Erzeugung neuer isomerer Kernzustände durch Kernphotoreaktionen am Antimon und Thallium

The systematic search for new short-lived isomeric states has been continued by irradiation of an additional 32 selected elements with 26 MeV bremsstrahlung. Isomeric transitions were detected using a conventional scintillation spectrometer. Irradiation of antimony led to the production of a new (530±50) μsec isomeric state which decays through emission of partially converted (62±2) keV and (76±3) keV gamma rays. The 530 μsec half-life is tentatively associated with the 136 keV level in Sb¹²². An apparent inconsistency in the previously proposed level scheme of Sb¹²² can be removed if the 3.5 min Sb¹²²-activity is assigned to an isomeric level in Sb¹²² lying less than 15 keV above the 136 keV isomeric state. A new measurement of the half-life of this level yielded a value of (4.1₅±0.2) min. Another new isomeric state with a (2.l±0.2) msec half-life was produced by irradiating thallium. The isomeric state decays by emission of two gamma rays of (335±8) keV and (597±12) keV which were found to be in coincidence. Irradiation of erbium led to the production of a short-lived isomeric transition which may be identical with a previously reported Ho-isomer. Results are discussed in the appendix.     

On the magnetization process in an ising-spin lattice

Gamma ray spectra of a mixture of the isotopes⁸⁶Br and⁸⁷Br have been measured by means of a Ge(Li) detector. Both manual and automated techniques were used to separate bromine from other fission products of natural uranium. A total of 13 gamma rays were observed. The most intense of the⁸⁶Br gamma peaks (1,565 keV) was found to grow in with a half-life of 4.5±1 s. This is explained to be due to an isomeric state in⁸⁶Br decaying to the ground state.     

Identification of a 3.2μs isomer in76Rb

Fusion evaporation reactions were investigated to search for short lived isomeric states of nuclei near the proton drip line. Gamma spectra were measured, both singles and in delayed coincidence with evaporation residues implanted into a silicon detector after a velocity separation. A short lived activity was measured in the⁴⁰Ca+⁴⁰Ca →⁸⁰Zr^* reaction at excitation energies between 55 and 79 MeV. A half-life of 3.20 (10) μs was determined from delayed coincidences between evaporation residues and gamma rays. AtE ^*=55 MeV the cross section is 9 mb. The activity was assigned to an isomeric state in⁷⁶Rb by investigation of excitation functions. The isomer decays by emission of four gamma rays with energies of 70.55(5), 101.30(4), 145.11 (5), and 246.32(10) keV. A first level scheme is proposed assigning to the isomeric state an energy of 316.94(7) keV above the ground state. The isomer decaying into the low spin 1^(?) ground state band is explained from systematics as a band head of a high spin (4⁺) (πg_9/2,νg_9/2) structure. A high hindrance factor of 3×10⁶ forE1 radiation compared to a single particle transition is due possibly to a change of the core particle structure in the transition.     

The decay of75Ga to levels in75Ge

The decay of⁷⁵Ga has been investigated with Ge(Li) spectrometers. Energy and intensity determinations for 37 gamma rays have been performed. A level scheme for⁷⁵Ge was deduced, where 31 gamma transitions could be placed. Beta branch intensities were estimated from the measured gamma intensities. Spin and parity assignments for most of the levels were made in agreement with reaction and neutron capture studies. Half life of⁷⁵Ga was measured to be (130±6) sec and that of the 139.3 keV isomeric state in⁷⁵Ge to be (47.7±0.5) sec.     

Calculation of the ratio of isomeric cross sections

A new, more rigorous method for calculating the ratio of isomeric cross sections has been developed. The method is particularly valuable when the energy and spin distribution are known before the gamma rays populating the isomeric and ground states start to cascade. The usefulness of the method was demonstrated by applying it to the analysis of the ratio of isomeric cross sections in the ¹⁹⁶Hg(n,γ)¹⁹⁷Hg reaction, which was initiated by thermal neutrons.     

On previous and present investigations of resonance gamma-ray interaction with nuclei at the Institute of Theoretical and Experimental Physics (ITEP, Moscow)

A brief survey of theoretical and experimental work that is devoted to studying the resonance absorption and scattering of gamma rays by nuclei and which was initiated at the Institute of Theoretical and Experimental Physics (ITEP, Moscow) in the 1950s and has been continued to date is given. Investigations of various versions of interaction in beta decay, magnetic-field-perturbed angular distributions of resonantly scattered gamma rays, the problem of the Mössbauer gamma resonance of long-lived isomeric states of nuclei, and the resonance scattering of annihilation photons by nuclei are described.     

