Organic Magnetic Materials Studied by Positive Muons

Positive muons can be implanted into organic and molecular magnets in order to study their internal magnetic field distribution and any associated dynamics. The muon behaves essentially as a microscopic magnetometer, sensitive to local magnetic order and magnetic fluctuations. We describe some recent experiments using this technique which were performed on a variety of organic systems, including nitronyl nitroxide magnets and materials with spin-Peierls ground states, MEM(TCNQ)₂ and DEM(TCNQ)₂, and demonstrate how the technique can give information concerning their ground states.     

Positive muon data analysis at ISIS

The pulsed surface muon beam of the Rutherford Appleton Laboratory is well suited to performing μSR measurements in zero and low magnetic fields with the longitudinal set-up. In this paper we describe our data analysis procedure and the effect of the collimation on the spectra. The determination of the efficiency ratio of the telescopes is discussed. We point out that for some measurements it is important to take into account the muon beam structure properly.     

Photo-Production of Muons

The total cross-section for the photo-production of muons in the reaction γ + e^? → μ^? + v_e + v_μ is calculated. The dependence of the total cross-section on the incident photon energy is explicitly shown.     

Development of the pulsed muon facility at ISIS

The ISIS pulsed surface muon facility at RAL is presently undergoing a major expansion to provide three experimental ports with simultaneous single muon pulses at 50 Hz. This upgrade, funded by the European Community (EC), is described together with recent development results which are relevant to its future scientific programme. These new beam lines are expected to be available for experiments in June 1993.     

The development of a facility for radio‐frequency experiments at ISIS

Ferromagnetism has been observed in a family of organic molecular crystals based on the nitronyl nitroxide radical. We present the results of μSR experiments on a number of nitronyl nitroxide compounds. The zero‐field spin precession of muons implanted in diamagnetic states can be used to follow the magnetic order parameter as a function of temperature. Five of the materials studied show magnetic transitions, although the transition temperature and the nature of the magnetic ground state in each case are quite different. μSR can be used to study these ground states and thus help to relate the observed magnetic properties to the crystal structure of each material. This revised version was published online in July 2006 with corrections to the Cover Date.     

A New High-intensity, Low-momentum Muon Beam for the Generation of Low-energy Muons at PSI

At the Paul Scherrer Institute (PSI, Villigen, Switzerland) a new high-intensity muon beam line with momentum p < 40 MeV/c is currently being commissioned. The beam line is especially designed to serve the needs of the low-energy, polarized positive muon source (LE-μ⁺) and LE-μ SR spectrometer at PSI. The beam line replaces the existing μ E4 muon decay channel. A large acceptance is accomplished by installing two solenoidal magnetic lenses close to the muon production target E that is hit by the 590-MeV PSI proton beam. The muons are then transported by standard large aperture quadrupoles and bending magnets to the experiment. Several slit systems and an electrostatic separator allow the control of beam shape, momentum spread, and to reduce the background due to beam positrons or electrons. Particle intensities of up to 3.5 × 10⁸ μ⁺/s and 10⁷ μ⁻/s are expected at 28 MeV/c beam momentum and 1.8 mA proton beam current. This will translate into a LE-μ⁺ rate of 7,000/s being available at the LE-μ SR spectrometer, thus achieving μ⁺ fluxes, that are comparable to standard μ SR facilities.     

Muons from high-energy cosmic photino

Summary The muon production at photino-nucleon interaction for high-energy photino (E⊂)10⁴GeV) is studied. The production of muons is the result of the creation and the subsequent decay of charmed hadrons. The quark subprocess considered is . In the calculation the chains of reactions and c→D→μ are taken into account. The main contribution to a muon flux is given by the production of -quark. Muon fluxes from high-energy cosmic photino absorbed in water (ground) and atmosphere are calculated. For muon energy above −2.10³GeV the ration of equilibrium underground muon flux to photino flux decreases with a rise of energyE because of nuclear interactions of D-mesons at decay length, and at energy −2·10⁵GeV the vertical muon flux created in the atmosphere becomes comparable with underground equilibrium flux. The production of muons by photino is less effective than by neutrino: the ratio is higher than for all energies. On the other hand, the cross-section at superhigh energies is by a factor of −10² larger than the cross-section. This fact gives some signature of photino flux from source in case of combined observations by sea-level EAS arrays and underground detectors: large EAS flux and relatively small flux of underground high-energy muons.

