---
title: B1 in Materials, Astronomy & MRI
url: https://www.emergentmind.com/topics/b1
type: topic
---

# B1 in Materials, Astronomy & MRI

B1 is a designation that occurs in several scientific contexts, notably as a structural label in crystallography and materials science, as a designation for specific astronomical regions and objects, and as an indicator for the transmit radiofrequency field (B1⁺) in magnetic resonance applications. Below, the article is organized into critical research domains in which "B1" plays a technically significant role, emphasizing the detailed physicochemical and observational properties established in published literature.

## 1. B1 Structure in Solid-State Physics and Materials Science

In crystallography, "B1" refers to the rock salt (NaCl-type) structure, characterized by a face-centered cubic (fcc) lattice with the formula unit MX (where M is a cation such as an alkali, alkaline earth, or lanthanide metal, and X is an anion such as O or F). Space group Fm$\bar{3}$m, Wyckoff positions M at (0,0,0) and X at (½,½,½), yields octahedral (six-fold) coordination for each species. The B1 structure is the ground state for many monoxides at ambient pressure, including MgO and all LnO (lanthanide oxides, Ln = La–Lu) [2604.11194, 2104.01347].

Key crystallographic properties for LnO B1 phases (from GGA-DFT calculations):

| Compound | $a_0$ (Å) | $V_0$ (ų) | $B_0$ (GPa) | $B_0'$ | $P_{\rm tr}$ (GPa, B1→B2) |
|---|---|---|---|---|---|
| LaO | 5.1643 | 137.7 | 125.1 | 4.51 | 102.6 |
| CeO | 5.1312 | 135.1 | 128.0 | 4.68 | 162.6 |
| ... | ... | ... | ... | ... | ... |
| LuO | 4.6566 | 101.0 | 131.1 | 3.01 | 209.0 |

Thermodynamic stability is pressure-dependent: all LnO remain in the B1 structure at low pressures, but undergo a reconstructive phase transition to the B2 (CsCl-type) structure at pressures $P_{\rm tr}$ ranging from as low as 29 GPa (YbO) to over 200 GPa (LuO), with an associated volume collapse of 7–8% [2604.11194].

For MgO, high-pressure melting at the B1 phase has been quantitatively captured by models that relate the melting temperature $T_m(P)$ to the isothermal bulk modulus $K_T(P)$ through moment-recurrence quantum statistical mechanics combined with work–heat equivalence considerations. For B1–MgO, $T_m$ spans from 3214 K at ambient pressure to $\sim$10,000 K at 370 GPa, with bulk moduli $K_T(0)$ typically in the range 160 GPa and pressure derivatives $K_T' \approx 4.3$ [2104.01347].

## 2. The Perseus B1 and B1-E Regions in Star Formation Studies

The "B1" and "B1-E" nomenclature is widely used in star formation to label dense clumps and subregions in the Perseus molecular cloud. B1-E is a $\sim$100 M$_\odot$, $T_d \approx 14$ K clump characterized by a ring-like distribution of compact substructures ($M_\mathrm{sub}\sim$0.3–2 M$_\odot$; $R\sim$5000–9000 AU), most of which are gravitationally unbound with virial parameters $\alpha \gg 2$ and turbulent non-thermal motions (Mach 1–3); only B1-E2 appears bound ($\alpha\sim1–3$) [1111.7021].

Key findings include:

- Herschel continuum mapping (160–500 μm) reveals that structure on scales above the column threshold $N_\mathrm{H_2} \approx 5×10^{21}$ cm$^{-2}$ corresponds to the onset of “core formation.”
- Spectroscopic surveys (NH$_3$, CCS, HC$_5$N) show supersonic linewidths and a spatial configuration of substructures with median separations $\sim$0.13 pc, smaller than the thermal Jeans length ($\lambda_J \sim 0.35$ pc), indicating local fragmentation post global collapse.
- Optical polarization measurements indicate a strong, uniform magnetic field, inferred to regulate fragmentation and suppress active star formation relative to neighboring regions [1111.7021].

Kinematic mapping with $^{13}$CO and C$^{18}$O lines displays a radial velocity gradient of $\sim$1 km s$^{-1}$ pc$^{-1}$ perpendicular to the main cloud gradient, while substructures display lower linewidths and are decoupled from the clump’s large-scale motions. The appearance of C$^{18}$O depletion is confined to the low-turbulence, near-transonic substructure (B1-E2), suggesting linkages between turbulence dissipation and grain-surface freeze-out chemistry in core evolution [1504.05206].

## 3. B1-bS and B1-bN: Candidate First Hydrostatic Cores in Perseus

B1-bS and B1-bN are two dense condensations in the Perseus B1 region that exhibit spectral energy distributions (SEDs) inconsistent with simple, single-component greybody fits. Their SEDs are adequately reproduced only with a two-component model (compact warm center + cool envelope), with bolometric temperatures $T_\mathrm{bol}$ of 18 K (B1-bS) and 14 K (B1-bN), substantial submillimeter luminosity fractions ($L_\mathrm{smm}/L_\mathrm{bol}\gtrsim25$%), and no 24 μm emission, matching theoretical predictions for first hydrostatic cores (FHSCs). Their projected separation is $\sim$4700 AU ($\sim$2 Jeans lengths), providing an opportunity to study interactions between proto-fragments at an extremely early evolutionary phase [1209.5290].