High-spin states in206Bi populated in the205Tl(α, 3n) reaction

Using alpha-particles in the energy range 35–51MeV and in-beam gamma ray and conversion electron spectroscopy techniques the reaction²⁰⁵Tl(α, 3n)²⁰⁶Bi was studied. A 15±1ns isomeric 15⁺ state was found at an excitation energy of 3147keV in²⁰⁶Bi. The main configuration of the isomeric state is suggested to beπh _9/2 vp ₁ ^2/?1 i ₁₃ ^2/?2 . The isomeric state decays mainly through a stretched cascade of five gamma rays to the previously known 0.88ms 10^? state of theπh _9/2 vi ₁₃ ^2/?1 (j ^?2)₀₊ configuration at an excitation energy of 1045 keV. A shell model calculation of the yrast states has been performed and it is found that the calculation agrees fairly well with the experiments. The average deviation between experimental and calculated energies for the yrast states with angular momenta in the region 6–18 is +4keV and the root mean square deviation is 22 keV.     

Lichtausbeute von Naphthalin bei planarem Channeling und Blocking von 4,50MeV-α-Teilchen

The 12^? isomeric state of²⁰⁶Tl formerly produced by charged particles, was produced in 14 MeV neutron induced (n, α) reaction on Bi. An intensity balance was deduced from known gamma lines and several new weak gamma lines were observed. Theoretical considerations on the production probability of the isomeric state and on some intensity ratios are given. The half-life of the isomeric state was determined in good agreement with former measurements.     

High-resolution studies of the gamma rays from isomeric states with half-lives of 10 μs - 30ms in nuclei with Z = 63−83

Eight new isomeric states with half-lives in the range 10 μs-30 ms have been identified following bombardment with 17.5 MeV protons of the natural elements and separated isotopes of the elements Eu to Pb. Improved data on 14, previously reported, isomeric states have also been obtained. The energies, half-lives and multipolarities of the gamma rays from these states have been measured using an 8 cm³ Ge(Li) detector. In most cases, level schemes have been constructed, and the spin and parity of the isomeric level and intermediate levels populated in the decay have been determined. A group of hindered E2 transitions have been observed, all of which are retarded by approximately the same degree e.g. 3 × 10⁻³ Weisskopf units. The results are discussed in terms of the Nilsson model and in terms of the selection rules for transitions between Nilsson states.     

Isomeric decay studies around 204Pt and 148Tb

Relativistic energy projectile fragmentation of ²⁰⁸Pb has been used to produce a range of exotic nuclei. The nuclei of interest were studied by detecting delayed gamma rays following the decay of isomeric states. Experimental information on the excited states of the neutron-rich N=126 nucleus, ²⁰⁴Pt, following internal decay of two isomeric states, was obtained for the first time. In addition, decays from the previously reported isomeric I=27ħ and I=(49/2)ħ states in ¹⁴⁸Tb and ¹⁴⁷Gd, respectively, have been observed. These isomeric decays represent the highest spin discrete states observed to date following a projectile fragmentation reaction, and opens further the possibility of doing `high-spin physics' using this technique.     

Analog states of 7He observed via the 6He(p,n) reaction

Isobaric analog states of 7He have been investigated by a novel technique involving the observation of the resonant yield of neutrons from the 6He(p,n) reaction in coincidence with gamma rays from the decay of the (0(+),T=1) state in 6Li. The gamma rays provide a clean signature for the isospin-conserving neutron decay of the low-lying isobaric analog resonances. It is conclusively shown that the analog of the recently observed low-lying spin-orbit partner of the 7He ground state does not exist. Evidence is presented that this state lies at much higher energies, in agreement with microscopic calculations.     

Levels in124Te populated in the decay of124Sb

The levels in¹²⁴Te have been investigated by studying the gamma rays emitted following the decay of 60d¹²⁴Sb. Gamma-gamma coincidence spectra have been taken with gates set at 603, 646, 709, 714 and 723 keV gamma rays by using 105 cm³ Ge(Li)-110 cm³ HPGe coincidence system. 69 gamma rays have been observed and nine of them are reported for the first time. Four new levels in¹²⁴Te at 2512, 2550.2, 2808 and 2814.5 keV are proposed. Levels reported in literatures at 2412 and 2733 keV are excluded from the level scheme of¹²⁴Te based on the present study. The experimentally determined energy spectrum of low-lying positive parity states, B(E2) ratios and electric quadrupole moment of the first excited state are compared with the IBM-1 predictions.     