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Riassunto Si studia la produzione di muoni nell'interazione fra il fotino e il nucleone per il fotino ad alta energia (E>-10⁴GeV). La produzione dei muoni è il risultato della creazione e del conseguente decadimento di adroni con charm. Il subprocesso dei quark considerato è . Nel calcolo sono considerate le catene di reazioni e c→D→μ. Il contributo principale al flusso dei muoni è dato dalla produzione del quark . Si calcolano i flussi dei muoni dal fotino cosmico ad alta energia assorbito nell'acqua (terra) e nell'atmosfera. Per un'energia dei muoni sopra ≈2·10³GeV il rapporto tra il flusso dei muoni sotterranei in equilibrio e il flusso dei fotini diminuisce al crescere dell'energiaE a causa delle interazioni dei mesoni D a lunghezza di decadimento, e ad un'energia ∼2·10⁵GeV il flusso dei muoni verticale creato nell'atmosfera diventa paragonabile al flusso in equilibrio sotterraneo. La produzione di muoni da parte del fotino è meno efficace di quella causata dal neutrino: il rapporto è maggiore di per tutte le energie. D'altra parte, la sezione d'urto ad energie super alte è maggiore della sezione d'urto di un fattore di ∼10². Essa dà un qualche segno del flusso dei fotini dalla sorgente in caso di osservazioni combinate da schiere EAS a livello del mare e rilevatori sotterranei: un alto flusso EAS e uno relativamente ridotto di muoni sotterranei ad alta energia.

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Реэуме Исспедется роздение муонов ири взаямцеиствиях фотино с нуклонами ири энергиях фотино (E>=10⁴ ГэВ). Роздение муонов ирецтавляет реэултат обраэования и поцледыюшего раццада ачарованных адронов. Рааццматqrиваетця кварковыи цубпроцецц . При вычициениях учитываутця кварковыи реакций и c→D→μ. Оцновной вклац в мюнный поток опредчтця рождением -кварка. Вычицяютця потокоцмичецнмх фотино, поглощенные в воде (эемле) и в атмосфере. Для мюонов с энергиями выще ∼ 2·10³ ГэВ отнощение равновесного потока мюонов поц эемлей к пооку фотино уменящается с ростом энерпии Э иэ-эа ядерных бэаимодействий Д-меэонов на длине распада, и при энергии ∼2·10⁵ ГэВ вертикальный поток мюнов, образованных в атмосфере, становится сравнимым с равновесным потоком под землей. Рождение мюонов фотино оказывается менее эффективным, чем рождение мюонов нейтрино: отношение выше, чем для всех энергиях. С другой стороны, поперечное сечение при супервысоких энергиях оказывается примерно в 10² раз больше, чем сечение. В работе приводятся некоторые сигнатуры для потока фотино от источника в случае комбинированных наблюдений с помощью антенн широких атмосферных ливней на уровне моря и с помщью подземных детекторов: большой поток широких атмосферных ливней и относительно малый поток подземных мюонов высоких энергий.

     

Muons and muonium in cryocrystals

We present a collection of measurements of the muon and muonium asymmetries and relaxation parameters in cryocrystals of N₂, CO, Xe,¹³⁶Xe and Ne as functions of temperature. Generally, the fractions of the two species can be attributed to a competition between the formation of muonium or a diamagnetic species, where processes involving transport of spur electrons are important.     

PEARL: the high pressure neutron powder diffractometer at ISIS

The PEARL instrument at ISIS has been designed for, and dedicated to, in situ studies of materials at high pressure, using the Paris–Edinburgh press. In recent years, upgrades to the instrument have led to improvements in data quality and the range of achievable pressures and temperatures; currently 0.5–28?GPa and 80–1400?K. This paper describes the technical characteristics of the instrument, its current capabilities, and gives a brief overview of the science that has been performed, using representative examples.     

