Anomalous nuclear spin relaxation in liquid 3He4He mixtures

The longitudinal relaxation time, T₁, was measured in liquid ³He⁴He mixtures with molar concentrations of ³He of 0.12, 0.20 and 0.45 under saturated vapor pressure. λ-anomaly was clearly observed in the temperature dependence of T₁.     

Temperature dependence of spin diffusion coefficient and T2 for dilute 3He in solid 4He

Spin diffusion coefficients D and NMR line widths 1/T₂ have been measured as a function of temperature for ³He in solid ⁴He at fractional concentrations down to 10^-4. Minima are seen in D and T₂ and the existence of impuritons is confirmed.     

Doppler-shift of fourth sound in flowing 3He4He mixtures

The Doppler-shift Δu₄ of fourth sound propagating in flowing superfluid ³He⁴He mixtures is calculated for arbitrary ³He concentration c. For c ? 0.15 and at T ? 1.4 K a cancellation of the dominant terms in the equation for Δu₄ results in a concentration independent shift.     

Cooling dilute 3He4He mixtures to 0.6 mK

We have cooled a ³He⁴He solution to the lowest temperatures yet achieved, 0.58 mK, and find no evidence for a superfluid transition in the dissolved ³He. We have measured the thermal boundary resistance between this solution and sintered 700 Å silver powder, and find that R is proportional to T^?2 between 0.8 mK and 4 mK.     

High temperature spontaneous ferromagnetism and other magnetic phenomena in liquid 3He and 3He4He dilute mixtures

Equilibrium ferromagnetic ordering in liquid ³He at temperatures T ? 0.3 K due to long-wavelength spin fluctuations is predicted. The magnetocaloric effect and other thermodynamic properties of ³He↑ are discussed. The properties of ³He↑⁴He solutions are considered in the case of a restricted geometry.     

Pulsed NMR frequency shifts in superfluid 3He

We report the first measurements of the NMR frequency in ³He A and B under conditions where the net magnetization, M, is tipped far from its equilibrium direction along H_O. In ³He A the frequency shift ω - γH_O varies from the continuous wave value at tipping angle Φ = 0 to a negative shift at Φ = 180°. In ³He B no frequency shift is observed, however for Φ ? 100° a beat pattern is seen to develop in the free induction decay envelope.     

A study of 3He-4He tunneling motion in solid 3He-4He mixtures by means of T1ϱ measurements

³He spin relaxation time in the rotating frame (T_1?) has been measured for 2% ³He in ⁴He solid samples of different molar volume at exchange plateau region (0.5 K). From the data, the characteristic frequency by which a ³He atom exchanges its position with a neighboring ⁴He atom is determined.     

Transverse zero sound propagation in superfluid 3He

Transverse zero sound should propagate in superfluid ³He only in a rather narrow range below T_c.     

Thermodynamics of textures in superfluid 3He

The contribution of the textures in the B-phase of superfluid ³He to the specific heat has been calculated. The specific heat is found to be divergent near T_c.     

The elastic scattering of 3He on 4He at medium energies

The differential cross section of the elastic scattering ³He(⁴He, ⁴He)³He has been measured at center of mass energies E_c.m. between 28 and 44 MeV and in the c.m. angular range of 20° to 160°. The ³He polarization P at E_c.m. = 42 MeV and θ_c.m. = 132° was determined in a double scattering experiment. The analysis of the cross section data with the optical and the cluster model has been described previously. The phase shifts obtained in the cluster model calculations were used as starting values in a phase shift analysis. The resulting final real phase shifts and elasticity parameters give good fits to the cross section data. At 44 MeV the elasticity parameters show a pronounced odd-even dependence on angular momentum which had been found already in the case of the real phase shifts. The result of the polarization experiment |P| < 0.22 is consistent with cluster model predictions.     

This mysterious liquid 3He

The spin contribution to the heat capacity and entropy of ³He has been singled out. With increasing T the spin entropy reaches a constant value, different from ln 2. The spin contribution ≈ ln T can be observed in the temperature dependence of the pressure.     

Study of the 8Be first T = 2 state with 4He + α and 7Li + p initiated excitation functions

In a high resolution study of the ⁴He + α initiated excitation functions in the region of the ⁸Be first T = 2 state, weak resonance excursions have been observed in some reaction channels yielding the total width Γ = 14.7 ± 4.0 keV. No resonance excursion has been observed in the ⁴He + α elastic scattering yielding the branching ratio Γ_α/Γ ≦ 0.003 for the decay of the ⁸Be first T = 2 state into two α-particles. For the decay to the low-lying states of ⁶Li and ⁷Li lower limits of the branching ratio are given. The reinvestigation of the ⁷Li+p initiated excitation functions revealed no resonance anomaly in the region of the ⁸Be first T = 2 state. The upper limit Γ_p/Γ ≦ 0.023 has been derived for the proton decay to the ⁷Li_g.s.. The results are compared with previous measurements and with shell-model calculations.     

