Interaction of slow neutrons with the isotopes of molybdenum

Coherent neutron scattering lengths and total cross sections were measured on samples of ordinary Mo and isotopically enriched samples. From the experiments with neutrons of 0.57 meV and 1.26 eV the following values have been obtained:

1. the coherent scattering lengths (in fm) of the bound atoms of Mo (6.715±0.020) and for the isotopes with the mass numbers 92 (6.93±0.08), 94 (6.82±0.07), 95 (6.93±0.06), 96 (6.22±0.06), 97 (7.26±0.08), 98 (6.60±0.07) and 100 (6.75±0.07);
2. the incoherent scattering cross section at zero-energy for ordinary Mo: σ_i=0.02 ± 0.02 barn;
3. the absorption cross sections (in barn) for Mo (2.48 ± 0.04) and for the isotopes with the mass numbers 95(13.4 ± 0.3), 97(2.5 ± 0.2) and 100(0.4 ± 0.2). The relation of the present results to the resonance parameters of the neutron — Mo interaction has been discussed.

     

Interactions of neutrons with gallium and its isotopes

Coherent neutron scattering lengths and total cross sections were measured on elemental Ga, Ga-compounds and on isotopically enriched samples at neutron energies from 0.5 meV up to 143 keV using different techniques. From the experimental data the following quantities could be obtained:

the coherent scattering length of Ga and the spin state scattering lengths of the isotopes.

the potential scattering radii (R′)

the absorption cross sections of Ga,⁶⁹Ga,⁷¹Ga and⁷⁵As.

As derived quantities are given the coherent and incoherent cross sections and the resonance spin scattering lengths for theJ=1 andJ=2 states of⁷⁰Ga and⁷²Ga. The physical meaning of these data and ofR′ and the comparison with the resonance parameters are considered.     

Scattering of slow neutrons by arsenic and selenium isotopes

Coherent neutron scattering lengths and free cross sections were measured for arsenic, for ordinary selenium and its isolated isotopes. By means of the Cristiansen filter technique the following scattering lengths for the bound atoms were obtained (in fm):b(As) =6.58(1) [b ₊=6.04(5) andb _?=7.47(8)],b(Se)=7.970(9),b(⁷⁶Se)=12.2(1),b(⁷⁷Se) =08.25(8),b(⁷⁸Se)=8.24(9),b(⁸⁰Se)=7.48(3) andb(⁸²Se)=6.34(8). Transmission measurements with neutrons of 1.26 eV and 5.19 eV resulted in an energy independent free scattering cross section for arsenic ofσ _{s, t}=5.40(3)b (in the eV-region). For ordinary selenium energy dependent free cross sections ofσ _{s, t}(1.26 eV)=7.9(1)b andσ _{s, t} (5.19 eV)=7.55(3)b were found. The results were compared with the resonance parameters of the nuclei and with different sets of potential scattering radii. Thus it could be concluded that there is no evidence for a bound state of the neutron-nucleus compound⁷⁵As+n but a clear evidence for strong bound levels of⁷⁶Se+n and⁷⁷Se+n.     

Interactions of slow neutrons with nuclides of antimony,tellurium and iodine

Coherent neutron scattering lengths and total cross sections have been measured on samples of ordinary Sb, Te, I and on isotopically enriched compounds. From the experimental data for neutron energies of 0.57 meV, 1.26 eV and 5.2 eV the following data were obtained: the coherent scattering lengths (in fm) of the bound atoms Sb (5.57±0.03);¹²¹Sb(5.71±0.06),¹²³Sb(5.38±0.07); Te(5.80±0.03) and for its isotopes of the mass number 122(3.8±0.2); 123(?0.05±0.25?i·0.100); 124(7.95±0.10); 125(5.01±0.08); 126(5.55±0.07); 128 (5.88±0.07); 130(6.01±0.07). the thermal absorption cross sections (in barn) for Sb(4.91±0.05);¹²¹Sb(5.77±0.12);¹²³Sb(3.8±0.2); Te(4.05±0.05) and I(6.15±0.06). The combination of the measured values of scattering lengths and -cross sections resulted in data for coherent and incoherent cross sections. Taking account of resonance data a complete set of spin state- and reconance scattering lengths has been obtained and discussed.     