## 4. B1 in Astrophysical Shock Chemistry: The L1157-B1 Proto-shock Laboratory

The B1 region in the L1157 outflow is a prototypical laboratory for molecular shock chemistry and the interplay of grain-surface and gas-phase reactions. High spatial resolution imaging, spectral-line surveys (CS, CH$_3$OH, HC$_3$N, H$_2$CO), and chemical modeling reveal:

- Morphology: arch-shaped cavity walls and compact high-velocity “bullets” (sizes $\sim$750–1500 AU).
- Kinematics: cavity-averaged gas at $n_{\mathrm{H_2}}\lesssim10^6$ cm$^{-3}$, bullets at $5\times10^3$–$5\times10^5$ cm$^{-3}$; velocities from systemic +2.6 km s$^{-1}$ to $-$16 km s$^{-1}$ [1309.0433].
- Shock models: C-type shocks ($v_s \sim 40$ km s$^{-1}$, $n_0\sim10^5$ cm$^{-3}$, $T_{\rm max}\gtrsim4000$ K) reproduce observed molecular abundances, line profiles, and the rapid transition from mantle-release to high-temperature gas-phase chemistry [1108.2892, 1309.0433, 1706.08834, 1801.03461].
- Astrochemistry: Deuterated species (DCN), cyanopolyynes (HC$_3$N, HC$_5$N), and their spatial distributions provide diagnostics of the interplay between grain mantle sputtering and warm gas-phase reactions, validating models that require both a high peak shock temperature (for HC$_3$N and DCN in post-shock gas) and a transient mantle release (for enhanced DCN in jet-impacted zones) [1706.08834, 1801.03461].

## 5. B1 as the RF Magnetic Field in Magnetic Resonance

In MR physics, "B1" (and B1⁺, the transmit component) denotes the oscillating magnetic field generated by the RF coil for excitation or spatial encoding of nuclear spins. Technical advancements in B1⁺ engineering have a direct impact on sensitivity, homogeneity, and safety in advanced MRI and MRS protocols:

- Dual-tuned multimodal surface coils, constructed from concentric stacks of coupled loops (e.g., three for $^1$H and three for $^{31}$P), utilize eigenmode selection principles to enhance B1⁺ efficiency. In such designs, the lowest-frequency in-phase eigenmodes reinforce the central field, yielding $+83\%$ (for $^{31}$P) and $+21\%$ (for $^1$H) B1⁺ gains over single-tuned reference coils of the same size, with negligible SAR penalty ($\pm7\%$) and strong inter-nuclear decoupling (>20 dB isolation) [2512.24786].
- In multinuclear and high-field applications, such as 7 T $^1$H/$^{31}$P MRSI, B1⁺ inhomogeneity and RF losses limit sensitivity for "X-nuclei." Engineering solutions based on coupling matrices and eigenmode decomposition circumvent the efficiency penalties common in standard dual-tuned platforms.
- Parallel transmit (pTx) and high-permittivity material (HPM) approaches further enable B1⁺ homogenization. For example, conformal barium-titanate HPM shells at 7 T act as dielectric potential wells, flattening B1⁺ distribution and reducing slice-by-slice coefficient of variation (CV) by 54% and peak SAR by 42% [1911.05313]. Multi-channel mapping and phase-only shims optimized from large-dynamic-range B1⁺ maps boost target ROI B1⁺ by 37–42% with concomitant improvements in homogeneity and SAR efficiency [2212.14596].
- Dedicated B1⁺ mapping methods using optimized pulse sequences (e.g., adiabatic Bloch-Siegert, multi-angle TSE for metal environments, joint T1/B1⁺ estimation in cardiac mapping) are indispensable for robust quantitative imaging and sequence calibration in challenging conditions [2501.06049, 2411.15709, 2111.07901, 2104.14878].

## 6. Related Astronomical and Chemical Contexts

"B1" labels have also been applied to a broad spectrum of astrophysical phenomena:

- In cometary science, C/2014 B1 (Schwartz) is a long-period comet exhibiting a stable, discus-shaped dust coma due to equatorial ejection of $>0.1$ mm grains, a morphology possible only when ejection velocities ($\sim$1–10 m s$^{-1}$) are comparable to nucleus escape velocities and dominated by gravitational, not radiation pressure, dynamics [1901.01438].
- In galactic center studies, "Sgr B1" refers to an evolved H II region in the central molecular zone whose ionization structure, mapped via SOFIA [O III] 52/88 μm, shows excitation by late-O stars augmented with fast-shock X-rays; SED fitting constrains electron densities to $N_e\sim10^2$–$8\times10^2$ cm$^{-3}$ [1810.08301].

## 7. Conclusion

"B1" is a multifaceted symbol whose meaning is sharply context-dependent but invariably denotes a critical structural, field, or regional property in both physical and observational sciences. Its precise technical definition—as a crystallographic ground state (NaCl-type), a key protostellar region (Perseus B1 and subregions), an RF magnetic field essential for MR, or a label for unique cometary morphology—anchors it as a keystone in contemporary research, methodologies, and instrument design across disciplines [2512.24786, 2604.11194, 2104.01347, 1111.7021, 1209.5290, 1309.0433, 1706.08834, 1801.03461, 1911.05313, 1901.01438, 1810.08301].

Source: https://www.emergentmind.com/topics/b1