of research
In this article, an overview of the development of research in the field of
experimental nuclear physics in Croatia is given for the period until about 1970.
In many parts, personal views are presented,while some important results, events
and/or decisions may have been omitted. The author apologizes for the possible lack
of completeness.
According to the knowledge of this author, no research work in experimental nuclear
physics was performed in Croatia prior to the work in the new "Atomic Physics
Institute", founded in 1951, later named "Rudjer Bošković" Institute (RBI), except
for some preparations in the Physics Department of the Zagreb University in the
development of detection techniques. The founding of the Institute was a great
success and a major step in the development of research work in physics,
electronics, chemistry and biology in Croatia. Earlier in 1950/51, Professor I.
Supek obtained the approval and funds from the Federal Government for the buildings,
staff and equipment in RBI. In the summer of 1951, the fundations of the first
building were laid. In the summer of 1953, the first and second laboratory buildings
and several workshops were finished and the cyclotron building was under
construction. Several groups had already been doing research work in the new
laboratories. They were mostly faculty members from various departments of the
Zagreb University who were employed part time in RBI. Gradually, more and more of
them as well as young graduates were engaged full time at RBI.
At that time, research work in chemistry, biochemistry and biology was already well
developed in several laboratories ot the University of Zagreb and also in some
firms. New opportunities, new equipment and services soon attracted a considerable
number of researchers. Respectable groups were formed which continued and expanded
their previous work in much improved conditions.
Some research work in physics has previously been done in Zagreb, but none in
experimental nuclear physics. No experienced researchers and no equipment had been
available. Two professors of the Zagreb University, I. Supek, head of the Department
of Theoretical Physics, and M. Paić, head of the Department of Physics, took up
the task to define lines of work and to form initial research groups.
In 1952, Supek succeeded to obtain approval from the Federal Government to build
a cyclotron in the RBI. It was a narrow win, because the proposal to have a cyclotron
built for the earlier founded "B. Kidrič" Institute near Belgrade, by the Dutch
firm Philips had already been considered. Main argument of Supek was that the
cyclotron would be built in the RBI, with many parts made by the strong Zagreb
electroindustry "R. Končar". It should be mentioned that an alternative to the
cyclotron was also considered. At that time, the strong-focussing principle was
discovered and plans for a strong-focussing proton synchrotron were under way in
the new European research centre CERN in Geneva. The idea was to build a small
strong-focussing electron accelerator in Zagreb with the aim to test the
strong-focussing principle. The idea had not been considered much in detail.
In 1954, the semi-subterranean cyclotron building was completed and parts of the
cyclotron were delivered (e.g., the magnet yoke, vacuum chamber, accelerating
electrodes, vacuum pumps, air-conditioning). Further work on the completion of the
machine progressed slowly.
No experienced researchers in experimental nuclear physics were available and
theoretical nuclear physics only started work in Zagreb. At that time, initiation
of research work "from scratch" was a major undertaking. The first problem was to
gather experienced researchers and to form research groups, but research
facilities, i.e. buildings, equipment, accelerator, etc presented serious
problems, too. As a first step, Supek decided to send several young physics
graduates and assistants abroad, to England (Birmingham and Manchester),
Switzerland (CERN), France (Saclay) and Denmark (Bohr Institute). That it was not
as simple. The political situation in the world was very tense. It was the first
phase of the cold war, the Korean war was flaring, nuclear weapons were built on
either side of the Iron Curtain, first hydrogen bombs were tested, etc.
Two lines of experimental nuclear-physics research were visualized, construction
of the cyclotron and work with the cyclotron beam and with radioisotopes produced
in the cyclotron for which Supek engaged several electrical engineers and several
of his graduates in theoretical physics, and the work in nuclear and high-energy
physics (cosmic-ray research) for which Professor Paić designated his young
assistants. So, in 1952, M. Lažanski went to CERN in Geneva to work for about a
year on the synchro-cyclotron. In 1951 M. Konrad and K. Ilakovac came to the
Department of Physics of the Birmingham University in England for graduate studies
to work on the cyclotron, and M. Turk and B. Leontić to the Department of Physics
of the Manchester University for graduate studies in cosmic-ray physics. In 1954,
Supek sent two further of his young graduates, V. Knapp and M. Petravić, for graduate
studies at the Birmingham University.
On his return from CERN in 1954, M. Lažanski was appointed head of the Cyclotron
Unit. K. Ilakovac obtained his Ph. D. from the Birmingham University in 1954 and
on his return in the autumn of 1954, he was appointed head of the Nuclear Structure
Group. M. Konrad returned in 1955, and he was appointed head of the Electronics
Group.
In 1954, two groups were designated for work in nuclear physics, the Nuclear Physics
Group (lead by M. Paić) and the Nuclear Structure Group (lead by K. Ilakovac). Ecept
for M. Paić, the Nuclear Physics Group consisted of M. V. Paić, B. Leontić, M. Turk,
B. Vošicki, K. Prelec, G. Thuro, P. Tomaš, ??? and six to eight technicians. They
were situated in several rooms in Buildings 1 and 2 at the RBI. They were developing
two detection techniques, the nuclear (ionographic) emulsions and the cloud
chamber. M. Paić made initial work already in 1950/51 at the Physics Department
of the Zagreb University where a small cloud chamber was built and operated, and
nuclear emulsions loaded with thorium or uranium compounds used to observe and
measure alpha-particle tracks with microscopes. This work was transferred to the
RBI in 1953/54. At that time, M. Paić and his associates already started to build
a 200 keV accelerator to be used as a “neutron generator”.
B. Leontić obtained his Ph. D. from the University of Manchester in 1954 and in
1955 he was appointed head of the High Energy Group. In the High Energy Group,
besides B. Leontić, there was M. Turk, and M. Paić was also engaged.
Girl-technicians were engaged for the microscopic measurements of tracks in nuclear
emulsions. A pack of nuclear emulsions (10 cm x 10 cm x 10 cm) was acquired and
exposed in a baloon flight abroad. Unfortunately, the emulsions were damaged to
such an extent that they could not be used for the investigation of nuclear tracks
produced by cosmic rays. Soon after, at the beginning of 1957, B. Leontić left to
work at CERN and the High Energy Group was dissolved. M. Turk joined Professor Paić’s
Nuclear Physics Group.
