T. Itahashi

Gamma rays and neutrons following preequilibrium 165Ho(p, xcnypγ) reactions at Ep = 60 MeV

Abstract Neutrons and γ-rays following 60 MeV proton bombardment of 165Ho were measured in coincidence with discrete γ-rays characteristic of the reaction channels (residual nuclei). The cross sections for the (p, xcnγ) reactions with x = 2–6, the γ-ray multiplicities, and the energy and angular distributions of the emitted neutrons were analyzed in terms of the preequilibrium and equilibrium deexcitation processes. Characteristic behaviours of the preequilibrium process were found in the (p, 2nγ) and (p, 4nγ) reactions where the sum ET, = ∑xEi of the energies Ei of the emitted neutrons was large, while those of the equilibrium process were typical for the (p, 6ny) reaction with small ET. The reactions are well reproduced by the expression σ. ≈0.35∑xσ (2, x−2) + 0.4∑xσ(1, χ−1)+ 0.25∑xσ(0, x), where σ(np, nc) stands for emission of np neutrons at the preequilibrium stage followed by evaporation of nc neutrons at the equilibrium stage.

Proton-neutron correlation in the deuteron breakup at 56 MeV and prior-form DWBA analysis

Abstract Proton-neutron angular correlations in the 12 C, 51 V and 118 Sn(d, pn) reactions have been measured at 56 MeV to investigate the deuteron breakup process. The elastic breakup which leaves the target nucleus in its ground state dominates the coincident spectra. The elastic breakup cross sections are estimated to be 36–48% of the inclusive breakup yields at 15° or 17.5°. In the angular correlations the protons are emitted predominantly on the side of the beam opposite to the neutrons. The experimental data have been analyzed using the prior-form DWBA. For both nuclear and Coulomb breakup, sufficient convergence of the calculations is obtained by including the pn angular momenta up to l = 2. For the nuclear breakup calculations, the l = 0 and 2 contributions dominate the cross sections. For the Coulomb breakup the l = 1 contribution is predominant. In the calculations the effect of the Coulomb breakup is seen at forward angles of the angular correlation. The DWBA calculations reproduce fairly well the coincident energy spectra and the angular correlations in the angular region where the protons are emitted on the side of the beam opposite to the neutrons. On the other hand the calculations overestimate the break-up cross sections by a factor of 2 to 10 in the angular region where the protons are emitted on the same side of the beam as the neutrons. The distributions of deuteron c.m. angular momenta that contribute to the breakup amplitude are examined to obtain information on the region of space in which the breakup reactions takes place.

Low-lying states in 95Tc studied with the 93Nb(α, 2nγ)95Tc reaction

Abstract Low-lying states in 95Tc were studied with the 93Nb(α, 2nγ)95Tc reaction. The level scheme was obtained from the γ-γ coincidence measurement. The spin assignment was made on the basis of the observed γ-ray angular distributions and the excitation functions. The 337 keV 7 2 + , 627 keV ( 5 2 + ), 882 keV 13 2 + and 957 keV 11 2 + states, and possibly state, are found to be strong candidates for the core multiplet states [(1 g 9 2 ) p ⊗2 + ] J . These states are discussed in term of a weak coupling model and the dressed three-quasiparticle model. The observed γ-ray angular distributions are compared with expectations based on a simple deexcitation model of the (α, 2nγ) reaction.

Cluster structure in 40Ca via the α-transfer reaction

Abstract About seventy levels up to E x = 15 MeV in 40 Ca have been studied via the ( 6 Li, d) reaction at E = 50 MeV. The members of the K π = 0 − band of a counterpart to the first K π = 0 + band in the parity doublet bands were observed, in some fragments, from the 1 − state at 8 MeV to the 7 − state at 12.65 MeV in excitation energy. The J π = 8 + state was found at 10.34 Me V, and the 6.93 MeV level was confirmed as a J π = 6 + state. These states are considered as the members of the K π = 0 + band starting from the 0 + state at E x = 3.35 MeV. The 0 + , 2 + , 4 + and 6 + members of a higher nodal K π = 0 + band with N = 14 were observed for the first time in the fp-shell nuclei. This band consists of the strongly populated states in an excitation energy region from the 0 + state at 11 MeV to the 6 + state at 15 MeV. The spectroscopic factors suggested the much stronger α-cluster character.

