Study of short-lived bromine isotopes

First experiments in the systematic study of the structure of ground states and isomeric states of Br isotopes as function of neutron number at ISOLDE, CERN are reported. The isotopes^{74g.74m,77,78,84g,84m}Br have been implanted into iron and studied with the techniques of low temperature nuclear orientation and nuclear magnetic resonance of oriented nuclei (NMR/ON). The experiments were performed with the NICOLE on-line nuclear orientation set-up using the isotope separator ISOLDE-3. NMR/ON experiments were successful for^74mBr with continuous on-line implantation and for⁷⁷Br. Using as value of the hyperfine field B_hf(BrFe)=+81.3S (3) T we obtain |g (^74mBr)|=0.455 (3) and |g (⁷⁷Br)|=0.6492 (3). Static nuclear orientation data have been measured for all above mentioned isotopes. From these data we derive |μ(⁷⁸Br, I=1)|=0.13 (3) and |μ(^84gBr, I=2)|=1.9 (7). The results are discussed within the systematics of the bromine isotopes.     

New directions in low temperature nuclear orientation

The basis of the low temperature nuclear orientation technique is summarized. The present limitations on accessible temperatures and the orders of magnitude of hyperfine interactions in the metallic systems currently studied are discussed briefly. The broad applicability to many elements and the high sensitivity of this singles counting method are emphasized. Specific recent developments are discussed in more detail. The use of a dilution refrigerator to cool to ≈ 10mK nuclei of isotopes far from stability ‘on-line’, after production in an accelerator and electromagnetic selection, is a major extension of the method. The minimum half-life is now limited by the nuclear spinlattice relaxation time, typically of order 10–100 s at 10 mK. Aspects of these experiments are considered and recent results given for Cs and I isotopes. Secondly, the extension of the related technique of nuclear magnetic resonance or oriented nuclei (NMR/ON) to antiferromagnetic insulators is described. A new cooling mechanism involving nuclear-magnon coupling gives access to much lower temperatures than previously reached in these systems. Recent precision work on MnCl₂, 4H₂O is discussed, along with its possible extension to nuclei of lanthanide elements. Finally, the use of nuclear orientation to study ordering below 10 mK of enhanced nuclear moment systems is briefly surveyed, with HoVO₄ as the test case. NMR/ON experiments at high pressure are proposed.     

Low temperature nuclear orientation of nuclei far from beta stability Spin — Facility at JINR

The experimental facility for the study of the decay of oriented nuclei in a broad range of atomic and mass number and half-lives based on hyperfine interactions at ultralow temperatures — the SPIN facility at JINR — is described. High cooling power top loading 3He-4He dilution refrigerator of the system is capable of fast cooling of the sample inserted into the mixing chamber to the base temperature 10 mK for about 1–2 h. Detection system is designed for the study of angular distribution and temperature dependence of the anisotropy of gamma rays, linear polarisation of gamma rays and NMR/ON studies. Some results of nuclear orientation studies in off-line mode of radioactive nuclei with the half-live down to 1 h produced by spallation reaction with 660 MeV protons are presented. The project of nuclear orientation system on-line to the mass-separator and the new 600 MeV Dubna proton phasotron is described.     

Magnetic hyperfine field at caesium in iron

We report temperature dependence of nuclear orientation (NO), and the first observation of NMR/ON on Cs in iron.^{132, 136}Cs were implanted at room temperature into polycrystalline and single crystal iron. NO values for the (average) magnetic hyperfine field B_hf (CsFe) are close to 34T, intermediate between the value of 40.7T found in on-line samples made at mK temperatures and the NMR/ON value of 27.8 (2)T. The latter studies. The site/field distribution is briefly discussed. ISOLDE Collaboration, CERN     

Magnetic Moment of the 3/2− Ground State of 185W

Nuclear magnetic resonance measurement have been performed for ¹⁸⁵W oriented at 8 mK in an Fe host. The magnetic hyperfine splitting frequency at an external magnetic field of 0.1 T was determined to be 196.6(2) MHz. With the known hyperfine field of B _hf = −71.4(18) T, the nuclear magnetic moment of ¹⁸⁵W is deduced as μ(¹⁸⁵W) = +0.543(14) μ_N.     

Measurement of the susceptibility of solid 3He along the melting curve from 20 mK down to the nuclear ordering temperature

The susceptibility of solid ³He is deduced from multiple echoes observed in pulsed NMR experiments. It follows a Curie Weiss law at high temperature, increases faster than this law below 5 mK and drops abruptly around 1 mK.     

On the possibility of accelerating α decay: To the problem of disposing of radioactive nuclear waste

A number of experimental tests of the recent information on the possibility of accelerating α decay by implanting α-emitting isotopes into metals with their further cooling to a low temperature were performed using the nuclear orientation technique. The measurement data on half-lives for ²⁵³Es in Fe at 4 K and 50 mK, ²²⁴Rn, ²²⁵Ra, and ²²⁷Ac in Fe at temperatures down to 25 mK, and ²²¹Fr in nonmetal (Si) and metal (Au) at 4 K and ∼20 mK are reviewed. In all cases, no change in half-life was found within an accuracy of 1%.     