In 1954, the Nuclear Structure Group consisted of K. Ilakovac (head), M. Petravić
and V. Knapp (graduate students at the University of Birmingham), three graduate
physicists, N. Došek-Vošicki, N. Cindro and I. Šlaus, and a technician. The group
had three rooms in Building 2 at the RBI. Main task of the group was to prepare
for experimental research work with the cyclotron. Both nuclear reactions with
the external beam and studies of decay of radioisotopes were planned.
In 1957, the RBI was reorganized. The Nuclear Physics Group was renamed the
Department of Nuclear Physics I (DNP-I) and the Nuclear Structure Group the
Department of Nuclear Physics II (DNP-II). Two new buildings were made, and DNP-II
moved to Building 3 where they got a much larger space. Since the main machine
workshop was very busy with orders from other departments, and the jobs were (in
principle) processed according to the waiting list (some departments had priority,
e.g. the Cyclotron Unit, some researchers used to put “advance” orders, i.e. they
would order construction of something they were not ready to specify yet, just to
gain advantage when needed). E.g., it took over three years to get a simple
scintillation detection system with a single-channel analyzer made for gamma-ray
measurements. This was the reason for a very slow advance in the preparations,
especially with small jobs. Therefore, K. Ilakovac asked for permission to engage
new engineers and technicians within the DNP-II who would build electronic
equipment and also to form a small machine workshop. Ing. B. Berkeš, who worked
in the Department of Electronics, was transferred to DPN-II and continued his work
on beta spectrometers. Two electronic engineers, S. Cucančić and B. Turko, and four
technicians were employed for the development of nuclear electronics, and a
workshop with several machine tools was installed. That changed the pace of
preparations very much. Various equipment was built for the work with the cyclotron
beam and radioisotopes. E.g., two double-focussing beta spectrometers including
magnet supplies and electronics, various electronic units like high tension
supplies, amplifiers, discriminators, coincidence units, single-channel
analyzers, a 20-channel pulse-height analyzer, two 100-channel pulse-height
analyzers with nickel-wire memory (after Hutchinson), etc. There were several
personal changes, new young physics graduates were engaged, several members of the
DNP-II went to work at laboratories abroad, some people left (B. Turko joined the
Electronics Department but continued to collaborate with members of the DNP-II,
a little later S. Cucančić also switched to the Electronics Department).
In autumn 1962, K. Ilakovac went on a leave of absence for two years to work at
the University of Washington in Seattle, U. S. A. At the end of 1962, the Department
for Nuclear and Atomic Investigations (DNAI) was formed by fusion of the DNP-I,
the DNP-II (the researchers were split between two laboratories, the Laboratory
for Nuclear Reactions and the Laboratory for Nuclear Spectroscopy), the Atomic
Physics Laboratory, the Cyclotron Unit and the Neutron Generator Unit. M. Paić was
appointed the head of the Department.
In 1963, a controversy arose between N. Cindro and M. Cerineo. M. Paić was trying
to solve the problems but did not succeed. The DNAI administration was in a building
situated in a valley at the RBI. The meetings of the Scientific Council of the DNAI
were held there. The valley soon became known as the "valley of pots" (after a region
of Laos during the Vietnam war). M. Paić resigned in the summer of 1964. Until the
end of 1964, the DNAI was led in turn by B. Marković, I. Šlaus, N. Cindro and V.
Knapp.
K. Ilakovac returned from the U.S.A. at the end of 1964 and accepted the new
appointment as associate professor at the Physics Department of the Faculty of
Science and Mathematics in Zagreb. He continued to work at the RBI as a part-time
collaborator. At the end of 1964, he was appointed head of DNAI. The controversies
in the DNAI continued until the autumn of 1965 when M. Cerineo left the RBI after
appointemnt to the position of associate professor at the University of Belgrade.
K. Ilakovac resigned in summer of 1967 and was succeeded by I. Šlaus. At the end
of 1970, P. Tomaš was appointed head of the DNAI and he held the position for several
following years.
Cyclotron
Large parts of the cyclotron were ordered either from abroad or from home industry.
By the end of 1954, most of them were delivered and mounted in the cyclotron
underground building which was also completed. Further work, almost entirely done
at the RBI, like installations, HF oscillator (the main oscillator tube was built
at the RBI), magnet stabilization, command table etc.) was underestimated and the
planned date of completion of the machine was postponed several times. For that
reason, progress appeared very slow.
In 1962, the cyclotron internal beam was achieved. The event was marked by a big
celebration. The cyclotron was officially opened by President Tito. It was the first
accelerator of the type (and size) installed in the region, and mostly home-built.
Just prior to the event, K. Ilakovac left for the U.S.A. to work at the University
of Washington in Seattle.
As with most new accelerators at the time, many problems were encountered in the
first years of running. The cyclotron had a pair of parts which were especially
troublesome, the "short circuits". A design feature of the cyclotron was the
possibility to change the resonance frequency of the system chamber - accelerating
electrodes (the D's). It was intended (with the corresponding change of the magnetic
field) for acceleration of ions to different energies at the maximal radius. For
that purpose, the position of the electrical connections between the chamber and
supports of the D's (the "short circuits") could be changed. Without the disruption
of vacuum, the short circuits could be released, moved and tightened. The HF current
at the contacts at working conditions was in excess of 15 kA, causing frequent
failure. Several years later, the short circuit was redesigned for a fixed frequency
and the problem was solved.
In the course of preparations for the work with the cyclotron external beam, an
additional (also underground) hall for experiments was built adjoint to the
cyclotron building, and the cyclotron external-beam system which was designed and
to a large extent completed (bending/analysing magnet, quadrupole lenses,
analysing magnet, vacuum system).
Unfortunately, most of the preparations for the work with the cyclotron external
beam were in vain. One reason was delays in the completion of the machine. The
completion was originally planned for 1958/59, but it was delayed every year anew.
For several years, the group of physicists in the DNP-II was in a rather bleak
situation since no measurements could be done with the primary tool they were
supposed to use.
