M.J. Hurst

Radiative decays of unbound high spin states in 24Mg: (I). Positive parity states

Abstract The 20Ne(α, γ)24Mg reaction has been used to measure radiative decay rates for known high spin levels at 12.86(6+), 13.44(6+) and 14.15(8+) MeV in 24Mg, and for previously unidentified levels at 12.00, 13.04 and 14.08 MeV. Gamma-ray angular distributions indicate that the 12.00 and 14.08 MeV levels are probably 6+ levels, while the 13.04 MeV level is the lowest 0+ T = 1 state. A new level at 11.005 MeV, populated in the radiative decay of the 14.08 MeV level, is most likely the lowest 5+ T = 1 state in 24Mg. Alpha-particle widths have also been measured for several of these levels and for the known 6+ level at 13.85 MeV using the 20Ne(α, α′γ)20Ne reaction and previously determined branching ratios. The results for both radiative and particle decay widths are compared with recent shell-model calculations performed within a full (sd)8 basis.

Radiative decays of unbound high-spin states in 24Mg (II)

Abstract Known negative-parity levels at 11.59(5 − ), 12.44 (7 − ), 13.06(5 − ), and 13.76(5 − ) MeV in 24 Mg have been studied as resonances in the 20 Ne(α, γ) 24 Mg reaction, and their radiative and α-particle decay widths deduced. The 12.44 MeV level is identified as the 7 − member of a K π = 0 − band by virtue of a strongly enhanced E2 γ-ray transition to the 10.03 MeV 5 − level. The 13.06 MeV level exhibits a strongly enhanced γ-ray transition to a probable 3 − level at 10.33 MeV, indicating the existence of a new negative-parity rotational band in 24 Mg. Known 4 + levels at 12.05, 12.12, 12.16, 12.51 and 13.05 MeV have also been studied as 20 Ne(α, γ) 24 Mg resonances in a search for the 4 + member of a proposed excited K π = 0 + band via an enhanced E2 transition to the 8.65 MeV 2 + level. No such transition was observed, but the 12.05 MeV level was identified as the second 4 + T = 1 level in 24 Mg. In addition, γ-ray decay schemes and angular distributions provided the following information on the spins and parities of three sharp resonances near 14 MeV in 24 Mg: 14.10, (2, 4) + ; 14.146, 4 + (3 − , 5 − ) and 14.32, 4 + .

Measurements of the radiative widths of the first T = 1, 2+ state of 20Ne and their relationship to analog β-decays

Abstract The radiative widths for decays of the 20 Ne T = 1, 2 + (10.27 MeV) state were measured by resonance α-capture in the reaction 16 O(α, γ) 20 Ne. A special windowless gas-cell target yielded a low-background spectrum enabling six γ-branches to be observed with a Ge(Li) detector. The six branches correspond to decays from the 10.27 MeV level to the following levels: 2 + (7.83 MeV), 2 + (7.42 MeV), 3 − (5.62 MeV), 2 − (4.97 MeV), 2 + (1.63 MeV) and 0 + (g.s.). The branching ratios and radiative widths Γ γ to these levels are: 7.83 MeV [(0.22 ± 0.06)%, 0.008 ± 0.002 eV], 7.42 MeV [(6.9 ± 0.4)%, 0.31 ± 0.04 eV], 5.62 MeV [(2.1 ± 0.2)%, 0.097 ± 0.014 eV], 4.97 MeV [(1.3 ± 0.1)%, 0.060 ± 0.008 eV], 1.63 MeV [(88.9 ± 0.5)%, 4.08 ± 0.43 eV] and 0.0 MeV [(0.64 ± 0.14)%, 0.029 ± 0.008 eV]. The radiative widths to the 1.63 MeV and 7.42 MeV levels are used to determine the CVC predictions of the weak magnetism form factors and their effects on certain β-decay observables are evaluated.

A study of the reaction 16O(3He,p)18F

The 16O(3He,p)18F reaction has been studied at 18 MeV and angular distributions have been measured for observed levels up to 10 MeV. The distributions for the 2p-0h positive parity state have been analysed in terms of the DWBA theory for a two-nucleon stripping process and good agreement has been obtained in most cases up to a centre-of-mass angle of 90 degrees . Eleven new levels in 18F have been observed between Ex=7 MeV and 10 MeV. Tentative Jpi assignments have been made for some of them.

An alpha-capture measurement of the radiative width of the first 8+ state in 20Ne

The radiative width of the 11.95 MeV 8+ Kpi =0+ level in 20Ne has been measured using the 16O( alpha , gamma )20Ne reaction and a differentially cryopumped gas target. The resonance strength was measured to be omega gamma =131+or-18 meV, which corresponds to a value of 9.2+or-1.3 Weisskopf units for the 8+ to 6+ E2 in-band transition probability. This is somewhat weaker than shell-model predictions normalised to the transitions between the lower members of the Kpi =0+ band.

