Simultaneous measurement of $\beta$-delayed proton and $\gamma$ decay of ${}^{27}\mathrm{P}$

This is the first study of ${}^{27}\mathrm{P}$ to measure both the $\beta$-delayed proton and $\beta$-delayed $\gamma$ decays. While no new proton groups in the astrophysically interesting energy region of 300–400 keV were observed, a new upper limit on the proton branching of 0.16% was estimated. Several new $\gamma$-ray lines were observed, mainly coming from the isobaric analog state in ${}^{27}\mathrm{Si}$, which has been assigned a more accurate energy value of 6638(1) keV.

Figure 1

Final beam composition and identification with the $\mathrm{\Delta }E$ silicon detector from the telescope located at the end of MARS with the momentum spread of the beam at $\mathrm{\Delta }p/p=\pm 0.25\%$. The vertical axis represents the energy deposited (arbitrary units) and the horizontal axis represents the position in the focal plane of MARS.

Figure 2

Top view of the implantation-decay station placed at the end of MARS where [1] beam, [2] rotating aluminum degrader, [3] silicon detectors (the order in which the beam sees them is $\beta 1$, proton detector, and then $\beta 2$), [4] HPGe detectors, [5] electronic feed-through, and [6] water cooling system input.

Figure 3

Implantation of ${}^{27}\mathrm{P}$ in the proton detector. The $y$ axis shows the energy deposited in the $\beta 1$ detector and the $x$ axis shows the energy deposited in the proton detector. Nuclei along the approximate ${45}^{\circ }$ diagonal punch through both detectors and therefore do not interfere with the proton measurement. Only after the corner in the upper right of the figure is passed are the nuclei stopped in the proton detector.

Figure 4

Gate created for the $E_x=E_y$ condition is shown in red for the thicker proton detector with the $m=1$ condition applied.

Figure 5

Proton spectrum obtained from the thinner proton detector with the $m=1$ and $E_x=E_y$ conditions applied. Energy values from Ref. [12].

Figure 6

The ${}^{27}\mathrm{Si}\gamma$-ray spectrum created from the total statistics obtained from HPGe 2. The top portion covers 0–3.5 MeV and the bottom section covers 3.5–8 MeV. All new ${}^{27}\mathrm{Si}\gamma$ rays are shown in red. All large peaks not coming directly from ${}^{27}\mathrm{Si}$ have also been labeled. They consist of single escapes (SE), double escapes (DE), and impurities ($\beta$-delayed $\gamma$ decay of ${}^{24}\mathrm{Al}$).

Figure 7

Partial-decay scheme for ${}^{27}\mathrm{P}$ with the most intense $\beta$ decays shown. Line thickness corresponds directly with intensity. Thus, the most intense transitions are represented by the thickest arrows.