On his return from the U.S.A. in December 1964, K. Ilakovac learned that there
a design error in the cyclotron which prevented raising of the high voltage on
beam-extraction electrode (beam splitter) to the required voltage of about 100
The reason was a too small space (height) inside the D’s, indirectly due to a
small magnet gap. Thus, all efforts in the preparations for experiments with
external cyclotron beam were a miss.
was
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The cyclotron continued to be used with internal beams until about 1990. Several
improvements were made, a very important one being the rotating targets. Many
bombardments were made for research in chemistry, some for experiments in physics
and biology, several radioisotopes were made on routine basis for use in medicine,
some irradiation of animals with fast neutrons was done, etc.
According to the author's knowledge, only two articles were published in scientific
journals related to the work on the cyclotron [1,2].
Neutron generator
In 1954, M. Paić undertook to build a 200 keV accelerator of the Cocksroft-Walton
type, with the Greinacker-type rectifier. It was intended to be used as a source
of fast (2.7 MeV) neutrons using the d + d reaction (the "neutron generator"). In
the group, later named "Neutron Generator Unit", were, besides M. Paić (head of
the group), P. Tomaš, M. Varićak, K. Prelec, B. Vošicki and about six technicians.
Each member of the group had a specific task and was taking care of the design,
construction, testing and mounting of parts. M. Paić had a considerable experience
with similar systems, the X-ray units, during the World War II, for he worked for
the French firm Companie Generale de Radiologie on the design and development of
such units. Later on, N. Stipčić and B. Antolković joined in the work on the assembly
and testing of the machine.
The neutron generator was completed and put into operation in 1959. The 200 keV
deuteron beam was magnetically analysed and directed onto a target of frozen heavy
ice in vacuum. The d + d -> 3He + n reaction produced 2.7 MeV neutrons of a
considerable intensity, emitted in all directions. The machine proved to be highly
reliable. Breakdowns were rare and the very experienced team of
operators-technicians would repair the unit soon after some malfunction appeared.
Several articles were published in scientific journals related to the construction,
testing and improvements of the neutron generator [3-13].
A setback was inadequate rooms where the neutron generator was placed. Of the two
rooms in the western part of Building 2 (lower ground floor), one was used for the
accelerator and the target area, and the other as a large experimental room
(nowadays, that large room is divided into two). The problem was that Building 2
was not designed to be used for work with a strong source of fast neutrons. Good
shielding around the neutron source was made (large watertanks and paraffin
blocks), but adequate shielding above the source could not be installed. The
personel in the rooms above the neutron generator (several researchers and the
administration) on the upper floor of the building was, therefore, not allowed to
be in the rooms when the neutron beam was on. The work with the fast neutrons was
restricted from 3 p.m. until 7 a.m. the next day.
In 1960, solid tritium targets became commercially available. They were small metal
plates with a thin layer of zirconium or titanium on one side. A high capacity
of Zr and Ti to adsorb hydrogen and its isotopes was used to hold tritium at a high
concentration. Instead of the frozen heavy-water deuterium targets, the tritium
targets were used in the 200 keV accelerator to produce neutrons of a considerably
higher energy of about 14.4 MeV. The 14.4 MeV neutrons offered entirely new
possibilities of nuclear-reaction research.
Research work with nuclear plates
As soon as the neutron generator was put in operation, measurements of 2.7 MeV
neutron scattering and reactions began. The only reasonable method of detection
of charged particles produced by neutrons were ionographic emulsions (the "nuclear
plates"). A team of three to four girl-technicians were engaged for the work with
the exposed plates, to develop them and to do microscopic measurements of tracks
produced by charged particles from scattering or reactions of 2.7 MeV neutrons.
It was a tedious and very slow work. Angular resolution of the measurements was
very good, particle identification restricted only to single- and double-charged
particles, while the energy resolution was relatively low. Several articles were
published in scientific journals using this method [14-24]. The titles of articles
give an overview of the achieved results.
Electronics
In the fifties and sixties of the 20th century, the world market for nuclear
electronic equipment was very scarce. Very few units could be purchased. For a
successful development of experimental nuclear-physics research as well as of many
other disciplines, home-building of electronics was mandatory. The Electronics
Department at the RBI, headed by M. Konrad, was very successful in that work. At
the peak of their activities, about 25 researchers and designers and up to eight
technicians were engaged in the Department. They supplied the physics, chemistry,
biology and biomedicine research departments at the RBI, some other research
laboratories in Zagreb and other centres in the country with various electronic
equipment. They also developed several industrial nuclear-electronics prototypes
which were taken over by the firms for larger-scale production.
Some achievements of the members of the Department are known throughout the n world,
such as application of field-effect transistors in low-noise preamplifiers for
nuclear detectors, mega-channel counting using small computers (associative
memories), registration of multiparameter events from many-detector systems, etc.
The electronic equipment supply to many research groups, especially the nuclear
physics, was essential for the progress of scientific work at the RBI.
An impression of the very successful research work of the Electronics Department
may be obtained by inspecting the titles of articles published in scientific
journals by members of the Department [25-51].
Nuclear electromagnetic processes
Various processes were studied: elastic scattering of gamma rays, capture of fast
neutrons by protons and deuterons, nuclear level widths, angular correlation of
gamma rays, internal Compton effect, two-electron decay of nuclear excited states,
linear polarization in gamma ray scattering, etc. V. Knapp made an interesting
measurement that gave the limit on the effect of a transversal magnetic field on
the velocity of light of opposite circular polarizations. The angular correlation
work was introduced by B. Hrastnik after his return from a research study in Cracow.
A. Ljubičić made extensive complete kinematic measurements of the Compton
scattering on K-electrons which are almost singular still now.
An overview of the titles of the published work in this field [52-66] shows the
variety of studied processes.
Reactions of 14.4 MeV neutrons by the thin crystal method
In order to discriminate deuterons from protons, N. Cindro introduced the
thin-crystal method. If of the same energy, protons have almost a two times larger
range than deuterons. A suitable choice of thickness of the detector sensitive
volume may stop the deuterons while protons pass through. Thus, the deuterons
deposit all of their energy and protons only a considerably smaller part. The use
of a thin scintillator (activated CsI monocrystals were used) mounted on a
photomultiplier (which give pulses proportional to the energy deposited in the
scintillator) permitted the detection of pulses from deuterons while the pulses
from protons could be avoided. Two measurements of angular distribution in (n,d)
reactions were made and published as well as two articles on the method [67-70].