Magnetic dipole moments near Sn: Measurement on isomeric 11/2 states in odd-A Te and Te by NMR/ON

On-line low temperature nuclear orientation (OLNO) experiments have been performed on the odd-A Te isotopes ¹³¹Te and ¹³³Te using the technique of nuclear magnetic resonance on oriented nuclei (NMR/ON). The magnetic moments of the isomeric 11/2⁻ states have been measured extending the known data on these states in the Te isotopes up to the neutron shell closure at N = 82. The contribution to the 11/2⁻ magnetic moment in ¹³³Te due to core polarisation is calculated using an RPA shell model as well as corrections to the magnetic dipole operator caused by mesonic exchange currents. The neutron number dependence of the magnetic moments of the 11/2⁻ isomers in heavy Te isotopes is discussed in terms of particle-core coupling model (PCM) calculations.     

Hyperfine magnetic field of Zn in iron

Precise hyperfine field value of zinc in iron has been determined by nuclear magnetic resonance on oriented nuclei (NMR/ON): B_hf (ZnFe)=−18.785 (35) T at 7 mK. The relaxation constant of Zn in iron is established C_K=14(3) Ks. The new hyperfine field value of zinc in iron allows a more precise reevaluation of the magnetic moments of^69mZn and^71mZn measured with NMR/ON. and the NICOLE Collaboration, CERN     

In‐situ temperature calibration below 1 K using the μ+ Knight shift in CMN

We present μ⁺ paramagnetic shift measurements between 12 K and about 65 mK in cerium magnesium nitrate (CMN) to investigate its utility as an in‐situ temperature calibration source for low temperature μSR experiments. CMN is a salt which exhibits Curie‐law susceptibility to temperatures as low as 5 mK. The μ⁺ Knight shift is measured to be -(1.46\pm 0.03)\times 10^-3/T+(0.004\pm 0.02)\times 10^-3, corresponding to a transferred hyperfine field of -39 Oe/\mu_ B. This revised version was published online in August 2006 with corrections to the Cover Date.     

Normal-metal hot-electron bolometer with Andreev reflection from superconductor boundaries

This paper describes the design and experimental testing of a high-sensitivity hot-electron bolometer based a film of normal metal, exploiting the Andreev reflection from superconductor boundaries, and cooled with the help of a superconductor-insulator-normal metal junction. At the measured thermal conductivity, G≈6×10⁻¹² W/K, and a time constant of τ=0.2 μs, and a temperature of 300 mK, the estimated noise-equivalent power NEP=5×10⁻¹⁸ W/Hz^1/2, assuming that temperature fluctuations are the major source of noise. At a temperature of 100 mK, the thermal conductivity drops to G≈7×10⁻¹⁴ W/K, which yields NEP=2×10⁻¹⁹ W/Hz^1/2 at a time constant of τ=5 μs. The microbolometer has been designed to serve as a detector of millimeter and FIR waves in space-based radio telescopes. Zh. éksp. Teor. Fiz. 115, 1085–1092 (March 1999)     

3He melting curve thermometry in a nuclear polarization experiment

Temperature measurement and control are important in brute force polarization experiments. We discuss the installation and use of³He melting curve thermometers in a crystat used to polarize a TiH₂ target. Comparison is made between the melting curve thermometers and the⁶⁰CoCo nuclear orientation thermometer, which is often used in such experiments. The melting curve thermometers provide increased temperature resolution and sensitivity, and were used in a feedback heating system to control temperature to ±5.5 μK at 16.5 mK. The³He melting curve and the⁶⁰CoCo temperature scales are found to agree within 2% at 15 mK. The present status of the melting curve scale and the effect of a magnetic field on melting curve thermometry are also discussed.     

Integrated target-ion source unit for on-line production of radioactive short-lived isotopes

A new version of integrated target-ion source unit (ionising target) has been developed for the on-line production of radioactive single-charged ions. The target is able to withstand temperatures up to 2500 ^°C and acts also as an ion source of the surface and laser ionisation. Off-line and on-line experiments with the ionising target, housing tantalum foils as a target material, have been carried out at the IRIS (Investigation of Radioactive Isotopes on Synchrocyclotron) facility. The off-line surface ionisation efficiency measured for stable atoms of Li, Rb and Cs was correspondingly 6% , 40% and 55% at the target temperature of 2000 ^°C and 3-10% for atoms of rare-earth elements Sm, Eu, Tm and Yb at a temperature of 2200 ^°C. The off-line measured values of the ionisation efficiency for stable Gd and Eu atoms by the laser beam ionisation inside the target were 1% and 7%, respectively. The radioactive beam intensities of neutron-deficient rare-earth nuclides from Eu to Lu produced by the integrated target-ion source unit have been measured at a temperature of 2500 ^°C. The results of the integrated target-ion source unit use for on-line laser resonance ionisation spectroscopy study of neutron-deficient Gd isotopes have been also presented.     