Tracks to therapy

Studies of the structure of particle tracks have led to models of track effects based on radial dose and radiobiological target theory that have been very successful in describing and predicting track effects in physical, chemical, and biological systems. For describing mammalian cellular inactivation two inactivation modes are required, called gamma-kill and ion-kill, the first due to synergistic effects of delta rays from adjacent ion paths thus resembling the effects from gamma rays, and the second to the effects of single ion transits through a cell nucleus. The ion-kill effect is more severe, where the fraction of cells experiencing ion kill is responsible for a decrease in the oxygen enhancement ratio, and an increase in relative biological effectiveness, but these are accompanied by loss of repair, hence to a reduction in the efficiency of fractionation in high LET therapy, as shown by our calculations for radiobiological effects in the “spread out Bragg Peak”.     

Measurement of the beta beta-decay rate of 100Mo to the first excited 0(+) State of 100Ru

The double-beta beta beta(2 nu)-decay rate of 100Mo to the first excited 0(+) state of 100Ru has been measured by a gamma-gamma coincidence technique that uses two HPGe detectors to observe the two gamma rays ( E(gamma 1) = 590.76 keV; E(gamma 2) = 539.53 keV) from the 100Ru nucleus as it deexcites to the ground state via the 0(+)-->2(+)-->0(+) sequence. Unlike all previous beta beta-decay experiments, this technique provides data which have a large signal-to-background ratio. After a 440-day measurement of a 1.05-kg isotopically enriched (98.4%) disk of 100Mo, 22 detected coincidence events (with an estimated background of 2.5 events) yield a half-life of [5.9(+1.7)(-1.1)(stat)+/-0.6(syst)] x 10(20) years.     

Doppler shift as a tool for studies of isobaric analog states of neutron-rich nuclei: application to 7He

We have developed a new technique to study exotic neutron-rich nuclei via their isobaric analog states (IAS). We populate high-isospin states in resonant reactions of radioactive ion beams with protons. Characteristic gamma rays emitted from excited decay products were used to identify the population of the IAS. We show that information on the differential and total cross section for formation of the IAS can be extracted from the energy spectrum of the Doppler-shifted gamma rays. This technique was applied to the study of T=3/2 states in 7Li, which are analogs of states in 7He. The analog of the 7He ground state was clearly observed, whereas the presence of the analog of a narrow 1/2(-) state at 0.6 MeV excitation in 7He reported by M. Meister et al. [Phys. Rev. Lett. 88, 102501 (2002)] was excluded at the 90% confidence level. Evidence is presented for a broad 1/2(-) state at a higher excitation energy in 7He.     

Electromagnetic decay of the 6+ isomer of102Rh

Conversion electrons, and X rays from¹⁰²Rh^m (6⁺,T _1/2=1057 d) have been studied. An electromagnetic branch (2.3±0.3) ·10^–3 feeding the¹⁰²Rh first excited state has been observed in the 6⁺ isomeric decay. The excitation energy of the 6⁺ isomer turns out to be 140.7 keV above the 2^– ground state.We wish to thank P. Del Carmine, M. Ottanelli, and A. Pecchioli for their skillful collaboration during the measurements and the Technical Staffs of LNS and LNL for operation of the Tandem Accelerators.     

Der Zerfall des 1,5 min-Isomers Co54m

Co^54m (T _1/2=1.43 min) was produced in iron-foils by irradiation with_dE=19 MeV deuterons. The gamma ray spectrum was investigated using a NaJ(Tl) scintillation spectrometer, a coincidence circuit and a Ge(Li)-counter. There were observed three gamma rays having the following energies and intensities per Co_54m decay: 411 keV (0.97±0.07), 1130keV (0.98±0.05), 1407 keV (1.00±0.05). The directional correlation between the pairs of gamma rays were determined. These results correspond to spin and parityJ _π=2⁺ for the 1407 keV,J _π=4⁺ for the 2537 keV, andJ _π=6⁺ for the 2948 keV energy level of Fe⁵⁴. The last-mentioned level was not excited in previous scattering experiments. Our results are compatible withE=210keV andJ _π=6⁺ or 7⁺ of the isomeric state of Co^54m .     

Albedo factor determination of rare-earth oxides

ABSTRACT

Gamma-ray albedo factors of rare-earth oxides were determined experimentally. The detection of albedo factors for selected materials includes albedo number, albedo energy and albedo dose calculations. 59.54 keV gamma rays of 5 Ci annular ²⁴¹Am were used as a gamma source. Gamma rays were scattered by selected samples and collected by High Purity Germanium semiconductor detector. The albedo factors were plotted as a function of atomic number of target materials.     

Reconstruction Et Traitement D''images En Tomographie Axiale Transverse Par Emission

A 3-D reconstruction method from parallel projections developed in nuclear medicine imaging is presented. The two specific problems arising are the absorption of gamma rays by the tissues and low count rate. The first problem is solved by approached means and the noise is reduced by pseudo-Wiener filtering techniques. “In vivo” results that show the practical possibilities of this method are presented.