Although simple, the method was soon abandoned in favour of the counter telescopes
because of many limitations and uncertainties in the interpretation of spectra in
many nuclear reactions.
Radioactivation studies with 14.4 MeV neutrons
Nuclear reactions often lead to radioactive nuclides because of the change of either
or both of the proton and neutron numbers. Measurement of specific radioactivity
of irradiated samples permits the determination of total cross-sections for the
corresponding reactions. Several measurements using this method were done with 14.4
MeV neutrons. A further attempt was made to study the fluctuations of the
cross-sections due to the statistical nature of the compound-nucleus processes,
as predicted by T. Ericsson. Due to the different states attained by incident
particles of variable energy, variations in the decay of the compound nucleus occur.
The group N. Cindro, P. Strohal and associates used the d + T neutrons at various
angles relative to the incident deuteron beam. Due to the effects of centre-of-mass
motion, neutron energy varied between 14.1 and 14.6 MeV. The results of the
measurements should be critically examined because the spread of energy of neutrons
emerging from the target at an angle was comparable to the observed periods of
variation of the cross-sections. Four articles have been published in scientific
journals [71-75].
14.4 MeV neutron direct reactions studied by counter telescopes
The advent of 14.4 MeV neutrons offered new unexpected possibilities for the studies
of nuclear reactions. That was first recognized by M. Petravić and his wife G.
Kuo-Petravić who took up the task to build a counter telescope for charged particles
with the aim to study direct nuclear reactions induced by 14.4 MeV neutrons. The
telescope was a state-of-the-art piece of work, sensitive enough to detect 14 MeV
protons with a high efficiency. It consisted of two proportional counters (the first
to ascertain that the particle emerged from the target and the longer, second
counter to measure its energy loss, (Delta E), a CsI scintillation counter (to stop
the particle and measure its remaining energy, E), while in front of the counters
was a four-position wheel onto which the targets were fastened. The wheel could
be turned and fixed by magnets in one of the four positions to choose the selected
target. These parts were all in one sealed chamber which would be filled with CO2
of high putity for the operation of the proportional counters. Energy calibration
and checks of the particle selection were done using the hydrogen and deuterium
targets. A 100-channel pulse height analyzer was used to measure the particle energy
(pulses from the scintillation counter, E-counter), while for the selection of
either protons or deuterons emerging from the target, the pulses from the second
proportional (Delta E) counter were used. The selection was done using an
oscilloscope. On the screen of the oscilloscope, the horizontal deflection was
proportional to the E-pulse while the vertical deflection to the Delta E-pulse.
When a coincidence of pulses from all three detectors was detected, the spot on
the screen would flash. The flash would be detected by a photo cell which would
open the gate to the 100-channel pulse-height analyzer. To choose either protons
or deuterons, a black mask was placed over the screen with a cut-out which would
allow detection of either protons or deuterons. Of course, the selection was based
on the fact that for protons and deuterons of the same incident energy, the latter
have almost two times larger energy loss in the Delta E counter.
The pick-up reaction 51V(n,d) was chosen for the start. The measurements started
at the end of 1960 and lasted for several months. The measured angular distribution
was used to determine the orbital angular momentum of the transferred proton. M.
Petravić and his wife G. Kuo-Petravić left the RBI at the beginning of 1962 to work
at the University of Birmingham in England where they previously had obtained their
Ph. D.'s. K. Ilakovac left the RBI at the end of 1962 to work in the U. S. A. I.
Šlaus and P. Tomaš continued the work with several younger assistants and other
researchers. Many improvements were made and new telescopes were built. The group
of N. Cindro was joined by Belgrade researchers who had introduced very thin
surface-barrier Delta E detectors. They also joined the former group in the studies
of few-nucleon processes. Most articles published about the work with 14.4 MeV
neutrons which was carried out in Zagreb were in the field of direct nuclear
reactions. Single-nucleon pick-up, two-nucleon pick-up, knock-out reactions etc.
were measured on many nuclei. The titles of articles [76-105] show the successful
work done in this field.
Studies of few-nucleon systems by counter telescopes
The best known experimental investigations with 14.4 MeV neutrons done in Croatia
are the breakup of deuterons and the first determination of the neutron - neutron
scattering length from the proton spectrum of the D(n,p)2n reaction at the
scattering angle of 00. Studies of few-nucleon systems were scarce around 1960.
In the academic year 1956/57, K. Ilakovac started teaching the course "Nuclear
Physics" to the fourth-year undergraduates at the Faculty of Science and
Mathematics as a honorary lecturer. During the measurements of the 51V(n,d)
reaction, he was preparing the lectures on nucleon - nucleon interaction, and was
studying the 10th chapter of the book R. D. Evans "The Aomic Nucleus". The chapter
presents an extensive description of general characteristics of nuclear forces,
charge independence of singlet nuclear forces, the deuteron, phase-shift analysis
of nucleon - nucleon scattering, scattering length, effective range theory,
non-existence of dineutron, etc. The study incited the idea of measurement of
neutron - neutron interaction by the D(n,p)2n reaction. The idea was readily
accepted by the group. On suggestion of M. Petravić, measurements were layed off
untill the 51V(n,d) work was completed. Only once, when K. Ilakovac was taking over
the shift from M. Petravić, they made a short run with the deuteron target which
was in the counter telescope for calibration purposes. The proton peak due to the
neutron - neutron final-state interaction was readily seen. The measurements were
completed in the early summer of 1961 and the differential cross-sections were
published in Phys. Rev. Letters [106]. At the time, K. Ilakovac gave a talk in the
Theoretical Physics Seminary on the effective range theory that was based on the
article by Schwinger (Phys. Rev. 78 (1950) 135]. He drew attention (using simple
kinematics) to the main feature of the D(n,p)2n reaction: proton energy is directly
related to the centre-of-mass energy of the two neutrons, i.e. the proton spectrum
reflects the probabilities of different energy states of the outgoing two-neutron
system.