Neutrino studies in 100Mo and MOON - Mo Observatory of neutrinos

Abstract The MOON (Molybdenum Observatory Of Neutrinos) project is a hybrid ββ and solar ν experiment with 100 Mo. It aims at high sensitive studies of ββ decays with a sensitivity of m ν > ∼ 0.03 eV and real-time studies of pp and 7 Be solar νs. The double β rays from 100 Mo are measured in prompt coincidence for the 0νββ studies, and the inverse β rays from solar-ν captures of 100 Mo are measured in delayed coincidence with the subsequent β decay of 100 Tc. Measurements with good position resolution enable one to select true signals by spatial and time correlations.

Reduced matrix elements of M2 and E3 γ-transitions between single-quasiparticle states in Sb isotopes and electromagnetic core polarization effects

Abstract Reduced M2 and E3 transition matrix elements were obtained for the single-quasiproton transitions of 1 h 11 2 → 1 g 7 2 and 1 h 11 2 → 2 d 5 2 in 115 Sb and 117 Sb. The effective M2 and E3 coupling constants are found to be g eff (M2)/ g free (M2) = 0.24±0.02 and g eff (E3)/ g free (E3)/ g free (E3) ≈ 2.5, respectively, for both 115 Sb and 117 Sb. They were explained in terms of the spin-isospin core polarization and the octupole core polarization, respectively. The isoscalar and isovector M2 polarizations are discussed by comparing the present g eff (M2) of the single-proton transitions with those of the similar single-neutron transitions in Sn isotopes.

Study of (d, α) Reactions on 40Ca and 40Ar

The nuclear structures of 38 K and 38 Cl are investigated by 40 Ca( d , α) 38 K and 40 Ar( d , α) 38 Cl reactions with 11.4 MeV deuterons. The excitation functions for 40 Ca( d , α) 38 K reaction have been obtained for the deuteron energy between 10.65 and 12.17 MeV. The angular distributions have been measured on the low excited states of 38 K and 38 Cl. The zero range DWBA analysis of the angular distributions on these excited states gives the spin, parity and isospin assignments as follows, the 2.63 MeV state (4, 3 or 2) - 0, the 2.85 MeV state (4, 3 or 2) - 0 and the 3.97 MeV state (3, 2 or 1) + 0 for 38 K. Four strongly excited states are found in 38 Cl at 1.82, 1.99, 2.51 and 2.82 MeV and are considered to have positive parity from DWBA calculations. The spin and parity are considered tentatively to be (3) + for the 1.99 MeV state in 38 Cl.

Lifetime Measurements of the Excited States in19Ne and23Mg

19 F( p , n ) 19 Ne, 16 O(α, n ) 19 Ne, and 23 Na( p , n ) 23 Mg endothermic reactions have been used to determine the mean lives of the excited states at 1508 and 1536 keV states in 19 Ne and 451 keV state in 23 Mg by the Doppler shift attenuation method. The results are τ=(1.4 -0.6 +0.5 )×10 -12 sec, τ=(2.8 -1.6 +1.8 )×10 -14 sec and τ=(3.6 -2.4 +9.1 )×10 -12 sec respectively. From the measurement of gamma ray energies, the accurate energies of the excited state have been determined.

Tensor analyzing powers of the proton continuum spectra from deuteron breakup at 56 MeV

Abstract Cross sections and tensor analyzing powers, A xx and A yy of the continuum spectra in 58 Ni and 90 Zr( d , pX) reactions were measured at 56 MeV in the angular range between 6° and 30°. A prominent bump due to deuteron breakup was observed in the proton spectra. The peak energy of the bump is about one half of the incident deuteron energy. Tensor analyzing powers of magnitude 0.1–0.2 were observed at the high-energy side of the breakup spectra. The cross section and tensor analyzing powers were calculated based on a projectile breakup model using the S- and D-state momentum distributions of the deuteron derived from the Reid soft-core wave functions. In the calculation the tensor analyzing powers originate from the deuteron D-state alone. The experimental data at forward angles were roughly explained by the calculations except for the low-energy end of the spectra. The observed tensor analyzing powers at forward angles seem to reflect the effect of the deuteron D-state.

The High Excited Levels of 27Al

The spectrum and angular distribution of alpha particles scattered by 27 Al at 22.2 MeV bombarding energy have been measured. Among the prominent peaks in the spectrum, those corresponding to excited states at 5.434, 6.547, 7.28 and 7.50 MeV were studied by measuring the gamma ray spectrum in coincidence with scattered alpha particle. From the measured gamma ray branching ratios, (5/2, 7/2, 9/2) + was assigned to the former two levels and 7/2 - was assigned to the latter two levels. In addition, from gamma ray transition rate consideration, 3/2 - , 9/2 + and (3/2, 5/2) + were found appropriate for 4.055, 4.508 and 5.491 MeV level respectively.