Thermal conductivity of PVD TiAlN films using pulsed photothermal reflectance technique

In the present work, we have measured thermal-conductivity of industrial thin film TiAlN with a thickness of around 3 μm. These films are used in machining industry for cutting tools in order to increase their service life. A series of TiAlN coating with a different Al/Ti atomic ratio were deposited on Fe-304 stainless steel (AISI304) substrate by a lateral rotating cathode arc process. The samples were then coated with a 0.8 μm gold layer on top by magnetron sputtering. We present the thermal-conductivity measurement of these samples using pulsed photothermal reflectance (PPR) technique at room temperature. The thermal conductivity of the pure TiN coating is about 11.9 W/mK. A significant decrease in thermal conductivity was found with increasing Al/Ti atomic ratio. A minimum thermal conductivity of about 4.63 W/mK was obtained at the Al/Ti atomic ratio of around 0.72.     

A 200 W diode-side-pumped CW 2 μm Tm:YAG laser with water cooling at 8°C

A water-cooled 785 nm diode-side-pumped high-power CW Tm:YAG laser system at 2 μm is reported. 200 W output power is achieved with cooling water running at 8°C. As far as we know, this is the highest output power for a diode-pumped all solid-state 2 μm Tm:YAG laser. The output corresponds to optical-to-optical conversion efficiency of 11.2%, with a slope efficiency of about 22.8%. To make the system structure simple, only deionized water is used as the coolant instead of alcohol- or glycol-water mixture or the liquid nitrogen in the reported high-power Tm rod laser experiments, which were performed at low temperature near the freezing point of water, or even below.     

First experiments and future prospects at the Daresbury On-Line Isotope Separator

The Daresbury On-Line Isotope Separator (DOLIS) has recently been commissioned, in conjunction with the Nuclear Structure Facility (NSF) 20 MV tandem accelerator, and a³He-⁴He dilution refrigerator. First experiments are concentrating on a study of the decay of the neutron deficient iodine isotopes, extracted from a FEBIAD ion source and implanted at 60 keV into an iron host at 15 mK. As well as measuring iodine magnetic moments, the role of proton excitations across the Z=50 shell gap is being investigated in the even-even tellurium daughter nuclei. An on-line laser facility is also being developed, and first measurements have been made for unstable samarium isotopes     

μ− SR in semiconductorsSR in semiconductors

μ⁻ SR experiments have been performed on Si between room temperature and 6 K. The amplitude of the muon spin precession signal in an applied magnetic field of 0.04 T decreased below 30 K. A zero-field measurement at 6 K revealed a μ⁻ spin precession frequency of 650 MHz. The muonic atom represents an aluminium acceptor in the silicon matrix, its electronic state is responsible for the μSR signal. A possible influence of the γ recoil produced by the X-ray cascade is discussed.     

Absence of low-temperature anomaly on the melting curve of <Superscript>4</Superscript>He

The melting pressure and pressure in the liquid at a constant density of ultrapure ⁴He (0.3 ppb of ³He impurities) have been measured with an accuracy of about 0.5 μbar in the temperature range from 10 to 320 mK. The measurements show that the anomaly on the melting curve below 80 mK, which was recently observed [I. A. Todoshchenko et al., Phys. Rev. Lett. 97, 165302 (2006)], is entirely due to an anomaly in the elastic modulus of Be-Cu from which our pressure gauge is made. Thus, the melting pressure of ⁴He follows the T ⁴ law due to phonons in the whole temperature range from 10 to 320 mK without any attribute of a supersolid transition. The text was submitted by the authors in English.     

Mass Measurements of 114–124,130Xe with the ISOLTRAP Penning Trap Spectrometer

The masses of the xenon isotopes with 114≤A≤123 were directly measured for the first time. The experiments were carried out at the ISOLTRAP triple trap spectrometer at the on-line mass separator ISOLDE/CERN. A mass resolving power of the Penning trap spectrometer of m/Δm≈500 000 was chosen and an accuracy of δm≈12keV for all investigated Xe isotopes was achieved. An atomic mass evaluation was performed and the results of this adjustment are compared with theoretical predictions. The new results for the xenon isotopes and their effects on neighboring nuclides are discussed within the two-neutron separation energy picture. This revised version was published online in July 2006 with corrections to the Cover Date.     

High‐pressure μSR studies of ferro‐ and antiferromagnetic metals

High‐pressure μSR experiments on ferromagnetic nickel and \alpha‐iron and antiferromagnetic chromium are reported. In Ni above 260 K B_Fermi was found to be proportional to the saturation magnetization, whereas at lower temperatures it is temperature independent apart from a small anomaly below 30 K which is presumably caused by a magnetoelastic interaction. There was no evidence for an occupation of metastable sites by the μ⁺ below the Curie temperature. By contrast, in \alpha‐Fe the temperature dependence of \curpartialB_μ/\curpartialp shows a structure which might be attributed to the occupation of excited muon states at elevated temperatures. High‐pressure zero‐field experiments on Cr performed in the temperature regime between 4.5 K and 8 K revealed a pressure dependence of B_μ as large as \curpartialB_μ/\curpartialp=-(89.15\pm 0.06)\times 10^-12 T/Pa. In terms of volume dependence a very large negative Grüneisen parameter \gamma =-27 was obtained. This revised version was published online in July 2006 with corrections to the Cover Date.