Static susceptibility and longitudinal resonance frequency of superfluid 3He B

The static susceptibility and the longitudinal resonance frequency of superfluid ³He B have been measured at 18.7 bar from T_c to 0.27 T_c using continuous wave transverse NMR.     

Investigation of the 6Li(d, α)4He reaction between 1.5 and 11.5 MeV

The differential cross section σ₀(θ) and the analysing powers T₁₁(θ), T₂₀(θ), T₂₁(θ) and T₂₂(θ) of the reaction ⁶Li(d, α)⁴He have been measured for twelve energies between 1.5 and 11.5 MeV at c.m. angles between 3.5° and 90°. The results were fitted with Legendre polynomials. The energy dependence of the resulting coefficients indicates resonance-like behaviour at several energies corresponding to excitation between 22 and 32 MeV in ⁸Be. The reaction ⁶Li(d, α)⁴He shows excellent features as an analyser for deuteron vector and tensor polarization over the whole energy range investigated.     

3He D-state effects in (d, 3He) reactions

The tensor analysing power of the ²⁷Al(d, ³He)²⁶Mg reaction has been measured at E_d = 12.4 MeV. The results are reproduced by predictions of the DWBA including D-state components in the ³He wave function. The magnitude of the tensor analysing power provides information on the asymptotic D-state to S-state ratio in the ³He wave function. The value obtained for ³He is in agreement with the corresponding value for ³H.     

Elastic scattering of 56 MeV polarized deuterons on 4He

The differential cross section and the vector and tensor analyzing powers A_y, A_xx, A_yy and A_xz were measured for the d-⁴He elastic scattering at 56 MeV. The measurement of A_xz was performed using a deuteron beam polarized in the horizontal plane. An optical-model analysis of the experimental data was carried out. The magnitude of the tensor analyzing powers could not be reproduced without the tensor potential. By including the T_R type tensor potential, the optical-model calculations give a reasonable reproduction of the experimental data at θ_c.m. < 120°. The obtained T_R tensor potential was much stronger than that predicted by the folding model. The strength of the real T_R potential was roughly in accordance with that obtained from the optical-model analysis of d-⁴He elastic scattering at 20.2 MeV.     

Superfluidity of 3He in dilute solutions of 3He in liquid 4He

The possibility of superfluidity of ³He in dilute solutions of ³He in liquid ⁴He is investigated, and the corresponding critical temperature is estimated. The results indicate S-state pairing, i.e., for small concentrations of ³He, the highest transition temperature is obtained for L = 0, but the obtained critical temperatures are very low.     

Search for a narrow resonance in 6Be with the 4He(3He,n) reaction

The ⁴He(³He, n)⁶Be reaction has been investigated at 36.20 MeV bombarding energy in search for a narrow resonance near the ³He-³He threshold which has been proposed as a possible explanation for the missing solar neutrinos in Davis' experiment. Neutrons have been detected at θ_b = 0° with an effective resolution < 25 keV in the c.m. system, in coincidence with protons emitted at θ_p = 50°. No indication for the existence of such a resonance has been found and an upper limit (dσ/dω)_res ≦ 7.5 μb/sr has been established.     

Measurement of the analyzing power of the 3He(d, p)4He reaction below 1 MeV

The analyzing powers iT₁₁, T₂₀, T₂₁ and T₂₂ have been measured for the reaction ³He(d, p)⁴He at laboratory energies of 344, 465 and 727 keV. A polarized deuteron beam was used with quantization axis oriented perpendicular to and at 54.7° to the incident beam direction. With semi-conductor proton detectors in two perpendicular planes all four analyzing powers could be determined. The beam polarization was determined using the ³H(d, n)⁴He reaction at a mean energy of 130 keV. The uncertainty in this analyzing power and the effect on the results is discussed. The analyzing powers have been fitted to a Legendre polynomial expansion to four or five terms and the resulting coefficients tabulated. The results indicate that d-waves contribute to the reaction only through the ${}^4\text{D}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ entrance channel and their contribution falls off both above and below the $\text{3}\text{2}{}^{\mathrm{+}}$ resonance at 430 keV.     

The elastic scattering of polarized 3He by 3He and excitation in the 6Be system

Angular distributions of the polarization in the elastic scattering of ³He by ³He have been measured at eight energies between 18 and 33 MeV, corresponding to excitation of ⁶Be between 20.5 and 28 MeV. The measurements were made using the 33 MeV polarised ³He beam at the University of Birmingham Radial Ridge cyclotron and a small gas target. The data have been analysed in terms of real and complex phase shifts. The deduced phase shift energy dependence cannot be associated with a single isolated level in ⁶Be, however an application of the two-level R-matrix formula reveals some broad L = 3 structures around E_x = 25 MeV.