Interaction of slow neutrons with natural terbium,holmium and erbium and its isotopes

Coherent neutron scattering lengths and total cross sections have been measured on samples of ordinary Tb, Ho and Er and on isotopically enriched Er-compounds. From the experiment the following data were obtained:

• - the coherent scattering lengths (in fm) of the bound atoms ¹⁵⁹Tb(7.34 ± 0.02), ¹⁶⁵Ho(8.44 ± 0.03), ^ordEr(7.79 ± 0.02), ¹⁶²Er(9.01 ± 0.11), ¹⁶⁴Er(7.95 ± 0.14), ¹⁶⁶Er(10.51 ± 0.19), ¹⁶⁷Er(3.06 ± 0.05), ¹⁶⁸Er(7.43 ± 0.08), and ¹⁷⁰Er(9.61 ± 0.06)
• - the thermal absorption cross sections (in b) ¹⁴¹Pr(12.7 ± 0.6), ^ordNd(58 ± 1), ¹⁵⁹Tb(30 ± 2), ¹⁶⁵Ho (65 ± 2), ^ordEr (145 ± 2), ¹⁶⁶Er (18 ± 2), ¹⁶⁷Er(568 ± 9), ¹⁶⁸Er(2.3 ± 0.3), and ¹⁷⁰Er(15 ± 1). In combination with the resonance parameters, the measured coherent scattering lengths allowed the determination of potential scattering radii R′ which are of particular interest for the optical model theory.

     

Scattering and resonance properties of the interaction of slow neutrons with the isotopes of silicon and sulfur

In¹¹⁷Te,¹¹⁹Te and¹²¹Te isomeric states withJ ^π=5/2⁺, 5/2⁺ and 7/2⁺ and half-lives of 19.1(9)ns, 2.2(2) ns and 86(6) ns, respectively, have been identified at low excitation energies using (α, 2n) reactions on enriched^115–119Sn targets. Positive parityΔJ=1 bands built on these isomeric states have been observed up to 17/2⁺. The states are interpreted as members of rotational bands built on deformation driving 5/2⁺ [402] and 7/2⁺ [404] Nilsson orbitals which overcome theN=64 subshell gap. The irregular level spacings and electromagnetic properties of the bands are well explained in Coriolis calculations. The moment of inertia parameter as function of collective angular momentum has been derived from the doubly even Te cores. The hindrance of the band head deexcitation may be caused by shape fluctuations of these transitional nuclei.     

Interaction of low-energy neutrons with Nd isotopes

Low-energy neutron data for even-even isotopes 1^142–150Nd are considered. It is shown that the diffuseness parameter noticeably changes in going from one isotope to another (from a = 0.55 fm for ¹⁴²Nd to a = 0.75 fm for ¹⁵⁰Nd), which agrees with the theoretical indications of a decrease in the skin thickness for nuclei with closed shells. The analysis points to the possible existence of the semimagic number Z = 58.     

Interaction of slow neutrons with natural Rutenium,Rhodium, Cadmium and Thallium and some of their isotopes

By means of Christiansen filter technique the following bound coherent neutron scattering lengths were obtained:^natRu:b=7.02 ± 0.02 fm¹⁰⁸Cd:b=5.31 ± 0.24 fm¹⁰³Rh:b=5.90 ± 0.04 fm¹¹⁰Cd:b=5.78 ± 0.08 fm^natTl:b=8.773 ± 0.015 fm¹¹¹Cd:b=6.47 ± 0.08 fm²⁰³Tl:b=8.51 ± 0.08 fm¹¹²Cd:b=6.34 ± 0.06 fm²⁰⁵Tl:b=8.87 ± 0.07 fm¹¹⁴Cd:b=7.48 ± 0.05 fm¹¹⁶Cd:b=6.26 ± 0.09 fm In combination with some total cross section measurements with neutrons in the eV-energy range and with the compiled resonance parameters we deduced consistent sets of spin state scattering lengths and potential radii.     

Interaction of neutrons with zinc and its isotopes

Coherent neutron scattering lengths and total cross sections have been measured for elemental Zn,Zn-compounds and on isotopicly enriched samples for neutron energies from 0.5 meV up to 143 keV using different techniques. From the experimental data the following quantities were obtained:

the coherent scattering lengths (b in fm) of Zn (5.689±0.014);⁶⁴Zn (5.23±0.04);⁶⁶Zn (5.98±0.05);⁶⁷Zn (7.58±0.08;b ₊=9.4±0.5/5.8±0.5;b _?=5.0±0.7/10.1±0.7);⁶⁸Zn (6.04 ±0.03);

the potential scattering radii (R′ in fm) of Zn (6.2±0.2),⁶⁴Zn (6.0±0.3) and⁶⁶Zn (6.2 ±0.3);

the absorption cross sections (σ _γ at 0.025 eV in barn) of Zn (1.11±0.02);⁶⁴Zn (1.1 ±0.1) and⁶⁶Zn (0.62±0.06).