A study of the 17 O( 3 He, p) 19 F reaction

SummaryThe17O(3He, p)19F reaction is studied at 18 MeV using the Tandem accelerator and multichannel magnetic spectrograph of the Nuclear Physics Laboratory, Oxford. Angular distributions have been measured for most of the levels observed up toEx∼7 MeV. Results for positive-parity levels with a dominant (sd)3 character are analysed in terms of the DWBA method using shell model two-nucleon spectroscopic amplitudes, while for other levels a pure configuration was used.RiassuntoSi studia la reazione17O(3He, p)19F a 18 MeV usando l’acceleratore Tandem e lo spettrografo magnetico a molti canali del laboratorio di fisica nucleare di Oxford. Sono state misurate le distribuzioni angolari per la maggior parte dei livelli osservati fino aEx∼7 MeV. Si analizzano i risultati per i livelli a parità positiva con un carattere dominante (sd)3 in termini del metodo DWBA usando le ampiezze spettroscopiche del modello a strati a due nucleoni, mentre per gli altri livelli è stata usata una configurazione pura.РезюмеИсследуется реакция17O(3He, p)19F при 18 МэВ, используя тандемускоритель и многоканальный магнитный спектрограф Лаборатории Ядерной Физики в Оксфорде. Были измерены угловые распределения большинства наблюденных уровней вплоть доEx∼7 МэВ. Результаты для уровней с положительной четностью с доминирующим (sd)3 характером анализируются с помощью метода DWBA, используя двух-нуклонные спектроскопические амплитуды оболочечной модели, тогда как для других уровней используются чистая конфигурация.

A study of the17O(3He, p)19F reactionИсследование реакции17O(3He, p)19F

SummaryThe17O(3He, p)19F reaction is studied at 18 MeV using the Tandem accelerator and multichannel magnetic spectrograph of the Nuclear Physics Laboratory, Oxford. Angular distributions have been measured for most of the levels observed up toEx∼7 MeV. Results for positive-parity levels with a dominant (sd)3 character are analysed in terms of the DWBA method using shell model two-nucleon spectroscopic amplitudes, while for other levels a pure configuration was used.RiassuntoSi studia la reazione17O(3He, p)19F a 18 MeV usando l’acceleratore Tandem e lo spettrografo magnetico a molti canali del laboratorio di fisica nucleare di Oxford. Sono state misurate le distribuzioni angolari per la maggior parte dei livelli osservati fino aEx∼7 MeV. Si analizzano i risultati per i livelli a parità positiva con un carattere dominante (sd)3 in termini del metodo DWBA usando le ampiezze spettroscopiche del modello a strati a due nucleoni, mentre per gli altri livelli è stata usata una configurazione pura.РезюмеИсследуется реакция17O(3He, p)19F при 18 МэВ, используя тандемускоритель и многоканальный магнитный спектрограф Лаборатории Ядерной Физики в Оксфорде. Были измерены угловые распределения большинства наблюденных уровней вплоть доEx∼7 МэВ. Результаты для уровней с положительной четностью с доминирующим (sd)3 характером анализируются с помощью метода DWBA, используя двух-нуклонные спектроскопические амплитуды оболочечной модели, тогда как для других уровней используются чистая конфигурация.

A study of the17O(3He, p)19F reaction

SummaryThe17O(3He, p)19F reaction is studied at 18 MeV using the Tandem accelerator and multichannel magnetic spectrograph of the Nuclear Physics Laboratory, Oxford. Angular distributions have been measured for most of the levels observed up toEx∼7 MeV. Results for positive-parity levels with a dominant (sd)3 character are analysed in terms of the DWBA method using shell model two-nucleon spectroscopic amplitudes, while for other levels a pure configuration was used.RiassuntoSi studia la reazione17O(3He, p)19F a 18 MeV usando l’acceleratore Tandem e lo spettrografo magnetico a molti canali del laboratorio di fisica nucleare di Oxford. Sono state misurate le distribuzioni angolari per la maggior parte dei livelli osservati fino aEx∼7 MeV. Si analizzano i risultati per i livelli a parità positiva con un carattere dominante (sd)3 in termini del metodo DWBA usando le ampiezze spettroscopiche del modello a strati a due nucleoni, mentre per gli altri livelli è stata usata una configurazione pura.РезюмеИсследуется реакция17O(3He, p)19F при 18 МэВ, используя тандемускоритель и многоканальный магнитный спектрограф Лаборатории Ядерной Физики в Оксфорде. Были измерены угловые распределения большинства наблюденных уровней вплоть доEx∼7 МэВ. Результаты для уровней с положительной четностью с доминирующим (sd)3 характером анализируются с помощью метода DWBA, используя двух-нуклонные спектроскопические амплитуды оболочечной модели, тогда как для других уровней используются чистая конфигурация.