What followed was the analysis of the proton spectrum with the aim to derive the
neutron - neutron scattering length. Facilities for numerical calculations were
inadequate at the time. Only desktop electro-mechanical calculation machines were
available (primarily Olivetti Tectractis). Therefore, only the simplest form of
the nucleon - nucleon potential was assumed and the Born approximation was applied.
The couple Petravić took up to numerically calculate one matrix element, I. Šlaus
the other one. K. Ilakovac analyzed the phase-space factor and did the statistical
analysis (curve fitting) to derive the published result, ann = (- 22 + - 2) fm, for
the neutron - neutron scattering length [107]. It was the first determination of
the neutron - neutron scattering length. The measurements of the D(n,p)2n reaction
were redone in Zagreb [110] and at several other laboratories with a very similar
result for ann. It should be noted that the measurements using the D(pi,gamma)2n
reaction, in which two nucleons and a relatively weakly interacting gamma ray are
present in the final state, resulted in the value ann = -16.7 fm.
During the work on the breakup of deuterons at 00, K. Ilakovac suggested several
further experiments which were carried out later, such as the measurement of
D(n,p)2n reaction at scattering angles different from 00, the capture of fast
neutrons by protons and light nuclei and the breakup of tritons by fast neutrons.
Measurements of the D(n,p)2n reaction at scattering angles of 100, 200, 300 and 450
were made at the end of 1961. The theoretical differential cross-sections at the
scattering angles different from 00 are more difficult to calculate because at 00
the integrals appearing in the matrix elements are simpler. K. Ilakovac made most
of the calculations (it was more than a month’s work with the Ollivetti calculator).
The results of the measurements and the calculated differential cross-sections were
published in Nucl. Phys. [108].
Work on few-body problems continued with the detection systems used in the studies
of 14.4 MeV-neutron direct reactions. An attempt was made to observe the
three-neutron resonance and the proton-three neutron resonance, the neutron neutron scattering length was determined from the deuteron spectrum of the T(n,d)2n
reaction at 14.4 MeV, reactions of 14.4 MeV neutron with 3He, elastic scattering
of 14.4 MeV neutrons by hydrogen isotopes and the neutron-proton-bremsstrahlung
at 14.4 MeV were measured. The charge symmetry and charge independence of forces
in the two-nucleon in the same states was questioned in several articles. 14.4 MeV
neutron-proton bremsstrahlung at was also measured. The titles of articles
[106-118] give an overview of the achieved results.
Literature
A) CYCLOTRON-RELATED ARTICLES
1) V. Lopašić, A note on the wire loop method for locating the median plane in a
cyclotron magnet, Glasnik Mat.-Fiz. i Astr. 10 (1955) 195.
2) M. Konrad, The equations for the ion motion in a fixed frequency cyclotron,
Glasnik Mat.-Fiz. i Astr. 11 (1956) 253.
B) CONSTRUCTION AND TESTING OF THE NEUTRON GENERATOR
3) M. Varićak, B. Vošicki and B. Saftić, Experimental determination of the
Penning-gauge characteristics, Glasnik Mat.-Fiz. i Astr. 10 (1955) 89.
4) M. Paić, K. Prelec, P. Tomaš et B. Vošicki, Sur un accelerateur Cockroft et Walton
de 200 keV pour la generation de neutrons, Glasnik Mat.-Fiz. i Astr. 12 (1957) 269.
5) P. Tomaš, Production of thin films by thermal evaporation, Glasnik Mat.-Fiz.
i Astr. 15 (1960) 119.
6) B. Antolković, M. Paić, K. Prelec and P. Tomaš, Magnetic mass analysis of a 200
keV ion beam from a Cockcroft and Walton accelerator, Glasnik Mat.-Fiz. i Astr.
15 (1960) 61.
7) B. Antolković, D. Winterhalter and M. Turk, Measurements of the yield and energy
spectra od D-D neutrons by means of nuclear emulsions, Glasnik Mat.-Fiz. i Astr.
15 (1960) 303.
8) B. Antolković, M. Paić, M. Turk and D. Winterhalter, Influence of collimation
on the energy spectrum of 2.7 MeV neutrons, Glasnik Mat.-Fiz. i Astr. 16 (1961)
135.
9) N. Stipčić, M. Paić and P. Tomaš, The ion optical system of a 200 keV
Cockcroft-Walton accelerator, Glasnik Mat.-Fiz. i Astr. 17 (1962) 107.
10) K. Prelec, Proton energy spectra from a high frequency ion source, Glasnik
Mat.-Fiz. i Astr. 18 (1963) 103.
11) K. Prelec, Extraction system of a high frequency proton source, Glasnik
Mat.-Fiz. i Astr. 18 (1963) 121.
12) M. Paić, B. Antolković, P. Tomaš and M. Turk, Comparative measurements of yields
for D-D neutrons from different targets, Nucl. Instr. and Methods 23 (1963) 19.
13) K. Prelec, On some similarity rules for extraction systems of a high frequency
ion source, Nucl. Instr. and Methods 26 (1964) 320.
C) FAST NEUTRON REACTIONS BY THE EMULSION METHOD
14) M. Paić and B. Čelustka, Etude autoradiographyque de quelque roche yougoslave,
Glasnik Mat.-Fiz. i Astr. 11 (1956) 149.
15) D. Winterhalter, Inelastic scattering of neutrons of 2.7 MeV on aluminium,
Glasnik Mat.-Fiz. i Astr. 16 (1961) 131.
16) B. Antolković, A device for dip angle measurement of tracks in nuclear
emulsions, Nuovo Cimento 19 (1961) 1.
17) B. Antolković, Protons from S32 bombarded by 14.4 MeV neutrons, Nuovo Cimento
22 (1961) 853.
18) B. Antolković, A device for dip angle measurement of tracks in nuclear
emulsions, Nuovo Cimento 44 (1963) 123.
19) D. Winterhalter, Angular distribution of fast neutrons scattered on aluminium,
Nucl. Phys. 43 (1963) 339.
