C. J. Ashworth

Deformation in the light Br isotopes

The nuclear ground state spins of the odd-A Br nuclides75, 77, 79Br with Z=35 are all 3/2−. Nilsson orbital calculations show that the 35th proton occupies the f5/2 [301]3/2− orbital for ε<0.20 and the p3/2 [312]3/2− orbital at larger deformations. The magnetic moments of these two states differ by a factor of two, giving clear evidence for the magnitude of the ground state deformation. Low Temperature Nuclear Orientation measurements made in Oxford and Bonn on76, 77gBrFe prepared at ISOLDE, and on line at the SERC Daresbury Laboratory on72, 74m, 75BrFe, have yielded the magnetic moments of these isotopes, using a two non-zero field model with magnetic hyperfine fields of +81.38(6) T and 26(2) T. The spin of the73Br ground state is also deduced. An interpretation of the ground state configurations of these isotopes is given.

On-line low-temperature nuclear orientation at DOLIS-COLD

Abstract The Daresbury On-Line Isotope Separator-Cryogenic On-Line Device (DOLIS-COLD), consisting of a 3He-4He dilution refrigerator coupled to an on-line isotope separator, has proved to be a powerful system for the study of nuclei far from stability. The design and performance of DOLIS-COLD is discussed. To illustrate the capabilities of the system, examples of magnetic moment measurements by static low-temperature nuclear orientation and by NMR on oriented nuclei (NMR/ON) are presented.

Nuclear orientation below 1 mK: Development and applications

The Oxford top-loading PrNi5 nuclear demagnetisation stage /1/ has been further developed to reach temperatures below 1 mK. The hyperfine field for71As in nickel has been measured by low temperature nuclear orientation as 14.61(36)T. Measurements on transitions in71Ge yield spin values 3/2 (1299 kev and 1139 kev) and 5/2 (1027 kev) and 5 E2/M1 mixing ratios are given.

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, 136Cs were implanted at room temperature into polycrystalline and single crystal iron. NO values for the (average) magnetic hyperfine field Bhf (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.

On-line nuclear orientation and relaxation studies of Cs isotopes

The hyperfine field of CsFe has been measured to be (+)40.8(0.7)T, using the technique of on-line low temperature nuclear orientation. The time dependent relaxation of121CsmFe has also been investigated using a new technique, giving a Korringa constant Ck of 0.059 (15) sK. From this, an effective relaxation time of 3.0 (0.8)s can be deduced for the short lived118Csm(T1/2=17s). This value has then been used to extract the magnetic moment of118Csm to be |μ|=5.4 (1.1) nm.

The NMR of 116Sbg cryogenically oriented on-line in iron

Abstract The resonant destruction of gamma-ray anisotropy from 116 Sb g (t 1 2 =16 m , I π =3 + ) has been observed at 161.65 ( MHz, using the technique of NMR/ON. The deduced magnetic moment is |μ|=2.175(9) μ N. The change in the Iπ=3+ magnetic moments between 116Sb and 120Sb can be accounted for by variation inthe odd-neutron contribution, the odd proton in these antimony states behaving as a spectator.

Electric quadrupole orientation in zinc. The variation of electric field gradient with atomic number through the 4sp series

Using the top-loading PrNi5 nuclear demagnetisation stage /1/ to reach temperatures close to 1mK, electric quadrupole orientation of trace 4sp series impurities in zinc has been measured. Results establish the variation of the electric field gradient at impurity nuclei in this series and also yield the ratio of the electric quadrupole moments of71As and72As.

Nuclear orientation of136Cs: Reorientation in the 0.3S 7-isomer of136Ba

Properties of the decay of136Cs to136Ba are deduced from low temperature nuclear orientation studies. Of particular interest is the observation of attenuated anisotropy in transitions from the 7- 0.3s isomer at 2031 keV. This is ascribed to the presence of mixed electric/magnetic interaction in this state which is not collinear with the parent136Cs quantisation axis.

Magnetic hyperfine field of arsenic in nickel by NMR/ON of71,72As

The magnetic hyperfine splitting frequencies of71AsNi and72AsNi in a 0.11 Tesla external magnetic field have been determined by NMR/ON method as 66.00(6) MHz and 106.17(13) MHz respectively. Using the known magnetic moments of μ(71As)=1.6735(18) and μ(72As)=−2.1566(3), the hyperfine fields were deduced asBhf(71AsNi)=12.824(19) Tesla andBhf(72AsNi)=12.807(16) Tesla.

The sign of the magnetic dipole moment of the ground state of122I

The sign of the nuclear magnetic dipole moment of the ground state of122I has been determined to be positive using a novel experimental technique. The technique investigates the asymmetry of positron emission by detecting the 511 keV gamma-rays produced on the annihilation of the positrons. The method would appear to have general validity for studying the sign of the magnetic moment in other cases where theβ+ decay is relatively simple.