Derived quantities are the “zero energy” scattering cross sections (σ ₀ in barn) for Zn (4.128±0.010) and⁶⁷Zn (7.8±0.3) and the incoherent bound cross sections of Zn (0.061 ±0.023) and⁶⁷Zn (0.6±0.4). In the epithermal region the Zn-cross section can be described by introduction of two strong bound levels of⁶⁷Zn+n for which estimated parameters are given.     

Focussing of slow neutrons with cylindrical zone plates

We report on the successful focussing of a slow neutron beam by means of a cyclindrical Fresnel zone plate.     

Interactions of fast neutrons with45Sc

The surface resistance of lead was measured in a coaxial cavity at frequencies between 375 and 5000 MHz and temperatures between 4.2 and 1.5 °K. The residual resistance was determined from these data.     

The scattering of slow neutrons by cobalt

Different techniques have been used to determine with slow neutrons the coherent scattering amplitude b_c and the total scattering cross-section σ_sc of Co. We found values for the bound atom b_c=2.78+0.04 fm and for the free nucleus σ_sc=5.95+0.05 barns.From these quantities, the spin state scattering amplitudes b₊ and b_? corresponding to the compound nucleus states of spin I+1/2 or I?1/2 have been determined as b₊=?2.78±0.04 fm and b_?=+9.91±0.06 fm. These results are not in agreement with previous data, but they are found to be consistent with data obtained from resonance parameters.     

Scattering of slow neutrons by bound nuclei

TheT-operator for scattering of slow neutrons by a system of bound nuclei is calculated up to quadratic terms in the scattering length. Binding effects as well as effects of multiple scattering have to be included in order to avoid inconsistencies. For the discussion of binding effects one can adopt methods developed by Dietze and Nowak [1] for treating scattering by an elastically bound nucleus. In particular the case of coherent elastic scattering is discussed: we show how the corrections can be expressed in terms of correlation functions and that binding effects are most important for scattering by light nuclei.     

Spin orbit interaction and polarization of slow neutrons

It is shown that the spin orbit (LS) interaction of an anomalous magnetic moment is twice that of a Dirac moment. In neutron scattering this interaction leads to an imaginary spindependent scattering amplitude. Possible experiments are discussed, where interference ofLS scattering and nuclear scattering in crystals without inversion symmetry leads to detectable neutron polarization.     

The scattering of slow neutrons by phosphorus and nitrogen

The coherent scattering lengthsb and the free cross sections for the scattering of slow neutrons by P and N were measured on powdered samples. From the results we derived data for the incoherent cross sections and for the spin state scattering lengths. We found for phosphorus:b=5.13±0.01 fm, σ_free=3.134±0.010b and σ_inc=0.006±0.016b, and for nitrogen:b=9.36±0.02 fm, σ_free=10.03 ±0.08 b and σ_inc=0.4±0.1 b. Derived values for resonance parameters of N are given.     

Hyperfine anomaly measurements in francium isotopes and the radial distribution of neutrons

We have performed precision measurements in a magneto-optical trap of the 7P_1/2 hyperfine structure of the isotopes ^209-210Fr. The ratio of these hyperfine constants to the previously measured 7S_1/2 ground state values reveals a significant hyperfine anomaly. This anomaly results from the different radial dependence of the electron density in the two atomic levels. The measurements are sensitive to changes in the radial distribution of the neutron magnetism. This revised version was published online in August 2006 with corrections to the Cover Date.     

Production of slow muonic hydrogen isotopes in vacuum

Muonic hydrogen isotopes (μ⁻ p, μ⁻ d, and μ⁻t) are simple quantum mechanical systems ideally suited for studies of numerous fundamental phenomena in electroweak and strong interactions as well as in applied areas such as muon chemistry or muon catalyzed fusion. Emission of muonic hydrogen isotopes into vacuum helps to overcome the limitations which are normally imposed on conventional investigations with gaseous and liquid targets. A proof of principle experiment for this new technique was performed at TRIUMF last year. Negative muons with 30 MeV/c momentum were stopped in a thin film of solid hydrogen and produced very low energy μ⁻d in vacuum. The distribution center of the normal velocity components of emitted μ⁻d atoms was measured to be ∼1 cm/μs. The yield of μ⁻d in vacuum is an increasing function of H₂ film thickness δ up to a value of δ≥1 mm.     

New experimental test of dispersion law for very slow neutrons

The results of an experiment on transmitting UCN through a rotating disc made of silicon single crystal are reported. They demonstrate that the transmission of the sample remains constant if it moves parallel to its surface. The range of neutron velocities in the system of reference associated with the sample is 6–38 m/s$6\text{–}38\text{m}/\text{s}$. It is found that the real and imaginary parts of the effective potential are constant to within 3×10⁻³$3\times {10}^{-3}$.