20) B. Antolković, Protons from S32 bombarded by 14.4 MeV neutrons, Nucl. Phys. 44
(1963) 123.
21) V. Paić and M. Paić, Discrimination of low energy protons and alpha particles
in Ilford K0 nuclear emulsions, Nucl. Instr. and Methods 26 (1964) 42.
22) M. Turk, Inelastic scattering of 14.6 MeV neutrons to excited states of
Z. Naturforsch. 22a (1967) 411.
12C,
23) D. Winterhalter, Elastic scattering of 2.76 MeV neutrons by
(1967) 487.
40Ca,
Z. Phys. 200
24) D. Winterhalter and M. Turk, A study of proton and alpha particles from neutron
induced reactions on 40Ca, Fizika 1 (1969) 137.
D) NUCLEAR ELECTRONICS
25) F. Marčelja, A simple fast-slow coincidence system for angular correlation
measurements, Glasnik Mat.-Fiz. i Astr. 17 (1962) 113.
26) L. Cucančić, A multiple pulse display system, Nucl. Instr. and Methods 21 (1963)
53.
27) I. Brčić, A fast decade counter, Elektrotehnika (1964) 40.
28) V. Radeka, The field-effect transistor - its characteristics and applications,
Trans. IEEE on Nucl. Sci. NS-11 (1964) 358.
29) V. Radeka, Fast decimal counting with binary-decimal logic, Trans. IEEE on Nucl.
Sci. NS-11 (1964) 296.
30) B. Souček, Distribution measurement errors due to the pile-up effect, Nucl.
Instr. and Methods, 28 (1964) 306.
31) B. Turko, Circulating memory applied for two dimensional pulse height analysis,
Elektrotehnika (1964) 51.
32) B. Souček, Loses in systems with variable dead time, Nucl. Instr. and Methods,
27 (1964) 306.
33) V. Radeka, Low-noise preamplifiers for nuclear detectors, Nucleonics 23 (1965)
52.
34) I. Brčić, “Ideally fast” decimal counters with bistables, IEEE Trans.
Electronic Computers EC-14 (1965) 733.
35) D. Iveković, A triple subnanosecond pulse generator with avalanche transistors
and charge - storage diodes, Nucl. Instr. and Methods, 32 (1965) 339.
36) B. Souček, Direct-recording megachannel analyzer through associative
programing of a small computer, Nucl. Instr. and Methods, 36 (1965) 181.
37) B. Souček, Stored program computer as an associative radiation analyzer, Nucl.
Instr. and Methods, 36 (1965) 750.
38) M. Konrad and B. Turko, Punched tape data sorting using a 256-channel memory,
Elektrotehnika (1965) 254.
39) M. Konrad, Monostable circuit triggered with pulse trains, Int. J. Control,
3 (1966) 275.
40) M. Konrad, Triggering of cathode or emitter coupled univibrators connected into
a chain, Int. J. Control, 3 (1966) 287.
41) O. Szavits, Analog-to-digital converter nonlinearity due to the loss current,
Nucl. Instr. and Methods, 39 (1966) 293.
42) V. Bonačić, An analog and digital readout system for the circulating memory,
Nucl. Instr. and Methods, 42 (1966) 154.
43) A. Hrisoho, Amelioration de la linearite differentielle des convertisseurs a
poids, Nucl. Instr. and Methods 55 (1967) 344.
44) D. Iveković, Fast transistorized pulse amplifiers, Electronic Eng. 39 (1967)
739.
45) V. Radeka, Effect of “baseline restoration” on signal-to-noise ratio in pulse
amplitude measurements, Rev. Sci. Instrum. 38 (1967) 1397.
46) V. Radeka and N. Karlovac, Least-square-error amplitude measurement of pulse
signals in presence of noise, Nucl. Instr. and Methods 52 (1967) 86.
47) B. Turko, 100 Mc/s gated clock oscillator, Nucl. Instr. and Methods 56 (1967)
261.
48) B. Vojnović, Fast coincidence circuit with variable resolution, Elektrotehnika
(1967) 272.
49) D. Iveković, A transistorized pulse amplifier for amplitude analysers,
Elektrotehnika (1968) 243.
50) B. Vojnović, Resolution stability of a tunnel diode subnanosecond coincidence
circuit, Z. Angew. Math. Phys. 19 (1968) 942.
51) B. Souček, V. Bonačić and K. Čuljat, Million channel pulse height analyser
through pseudo-random digital transformation, Nucl. Instr. and Methods, 66 (1968)
202.
E) NUCLEAR ELECTROMAGNETIC PROCESSES
52) N. Cindro and K. Ilakovac, Elastic scattering of gamma-rays, Nucl. Phys. 5
(1958) 647.
53) M. Cerineo, K. Ilakovac, I. Šlaus, and P. Tomaš, Capture of 14.4 MeV neutrons
by protons and deuterons, Phys. Rev. 124 (1961) 1947.
54) K. Ilakovac and V. Knapp, Proposals for the investigation of fast neutron
capture by the lightest nuclei, Nucl. Phys. 43 (1963) 69.
55) V. Knapp, Equality of velocity of gamma rays of opposite circular polarization
in a transverse magnetic field, Nature 197 (1963) 659.
56) B. Hrastnik, V. Knapp and M. Vlatković, Lifetimes of the first excited states
in 118Sn and 120Sn, Nucl. Phys. 89 (1966) 412.
57) J. Tudorić-Ghemo, Neutron-proton capture at 14.4 MeV, Nucl. Phys. A 92 (1967)
233.
58) A. Ljubičić, K. Ilakovac, V. Knapp and K. Pisk, Incoherent scattering of 662
keV gamma rays by K-shell electrons in gold, in Symposium on Nuclear Beta Decay
and Weak Interactions, editors B. Eman and D. Tadić, Zagreb 1967, p. 285.
59) B. Hrastnik, V. Knapp and M. Vlatković, Yadernie rezonansy gama lučei v
i 120Sn, Izv. Akad. Nauk SSSR, Ser. Fiz. 31 (1967) 98.
