Indiana University Cyclotron Research Articles

INPOL – the Indiana University Neutron Polarimeter

We describe the upgraded time-of-flight facility at the Indiana University Cyclotron which has been used to measure the polarization transfer induced in ( p → , n → ) reactions at intermediate energies, E p=100–200 MeV. The Indiana Neutron POLarimeter (INPOL) is able to measure simultaneously two orthogonal neutron spin polarizations induced in charge exchange reactions with polarized proton beams oriented in each of the three spin states, normal ( N → ), sideways ( S → ) and longitudinal ( L → ).

Phantom assessment of lung dose from proton arc therapy

To compare resultant lung dose from proton arc therapy of the chest wall to that from electron arc therapy. A 200 MeV proton beam from the Indiana University Cyclotron was range shifted and modulated to provide a spread out Bragg peak extending from the surface to a depth of 4 cm in water. The chest wall of an Alderson Rando phantom was irradiated by this beam, collimated to a 20 x 4 cm field size, while it rotated on a platform at approximately 1 rpm. For comparison, electron arc therapy of the Rando phantom chest wall was similarly performed with 12 MeV electrons and the resultant lung dose measured in each case. Dose-volume histograms for the Rando phantom left lung indicate a reduced volume of irradiated lung for protons at all dose levels and an integral lung dose that is half that for electron arc therapy in the case studied. In addition, a more uniform dose coverage of the target volume was achieved with the proton therapy. This study demonstrates a potential role for proton arc therapy as an alternative to electron arc therapy when lung dose must be minimized.

Overview of some time-of-flight (p, n) studies

An overview of some experimental work with the (p, n) reaction at Indiana University is given. The scientific motivation for the studies is discussed. A description of the apparatus at the Indiana University cyclotron is given. Some results of the experiments are displayed. It is shown that the cross section per unit Gamow–Teller strength does not vary smoothly with target mass. This is noted as an open problem in the field. A discussion of another open problem, the missing Gamow–Teller strength, is given.

The 19F(p, n) 19Ne and 39K(p, n) 39Ca reactions at intermediate energies and quenching of the Gamow-Teller strength

The (p, n) reactions on 19F and 39K targets have been studied at 120 MeV and 160 MeV using the Indiana University Cyclotron time-of-flight facility. States up to 12 MeV excitation energy have been observed and angular distributions for these neutron groups are presented. The ground-state mirror transitions have accurately measured ft values. This information is used to normalize the zero-degree energy spectra to a scale of Gamow-Teller (GT) transition probability to obtain GT strenghts to excited states. The experimental sum GT strengths are smaller than the sum-rule-limit values showing strong evidence for GT quenching.

Search for finite-mass neutrinos in the decay [formula omitted

If neutrinos possess non-zero mass, pion decay might have small decay branches to neutrino states with large masses. We have searched for such branches in the decay of pions produced at the Indiana University Cyclotron. The energy spectrum of decay muons shows no evidence for such neutrino branches and if these decays do exist, their branching ratios must be less than 10 −2 to 10 −3 for neutrino masses in the ranFge 7–33 MeV.

Excitation of giant spin-isospin multipole vibrations

The (p, n) reactions on several targets from 40Ca to 208Pb have been studied at 200 MeV using the Indiana University Cyclotron time-of-flight facilities. In addition to giant Gamow-Teller (GT) resonances that dominate the zero degree spectra, other broad resonance structures appear at angles larger than zero degrees which are interpreted as spin-isospin multipole vibrations. GT strength and energy systematics as well as dipole spin strength and energy systematics are discussed.

Doppler-Shift Lifetime Measurements inMg24,Mg26, andSi28

The lifetimes of nuclear levels in ${\mathrm{Mg}}^{24}$, ${\mathrm{Mg}}^{26}$, and ${\mathrm{Si}}^{28}$ have been measured by the Doppler-shift attenuation method. Excited states were produced by inelastic scattering of 22-MeV $\ensuremath{\alpha}$ particles from the Indiana University cyclotron. $\ensuremath{\gamma}$-ray spectra were taken in coincidence with $\ensuremath{\alpha}$-particles striking an annular detector in the backward direction. The Doppler shifts of the $\ensuremath{\gamma}$-ray peaks were attenuated by thick gold backings behind the targets, allowing the lifetimes of the levels to be calculated in terms of the attenuation and the stopping power of the gold backing. Lifetimes were measured for the 1.37-, 4.12-, and 4.23-MeV levels of ${\mathrm{Mg}}^{24}$; the 1.81- and 2.94-MeV levels of ${\mathrm{Mg}}^{26}$; and the 1.77-, 4.61-, and 4.97-MeV levels of ${\mathrm{Si}}^{28}$. In addition, studies were made of the decay rates of the 5.25-, 6.01-, and 6.43-MeV levels of ${\mathrm{Mg}}^{24}$; the triplet at 4.32-4.35 MeV in ${\mathrm{Mg}}^{26}$; and the 6.889-MeV level in ${\mathrm{Si}}^{28}$. The results for these three even-even $s\ensuremath{-}d$ shell nuclei are compared with the predictions of several collective theories of nuclear structure, with shell-model calculations based on the $S{U}_{3}$ classification of states, and with Hartree-Fock calculations.

4.48-MeV Level ofCa40

The reaction ${\mathrm{Ca}}^{40}(\ensuremath{\alpha}, {\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{\gamma})$ was studied using particle-gamma coincidence techniques and the 22-MeV alpha-particle beam from the Indiana University cyclotron. The 4.48-MeV level of ${\mathrm{Ca}}^{40}$ is observed to decay strongly to the 3.73-MeV ${3}^{\ensuremath{-}}$ level. An upper limit of 5% is placed on the intensity of the ground-state transition. The weakness of the ground-state transition is strong evidence against a ${1}^{\ensuremath{-}}$ assignment for the 4.48-MeV level. This result, together with other data, indicates that the 4.48-MeV level is ${5}^{\ensuremath{-}}$.

Gamma Radiation from Low Levels ofAl27

The ${\mathrm{Al}}^{27}(\ensuremath{\alpha}, {\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{\gamma})$ reaction was investigated by using particle-gamma coincidence techniques and the 22-Mev alpha-particle beam from the Indiana University cyclotron. A 0.79\ifmmode\pm\else\textpm\fi{}0.03 Mev gamma-ray transition between the 3.0- and 2.21-Mev states of ${\mathrm{Al}}^{27}$ was observed. This result, together with other data, suggests that the 3.0- and 2.21-Mev states are the $\frac{9}{{2}^{+}}$ and ${\frac{7}{2}}^{+}$ members of a $K=\frac{5}{2}$ rotational band.