Radio-frequency μSR experiments at the ISIS pulsed muon facility

This paper explores the use of pulsed radio-frequency (RF) techniques to remove the frequency limitations imposed on conventional transverse muon spin rotation (μSR) experiments at a pulsed muon source by the finite muon pulse width. The implementation of the 90° pulse technique is demonstrated by observing the free precession signal of diamagnetic muons implanted in polythene, the change in signal amplitude as a function of RF pulse length is plotted and the precise condition for a 90° pulse determined. The technique is evaluated by comparing measurements made using conventional spin rotation experiments to those employing pulsed RF methods. The potential for applying standard NMR multiple-pulse methods to the μSR experiment is considered and the use of two-pulse RF sequences (90° _x ?τ?90° _x and 90° _x ?τ?180° _x ) to form a muon spin echo demonstrated.     

无机物高温下微结构的研究

上海市钢铁冶金新技术开发应用重点实验室 ( SELF)的 U- 1 0 0 0型 Raman谱仪经过改造已能用两种方式在高温下进行测定。其一是由共焦显微镜 -显微加热台构成的“空间分辨法”。其二是利用电阻炉加热的“时间分辨法”。SELF正在进行冶金熔渣的微结构研究。这类物质的物性 (从冶金学考虑 ,首先是熔渣中的组元活度 )数据已有不少报道 ,但为了促进技术的发展 ,急需鉴别它们的可靠程度。并且 ,还有大量未定值的物性 (例如 :粘度、表面张力、介电常数、扩散系数等 )有待预测。而打通微观结构和宏观物性之间的渠道 ,则是解决上述问题的根本途径。本文介绍了 SELF在 <2 0 0 0 K条件下的 HTRS(高温 Raman谱 )实测和 DFT- MD计算机模拟两种研究手段 ,定量分析冶金熔渣微结构的基本思路以及若干初步的结果。事实上 ,冶金熔渣、地学中的岩浆、玻璃和陶瓷 ,乃致某些宝石都可认为是一大物类 ,所以 SEL F同时也正在进行着烯土类熔盐和功能晶体的研究。     

Variations of Cosmic Ray Muons during Thunderstorms

Journal of Experimental and Theoretical Physics - This article briefly reviews the results of an experiment initiated by A.E. Chudakov. The first results were obtained in pioneering works under his...     

On the Mechanism of Temperature Variations in the Average Energy of Muons at Large Depths

Journal of Experimental and Theoretical Physics - Sources of seasonal temperature variations in the average energy of the muon flux detected in the LVD experiment have been discussed. It has been...     

Muons and neutrinos in the cosmic radiation

Summary This report covers 86 papers presented in HE4 and HE5 sessions of the XXIV ICRC. The topics of the papers are atmospheric muons and neutrinos, muon bundles, horizontal air showers, ?muon astronomy?, neutrino oscillations, high-energy neutrinos and neutrinos from collapsing stars. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

On the Decay Rate of Bound Muons

The rigorous calculation of the Bound muon decay rate performed by Überall seems exhaustive. However an important effect not considered by him is the recoil of the nucleus. The present paper reports the computation of the decay rate using a perturbative type of wavefunction, similar to that used by Überall. In addition, the nuclear recoil effect has been taken into account and the results, as expected, exhibit a light increase over Überall's values, in particular for the lighter elements, where recoil is more pronounced. Screening by the atomic electrons and the effect of vacuum polarisation have also been considered, but eventually found to be negligible.     

宇宙线μ子的大气契仑柯夫光像

给出理想条件下聚光镜焦平面上单个μ子大气契仑柯夫光像的理论结果．简要地介绍在标定第二代大气契仑柯夫光成像望远镜中的应用．     

Muons of very and ultra-high energy cosmic rays

In many cosmic rays experiments at very and ultra-high energies, an excess of muons (including those of very high energy, >100 TeV) is observed that cannot be explained within existing models of hadron interactions. This excess is usually explained in terms of the heavier mass composition of primary cosmic rays. However, the excess over the predicted values even for extremely heavy compositions, and especially the observed excesses of muons with energies of >100 TeV, requires that we consider other possibilities with respect to the generation of muons, including changes in models of hadron interaction.