118Sn
60) B. Hrastnik, A. Ljubičić, B. Vojnović, K. Ilakovac and M. Jurčević, Directional
gamma - gamma correlation of the 71.66 - 249.69 keV cascade in 177Hf, Fizika 1 (1969)
117.
61) B. Hrastnik, A. Ljubičić, B. Vojnović, K. Ilakovac and M. Jurčević, A Ge(Li)
- NaI(Tl) system for gamma-gamma angular correlation measurements, Fizika 1 (1969)
127.
62) A. Ljubičić, B. Hrastnik, K. Ilakovac, V. Knapp and B. Vojnović, Energy
distribution measurement in the double decay of 137Ba, Phys. Rev. 187 (1969) 1512.
63) B. Hrastnik, I. Basar, M. Dikšić, K. Ilakovac, V. Los and A. Ljubičić,
Directional correlation studies in the decay of 177gLu, Z. Physik 239 (1970) 25.
64) A. Ljubičić, B. Hrastnik, K. Ilakovac, M. Jurčević, and I. Basar, Deexcitation
of the 662-keV state in 137Ba by the internal Compton effect, Phys. Rev. C 3 (1971)
824.
65) A. Ljubičić, M. Jurčević, K. Ilakovac, and B. Hrastnik, Double electron ejection
in the decay of 137Ba, Phys. Rev. C 3 (1971) 831.
66) B. Molak, K. Ilakovac and A. Ljubičić, Z dependence of linear polarization in
elastic scattering, Fizika 3 (1971) 239.
F) REACTIONS OF 14.4 MeV NEUTRONS BY THE THIN CRYSTAL METHOD
67) N. Cindro, A method for charged particles selection, Glasnik Mat.-Fiz. i Astr.
15 (1960) 113.
68) N. Cindro, A possible method for distinguishing charged particles with
semiconductor detectors, Nucl. Instr. and Methods 13 (1961) 99.
69) N. Cindro, I. Šlaus, P. Tomaš and B. Eman, The O16(n,alpha) reaction by the thin
crystal method, Nucl. Phys. 22 (1961) 96.
70) I. Šlaus, P. Tomaš and N. Stipčić, Angular distribution of the V51(n,d) ground
state deuterons, Nucl. Phys. 22 (1961) 692.
G) RADIOACTIVATION WORK WITH 14.4 MeV NEUTRONS
71) N. Cindro, P. Kulišić and P. Strohal, Fluctuations in the total cross sections
of the reaction Al27(n,alpha)Na24, Phys. Letters 6 (1963) 205.
72) J. Vuletin and N. Cindro, Cross sections for some (n,2n) reactions, Glasnik
Mat.-Fiz. i Astr. 19 (1964) 269.
73) P. Strohal, P. Kulišić, Z. Kolar and N. Cindro, An experimental test for the
nature of fluctuations in the reaction cross sections, Phys. Letters 10 (1964) 104.
74) Z. Kolar, P. Strohal and N. Cindro, Isomeric cross-section ratios for 14.4 MeV
neutron induced reactions, J. Inorg. Nucl. Chem. 27 (1965) 2471.
75) S. Lulić, P. Strohal, B. Antolković and G. Paić, Activation cross sections of
Sn isotopes for 14 MeV neutrons, Nucl. Phys. A 119 (1968) 517.
H) DIRECT REACTIONS BY 14.4 MeV NEUTRON USING COUNTER TELESCOPES
76) L. G. Kuo, M. Petravić and B. Turko, A dE/dx - E counter telescope for charged
particles produced in reactions with 14 MeV neutrons, Nucl. Instr. and Methods 10
(1961) 53.
77) M. Konrad and B. Turko, Sorting of two coincident pulses according to their
amplitudes, Nucl. Instr. and Methods 13 (1961) 29.
78) K. Ilakovac, L. G. Kuo, M. Petravić, I. Šlaus, and P. Tomaš, Reaction V51(n,d)Ti50
at 14.4 Mev, Phys. Rev. 128 (1962) 2739.
79) G. Paić, I. Šlaus and P. Tomaš, O16(n,d)N15 and O16(n,p)N16 reactions at 14.4 MeV,
Phys. Letters 9 (1964) 147.
80) V. Valković, P. Tomaš, I. Šlaus and M. Cerineo, Study of (n,p) and (n,d)
reactions of B10 at 14.4 MeV, Glasnik Mat.-Fiz. i Astr. 19 (1964) 285.
81) P. Kulišić, V. Ajdačić, N. Cindro, B. Lalović and P. Strohal, A study of
Nb93(n,alpha)Y90 and Pr141(n,alpha)La138 reactions at 14 MeV, Nucl. Phys. 54 (1964)
17.
82) V. Valković, Angular distribution of tritons from the reaction B 10 + n at 14.4
MeV, Nucl. Phys. 54 (1964) 465.
83) V. Valković, Triton spectrum from the n+Li7 reaction, Nucl. Phys. 60 (1964)
561.
84) G. Paić, I. Šlaus and P. Tomaš, Counter telescope for the study of (n,charged
particle) reactions, Nucl. Instr. and Methods 34 (1965) 40.
85) V. Valković, G. Paić, I. Šlaus, P. Tomaš, M. Cerineo and G. R. Satchler, The
reactions 48Ti(n,d)47Sc, 16O(n,d)15N, 10B(n,d)9Be and 6Li(n,d)5He at 14.4 MeV, Phys.
Rev. 139 ( 1965) B331.
86) P. Kulišić, N. Cindro, P. Strohal and B. Lalović, Direct processes in (n,alpha)
reactions, Nucl. Phys. 73 (1965) 548.
87) I. M. Turkiewicz, N. Cindro, P. Kulišić, P. Strohal and Đ. Veselić, The compound
nucleus process in (n,alpha) reactions on P31, S32 and Ca40, Nucl. Phys. 77 (1966)
276.
88) N. Cindro, A survey of fast neutron reactions, Rev. Mod. Phys. 38 (1966) 391.
89) D. Rendić, The reaction
14N(n,t)12C
at En=14.4 MeV, Nucl. Phys. A 91 (1967) 604.
90) B. Antolković and Đ. Miljanić, (n,p) i (n,d) reakcii pri En=14.4 MeV, Izv. Akad.
Nauk SSSR, Ser. Fiz. 31 (1967) 105.
91) B. Antolković, G. Paić, D. Rendić and P. Tomaš, Vzaimodeistvie neitronov energii
14 MeV s 14N, Izv. Akad. Nauk SSSR, Ser. Fiz. 31 (1967) 110.
92) G. Paić, D. Rendić and P. Tomaš, The 9Be(n,alpha)6He reaction induced by 14.4
MeV neutrons, Nucl. Phys. A 96 (1967) 476.
93) V. Valković, I. Šlaus, P. Tomaš and M. Cerineo, The reactions
and 6Li(n,d)alpha at 14.4 MeV, Nucl. Phys. A 98 (1967) 305.
10B(n,t)alpha
94) Đ. Miljanić, G. Paić, B. Antolković and P. Tomaš, (n,d) reactions on
39K, 40Ca, and 75As at 14.4 MeV, Nucl. Phys. A 106 (1967) 401.
alpha
14N, 35Cl,
95) B. Antolković, G. Paić, D. Rendić, P. Tomaš and M. Turk, Neutron induced
reactions on 19F, Izv. Akad. Nauk SSSR, Ser. Fiz. 32 (1968) 1658.
96) Đ. Veselić and J. Tudorić-Ghemo, Neutron-induced (n,alpha) reactions on
and indium at En=14 MeV, Nucl. Phys. A 110 (1968) 225.
103Rh
97) D. Rendić, B. Antolković, G. Paić, M. Turk and P. Tomaš, 14.4 MeV neutron induced
reactions on 19F, Nucl. Phys. A 117 (1968) 113.
98) Đ. Miljanić, M. Furić and V. Valković, Pick-up reactions on
A 119 (1968) 379.
11B,
Nucl. Phys.
99) P. Tomaš, B. Antolković, I. Basar, G. Paić and D. Rendić, Angular distribution
of charged particles from the interaction of 14.4 MeV neutrons with tritons and
helium-3, J. Phys. Soc. Japan (Suppl.) (1968) 38.
100) B. Antolković, J. Hudomalj, B. Janko, G. Paić and M. Turk, Measurement of the
10B(n,alpha) reaction at E =14.4 MeV, Nucl. Phys. A 139 (1969) 10.
n
101) V. Valković, Đ. Miljanić, P. Tomaš, B. Antolković and M. Furić, Neutron charged particle coincidence measurements from 14.4 MeV neutron induced reactions,
Nucl. Instr. and Methods 76 (1969) 19.
102) Đ. Miljanić, B. Antolković and V. Valković, Application of time measurement
to charged particle detection in reactions with 14.4 MeV neutrons, Nucl. Instr.
and Methods 76 (1969) 23.
103) V. Ajdačić, M. L. Chatterjee, N. Cindro and M. Jurčević, A low background
telescopic system for the study of (n,alpha) reactions, Nucl. Instr. and Methods
79 (1970) 77.
104) Đ. Miljanić and V. Valković, The (n,d) reactions on light nuclei, Nucl. Phys.
A 176 (1971) 110.
105) V. Valković and P. Tomaš, A position sensitive counter telescope for the study
of nuclear reactions induced by 14 MeV neutrons, Nucl. Instr. and Methods 92 (1971)
559.
I) FEW-BODY PROCESSES STUDIED WITH 14.4 MeV NEUTRONS
106) K. Ilakovac, L. G. Kuo, M. Petravić, I. Šlaus, and P. Tomaš, Proton spectra
from the D(n,p)2n reaction at 14.4 Mev, Phys. Rev. Letters 6 (1961) 356.
107) K. Ilakovac, L. G. Kuo, M. Petravić, and I. Šlaus, Attempt to determine the
n-n scattering length from the reaction D(n,p)2n, Phys. Rev. 124 (1961) 1923.
108) K. Ilakovac, L. G. Kuo, M. Petravić, I. Šlaus and Tomaš, Breakup of deuterons
by 14.4 MeV neutrons, Nucl. Phys. 43 (1963) 254.
109) M. Cerineo, K. Ilakovac, I. Šlaus, P. Tomaš, and V. Valković, Charge dependence
of nuclear forces and the breakup of deuterons and tritons, Phys. Rev. 133 (1964)
B948.
110) D. Rendić, M. Cerineo, I. Šlaus and P. Tomaš, Another attempt to determine
the n - n scattering length, Glasnik Mat.-Fiz. i Astr. 19 (1964) 275.
111) V. Ajdačić, M. Cerineo, B. Lalović, G. Paić, I. Šlaus and P. Tomaš, Reactions
H3(n,p)3n and H3(n,H4) gamma at 14.4 MeV, Phys. Rev. Letters 14 (1965) 442.
112) V. Ajdačić, M. Cerineo, B. Lalović, G. Paić, I. Šlaus and P. Tomaš, Information
about the neutron - neutron scattering length from the reaction H3(n,d)2n, Phys.
Rev. Letters 14 (1965) 444.
113) B. Antolković, M. Cerineo, G. Paić, P. Tomaš, V. Ajdačić, B. Lalović, W. Th.
Van Oers and I. Šlaus, A study of the neutron - 3He interaction at 14.4 MeV, Phys.
Letters 23 (1966) 477.
114) I. Šlaus, Neutron - neutron interaction, Rev. Mod. Phys. 39 (1967) 575.
115) B. Antolković, G. Paić, P. Tomaš and D. Rendić, Study of the neutron induced
reactions on He3 at 14.4 MeV, Phys. Rev. 159 (1967) 777.
116) W. T. H. van Oers and I. Šlaus, Comparison procedure and the neutron - neutron
scattering length, Phys. Rev. 160 (1967) 853.
117) I. Basar, M. Cerineo, P. Tomaš and Đ. Miljanić, Differential elastic scattering
cross sections of 14.4 MeV neutrons by hydrogen isotopes, Fizika 1 (1968) 105.
118) M. Furić, V. Valković, Đ. Miljanić, P. Tomaš and B. Antolković,
Neutron-proton-bremsstrahlung at 14.4 MeV, Nucl. Phys. A 158 (1970) 105.